Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Gene Heskett]

On Wednesday 15 July 2020 08:29:55 Gene Heskett wrote:

> On Wednesday 15 July 2020 07:40:50 Gene Heskett wrote:
> > On Wednesday 15 July 2020 00:58:43 Gregg Eshelman via Emc-users 
wrote:
> > > There are sine wave controllers that do various smoothing things
> > > to run steppers smooth and silent. Trinamic calls it Spread Cycle
> > > and Stealth Chop. https://www.youtube.com/watch?v=Q0sJlGh9WNY On
> > > Tuesday, July 14, 2020, 11:18:22 AM MDT, Todd Zuercher
> > >  wrote:
> > >
> > >  If you can hear it, it isn't smooth.  I'd recommend using the
> > > finest micro stepping setting your driver offers, but simply not
> > > counting on more than 1/4 of a full step in your resolution
> > > accuracy.  But just because the motor and drive may not be able to
> > > physically achieve positioning accuracy much better than 1/4 step,
> > > doesn't mean that having the finer micro step resolution won't
> > > significantly contribute to smoother quieter motion.
> >
> > I would tend to agree with this, except for the slewing. There.
> > using a microstepping of more than 16 will run out of bandwidth in
> > the dm542's opto's and he may get stalls, which will require
> > rehomeing on polaris again before it knows where its at. So there it
> > might be advantageos to use pulse lengths that would set an overall
> > clocking limit below 200 kilohertz.
> >
> > Been there, done that on my machinery. A dm542 can turn a much
> > bigger motor just laying on the table at just above 3000 revs, but
> > when it stalls, its so sudden it jumps up in the air about an inch.
> > But with the divisor set at 16 or more, I lost speed at 32 and was
> > slower yet at 64.
> >
> > So most of my stuff is running on /8, which seems to be a good
> > compromise between speed and noise. The dm542 is a decent driver,
> > I'm running 9 of them here, 2 on TLM, 4 on the 6040, and 3 of them
> > on the GO704. Software stepping, as opposed to a mesa card, will
> > limit slew rates because the step rates are limited by base thread
> > speeds and the next increment faster is something the motor can't
> > accel to in one step so it stalls. And it was doing that on the
> > little hf mill at speeds it could cut at!
> >
> > So eventually a Mesa 5i25 found a home in that machine, at which
> > point I thought the psu voltage was the limit. That whole kit,
> > computer and all, is now runniing the 6040 at 200ipm rapids.  The
> > diff is the smaller, lower inductance motors. The one thing they did
> > right on the 6040. The rest of the electronics was BBLB stuff and
> > not capable of even being interfaced with linuxcnc. The vfd started
> > the spindle ok, but in random directions I couldn't control, so the
> > usual clone vfd from ebay now does exactly what linuxcnc tells it
> > to.
> >
> > What I am interested in is the stellarium interface, that seems to
> > be an extra cost option from a different source. My googling has not
> > found it for sale or even a price quote, but then my goggle-foo has
> > been found wanting before. I have a 10" Meade newtonian thats now
> > been standing face down behind the back door for about 20 years.
> > I've also the motorized pier mount. But I'm down in a cul-de-sac and
> > can just barely get down to polaris due to the tree line on the hill
> > to the north.  And a huge 60+ yo maple I don't own blocks much of
> > the below equatorial southern sky view. I should make it a building
> > as I'd like to do frame a week movie of eta-carinae, probably the
> > next supernova we'll get to see. I also have a lack of dark sky
> > problem, street lights are old and unshielded. Sigh... But that
> > interface interests me greatly.
>
> Better google-fu, found several sw packages that work with stellarium,
> and investigated EQMOD, a freebie DL that looks quite capable. UNK if
> winderz only. Talks over rs232.  Now need schematics for pier control,
> and there seem to be several such kits available that EQMOD can talk
> to. All I have is a hand tracking motor and a very simple speed
> control, teeny little thing, might be able to track for an hour. More
> research needed to make a proper az/el drive... But first I'm low on
> caffiene.
>

This pier it appears, has a 60 hz clock motor on the polar axis. Plugs 
into the wall, so zero smarts there. The teeny little stepper is on the 
end of an arm about 9" long and can drive it maybe 20 minutes in each 
direction, at 90 dgrees to the polar motion.  So a full polar mount is 
going to take some re-engineering. I can't make a vector wheel that big 
on an ender-3.  And I'm still calibrating it, as its currently making a 
32 tooth half pulley, with some slack at the rear of a 180 toothed belt 
wrapped around it, so I'm increaseing the x-y steps per mm about .05% at 
a pass until I get a good fit.  I doubled the speed of the slice, and 
the finish is actually better. Somewhere I have a box of nema 17 motors 
like original 5.25" floppy drives used for head carriage, would be ideal 
for this. But we had 

Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Gene Heskett]

On Wednesday 15 July 2020 07:40:50 Gene Heskett wrote:

> On Wednesday 15 July 2020 00:58:43 Gregg Eshelman via Emc-users wrote:
> > There are sine wave controllers that do various smoothing things to
> > run steppers smooth and silent. Trinamic calls it Spread Cycle and
> > Stealth Chop. https://www.youtube.com/watch?v=Q0sJlGh9WNY On
> > Tuesday, July 14, 2020, 11:18:22 AM MDT, Todd Zuercher
> >  wrote:
> >
> >  If you can hear it, it isn't smooth.  I'd recommend using the
> > finest micro stepping setting your driver offers, but simply not
> > counting on more than 1/4 of a full step in your resolution
> > accuracy.  But just because the motor and drive may not be able to
> > physically achieve positioning accuracy much better than 1/4 step,
> > doesn't mean that having the finer micro step resolution won't
> > significantly contribute to smoother quieter motion.
>
> I would tend to agree with this, except for the slewing. There. using
> a microstepping of more than 16 will run out of bandwidth in the
> dm542's opto's and he may get stalls, which will require rehomeing on
> polaris again before it knows where its at. So there it might be
> advantageos to use pulse lengths that would set an overall clocking
> limit below 200 kilohertz.
>
> Been there, done that on my machinery. A dm542 can turn a much bigger
> motor just laying on the table at just above 3000 revs, but when it
> stalls, its so sudden it jumps up in the air about an inch. But with
> the divisor set at 16 or more, I lost speed at 32 and was slower yet
> at 64.
>
> So most of my stuff is running on /8, which seems to be a good
> compromise between speed and noise. The dm542 is a decent driver, I'm
> running 9 of them here, 2 on TLM, 4 on the 6040, and 3 of them on the
> GO704. Software stepping, as opposed to a mesa card, will limit slew
> rates because the step rates are limited by base thread speeds and the
> next increment faster is something the motor can't accel to in one
> step so it stalls. And it was doing that on the little hf mill at
> speeds it could cut at!
>
> So eventually a Mesa 5i25 found a home in that machine, at which point
> I thought the psu voltage was the limit. That whole kit, computer and
> all, is now runniing the 6040 at 200ipm rapids.  The diff is the
> smaller, lower inductance motors. The one thing they did right on the
> 6040. The rest of the electronics was BBLB stuff and not capable of
> even being interfaced with linuxcnc. The vfd started the spindle ok,
> but in random directions I couldn't control, so the usual clone vfd
> from ebay now does exactly what linuxcnc tells it to.
>
> What I am interested in is the stellarium interface, that seems to be
> an extra cost option from a different source. My googling has not
> found it for sale or even a price quote, but then my goggle-foo has
> been found wanting before. I have a 10" Meade newtonian thats now been
> standing face down behind the back door for about 20 years. I've also
> the motorized pier mount. But I'm down in a cul-de-sac and can just
> barely get down to polaris due to the tree line on the hill to the
> north.  And a huge 60+ yo maple I don't own blocks much of the below
> equatorial southern sky view. I should make it a building as I'd like
> to do frame a week movie of eta-carinae, probably the next supernova
> we'll get to see. I also have a lack of dark sky problem, street
> lights are old and unshielded. Sigh... But that interface interests me
> greatly.
>
Better google-fu, found several sw packages that work with stellarium, 
and investigated EQMOD, a freebie DL that looks quite capable. UNK if 
winderz only. Talks over rs232.  Now need schematics for pier control, 
and there seem to be several such kits available that EQMOD can talk to.  
All I have is a hand tracking motor and a very simple speed control, 
teeny little thing, might be able to track for an hour. More research 
needed to make a proper az/el drive... But first I'm low on caffiene.

Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.
 - Louis D. Brandeis
Genes Web page 


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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Gene Heskett]

On Wednesday 15 July 2020 00:58:43 Gregg Eshelman via Emc-users wrote:

> There are sine wave controllers that do various smoothing things to
> run steppers smooth and silent. Trinamic calls it Spread Cycle and
> Stealth Chop. https://www.youtube.com/watch?v=Q0sJlGh9WNY On Tuesday,
> July 14, 2020, 11:18:22 AM MDT, Todd Zuercher 
> wrote:
>
>  If you can hear it, it isn't smooth.  I'd recommend using the finest
> micro stepping setting your driver offers, but simply not counting on
> more than 1/4 of a full step in your resolution accuracy.  But just
> because the motor and drive may not be able to physically achieve
> positioning accuracy much better than 1/4 step, doesn't mean that
> having the finer micro step resolution won't significantly contribute
> to smoother quieter motion.
>
I would tend to agree with this, except for the slewing. There. using a 
microstepping of more than 16 will run out of bandwidth in the dm542's 
opto's and he may get stalls, which will require rehomeing on polaris 
again before it knows where its at. So there it might be advantageos to 
use pulse lengths that would set an overall clocking limit below 200 
kilohertz.

Been there, done that on my machinery. A dm542 can turn a much bigger 
motor just laying on the table at just above 3000 revs, but when it 
stalls, its so sudden it jumps up in the air about an inch. But with the 
divisor set at 16 or more, I lost speed at 32 and was slower yet at 64.  

So most of my stuff is running on /8, which seems to be a good compromise 
between speed and noise. The dm542 is a decent driver, I'm running 9 of 
them here, 2 on TLM, 4 on the 6040, and 3 of them on the GO704. Software 
stepping, as opposed to a mesa card, will limit slew rates because the 
step rates are limited by base thread speeds and the next increment 
faster is something the motor can't accel to in one step so it stalls. 
And it was doing that on the little hf mill at speeds it could cut at!

So eventually a Mesa 5i25 found a home in that machine, at which point I 
thought the psu voltage was the limit. That whole kit, computer and all, 
is now runniing the 6040 at 200ipm rapids.  The diff is the smaller, 
lower inductance motors. The one thing they did right on the 6040. The 
rest of the electronics was BBLB stuff and not capable of even being 
interfaced with linuxcnc. The vfd started the spindle ok, but in random 
directions I couldn't control, so the usual clone vfd from ebay now does 
exactly what linuxcnc tells it to.

What I am interested in is the stellarium interface, that seems to be an 
extra cost option from a different source. My googling has not found it 
for sale or even a price quote, but then my goggle-foo has been found 
wanting before. I have a 10" Meade newtonian thats now been standing 
face down behind the back door for about 20 years. I've also the 
motorized pier mount. But I'm down in a cul-de-sac and can just barely 
get down to polaris due to the tree line on the hill to the north.  And 
a huge 60+ yo maple I don't own blocks much of the below equatorial 
southern sky view. I should make it a building as I'd like to do frame a 
week movie of eta-carinae, probably the next supernova we'll get to see. 
I also have a lack of dark sky problem, street lights are old and 
unshielded. Sigh... But that interface interests me greatly.
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Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.
 - Louis D. Brandeis
Genes Web page 


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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Gregg Eshelman via Emc-users]

There are sine wave controllers that do various smoothing things to run 
steppers smooth and silent. Trinamic calls it Spread Cycle and Stealth Chop. 
https://www.youtube.com/watch?v=Q0sJlGh9WNY 
On Tuesday, July 14, 2020, 11:18:22 AM MDT, Todd Zuercher 
 wrote:  
 
 If you can hear it, it isn't smooth.  I'd recommend using the finest micro 
stepping setting your driver offers, but simply not counting on more than 1/4 
of a full step in your resolution accuracy.  But just because the motor and 
drive may not be able to physically achieve positioning accuracy much better 
than 1/4 step, doesn't mean that having the finer micro step resolution won't 
significantly contribute to smoother quieter motion.

  
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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Chris Albertson]

This person makes basically comedy videos with one totally impossible robot
after another.  The "robots" are props.  He does not try to be serious.   I
suspect the kid is the actor and others make the props.   The background
sets are built and the lighting is certainly not what is found in a home
garage.   Making a video like this is a lot of work.   They do it well and
with decent production quality, even the sound is good which is rare on
Youtube.

Back to belt reductions.  Yes of course a belt reduction can have any ratio
but always there is a minimum gear diameter lets call it "d" and if the
reduction ratio is N:1 the larger gear must by dN diameter.   Many times dN
will not fit in the available space.

On Tue, Jul 14, 2020 at 12:59 PM Jon Elson  wrote:

>
> > https://youtu.be/7zBrbdU_y0s
> >
> OH MY!  Some people REALLY have too much time on their
> hands!  Did anyone tell this guy that scissors are made to
> be held in a person's hands?  Two fingers do the snip snip
> just fine.
>
-- 

Chris Albertson
Redondo Beach, California

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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[R C]

Hi Chris,

On 7/14/20 12:10 PM, Chris Albertson wrote:

On Tue, Jul 14, 2020 at 10:50 AM John Dammeyer 
wrote:


https://youtu.be/tlMTksuOuZQ


Were you using LinuxCNC for this?  Or did you write your own control
software?


This was done with Linux CNC.   However, The purpose of me owning a mill is
for robotics.  I have not yet figured how to use LCNC for robot projects so
in those cases I do my own low-level motion control, typically using STM32
and an RTOS.


Same here,  I am using the same drivers and motors in my Sherline CNC 
machines...   BUT  trying to make my own interface fr the telescope.


(would be interesting if there could be a telescope "option"    I don't 
think a telescope is probably not that different...    but outside the 
scpe,  since it is not a CNC machine.





The video is not meant to stand alone.  It will be part of a web site that
has other videos and some text and photos.  But it does show how motors
must be ramped up and down.




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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[R C]

On 7/14/20 11:48 AM, John Dammeyer wrote:



-Original Message-
From: Chris Albertson [mailto:albertson.ch...@gmail.com]
Sent: July-14-20 2:49 AM
To: Enhanced Machine Controller (EMC)
Subject: Re: [Emc-users] off topic: pwm with a stepper driver/motor

Gene is correct when he wrote the precision might be off when
micro-stepping.


Yes.  Micro-stepping is only for harmonic reduction.  You cannot rely on 
positioning with micro-stepping. It can take 3 or 4 micro-steps to even start 
moving to overcome static friction.



Motors are mechanically built for 1.8 degree steps so that is likely to be
accurate but half steps depend on the driver.

Half steps rely on only one coil energized so you lose half the torque.  For 
static motion that may well be enough depending on the size of the motor and 
the load.

But what I wanted to add is that when you read the speed vs. torque curve
it is for FULL steps.  The amount of holding torque is reduced with
microsteps.   It makes sense too, full steps use full current that is
switched between coils just 100% on or 100% off.   With microsteps one
coild gets perhaps 3/8 of full current and the other gets something like
5/8.  So the current is overall reduced.

70.7% is the number you are looking for.


In any case, run the motors at a step rate that causes them to run smoothly
without actually stepping.  You want to see continuous motion.

BTW I'm using a DM542, the same driver you have on this vertical axis test
(link below).   It has enough power even when doing 1/2 steps to move a 35
pound chunk of steel up and up at a decent rate of speed.   machine is
obviously not balanced like a telescope  The DM542 is set for only 2.0 amps
so it is not running at full power. SO you will be fine even with the
reduced torque.


This is the first time this axis ran.  Just some jogs up and down.
https://youtu.be/tlMTksuOuZQ


Were you using LinuxCNC for this?  Or did you write your own control software?



Actually,  both.   I have a Sherline mill and lathe that I am running 
with lnux cnc  and...  the same motors and stepper drivers.



The telescope will have the same drivers and stepper motors, BUT  
writing my own interface to try and control them,...  well that before I 
try to hook it up to Stellarium directly.








John Dammeyer





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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Jon Elson]

On 07/14/2020 01:51 PM, andy pugh wrote:

On Fri, 10 Jul 2020 at 10:34, andy pugh  wrote:


I don't see why there is any limit to the possible reduction of a belt
drive, if idlers are added to increase the wrap.

And here is an example:

https://youtu.be/7zBrbdU_y0s

OH MY!  Some people REALLY have too much time on their 
hands!  Did anyone tell this guy that scissors are made to 
be held in a person's hands?  Two fingers do the snip snip 
just fine.


Jon


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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[andy pugh]

On Fri, 10 Jul 2020 at 10:34, andy pugh  wrote:

> I don't see why there is any limit to the possible reduction of a belt
> drive, if idlers are added to increase the wrap.

And here is an example:

https://youtu.be/7zBrbdU_y0s

-- 
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1912


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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Chris Albertson]

On Tue, Jul 14, 2020 at 10:50 AM John Dammeyer 
wrote:

>
> > https://youtu.be/tlMTksuOuZQ
> >
> Were you using LinuxCNC for this?  Or did you write your own control
> software?
>

This was done with Linux CNC.   However, The purpose of me owning a mill is
for robotics.  I have not yet figured how to use LCNC for robot projects so
in those cases I do my own low-level motion control, typically using STM32
and an RTOS.

The video is not meant to stand alone.  It will be part of a web site that
has other videos and some text and photos.  But it does show how motors
must be ramped up and down.

-- 

Chris Albertson
Redondo Beach, California

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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[John Dammeyer]

> -Original Message-
> From: Chris Albertson [mailto:albertson.ch...@gmail.com]
> Sent: July-14-20 2:49 AM
> To: Enhanced Machine Controller (EMC)
> Subject: Re: [Emc-users] off topic: pwm with a stepper driver/motor
> 
> Gene is correct when he wrote the precision might be off when
> micro-stepping.
> 

Yes.  Micro-stepping is only for harmonic reduction.  You cannot rely on 
positioning with micro-stepping. It can take 3 or 4 micro-steps to even start 
moving to overcome static friction.


> Motors are mechanically built for 1.8 degree steps so that is likely to be
> accurate but half steps depend on the driver.

Half steps rely on only one coil energized so you lose half the torque.  For 
static motion that may well be enough depending on the size of the motor and 
the load.
> 
> But what I wanted to add is that when you read the speed vs. torque curve
> it is for FULL steps.  The amount of holding torque is reduced with
> microsteps.   It makes sense too, full steps use full current that is
> switched between coils just 100% on or 100% off.   With microsteps one
> coild gets perhaps 3/8 of full current and the other gets something like
> 5/8.  So the current is overall reduced.

70.7% is the number you are looking for.

> 
> In any case, run the motors at a step rate that causes them to run smoothly
> without actually stepping.  You want to see continuous motion.
> 
> BTW I'm using a DM542, the same driver you have on this vertical axis test
> (link below).   It has enough power even when doing 1/2 steps to move a 35
> pound chunk of steel up and up at a decent rate of speed.   machine is
> obviously not balanced like a telescope  The DM542 is set for only 2.0 amps
> so it is not running at full power. SO you will be fine even with the
> reduced torque.
> 
> 
> This is the first time this axis ran.  Just some jogs up and down.  

> https://youtu.be/tlMTksuOuZQ
> 
Were you using LinuxCNC for this?  Or did you write your own control software?

John Dammeyer





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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Todd Zuercher]

If you can hear it, it isn't smooth.  I'd recommend using the finest micro 
stepping setting your driver offers, but simply not counting on more than 1/4 
of a full step in your resolution accuracy.  But just because the motor and 
drive may not be able to physically achieve positioning accuracy much better 
than 1/4 step, doesn't mean that having the finer micro step resolution won't 
significantly contribute to smoother quieter motion.

Todd Zuercher
P. Graham Dunn Inc.
630 Henry Street 
Dalton, Ohio 44618
Phone:  (330)828-2105ext. 2031

-Original Message-
From: R C  
Sent: Tuesday, July 14, 2020 9:39 AM
To: emc-users@lists.sourceforge.net
Subject: Re: [Emc-users] off topic: pwm with a stepper driver/motor

[EXTERNAL EMAIL] Be sure links are safe.

Hi Chris,


for the go to part I am not "too worried"about that possibly not being too 
smooth, of course it is the goal to do that, but

the point there is to get there.

The equatorial tracking indeed needs to be as smooth as possible.  With the 
hearing I have I think I can run the stepper motors smooth

without having to do any micro stepping.


thanks,


Ron



On 7/14/20 3:49 AM, Chris Albertson wrote:
> Gene is correct when he wrote the precision might be off when 
> micro-stepping.
>
> Motors are mechanically built for 1.8 degree steps so that is likely 
> to be accurate but half steps depend on the driver.
>
> But what I wanted to add is that when you read the speed vs. torque 
> curve it is for FULL steps.  The amount of holding torque is reduced with
> microsteps.   It makes sense too, full steps use full current that is
> switched between coils just 100% on or 100% off.   With microsteps one
> coild gets perhaps 3/8 of full current and the other gets something 
> like 5/8.  So the current is overall reduced.
>
> In any case, run the motors at a step rate that causes them to run 
> smoothly without actually stepping.  You want to see continuous motion.
>
> BTW I'm using a DM542, the same driver you have on this vertical axis test
> (link below).   It has enough power even when doing 1/2 steps to move a 35
> pound chunk of steel up and up at a decent rate of speed.   machine is
> obviously not balanced like a telescope  The DM542 is set for only 2.0 amps
> so it is not running at full power. SO you will be fine even with the
> reduced torque.
>
>
> This is the first time this axis ran.  Just some jogs up and down.   But
> listen to the motor, you can't start and stop these stepper motors 
> instantly the velocity ramps up and down.  In fact this rate of change 
> is as fast as I can go with this setup and the DM542's  2.0 amp current limit.
>If you do a fast slew to a target, you need to ramp up the speed 
> then slow down and hit the mark and then pick up the star tracking 
> rate.  That second loop controls the speed and the rate of change of that 
> speed.
> Software was to plan the motion in advance so that it start to slow 
> soon enough not to over shoot https://youtu.be/tlMTksuOuZQ
>
> On Mon, Jul 13, 2020 at 11:51 PM Gene Heskett  wrote:
>
>>> The driver tech-sheet  basically says it can do pretty all it's 
>>> available micro stepping with a 1.8 degree stepper motor, I wonder 
>>> if that is really true.
>>>
>> In theory yes, in practice, no. There is resistor tolerances and all 
>> sorts of errors that can creep into a motor being held by the 
>> relative balance of the currents thru 2 sets of coils.
>


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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Jon Elson]

On 07/14/2020 04:49 AM, Chris Albertson wrote:

But what I wanted to add is that when you read the speed vs. torque curve
it is for FULL steps.  The amount of holding torque is reduced with
microsteps.   It makes sense too, full steps use full current that is
switched between coils just 100% on or 100% off.   With microsteps one
coild gets perhaps 3/8 of full current and the other gets something like
5/8.  So the current is overall reduced.

Well, this is only partially true.  It is a rare case where 
the actual standstill holding torque is exceeded by the 
load.  Most often, the motor is stalled while moving.  The 
running torque of a stepper is less (sometimes MUCH less) 
than the holding torque, and resonances really hurt the 
running torque.  A microstepping drive reduces the 
resonances, and smart microstepping like Gecko uses adds 
active damping to absorb the resonant energy.  These systems 
will have much higher running torque than a full-step drive.


Jon


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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[R C]

Hi Chris,


for the go to part I am not "too worried"about that possibly not being 
too smooth, of course it is the goal to do that, but


the point there is to get there.

The equatorial tracking indeed needs to be as smooth as possible.  With 
the hearing I have I think I can run the stepper motors smooth


without having to do any micro stepping.


thanks,


Ron



On 7/14/20 3:49 AM, Chris Albertson wrote:

Gene is correct when he wrote the precision might be off when
micro-stepping.

Motors are mechanically built for 1.8 degree steps so that is likely to be
accurate but half steps depend on the driver.

But what I wanted to add is that when you read the speed vs. torque curve
it is for FULL steps.  The amount of holding torque is reduced with
microsteps.   It makes sense too, full steps use full current that is
switched between coils just 100% on or 100% off.   With microsteps one
coild gets perhaps 3/8 of full current and the other gets something like
5/8.  So the current is overall reduced.

In any case, run the motors at a step rate that causes them to run smoothly
without actually stepping.  You want to see continuous motion.

BTW I'm using a DM542, the same driver you have on this vertical axis test
(link below).   It has enough power even when doing 1/2 steps to move a 35
pound chunk of steel up and up at a decent rate of speed.   machine is
obviously not balanced like a telescope  The DM542 is set for only 2.0 amps
so it is not running at full power. SO you will be fine even with the
reduced torque.


This is the first time this axis ran.  Just some jogs up and down.   But
listen to the motor, you can't start and stop these stepper motors
instantly the velocity ramps up and down.  In fact this rate of change is
as fast as I can go with this setup and the DM542's  2.0 amp current limit.
   If you do a fast slew to a target, you need to ramp up the speed then
slow down and hit the mark and then pick up the star tracking rate.  That
second loop controls the speed and the rate of change of that speed.
Software was to plan the motion in advance so that it start to slow soon
enough not to over shoot
https://youtu.be/tlMTksuOuZQ

On Mon, Jul 13, 2020 at 11:51 PM Gene Heskett  wrote:


The driver tech-sheet  basically says it can do pretty all it's
available micro stepping with a 1.8 degree stepper motor, I wonder if
that is really true.


In theory yes, in practice, no. There is resistor tolerances and all
sorts of errors that can creep into a motor being held by the relative
balance of the currents thru 2 sets of coils.





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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Chris Albertson]

Gene is correct when he wrote the precision might be off when
micro-stepping.

Motors are mechanically built for 1.8 degree steps so that is likely to be
accurate but half steps depend on the driver.

But what I wanted to add is that when you read the speed vs. torque curve
it is for FULL steps.  The amount of holding torque is reduced with
microsteps.   It makes sense too, full steps use full current that is
switched between coils just 100% on or 100% off.   With microsteps one
coild gets perhaps 3/8 of full current and the other gets something like
5/8.  So the current is overall reduced.

In any case, run the motors at a step rate that causes them to run smoothly
without actually stepping.  You want to see continuous motion.

BTW I'm using a DM542, the same driver you have on this vertical axis test
(link below).   It has enough power even when doing 1/2 steps to move a 35
pound chunk of steel up and up at a decent rate of speed.   machine is
obviously not balanced like a telescope  The DM542 is set for only 2.0 amps
so it is not running at full power. SO you will be fine even with the
reduced torque.


This is the first time this axis ran.  Just some jogs up and down.   But
listen to the motor, you can't start and stop these stepper motors
instantly the velocity ramps up and down.  In fact this rate of change is
as fast as I can go with this setup and the DM542's  2.0 amp current limit.
  If you do a fast slew to a target, you need to ramp up the speed then
slow down and hit the mark and then pick up the star tracking rate.  That
second loop controls the speed and the rate of change of that speed.
Software was to plan the motion in advance so that it start to slow soon
enough not to over shoot
https://youtu.be/tlMTksuOuZQ

On Mon, Jul 13, 2020 at 11:51 PM Gene Heskett  wrote:

>
> > The driver tech-sheet  basically says it can do pretty all it's
> > available micro stepping with a 1.8 degree stepper motor, I wonder if
> > that is really true.
> >
> In theory yes, in practice, no. There is resistor tolerances and all
> sorts of errors that can creep into a motor being held by the relative
> balance of the currents thru 2 sets of coils.


-- 

Chris Albertson
Redondo Beach, California

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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[R C]

Hello Gene,

On 7/14/20 12:49 AM, Gene Heskett wrote:

On Monday 13 July 2020 22:44:37 R C wrote:


well,  I can calculate what the speed needs to be, also I can actually
"observe" it too..  by pointing the  telescope at a star and see how
much the deviation is.  I have encoder to check the actual speed of a
shaft.

I found some information in a manual/tech-sheet that comes with the
drivers, so I am trying to figure out what the best stepping rate is
and what the best way of actually sending pulses to the stepper-driver
is.

I wrote some c-code that runs the motors in pthreads, I just want to
know what the best way is.  pulse lengths, pause/gap length etc.
(basically the best way to use a dm542  (all those steppers are sorta
the same I understand)

The driver tech-sheet  basically says it can do pretty all it's
available micro stepping with a 1.8 degree stepper motor, I wonder if
that is really true.


In theory yes, in practice, no. There is resistor tolerances and all
sorts of errors that can creep into a motor being held by the relative
balance of the currents thru 2 sets of coils. So while a full switch
will move it 1.8 dgreees, or 1.2 with the newer 3 phase models, between
magnetics and parts tolerances, half current in each coil might be out
of balance as much as 10% in off the shelf stuff. Sometimes its fairly
obvious, I have a dm860 driver that when moving a 1600 oz/in motor at
a /8 divisor, moves 7 steps rather noisily, and the 8th step cannot be
seen or heard.  Worked fine on my mill as long as I stayed below 26 ipm.
But thats too slow for rigid tapping. A 960oz/in and ac powered driver
was subbed, moves that heavy head at nearly 100 ipm, dead smooth.

Right, but I can probably get it close by calculating, and then adjust  
for "tolerances" and


feedback from the encoders I have.


I also have a dm860, using it in a Sherline mill where I put a bigger 
stepper motor on the Z-axis.


(I replaced all stepper motors and drivers in a Sherline mill and lathe 
(they came in a Paxton/Patterson enclosure).



thanks,


Ron





Ron

On 7/13/20 8:35 PM, Chris Albertson wrote:

A fast control loop that drives each motor at a given speed and a
second slower control loop that figures out what that speed should
be.   The second loop typically uses "PID" even if only in fact the
"P" is used.

That can be used to drive any number of motors all at their correct
speeds.

On Mon, Jul 13, 2020 at 7:28 PM R C  wrote:

Interesting,


but I already have the motors,  and  the gears are on their way.
What I was really looking for is how to drive the stepper-drivers,
he DM542 series ones.


Ron

On 7/13/20 7:53 PM, cogoman via Emc-users wrote:

I recently discovered geared stepper motors.

http://www.zyltech.com/nema-17-stepper-motor-geared-planetary-gearb
ox-1-7-a-3-1-nm-435-ozin/


I've been happy with zyltech in the past.  I bought one of these
for evluation, but the specs seem to be great for CNC. Low enough
current to work with a stepstick, High enough torque for a fairly
powerful machine, and less than 4 mH inductance should let it step
pretty fast.

5.18:1 gear ratio should reduce that 4 meter spur gear, but the
link below has higher gear ratios that would reduce that spur gear
greatly! Backlash could be a problem for CNC, but if you are only
going one way, the less precision gearboxes might be fine.

https://www.omc-stepperonline.com/geared-stepper-motor/?sort=p.pric
e&order=ASC


Once you visit the stepperonline web page you know as much about
them as I do, but their offerings might be just right for your
application.

On 7/9/20 2:23 PM, R C wrote:

Hello,

this is (probably) off topic, been seen that happen.  If it is
please ignore it.


I am building a "motorized"  telescope mount (dobsonian) with
what is called an equatorial platform, it has 3 axis which I am
going to drive with stepper motors.


The stepper motors I use with a stepper driver, those common
DM542 ones, the stepper motors themselves are 2A and 1.8 degrees
per step.


What I want to accomplish with the equatorial platform)  (it
compensates for the rotation of the earth) is that,  the start
and end position accuracy is not that important,  smooth and
constant/consistent movement is.  for the azimuth/altitude
precision is not a really big deal, but you'd want to move these
2 axis somewhat swift.


So there are a few factors to decide.


I probably want micro stepping,  what settings on the driver for
pulses per rev, is best to use (or is that just trial and error?)


As with PWM itself, I am probably just not too familiar with it.
 From what I understand, the voltage I use for the motors
determines how fast I can go (I am going to use a 48V switching
power supply).


as for PWM,  I can of course  change the length of the pulse
itself and, independently, change the time between two pulses.
What is the relation ship there?  WHat does a longer  width of
the pulse itself do?  and what exactly does a longer gap between
the pulses do (of course the wid

Re: [Emc-users] off topic: pwm with a stepper driver/motor

[R C]

Hello Chris,


On 7/14/20 12:31 AM, Chris Albertson wrote:

On Mon, Jul 13, 2020 at 7:28 PM R C  wrote:


Interesting,


but I already have the motors,  and  the gears are on their way.   What
I was really looking for is how to drive the stepper-drivers, he DM542
series ones.



Do you have the user manual for the DM542?   If not look at the top top
half of page 9 here https://www.omc-stepperonline.com/download/DM542T.pdf


Actually I do have it,  it is very similar to the one you mentioned above.


It tells you things like how long you need to hold the "DIR" pin before the
next step pulse and  the minimum pulse widths.
The one I have also needs to have the DIR set 5us before you do anything 
else

I'd make them all larger than needed by about 4X because you are not trying
to make these go fast.  In fact, a 50% duty cycle square wave works fine.


So you'd set the wait after the DIR 20us?   and PUL the duty cycle  
10us,  5us hi then 5us lo?


I set it up so that it is 'variable' in a mem-shared array, so I can 
change some parameters (for example because of feedback from the 
encoders, or by 'manually' adjusting it.) while the threads keep running.



What you do is in the loop when you set a pin high you store the time for
when it must be set low and every time through the loop you do whatever has
a time-to-do that is expired.  You can juggle N balls at once in one loop
this way.


What I am doing is use multiple threads,  I am writing it in C, and use 
a separate pthread for each stepper-driver / motor.


Once the telescope starts tracking, only one motor/thread will run, the 
other two are mostly 'idling. '.



thanks! that was what I was somewhat looking for, some actuall number I 
can use that work and go from there.  The speed just depends on how much 
time there is between the duty cycles,  at least tat is what I noticed, 
correct?



Would it be better to use a higher number of steps?  The manual seems to 
indicate that I can almost use any setting there with a "1.8 degrees 
steppermotor", which somewhat surprised me.


Ron



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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Gene Heskett]

On Monday 13 July 2020 22:44:37 R C wrote:

> well,  I can calculate what the speed needs to be, also I can actually
> "observe" it too..  by pointing the  telescope at a star and see how
> much the deviation is.  I have encoder to check the actual speed of a
> shaft.
>
> I found some information in a manual/tech-sheet that comes with the
> drivers, so I am trying to figure out what the best stepping rate is
> and what the best way of actually sending pulses to the stepper-driver
> is.
>
> I wrote some c-code that runs the motors in pthreads, I just want to
> know what the best way is.  pulse lengths, pause/gap length etc.
> (basically the best way to use a dm542  (all those steppers are sorta
> the same I understand)
>
> The driver tech-sheet  basically says it can do pretty all it's
> available micro stepping with a 1.8 degree stepper motor, I wonder if
> that is really true.
>
In theory yes, in practice, no. There is resistor tolerances and all 
sorts of errors that can creep into a motor being held by the relative 
balance of the currents thru 2 sets of coils. So while a full switch 
will move it 1.8 dgreees, or 1.2 with the newer 3 phase models, between 
magnetics and parts tolerances, half current in each coil might be out 
of balance as much as 10% in off the shelf stuff. Sometimes its fairly 
obvious, I have a dm860 driver that when moving a 1600 oz/in motor at 
a /8 divisor, moves 7 steps rather noisily, and the 8th step cannot be 
seen or heard.  Worked fine on my mill as long as I stayed below 26 ipm. 
But thats too slow for rigid tapping. A 960oz/in and ac powered driver 
was subbed, moves that heavy head at nearly 100 ipm, dead smooth.

> Ron
>
> On 7/13/20 8:35 PM, Chris Albertson wrote:
> > A fast control loop that drives each motor at a given speed and a
> > second slower control loop that figures out what that speed should
> > be.   The second loop typically uses "PID" even if only in fact the
> > "P" is used.
> >
> > That can be used to drive any number of motors all at their correct
> > speeds.
> >
> > On Mon, Jul 13, 2020 at 7:28 PM R C  wrote:
> >> Interesting,
> >>
> >>
> >> but I already have the motors,  and  the gears are on their way.  
> >> What I was really looking for is how to drive the stepper-drivers,
> >> he DM542 series ones.
> >>
> >>
> >> Ron
> >>
> >> On 7/13/20 7:53 PM, cogoman via Emc-users wrote:
> >>> I recently discovered geared stepper motors.
> >>
> >> http://www.zyltech.com/nema-17-stepper-motor-geared-planetary-gearb
> >>ox-1-7-a-3-1-nm-435-ozin/
> >>
> >>> I've been happy with zyltech in the past.  I bought one of these
> >>> for evluation, but the specs seem to be great for CNC. Low enough
> >>> current to work with a stepstick, High enough torque for a fairly
> >>> powerful machine, and less than 4 mH inductance should let it step
> >>> pretty fast.
> >>>
> >>> 5.18:1 gear ratio should reduce that 4 meter spur gear, but the
> >>> link below has higher gear ratios that would reduce that spur gear
> >>> greatly! Backlash could be a problem for CNC, but if you are only
> >>> going one way, the less precision gearboxes might be fine.
> >>
> >> https://www.omc-stepperonline.com/geared-stepper-motor/?sort=p.pric
> >>e&order=ASC
> >>
> >>> Once you visit the stepperonline web page you know as much about
> >>> them as I do, but their offerings might be just right for your
> >>> application.
> >>>
> >>> On 7/9/20 2:23 PM, R C wrote:
>  Hello,
> 
>  this is (probably) off topic, been seen that happen.  If it is
>  please ignore it.
> 
> 
>  I am building a "motorized"  telescope mount (dobsonian) with
>  what is called an equatorial platform, it has 3 axis which I am
>  going to drive with stepper motors.
> 
> 
>  The stepper motors I use with a stepper driver, those common
>  DM542 ones, the stepper motors themselves are 2A and 1.8 degrees
>  per step.
> 
> 
>  What I want to accomplish with the equatorial platform)  (it
>  compensates for the rotation of the earth) is that,  the start
>  and end position accuracy is not that important,  smooth and
>  constant/consistent movement is.  for the azimuth/altitude
>  precision is not a really big deal, but you'd want to move these
>  2 axis somewhat swift.
> 
> 
>  So there are a few factors to decide.
> 
> 
>  I probably want micro stepping,  what settings on the driver for
>  pulses per rev, is best to use (or is that just trial and error?)
> 
> 
>  As with PWM itself, I am probably just not too familiar with it.
>  From what I understand, the voltage I use for the motors
>  determines how fast I can go (I am going to use a 48V switching
>  power supply).
> 
> 
>  as for PWM,  I can of course  change the length of the pulse
>  itself and, independently, change the time between two pulses.
>  What is the relation ship there?  WHat does a longer  width of
>  th

Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Chris Albertson]

On Mon, Jul 13, 2020 at 7:28 PM R C  wrote:

> Interesting,
>
>
> but I already have the motors,  and  the gears are on their way.   What
> I was really looking for is how to drive the stepper-drivers, he DM542
> series ones.
>


Do you have the user manual for the DM542?   If not look at the top top
half of page 9 here https://www.omc-stepperonline.com/download/DM542T.pdf

It tells you things like how long you need to hold the "DIR" pin before the
next step pulse and  the minimum pulse widths.

I'd make them all larger than needed by about 4X because you are not trying
to make these go fast.  In fact, a 50% duty cycle square wave works fine.

What you do is in the loop when you set a pin high you store the time for
when it must be set low and every time through the loop you do whatever has
a time-to-do that is expired.  You can juggle N balls at once in one loop
this way.

-- 

Chris Albertson
Redondo Beach, California

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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[R C]

yup exactly,  actually in a way  so I can point at things that you can't 
really see but  would need longer exposures for.


On 7/13/20 9:28 PM, Chris Albertson wrote:

On Mon, Jul 13, 2020 at 8:02 PM Dave Matthews  wrote:


It may just be my age but wouldn't it be easier to just use a 555 (do they
still make them) and a knob to tweak the pulse rate to match the star?


That would be easy but I think there is some plan to have a "go to"
ability where the 'scope slews to a target selected from a database.

Also, a full-up computer today sells for the same price as a 555 chip.  You
can get an AVR (Arduino chip) in an 8-pin package for just a few cents.



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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[R C]

yeah that would be easiest,  but I want to do something similar for 
azimuth and altitude.


On 7/13/20 9:00 PM, Dave Matthews wrote:

It may just be my age but wouldn't it be easier to just use a 555 (do they
still make them) and a knob to tweak the pulse rate to match the star?  Add
a slew button to change the speed while the button is pushed and a
direction switch to toggle the direction pin on the driver.  I guess I
don't see the need for a computer to run a stepper at a constant speed.

Dave

On Mon, Jul 13, 2020, 22:46 R C  wrote:


well,  I can calculate what the speed needs to be, also I can actually
"observe" it too..  by pointing the  telescope at a star and see how
much the deviation is.  I have encoder to check the actual speed of a
shaft.

I found some information in a manual/tech-sheet that comes with the
drivers, so I am trying to figure out what the best stepping rate is and
what the best way of actually sending pulses to the stepper-driver is.

I wrote some c-code that runs the motors in pthreads, I just want to
know what the best way is.  pulse lengths, pause/gap length etc.
(basically the best way to use a dm542  (all those steppers are sorta
the same I understand)

The driver tech-sheet  basically says it can do pretty all it's
available micro stepping with a 1.8 degree stepper motor, I wonder if
that is really true.


Ron


On 7/13/20 8:35 PM, Chris Albertson wrote:

A fast control loop that drives each motor at a given speed and a second
slower control loop that figures out what that speed should be.   The
second loop typically uses "PID" even if only in fact the "P" is used.

That can be used to drive any number of motors all at their correct

speeds.


On Mon, Jul 13, 2020 at 7:28 PM R C  wrote:


Interesting,


but I already have the motors,  and  the gears are on their way.   What
I was really looking for is how to drive the stepper-drivers, he DM542
series ones.


Ron



On 7/13/20 7:53 PM, cogoman via Emc-users wrote:

I recently discovered geared stepper motors.



http://www.zyltech.com/nema-17-stepper-motor-geared-planetary-gearbox-1-7-a-3-1-nm-435-ozin/

I've been happy with zyltech in the past.  I bought one of these for
evluation, but the specs seem to be great for CNC. Low enough current
to work with a stepstick, High enough torque for a fairly powerful
machine, and less than 4 mH inductance should let it step pretty fast.

5.18:1 gear ratio should reduce that 4 meter spur gear, but the link
below has higher gear ratios that would reduce that spur gear greatly!
Backlash could be a problem for CNC, but if you are only going one
way, the less precision gearboxes might be fine.



https://www.omc-stepperonline.com/geared-stepper-motor/?sort=p.price&order=ASC

Once you visit the stepperonline web page you know as much about them
as I do, but their offerings might be just right for your application.

On 7/9/20 2:23 PM, R C wrote:

Hello,

this is (probably) off topic, been seen that happen.  If it is please
ignore it.


I am building a "motorized"  telescope mount (dobsonian) with what is
called an equatorial platform, it has 3 axis which I am going to
drive with stepper motors.


The stepper motors I use with a stepper driver, those common DM542
ones, the stepper motors themselves are 2A and 1.8 degrees per step.


What I want to accomplish with the equatorial platform)  (it
compensates for the rotation of the earth) is that,  the start and
end position accuracy is not that important,  smooth and
constant/consistent movement is.  for the azimuth/altitude precision
is not a really big deal, but you'd want to move these 2 axis
somewhat swift.


So there are a few factors to decide.


I probably want micro stepping,  what settings on the driver for
pulses per rev, is best to use (or is that just trial and error?)


As with PWM itself, I am probably just not too familiar with it. From
what I understand, the voltage I use for the motors determines how
fast I can go (I am going to use a 48V switching power supply).


as for PWM,  I can of course  change the length of the pulse itself
and, independently, change the time between two pulses. What is the
relation ship there?  WHat does a longer  width of the pulse itself
do?  and what exactly does a longer gap between the pulses do (of
course the wider the gap between two pulses the slower the motor

turns).


for, especially, the equatorial platform, I want to avoid "jerking"
it,  meaning  starting and stopping the stepper motor as little as
possible and just go at a 'slow' constant speed.



sorry if totally of topic


thanks,


Ron



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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Chris Albertson]

On Mon, Jul 13, 2020 at 8:02 PM Dave Matthews  wrote:

> It may just be my age but wouldn't it be easier to just use a 555 (do they
> still make them) and a knob to tweak the pulse rate to match the star?


That would be easy but I think there is some plan to have a "go to"
ability where the 'scope slews to a target selected from a database.

Also, a full-up computer today sells for the same price as a 555 chip.  You
can get an AVR (Arduino chip) in an 8-pin package for just a few cents.
-- 

Chris Albertson
Redondo Beach, California

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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Dave Matthews]

It may just be my age but wouldn't it be easier to just use a 555 (do they
still make them) and a knob to tweak the pulse rate to match the star?  Add
a slew button to change the speed while the button is pushed and a
direction switch to toggle the direction pin on the driver.  I guess I
don't see the need for a computer to run a stepper at a constant speed.

Dave

On Mon, Jul 13, 2020, 22:46 R C  wrote:

> well,  I can calculate what the speed needs to be, also I can actually
> "observe" it too..  by pointing the  telescope at a star and see how
> much the deviation is.  I have encoder to check the actual speed of a
> shaft.
>
> I found some information in a manual/tech-sheet that comes with the
> drivers, so I am trying to figure out what the best stepping rate is and
> what the best way of actually sending pulses to the stepper-driver is.
>
> I wrote some c-code that runs the motors in pthreads, I just want to
> know what the best way is.  pulse lengths, pause/gap length etc.
> (basically the best way to use a dm542  (all those steppers are sorta
> the same I understand)
>
> The driver tech-sheet  basically says it can do pretty all it's
> available micro stepping with a 1.8 degree stepper motor, I wonder if
> that is really true.
>
>
> Ron
>
>
> On 7/13/20 8:35 PM, Chris Albertson wrote:
> > A fast control loop that drives each motor at a given speed and a second
> > slower control loop that figures out what that speed should be.   The
> > second loop typically uses "PID" even if only in fact the "P" is used.
> >
> > That can be used to drive any number of motors all at their correct
> speeds.
> >
> >
> > On Mon, Jul 13, 2020 at 7:28 PM R C  wrote:
> >
> >> Interesting,
> >>
> >>
> >> but I already have the motors,  and  the gears are on their way.   What
> >> I was really looking for is how to drive the stepper-drivers, he DM542
> >> series ones.
> >>
> >>
> >> Ron
> >>
> >>
> >>
> >> On 7/13/20 7:53 PM, cogoman via Emc-users wrote:
> >>> I recently discovered geared stepper motors.
> >>>
> >>>
> >>
> http://www.zyltech.com/nema-17-stepper-motor-geared-planetary-gearbox-1-7-a-3-1-nm-435-ozin/
> >>>
> >>> I've been happy with zyltech in the past.  I bought one of these for
> >>> evluation, but the specs seem to be great for CNC. Low enough current
> >>> to work with a stepstick, High enough torque for a fairly powerful
> >>> machine, and less than 4 mH inductance should let it step pretty fast.
> >>>
> >>> 5.18:1 gear ratio should reduce that 4 meter spur gear, but the link
> >>> below has higher gear ratios that would reduce that spur gear greatly!
> >>> Backlash could be a problem for CNC, but if you are only going one
> >>> way, the less precision gearboxes might be fine.
> >>>
> >>>
> >>
> https://www.omc-stepperonline.com/geared-stepper-motor/?sort=p.price&order=ASC
> >>>
> >>> Once you visit the stepperonline web page you know as much about them
> >>> as I do, but their offerings might be just right for your application.
> >>>
> >>> On 7/9/20 2:23 PM, R C wrote:
>  Hello,
> 
>  this is (probably) off topic, been seen that happen.  If it is please
>  ignore it.
> 
> 
>  I am building a "motorized"  telescope mount (dobsonian) with what is
>  called an equatorial platform, it has 3 axis which I am going to
>  drive with stepper motors.
> 
> 
>  The stepper motors I use with a stepper driver, those common DM542
>  ones, the stepper motors themselves are 2A and 1.8 degrees per step.
> 
> 
>  What I want to accomplish with the equatorial platform)  (it
>  compensates for the rotation of the earth) is that,  the start and
>  end position accuracy is not that important,  smooth and
>  constant/consistent movement is.  for the azimuth/altitude precision
>  is not a really big deal, but you'd want to move these 2 axis
>  somewhat swift.
> 
> 
>  So there are a few factors to decide.
> 
> 
>  I probably want micro stepping,  what settings on the driver for
>  pulses per rev, is best to use (or is that just trial and error?)
> 
> 
>  As with PWM itself, I am probably just not too familiar with it. From
>  what I understand, the voltage I use for the motors determines how
>  fast I can go (I am going to use a 48V switching power supply).
> 
> 
>  as for PWM,  I can of course  change the length of the pulse itself
>  and, independently, change the time between two pulses. What is the
>  relation ship there?  WHat does a longer  width of the pulse itself
>  do?  and what exactly does a longer gap between the pulses do (of
>  course the wider the gap between two pulses the slower the motor
> turns).
> 
> 
>  for, especially, the equatorial platform, I want to avoid "jerking"
>  it,  meaning  starting and stopping the stepper motor as little as
>  possible and just go at a 'slow' constant speed.
> 
> 
> 
>  sorry if tot

Re: [Emc-users] off topic: pwm with a stepper driver/motor

[R C]

well,  I can calculate what the speed needs to be, also I can actually 
"observe" it too..  by pointing the  telescope at a star and see how 
much the deviation is.  I have encoder to check the actual speed of a shaft.


I found some information in a manual/tech-sheet that comes with the 
drivers, so I am trying to figure out what the best stepping rate is and 
what the best way of actually sending pulses to the stepper-driver is.


I wrote some c-code that runs the motors in pthreads, I just want to 
know what the best way is.  pulse lengths, pause/gap length etc. 
(basically the best way to use a dm542  (all those steppers are sorta 
the same I understand)


The driver tech-sheet  basically says it can do pretty all it's 
available micro stepping with a 1.8 degree stepper motor, I wonder if 
that is really true.



Ron


On 7/13/20 8:35 PM, Chris Albertson wrote:

A fast control loop that drives each motor at a given speed and a second
slower control loop that figures out what that speed should be.   The
second loop typically uses "PID" even if only in fact the "P" is used.

That can be used to drive any number of motors all at their correct speeds.


On Mon, Jul 13, 2020 at 7:28 PM R C  wrote:


Interesting,


but I already have the motors,  and  the gears are on their way.   What
I was really looking for is how to drive the stepper-drivers, he DM542
series ones.


Ron



On 7/13/20 7:53 PM, cogoman via Emc-users wrote:

I recently discovered geared stepper motors.



http://www.zyltech.com/nema-17-stepper-motor-geared-planetary-gearbox-1-7-a-3-1-nm-435-ozin/


I've been happy with zyltech in the past.  I bought one of these for
evluation, but the specs seem to be great for CNC. Low enough current
to work with a stepstick, High enough torque for a fairly powerful
machine, and less than 4 mH inductance should let it step pretty fast.

5.18:1 gear ratio should reduce that 4 meter spur gear, but the link
below has higher gear ratios that would reduce that spur gear greatly!
Backlash could be a problem for CNC, but if you are only going one
way, the less precision gearboxes might be fine.



https://www.omc-stepperonline.com/geared-stepper-motor/?sort=p.price&order=ASC


Once you visit the stepperonline web page you know as much about them
as I do, but their offerings might be just right for your application.

On 7/9/20 2:23 PM, R C wrote:

Hello,

this is (probably) off topic, been seen that happen.  If it is please
ignore it.


I am building a "motorized"  telescope mount (dobsonian) with what is
called an equatorial platform, it has 3 axis which I am going to
drive with stepper motors.


The stepper motors I use with a stepper driver, those common DM542
ones, the stepper motors themselves are 2A and 1.8 degrees per step.


What I want to accomplish with the equatorial platform)  (it
compensates for the rotation of the earth) is that,  the start and
end position accuracy is not that important,  smooth and
constant/consistent movement is.  for the azimuth/altitude precision
is not a really big deal, but you'd want to move these 2 axis
somewhat swift.


So there are a few factors to decide.


I probably want micro stepping,  what settings on the driver for
pulses per rev, is best to use (or is that just trial and error?)


As with PWM itself, I am probably just not too familiar with it. From
what I understand, the voltage I use for the motors determines how
fast I can go (I am going to use a 48V switching power supply).


as for PWM,  I can of course  change the length of the pulse itself
and, independently, change the time between two pulses. What is the
relation ship there?  WHat does a longer  width of the pulse itself
do?  and what exactly does a longer gap between the pulses do (of
course the wider the gap between two pulses the slower the motor turns).


for, especially, the equatorial platform, I want to avoid "jerking"
it,  meaning  starting and stopping the stepper motor as little as
possible and just go at a 'slow' constant speed.



sorry if totally of topic


thanks,


Ron



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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Chris Albertson]

A fast control loop that drives each motor at a given speed and a second
slower control loop that figures out what that speed should be.   The
second loop typically uses "PID" even if only in fact the "P" is used.

That can be used to drive any number of motors all at their correct speeds.


On Mon, Jul 13, 2020 at 7:28 PM R C  wrote:

> Interesting,
>
>
> but I already have the motors,  and  the gears are on their way.   What
> I was really looking for is how to drive the stepper-drivers, he DM542
> series ones.
>
>
> Ron
>
>
>
> On 7/13/20 7:53 PM, cogoman via Emc-users wrote:
> > I recently discovered geared stepper motors.
> >
> >
> http://www.zyltech.com/nema-17-stepper-motor-geared-planetary-gearbox-1-7-a-3-1-nm-435-ozin/
> >
> >
> > I've been happy with zyltech in the past.  I bought one of these for
> > evluation, but the specs seem to be great for CNC. Low enough current
> > to work with a stepstick, High enough torque for a fairly powerful
> > machine, and less than 4 mH inductance should let it step pretty fast.
> >
> > 5.18:1 gear ratio should reduce that 4 meter spur gear, but the link
> > below has higher gear ratios that would reduce that spur gear greatly!
> > Backlash could be a problem for CNC, but if you are only going one
> > way, the less precision gearboxes might be fine.
> >
> >
> https://www.omc-stepperonline.com/geared-stepper-motor/?sort=p.price&order=ASC
> >
> >
> > Once you visit the stepperonline web page you know as much about them
> > as I do, but their offerings might be just right for your application.
> >
> > On 7/9/20 2:23 PM, R C wrote:
> >> Hello,
> >>
> >> this is (probably) off topic, been seen that happen.  If it is please
> >> ignore it.
> >>
> >>
> >> I am building a "motorized"  telescope mount (dobsonian) with what is
> >> called an equatorial platform, it has 3 axis which I am going to
> >> drive with stepper motors.
> >>
> >>
> >> The stepper motors I use with a stepper driver, those common DM542
> >> ones, the stepper motors themselves are 2A and 1.8 degrees per step.
> >>
> >>
> >> What I want to accomplish with the equatorial platform)  (it
> >> compensates for the rotation of the earth) is that,  the start and
> >> end position accuracy is not that important,  smooth and
> >> constant/consistent movement is.  for the azimuth/altitude precision
> >> is not a really big deal, but you'd want to move these 2 axis
> >> somewhat swift.
> >>
> >>
> >> So there are a few factors to decide.
> >>
> >>
> >> I probably want micro stepping,  what settings on the driver for
> >> pulses per rev, is best to use (or is that just trial and error?)
> >>
> >>
> >> As with PWM itself, I am probably just not too familiar with it. From
> >> what I understand, the voltage I use for the motors determines how
> >> fast I can go (I am going to use a 48V switching power supply).
> >>
> >>
> >> as for PWM,  I can of course  change the length of the pulse itself
> >> and, independently, change the time between two pulses. What is the
> >> relation ship there?  WHat does a longer  width of the pulse itself
> >> do?  and what exactly does a longer gap between the pulses do (of
> >> course the wider the gap between two pulses the slower the motor turns).
> >>
> >>
> >> for, especially, the equatorial platform, I want to avoid "jerking"
> >> it,  meaning  starting and stopping the stepper motor as little as
> >> possible and just go at a 'slow' constant speed.
> >>
> >>
> >>
> >> sorry if totally of topic
> >>
> >>
> >> thanks,
> >>
> >>
> >> Ron
> >>
> >>
> >>
> >> ___
> >> Emc-users mailing list
> >> Emc-users@lists.sourceforge.net
> >> https://lists.sourceforge.net/lists/listinfo/emc-users
> >
> >
> >
> > ___
> > Emc-users mailing list
> > Emc-users@lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/emc-users
>
>
> ___
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>


-- 

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Redondo Beach, California

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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[R C]

Interesting,


but I already have the motors,  and  the gears are on their way.   What 
I was really looking for is how to drive the stepper-drivers, he DM542 
series ones.



Ron



On 7/13/20 7:53 PM, cogoman via Emc-users wrote:

I recently discovered geared stepper motors.

http://www.zyltech.com/nema-17-stepper-motor-geared-planetary-gearbox-1-7-a-3-1-nm-435-ozin/ 



I've been happy with zyltech in the past.  I bought one of these for 
evluation, but the specs seem to be great for CNC. Low enough current 
to work with a stepstick, High enough torque for a fairly powerful 
machine, and less than 4 mH inductance should let it step pretty fast.


5.18:1 gear ratio should reduce that 4 meter spur gear, but the link 
below has higher gear ratios that would reduce that spur gear greatly! 
Backlash could be a problem for CNC, but if you are only going one 
way, the less precision gearboxes might be fine.


https://www.omc-stepperonline.com/geared-stepper-motor/?sort=p.price&order=ASC 



Once you visit the stepperonline web page you know as much about them 
as I do, but their offerings might be just right for your application.


On 7/9/20 2:23 PM, R C wrote:

Hello,

this is (probably) off topic, been seen that happen.  If it is please 
ignore it.



I am building a "motorized"  telescope mount (dobsonian) with what is 
called an equatorial platform, it has 3 axis which I am going to 
drive with stepper motors.



The stepper motors I use with a stepper driver, those common DM542 
ones, the stepper motors themselves are 2A and 1.8 degrees per step.



What I want to accomplish with the equatorial platform)  (it 
compensates for the rotation of the earth) is that,  the start and 
end position accuracy is not that important,  smooth and 
constant/consistent movement is.  for the azimuth/altitude precision 
is not a really big deal, but you'd want to move these 2 axis  
somewhat swift.



So there are a few factors to decide.


I probably want micro stepping,  what settings on the driver for 
pulses per rev, is best to use (or is that just trial and error?)



As with PWM itself, I am probably just not too familiar with it. From 
what I understand, the voltage I use for the motors determines how 
fast I can go (I am going to use a 48V switching power supply).



as for PWM,  I can of course  change the length of the pulse itself  
and, independently, change the time between two pulses. What is the 
relation ship there?  WHat does a longer  width of the pulse itself 
do?  and what exactly does a longer gap between the pulses do (of 
course the wider the gap between two pulses the slower the motor turns).



for, especially, the equatorial platform, I want to avoid "jerking" 
it,  meaning  starting and stopping the stepper motor as little as 
possible and just go at a 'slow' constant speed.




sorry if totally of topic


thanks,


Ron



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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[cogoman via Emc-users]

I recently discovered geared stepper motors.

http://www.zyltech.com/nema-17-stepper-motor-geared-planetary-gearbox-1-7-a-3-1-nm-435-ozin/

I've been happy with zyltech in the past.  I bought one of these for 
evluation, but the specs seem to be great for CNC. Low enough current to 
work with a stepstick, High enough torque for a fairly powerful machine, 
and less than 4 mH inductance should let it step pretty fast.


5.18:1 gear ratio should reduce that 4 meter spur gear, but the link 
below has higher gear ratios that would reduce that spur gear greatly! 
Backlash could be a problem for CNC, but if you are only going one way, 
the less precision gearboxes might be fine.


https://www.omc-stepperonline.com/geared-stepper-motor/?sort=p.price&order=ASC

Once you visit the stepperonline web page you know as much about them as 
I do, but their offerings might be just right for your application.


On 7/9/20 2:23 PM, R C wrote:

Hello,

this is (probably) off topic, been seen that happen.  If it is please 
ignore it.



I am building a "motorized"  telescope mount (dobsonian) with what is 
called an equatorial platform, it has 3 axis which I am going to drive 
with stepper motors.



The stepper motors I use with a stepper driver, those common DM542 
ones, the stepper motors themselves are 2A and 1.8 degrees per step.



What I want to accomplish with the equatorial platform)  (it 
compensates for the rotation of the earth) is that,  the start and end 
position accuracy is not that important,  smooth and 
constant/consistent movement is.  for the azimuth/altitude precision 
is not a really big deal, but you'd want to move these 2 axis  
somewhat swift.



So there are a few factors to decide.


I probably want micro stepping,  what settings on the driver for 
pulses per rev, is best to use (or is that just trial and error?)



As with PWM itself, I am probably just not too familiar with it. From 
what I understand, the voltage I use for the motors determines how 
fast I can go (I am going to use a 48V switching power supply).



as for PWM,  I can of course  change the length of the pulse itself  
and, independently, change the time between two pulses. What is the 
relation ship there?  WHat does a longer  width of the pulse itself 
do?  and what exactly does a longer gap between the pulses do (of 
course the wider the gap between two pulses the slower the motor turns).



for, especially, the equatorial platform, I want to avoid "jerking" 
it,  meaning  starting and stopping the stepper motor as little as 
possible and just go at a 'slow' constant speed.




sorry if totally of topic


thanks,


Ron



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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[R C]

On 7/10/20 8:26 PM, Ken Strauss wrote:

"You need more gearing with the DC motor." Correct and this could be
considered an advantage since a very small DC motor + gearing (multiple
planetary stages) would have sufficient torque to move the scope. I have no
idea if a RPI can keep up with 3 quadrature encoders and control 3 motors
and manage a UI. However, you could make a compact unit at low cost
containing a microprocessor that takes step/dir, tracks encoder position and
generates PWM to run the motor. Rather like a low power, low RPM, high
torque version of a Clearpath servo.



Well   the shafts are not rotating "that" fast  if an RPI can easily do  
2000rpm, with a 100ppr encoder it can do 3 400 ppr encoders at 1 or 2 or 
3 rpm easily


These RPIs are pretty fast little things; with a 400 PPR encoder,  with 
3 there would be 1000-2000 pulses in a minute... that is easy to do





-Original Message-
From: Chris Albertson [mailto:albertson.ch...@gmail.com]
Sent: Friday, July 10, 2020 10:14 PM
To: Enhanced Machine Controller (EMC)
Subject: Re: [Emc-users] off topic: pwm with a stepper driver/motor

Stepper motors are good for this.   A stepper has the most torque at zero
RPM and the torque falls as speed increases while a DC brushed motor has
very little power when moving slowly.  You need more gearing with the DC
motor.

The problem is you need to generate precise pulses.  If the pulse spacing
is not accurate then you are asking a large telescope to accelerate and
decelerate instantly. So to generat pulses need either
1) a hardware solution like a microcontroller or FPGA or pulse generator.
2) A real time kernel on the Linux system or
3) A PID loop to supervise a non-real-time software pulse generator

When I build stuff, my preference is the microcontroller.  I design it so
the microcontroller can work independent of a larger Linux computer or

take

commands from a large Linux computer.  I want some basic functionality
when
power is applied then adding the Linux PC adds more functionality.

Linux CNC uses a slightly different idea they either go with Real-Time
Linux or use a very simple pulse generator running in an FPGA.

Reading up to three quadrature encoders with just a Raspberry Pi might
work, or not.  I don't know.  A lot depends on the speed of the encoders.

On Fri, Jul 10, 2020 at 6:45 PM R C  wrote:


I don't think anyone did,  but I know that's how most do it...

But that's just too easy  :)I would just like to see if I can do it,
killing time


On 7/10/20 7:39 PM, Ken Strauss wrote:

I haven't been following this closely but has anyone suggested that

you

use a

DC motor with an encoder? With a PID loop and PWM power to the motor

you

could

run the motor continuously. DC motors with integrated encoder and

planetary

gearbox are readily available for a few dollars. Just a thought.




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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[R C]

right that is how most people use it...   BUT it would still be hard to 
calibrate the movement to the earths rotation.



and also  ..   I just want to do it with steppers   :)    I am weird

On 7/10/20 8:14 PM, Ken Strauss wrote:

You could use the DC motor + PID exactly the same as using steppers. With the
encoders you would always know the exact angle though which the motor had
rotated. The advantage would be the lack of any jerks in motion which are
inherent with a stepper. Have you considered using the Clearpath units? See
https://www.teknic.com/



-Original Message-
From: R C [mailto:cjv...@gmail.com]
Sent: Friday, July 10, 2020 10:05 PM
To: emc-users@lists.sourceforge.net
Subject: Re: [Emc-users] off topic: pwm with a stepper driver/motor

yep..  true..  but it is also knd of what I do for a living...


I think it can be done,  to build an equatorial platform, and really
control it's speed/angle over time.


On 7/10/20 7:52 PM, Ken Strauss wrote:

I also waste a lot of time exploring different ways of doing things but
frequently end up doing it the traditional way. One should never just
accept
"how it is done" but for many (most?) things there are good reasons for
traditional ways.


-Original Message-
From: R C [mailto:cjv...@gmail.com]
Sent: Friday, July 10, 2020 9:43 PM
To: emc-users@lists.sourceforge.net
Subject: Re: [Emc-users] off topic: pwm with a stepper driver/motor

I don't think anyone did,  but I know that's how most do it...

But that's just too easy  :)I would just like to see if I can do it,
killing time


On 7/10/20 7:39 PM, Ken Strauss wrote:

I haven't been following this closely but has anyone suggested that you
use a
DC motor with an encoder? With a PID loop and PWM power to the

motor

you could

run the motor continuously. DC motors with integrated encoder and

planetary

gearbox are readily available for a few dollars. Just a thought.




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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[R C]

On 7/10/20 8:13 PM, Chris Albertson wrote:

Stepper motors are good for this.   A stepper has the most torque at zero
RPM and the torque falls as speed increases while a DC brushed motor has
very little power when moving slowly.  You need more gearing with the DC
motor.


that is exactly right, that is why I wanted to try going that route


The problem is you need to generate precise pulses.  If the pulse spacing
is not accurate then you are asking a large telescope to accelerate and
decelerate instantly. So to generat pulses need either
1) a hardware solution like a microcontroller or FPGA or pulse generator.
2) A real time kernel on the Linux system or
3) A PID loop to supervise a non-real-time software pulse generator


yes I agree on the first part..   :)   BUT   this is not a high speed 
thing and changes at high speed are more "disruptive"  then changes at 
something that goes rather slow


the 3 solutions you mention work if you really want to be on top.  The 
thing is..   it is not really that bad if you're a fraction of a second 
off, with an amature telescope.


(but perfect is cool  :)   )



When I build stuff, my preference is the microcontroller.  I design it so
the microcontroller can work independent of a larger Linux computer or take
commands from a large Linux computer.  I want some basic functionality when
power is applied then adding the Linux PC adds more functionality.


Yes definitely... a micro controller would be something "small" that 
works predictable   BUT it is hard to interact with and make adjustments.


I worked with micro controllers,  they are great for repetitive stuff 
that don't need interaction/correction




Linux CNC uses a slightly different idea they either go with Real-Time
Linux or use a very simple pulse generator running in an FPGA.


right.  I use linux cnc and really like it for my mill and lathe. 
Actually, if you abstract it..  a telescope is sort of a machine that 
points at "something" similar like a mill does.


the degrees of freedom are different, but not that different. I think a 
telescope can be sort of "defined"  with 4 degrees of freedom,  however, 
2 of them (orbit and rotation of the earth) are constrained.  If you 
look at it,  it would be like a 4 or 5 axis mill  running a program 
doing nothing except pointing at some star, which is the same 
functionality as it milling some "object"


That is not why I posed the question here though.   I did because I  
knew that Linux CNC knows how to work with drivers and steppers,  and I 
am trying to do something similar with the hardware that I use in my 
little mill and lathe and mill, running linux cnc





Reading up to three quadrature encoders with just a Raspberry Pi might
work, or not.  I don't know.  A lot depends on the speed of the encoders.


well   the speed of rotation is not that high, so one is not as much 
measuring speed,  but more position...   so  that would be a few hundred 
pulses per revolution


I tried a few scenarios...  it doesn't seem to be a real problem to get 
a few hundred pulses in a few seconds at all.





On Fri, Jul 10, 2020 at 6:45 PM R C  wrote:


I don't think anyone did,  but I know that's how most do it...

But that's just too easy  :)I would just like to see if I can do it,
killing time


On 7/10/20 7:39 PM, Ken Strauss wrote:

I haven't been following this closely but has anyone suggested that you

use a

DC motor with an encoder? With a PID loop and PWM power to the motor you

could

run the motor continuously. DC motors with integrated encoder and

planetary

gearbox are readily available for a few dollars. Just a thought.




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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Gene Heskett]

On Friday 10 July 2020 22:26:12 Ken Strauss wrote:

> "You need more gearing with the DC motor." Correct and this could be
> considered an advantage since a very small DC motor + gearing
> (multiple planetary stages) would have sufficient torque to move the
> scope. I have no idea if a RPI can keep up with 3 quadrature encoders
> and control 3 motors and manage a UI. However, you could make a
> compact unit at low cost containing a microprocessor that takes
> step/dir, tracks encoder position and generates PWM to run the motor.
> Rather like a low power, low RPM, high torque version of a Clearpath
> servo.

The rpi4 w/2gigs, and a mesa 7i90HD controller would be an expensive 
overkill, but consider that it could not only run the telescope but the 
rest of the building its in. One of the firmwares that can be loaded 
into the 7i90 gives 4 stepgens, 4 encoders and 4 pwmgens.  And still 
leaves you about 60 other gpio pins to keep track of the whole 
environment, like a motorized sliding roof, or even the whole building 
over the scope that could take protective action based on wind velocity 
exceeding a set limit value, or sensing rain, parking the scope, 
bringing the roof or building back over it and even starting a small 
heater and vent fan to dry it out until the humidity is safe.

My hal files have quite a bit of "gingerbread" that runs in a 200 hz 
thread doing lots of stuff, like tracking the z position and running the 
x in and out to correct for several thousandths of bed wear. The jog 
dials that replace the hand cranks all work in this slower thread. It 
also tracks the distance it overtravels at spindle reversal due to the 
mass of a 40 lb chuck, sending back to the driver gcode if you want to 
use it, to shorten a rigid tap stroke after the first hit on the hole, 
giving me the ability to set the depth of a hole to be tapped, but 
reducing the stroke to prevent the overtravel from hitting the bottom of 
the hole and breaking the tap.

Even with all that, I still have around 40 gpio pins that are not 
committed.  Two of those gpio's control the AC power via 40 amp ssr's so 
that when motion is disabled, the only power left on is the raspi's and 
monitor. Thats about 15 watts, so its on 24/7. My ability to do stuff 
around that lathe is limited only by my imagination, which I have a 
reputation for allowing out to play without a chaperon. :-)

Running an 8" Dob would be a piece of cake.  Might have to teach 
stellarium how to drive a scope thru an spi interface. Serial, very high 
speed.  Installed and ran stellarium but didn't find an interface as it 
seems to need ASCOM drivers, and they give very limited control. I'm 
disappointed. Looks like a new wheel will need to be written.

Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.
 - Louis D. Brandeis
Genes Web page 


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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Ken Strauss]

"You need more gearing with the DC motor." Correct and this could be
considered an advantage since a very small DC motor + gearing (multiple
planetary stages) would have sufficient torque to move the scope. I have no
idea if a RPI can keep up with 3 quadrature encoders and control 3 motors
and manage a UI. However, you could make a compact unit at low cost
containing a microprocessor that takes step/dir, tracks encoder position and
generates PWM to run the motor. Rather like a low power, low RPM, high
torque version of a Clearpath servo.

> -Original Message-
> From: Chris Albertson [mailto:albertson.ch...@gmail.com]
> Sent: Friday, July 10, 2020 10:14 PM
> To: Enhanced Machine Controller (EMC)
> Subject: Re: [Emc-users] off topic: pwm with a stepper driver/motor
>
> Stepper motors are good for this.   A stepper has the most torque at zero
> RPM and the torque falls as speed increases while a DC brushed motor has
> very little power when moving slowly.  You need more gearing with the DC
> motor.
>
> The problem is you need to generate precise pulses.  If the pulse spacing
> is not accurate then you are asking a large telescope to accelerate and
> decelerate instantly. So to generat pulses need either
> 1) a hardware solution like a microcontroller or FPGA or pulse generator.
> 2) A real time kernel on the Linux system or
> 3) A PID loop to supervise a non-real-time software pulse generator
>
> When I build stuff, my preference is the microcontroller.  I design it so
> the microcontroller can work independent of a larger Linux computer or
take
> commands from a large Linux computer.  I want some basic functionality
> when
> power is applied then adding the Linux PC adds more functionality.
>
> Linux CNC uses a slightly different idea they either go with Real-Time
> Linux or use a very simple pulse generator running in an FPGA.
>
> Reading up to three quadrature encoders with just a Raspberry Pi might
> work, or not.  I don't know.  A lot depends on the speed of the encoders.
>
> On Fri, Jul 10, 2020 at 6:45 PM R C  wrote:
>
> > I don't think anyone did,  but I know that's how most do it...
> >
> > But that's just too easy  :)I would just like to see if I can do it,
> > killing time
> >
> >
> > On 7/10/20 7:39 PM, Ken Strauss wrote:
> > > I haven't been following this closely but has anyone suggested that
you
> > use a
> > > DC motor with an encoder? With a PID loop and PWM power to the motor
> you
> > could
> > > run the motor continuously. DC motors with integrated encoder and
> > planetary
> > > gearbox are readily available for a few dollars. Just a thought.
> > >
> > >
> > >
> > >
> > > ___
> > > Emc-users mailing list
> > > Emc-users@lists.sourceforge.net
> > > https://lists.sourceforge.net/lists/listinfo/emc-users
> >
> >
> > ___
> > Emc-users mailing list
> > Emc-users@lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/emc-users
> >
>
>
> --
>
> Chris Albertson
> Redondo Beach, California
>
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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Ken Strauss]

You could use the DC motor + PID exactly the same as using steppers. With the 
encoders you would always know the exact angle though which the motor had 
rotated. The advantage would be the lack of any jerks in motion which are 
inherent with a stepper. Have you considered using the Clearpath units? See 
https://www.teknic.com/


> -Original Message-
> From: R C [mailto:cjv...@gmail.com]
> Sent: Friday, July 10, 2020 10:05 PM
> To: emc-users@lists.sourceforge.net
> Subject: Re: [Emc-users] off topic: pwm with a stepper driver/motor
>
> yep..  true..  but it is also knd of what I do for a living...
>
>
> I think it can be done,  to build an equatorial platform, and really
> control it's speed/angle over time.
>
>
> On 7/10/20 7:52 PM, Ken Strauss wrote:
> > I also waste a lot of time exploring different ways of doing things but
> > frequently end up doing it the traditional way. One should never just 
> > accept
> > "how it is done" but for many (most?) things there are good reasons for
> > traditional ways.
> >
> >> -Original Message-
> >> From: R C [mailto:cjv...@gmail.com]
> >> Sent: Friday, July 10, 2020 9:43 PM
> >> To: emc-users@lists.sourceforge.net
> >> Subject: Re: [Emc-users] off topic: pwm with a stepper driver/motor
> >>
> >> I don't think anyone did,  but I know that's how most do it...
> >>
> >> But that's just too easy  :)I would just like to see if I can do it,
> >> killing time
> >>
> >>
> >> On 7/10/20 7:39 PM, Ken Strauss wrote:
> >>> I haven't been following this closely but has anyone suggested that you
> >>> use a
> >>> DC motor with an encoder? With a PID loop and PWM power to the
> motor
> >> you could
> >>> run the motor continuously. DC motors with integrated encoder and
> >> planetary
> >>> gearbox are readily available for a few dollars. Just a thought.
> >>>
> >>>
> >>>
> >>>
> >>> ___
> >>> Emc-users mailing list
> >>> Emc-users@lists.sourceforge.net
> >>> https://lists.sourceforge.net/lists/listinfo/emc-users
> >>
> >> ___
> >> Emc-users mailing list
> >> Emc-users@lists.sourceforge.net
> >> https://lists.sourceforge.net/lists/listinfo/emc-users
> >
> >
> >
> > ___
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> > Emc-users@lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/emc-users
>
>
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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Chris Albertson]

Stepper motors are good for this.   A stepper has the most torque at zero
RPM and the torque falls as speed increases while a DC brushed motor has
very little power when moving slowly.  You need more gearing with the DC
motor.

The problem is you need to generate precise pulses.  If the pulse spacing
is not accurate then you are asking a large telescope to accelerate and
decelerate instantly. So to generat pulses need either
1) a hardware solution like a microcontroller or FPGA or pulse generator.
2) A real time kernel on the Linux system or
3) A PID loop to supervise a non-real-time software pulse generator

When I build stuff, my preference is the microcontroller.  I design it so
the microcontroller can work independent of a larger Linux computer or take
commands from a large Linux computer.  I want some basic functionality when
power is applied then adding the Linux PC adds more functionality.

Linux CNC uses a slightly different idea they either go with Real-Time
Linux or use a very simple pulse generator running in an FPGA.

Reading up to three quadrature encoders with just a Raspberry Pi might
work, or not.  I don't know.  A lot depends on the speed of the encoders.

On Fri, Jul 10, 2020 at 6:45 PM R C  wrote:

> I don't think anyone did,  but I know that's how most do it...
>
> But that's just too easy  :)I would just like to see if I can do it,
> killing time
>
>
> On 7/10/20 7:39 PM, Ken Strauss wrote:
> > I haven't been following this closely but has anyone suggested that you
> use a
> > DC motor with an encoder? With a PID loop and PWM power to the motor you
> could
> > run the motor continuously. DC motors with integrated encoder and
> planetary
> > gearbox are readily available for a few dollars. Just a thought.
> >
> >
> >
> >
> > ___
> > Emc-users mailing list
> > Emc-users@lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/emc-users
>
>
> ___
> Emc-users mailing list
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> https://lists.sourceforge.net/lists/listinfo/emc-users
>


-- 

Chris Albertson
Redondo Beach, California

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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[R C]

yep..  true..  but it is also knd of what I do for a living...


I think it can be done,  to build an equatorial platform, and really 
control it's speed/angle over time.



On 7/10/20 7:52 PM, Ken Strauss wrote:

I also waste a lot of time exploring different ways of doing things but
frequently end up doing it the traditional way. One should never just accept
"how it is done" but for many (most?) things there are good reasons for
traditional ways.


-Original Message-
From: R C [mailto:cjv...@gmail.com]
Sent: Friday, July 10, 2020 9:43 PM
To: emc-users@lists.sourceforge.net
Subject: Re: [Emc-users] off topic: pwm with a stepper driver/motor

I don't think anyone did,  but I know that's how most do it...

But that's just too easy  :)I would just like to see if I can do it,
killing time


On 7/10/20 7:39 PM, Ken Strauss wrote:

I haven't been following this closely but has anyone suggested that you
use a
DC motor with an encoder? With a PID loop and PWM power to the motor

you could

run the motor continuously. DC motors with integrated encoder and

planetary

gearbox are readily available for a few dollars. Just a thought.




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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Ken Strauss]

I also waste a lot of time exploring different ways of doing things but 
frequently end up doing it the traditional way. One should never just accept 
"how it is done" but for many (most?) things there are good reasons for 
traditional ways.

> -Original Message-
> From: R C [mailto:cjv...@gmail.com]
> Sent: Friday, July 10, 2020 9:43 PM
> To: emc-users@lists.sourceforge.net
> Subject: Re: [Emc-users] off topic: pwm with a stepper driver/motor
>
> I don't think anyone did,  but I know that's how most do it...
>
> But that's just too easy  :)I would just like to see if I can do it,
> killing time
>
>
> On 7/10/20 7:39 PM, Ken Strauss wrote:
> > I haven't been following this closely but has anyone suggested that you 
> > use a
> > DC motor with an encoder? With a PID loop and PWM power to the motor
> you could
> > run the motor continuously. DC motors with integrated encoder and
> planetary
> > gearbox are readily available for a few dollars. Just a thought.
> >
> >
> >
> >
> > ___
> > Emc-users mailing list
> > Emc-users@lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/emc-users
>
>
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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[R C]

I don't think anyone did,  but I know that's how most do it...

But that's just too easy  :)    I would just like to see if I can do it, 
killing time



On 7/10/20 7:39 PM, Ken Strauss wrote:

I haven't been following this closely but has anyone suggested that you use a
DC motor with an encoder? With a PID loop and PWM power to the motor you could
run the motor continuously. DC motors with integrated encoder and planetary
gearbox are readily available for a few dollars. Just a thought.




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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Ken Strauss]

I haven't been following this closely but has anyone suggested that you use a 
DC motor with an encoder? With a PID loop and PWM power to the motor you could 
run the motor continuously. DC motors with integrated encoder and planetary 
gearbox are readily available for a few dollars. Just a thought.




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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[R C]

from what I understand,  worm gears work really well  and because of the 
reduction, the motor needs to sping at a decent rpm, it doesn't have 
tospin that slow. I am using steppers, because it is easy to count the 
steps and then calibrate because of how much you're drifting.While with 
a regular DC motor you could only do something like that in a 
Monte-Carlo/binary kinda way. also, adjusting DC motors is not 
necessarilly  linear and since adjusting a stepper is "discrete" it 
would be way easier.


On 7/10/20 1:21 PM, andy pugh wrote:

On Fri, 10 Jul 2020 at 20:14, Chris Albertson  wrote:


You need to move at 1/2 the resolution otherwise you can see the steps.  So
let's say each step would be 1/4 arc-second

I was going with one step per thingy, and then assuming microstepping
to get sub-thingy :-)

I will just mention: https://www.hpcgears.com/pdf_c33/22.0.pdf as an option.
(With a home-made worm. I am assuming that anyone here can cut a module thread)




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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[R C]

On 7/10/20 1:12 PM, Chris Albertson wrote:

On Fri, Jul 10, 2020 at 10:33 AM andy pugh  wrote:


Sprockets for T2.5 belts are available with 10 teeth, so that would be
a 2.3m table for the 300:1. Which is also probably too big. I suppose
that the design criterion is that one stepper step should be less than
the angular resolution of the telescope. So what is that, in this
case?

We don't know the size of this 'scope but let's assume about 12" 
diameter.

then it is on the order of 1/2 arc-second


If you're talking about my telescope, it's an 8"



You need to move at 1/2 the resolution otherwise you can see the 
steps.  So

let's say each step would be 1/4 arc-second

Stars move 15 degrees per hour or 15 arc-seconds per second.   So he 
needs

to step at about 60 Hz.


That sounds about right, but I am planning on using a worm gear too..  
so the motor can continuously spin.


(I also heard from people that built those platforms and experimented 
with them, that some "shaft couplers"


reduce vibration quite a bit




Let's assume 1/64th micro steps  these are roughly 100 arc-seconds per
step.  He needs about 400:1 gear reduction.

This is getting unreasonable because the telescope will NEVER achieve the
theoretical resolution because of the atmospheric blurring  Lets say 
we do

1 arc-second steps and 100:1 gears.


Yup, and then there's wind etc too, and telescopes are also good 
detectors for picking up vibrations from the ground.




The traditional professional-level method is to use very nice and very
expensive brass wheels and stainless steel worms and even more expensive
bearings and shafts.   But nowadays with computers, we can place a camera
such that it looks at the image of a highly magnified star then we 
measure
the X,Y location of the image on the CCD sensor and use a PID feedback 
loop
to keep the star image from moving.  So the servo loop tries to keep 
drift

to zero.  They measure drift with units called "mas" for milliarcseconds.

I am actually trying to see if I can build something like that too


But this is a "Dobsonian" scope and the goal of these is to be cheap and
portable, exactly the opposite of a professional level scope. Most of
these use a door hinge as the axis that is roughly aligned by eyeball 
with

"north" and the drive is a hardware store threaded rod turned by a DC
geared DC motor and the operator sets the tracking speed by eye and hand.
These things reduce the drift to what can be tracked with the eye.
I read about barndoor equatorial platforms, those are mostly used for 
cameras. Also wouldn't really work with a dobsonian mount, since the 
telescope would start tipping. The actul equatorial platform runs in a 
"cone", with elliptical  tracks on a bearing. You'd turn one of the axis 
in a bearing and move the whole platform around the center of gravity 
(or close) of the telescope. At least that is what most of the plans say 
to do.


It seems our OP is trying to do better than the common door hinge and
threaded rod tracker but still wants a 'scope that fits in the back of 
his
car and costs less than the car.   So sub-arcsecond pointing is going 
to be

hard.


Yes definitely. A dobsonian telescope has a newtonian tube, also called 
light buckets, they can collect a lot of light, however because of their 
size, having a good stable equatorial mount is difficult, that's why 
they came up with the dobsonian mount. That mount works very well for 
"direct" star gazing,  you just move it when you need to. Looking at 
Saturn is a bit of a challenge that way already though. The equatorial 
platform seems to work really well and one can track something for 
approx. an hour or hour and a half.



The barndoor platform  seems to work well when you  look at stars near 
polaris, or opposite of it, but other directions make it just 
unpractical because of "balancing issues"



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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[andy pugh]

On Fri, 10 Jul 2020 at 20:14, Chris Albertson  wrote:

> You need to move at 1/2 the resolution otherwise you can see the steps.  So
> let's say each step would be 1/4 arc-second

I was going with one step per thingy, and then assuming microstepping
to get sub-thingy :-)

I will just mention: https://www.hpcgears.com/pdf_c33/22.0.pdf as an option.
(With a home-made worm. I am assuming that anyone here can cut a module thread)

-- 
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1912


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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Chris Albertson]

On Fri, Jul 10, 2020 at 10:33 AM andy pugh  wrote:

>
> Sprockets for T2.5 belts are available with 10 teeth, so that would be
> a 2.3m table for the 300:1. Which is also probably too big. I suppose
> that the design criterion is that one stepper step should be less than
> the angular resolution of the telescope. So what is that, in this
> case?
>

We don't know the size of this 'scope but let's assume about 12" diameter.
then it is on the order of 1/2 arc-second

You need to move at 1/2 the resolution otherwise you can see the steps.  So
let's say each step would be 1/4 arc-second

Stars move 15 degrees per hour or 15 arc-seconds per second.   So he needs
to step at about 60 Hz.

Let's assume 1/64th micro steps  these are roughly 100 arc-seconds per
step.  He needs about 400:1 gear reduction.

This is getting unreasonable because the telescope will NEVER achieve the
theoretical resolution because of the atmospheric blurring  Lets say we do
1 arc-second steps and 100:1 gears.

The traditional professional-level method is to use very nice and very
expensive brass wheels and stainless steel worms and even more expensive
bearings and shafts.   But nowadays with computers, we can place a camera
such that it looks at the image of a highly magnified star then we measure
the X,Y location of the image on the CCD sensor and use a PID feedback loop
to keep the star image from moving.  So the servo loop tries to keep drift
to zero.  They measure drift with units called "mas" for milliarcseconds.

But this is a "Dobsonian" scope and the goal of these is to be cheap and
portable, exactly the opposite of a professional level scope.  Most of
these use a door hinge as the axis that is roughly aligned by eyeball with
"north" and the drive is a hardware store threaded rod turned by a DC
geared DC motor and the operator sets the tracking speed by eye and hand.
These things reduce the drift to what can be tracked with the eye.

It seems our OP is trying to do better than the common door hinge and
threaded rod tracker but still wants a 'scope that fits in the back of his
car and costs less than the car.   So sub-arcsecond pointing is going to be
hard.


-- 

Chris Albertson
Redondo Beach, California

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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[andy pugh]

On Fri, 10 Jul 2020 at 17:59, Chris Albertson  wrote:

> There is also a minimum amount number of degrees of contact required with
> the small pulley.  The pulley must be far enough away so the minimum number
> of teeth are engaged.

Or you can use idlers to modify the belt shape. This is done very
frequently on car engine front-end accessory drives, for example.

Sprockets for T2.5 belts are available with 10 teeth, so that would be
a 2.3m table for the 300:1. Which is also probably too big. I suppose
that the design criterion is that one stepper step should be less than
the angular resolution of the telescope. So what is that, in this
case?

But I was coming at this from the opposite direction: If you have to
rotate something that is large and circular (or potentially just a
sector of a circle) how can you rotate it economically?

This is one way. And in this case you probably would want to combine
it with a geared motor to get the required ratio.

-- 
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1912


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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Chris Albertson]

Yes in theory one could design a 300:1 belt reduction in one stage.  But
according to the belt manufacturer, you do need to have a minimum number of
belt teeth engaged.  I think about 11 teeth.  If only 180 degrees of the
small pulley is engaged with the belt then the minim pulley size is 22.
 So to get 300:1 you use a 6600 tooth pulley.   But this is a 6 meter
diameter pulley.   The worm gear works so much better because it is in
effect a "one tooth" gear and so for the same pitch reduces the diameter of
the larger gear by a factor of 22.

There is also a minimum amount number of degrees of contact required with
the small pulley.  The pulley must be far enough away so the minimum number
of teeth are engaged.  Getts 180 degrees of corverage is impossible if one
pulley is larger then the other  So in order to get (say) 120 degrees of
bend around the smaller pulley, it must be pretty darn far away from the 6
meter diameter pulley. But now you need 33 teeth on the small one and the
big one is up to 9 meters diameter.

With pulleys, if the reduction ratio is 100:1 the larger pully must be
literally 100X larger than the smaller pulley and there is always a
minimum size for a small pulley.   So typically high reduction ratio belt
drives use two or three stages. 6:1 is a reasonable reduction, 10:1
gets hard to fit into many spaces.

With these high rations you use worm gears, multiple stages or cycloid
reductions (or silly things like a 1/2 inch pulley paired with a 50-inch
pulley)

On Fri, Jul 10, 2020 at 2:39 AM andy pugh  wrote:

> On Fri, 10 Jul 2020 at 02:00, Chris Albertson 
> wrote:
>
> > Belts can go to about 6:1 at best a double belt reduction only goes to
> 36:1
>
> I don't see why there is any limit to the possible reduction of a belt
> drive, if idlers are added to increase the wrap.
> If I was doing this (and this particular application is something that
> I have considered) I think that I would use a rotary variant of the
> "servobelt" system: Glue a length of T-section beliting to a circular
> component with the teeth pointing out to make a sprocket, and then
> have a close-spaced  pair of rollers to keep the belt wrapped round
> the sprocket except for a short loop that pops out and wraps round the
> stepper pulley.
>
>
> > He is doing only
> > about 10 Hz.
>
> In that case I think that a user-space loop in something like Python
> would be fine, just monitor the time using an accurate RTC (GPS
> module?) and have the loop say "have I made as many pulses as I should
> have for this time of day?" and either make a pulse on a GPIO pin, or
> not, accordingly.
>
> --
> atp
> "A motorcycle is a bicycle with a pandemonium attachment and is
> designed for the especial use of mechanical geniuses, daredevils and
> lunatics."
> — George Fitch, Atlanta Constitution Newspaper, 1912
>
>
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-- 

Chris Albertson
Redondo Beach, California

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[Emc-users] off topic: pwm with a stepper driver/motor

[Roland Jollivet]

I had a friend that had a motorised telescope.
It had a DC motor, with a very high reduction ratio. I think one would see
fluctuations with a stepper motor.

Also, I wouldn't use a belt at all. Drive a smooth roller and use a
friction drive against a large disc. This also allows you to manually turn
by slipping the disc on the roller for an easy setup. Most theodolites use
this arrangement. Teeth will just be too jerky when viewing stars..



On Fri, 10 Jul 2020 at 11:39, andy pugh  wrote:

> On Fri, 10 Jul 2020 at 02:00, Chris Albertson 
> wrote:
>
> > Belts can go to about 6:1 at best a double belt reduction only goes to
> 36:1
>
> I don't see why there is any limit to the possible reduction of a belt
> drive, if idlers are added to increase the wrap.
> If I was doing this (and this particular application is something that
> I have considered) I think that I would use a rotary variant of the
> "servobelt" system: Glue a length of T-section beliting to a circular
> component with the teeth pointing out to make a sprocket, and then
> have a close-spaced  pair of rollers to keep the belt wrapped round
> the sprocket except for a short loop that pops out and wraps round the
> stepper pulley.
>
>
> > He is doing only
> > about 10 Hz.
>
> In that case I think that a user-space loop in something like Python
> would be fine, just monitor the time using an accurate RTC (GPS
> module?) and have the loop say "have I made as many pulses as I should
> have for this time of day?" and either make a pulse on a GPIO pin, or
> not, accordingly.
>
> --
> atp
> "A motorcycle is a bicycle with a pandemonium attachment and is
> designed for the especial use of mechanical geniuses, daredevils and
> lunatics."
> — George Fitch, Atlanta Constitution Newspaper, 1912
>
>
> ___
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>

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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Gene Heskett]

On Friday 10 July 2020 05:34:58 andy pugh wrote:

> On Fri, 10 Jul 2020 at 02:00, Chris Albertson 
 wrote:
> > Belts can go to about 6:1 at best a double belt reduction only goes
> > to 36:1
>
> I don't see why there is any limit to the possible reduction of a belt
> drive, if idlers are added to increase the wrap.
> If I was doing this (and this particular application is something that
> I have considered) I think that I would use a rotary variant of the
> "servobelt" system: Glue a length of T-section beliting to a circular
> component with the teeth pointing out to make a sprocket, and then
> have a close-spaced  pair of rollers to keep the belt wrapped round
> the sprocket except for a short loop that pops out and wraps round the
> stepper pulley.

That could work great even for a 340 degree turn. But I'd have the belt 
teeth pointing inward so the pop-out between the idlers could wrap the 
little pulley by at least 190 degrees.  With the lack of stretch, one 
end could be anchored solidly to the big wheel, while a heavy spring 
maintains the belt tension on the belt on an otherwise smooth pulley. A 
matching belt glued on and teeth facing outward would be optional. With 
full time tension on the belt from a stout spring, only the idlers would 
need flanges. Their flanges could straddle the big wheel. That could 
work for az/el, but the base would need a full turn+ (I think). That 
could be handled by glueing on an endless belt to make the sprocket 
teeth, and using another belt facing inward so there would not be a gap 
at the anchor points. Diameter of the big wheel might need a tweak so 
theres no discontinuity when passing over the inner belts end gap.
Still relatively cheap, no backlash.

> > He is doing only
> > about 10 Hz.
>
> In that case I think that a user-space loop in something like Python
> would be fine, just monitor the time using an accurate RTC (GPS
> module?) and have the loop say "have I made as many pulses as I should
> have for this time of day?" and either make a pulse on a GPIO pin, or
> not, accordingly.

I love playing what if...

Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.
 - Louis D. Brandeis
Genes Web page 


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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[andy pugh]

On Fri, 10 Jul 2020 at 02:00, Chris Albertson  wrote:

> Belts can go to about 6:1 at best a double belt reduction only goes to 36:1

I don't see why there is any limit to the possible reduction of a belt
drive, if idlers are added to increase the wrap.
If I was doing this (and this particular application is something that
I have considered) I think that I would use a rotary variant of the
"servobelt" system: Glue a length of T-section beliting to a circular
component with the teeth pointing out to make a sprocket, and then
have a close-spaced  pair of rollers to keep the belt wrapped round
the sprocket except for a short loop that pops out and wraps round the
stepper pulley.


> He is doing only
> about 10 Hz.

In that case I think that a user-space loop in something like Python
would be fine, just monitor the time using an accurate RTC (GPS
module?) and have the loop say "have I made as many pulses as I should
have for this time of day?" and either make a pulse on a GPIO pin, or
not, accordingly.

-- 
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1912


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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Chris Albertson]

How to generate pulse at the exact rate you need...

First make a loop that runs as fast as you can make it run.  The first
thing it does is "sleep" for a hundred or so microseconds.  Then it checks
the time of day and to see if it is time yet to do the next pulse.  If not
it fall to the end of the loop and does the slepp again.   Finally it is
time.  So the program sets the GPIO bt "high" and then adds (say) 20
microseconds to the current time and calls the "TimeToShutOffThePulse"
Then the loop checks if the system time is equal or greater than
TimeToShutOffThePulse.
If true it sets the GPIO pin to low.   It them computers the time when the
pulse needs to be high again and goes back to sleep and when finally it is
time to set the pulse high it does.

The key here is that you loop must spend most of it's time sleeping but
also needs to check very frequently.

Actually the program might be moving three motors so it neds to track the
next time to move a pulse up or down and has a table fullof things o do in
the future and keep chacking if it is time yet to do the first thing on the
table.  If so it does it, then maybe adds one more entry to the table.

BIG PROBLEM.   This will work more or less and avreraged ver long periods
like 0.5 secondsthe pulse rate will be good.  But Linux is a
multi-tasking OSand it will have to run other tasks so many pulses will get
delays and the moterwill notkeep aperfectly even speed.  You may not notice
but it will never be perfect.

How to fix this:   Funny you aks this on a LinuxCNC list.LinuxCNC uses
a specal real-time version of the Linux kernal and the above
describbed loop runs as a real-time task.   This is a new thing that normal
Linux does not do.  These real-time tasks run inside the Kernal and there
is never any task swapping of CPU sharing to get in the way of your loop.
 But still it si not perfect, but likey good enough for this.

10 years ago I wrotesoftware to rrack stars in the sky using RT Linux.  It
worked well enough because starsreally don't move very fast.

And second solution is to use a normal Linux Kernalandthen place the
real-time loop inside a micro controller.   THis is easier because you cn
use a "stock" Linux and not have to compile and install a custom Kernal.
In is also about three orders of magnitude more accurate then enven the RT
version of Linux.


So running that loop that continously askes "Is it time yet?" in a normal
Linux process will almost work but not really well because the CPU cores
are shared between many tasks. Yes you can fiddle to priorities and almost
get it to work.

The "good enough" solution is to run the loop as a Real-Time task under the
a Real-Time version of the Linux kernal but this requires you to understand
mess with Linux kernals  You also need a normal user-level non-real-time
task to send control parameters to the RT kernal task   (this is mostly how
LinuxCNC works)

THe other "good enough" solution is the run the loop inside it's own small
computer where theis to is operting system and no multi-tasking and the the
Linux system simple passing parameters to the microcontroller.  (Linux CNC
can also work in this mode, the LinuxPC taking to special hardware that
genertes the sulses.

Almost there.  Reading the encoders.  This is REALLY hard to do using a
Raspberry Pi.  Each encoder has two pins andthe signals change fast.   They
can change REALLY fast on the Az and El axis if you are moving to a new
target quickly. Best to use the microcontroller but you can also
connect to the Pi's interrupt pins  Use 6 GPIO pins are interrupts and just
keep three counters.   You need to look up how to handle quadrature encoders

On Thu, Jul 9, 2020 at 8:30 PM R C  wrote:

>
> On 7/9/20 6:47 PM, Chris Albertson wrote:
> > OK, got it a "Dob, on a Ea, platform and the platform on an Az, El mount.
>
>
> Yup.
>
> >
> > Again PWM is "Pisle Width Modulation"  Steppers and stepper drivers don't
> > use PWM.  They use what we cal "Pulse/Direction"
> I didn't know that,  I read the product manual, it mentioned PWM, with
> some specs, I tried that, seems to kinda work   well work as in a
> okcupid profile that says "I don't like drama and games" but some how it
> doesn't seem to do what expected.
> >
> > PWM uses a constant square wave rate like that is always between 60 Hz
> and
> > maybe up to 1,000 Hz.  What changes is the "duty cycle" or the ratio of
> > "on" to "off".  But it just runs at about 60Hz.  PWM uses just one wire.
>
> Right,  and some hardware let's you pick the frequency, up front..  and
> then change the duty cycles.  that is what I figured. However, I saw in
> the manual,  the "high" side of the pulse in the duty cycle" lasts
> always 2.5usec and you change the length of the cycle. To me that just
> seems that you change the duty cycle, relative to the frequency...   as
> in the frequency is determined by how you build the cycles..   which is
> what I see happening.
>
>
> >
> > Pulse/Direction uses two wires.  On

Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Thaddeus Waldner]

Stepper motors are called that because they move in steps. Usually they have 
two coils. Both coils are powered when the motor is powered on, and this is 
what holds the motor in position. Reversing the current to one of these coils 
will advance the motor to the next step. The direction the motor goes is 
determined by which of the two coils is reversed. You really don’t need to know 
this unless you are building your own stepper driver. The driver will control 
the current to the motor coils

 The distance the motor turns with one step is a key spec of the stepper motor. 
1.8 degree is very common for NEMA 17 and NEMA 23 motors(motors measuring about 
1.7 and 2.3 inches respectively). 360/1.8=200 steps per 1 full revolution.

As mentioned earlier, the motor driver is controlled via 2 pins; step and 
direction. To turn the motor one step, you send one pulse to the “step” pin of 
the driver. To turn the motor at a rate of n steps per second, you send a 
n-hertz pulse train to the step pin. To change the direction of rotation, you 
invert the direction pin. You don’t use PWM to control a stepper driver.

Most stepper drivers have a feature called micro stepping. With micro stepping 
enabled, instead of turning a full step with each step pulse, the motor will 
turn a fractional step. Most applications use micro stepping because it also 
makes the motor run smoother at low RPM.


> On Jul 9, 2020, at 10:31 PM, R C  wrote:
> 
> 
>> On 7/9/20 6:47 PM, Chris Albertson wrote:
>> OK, got it a "Dob, on a Ea, platform and the platform on an Az, El mount.
> 
> 
> Yup.
> 
>> 
>> Again PWM is "Pisle Width Modulation"  Steppers and stepper drivers don't
>> use PWM.  They use what we cal "Pulse/Direction"
> I didn't know that,  I read the product manual, it mentioned PWM, with some 
> specs, I tried that, seems to kinda work   well work as in a  okcupid 
> profile that says "I don't like drama and games" but some how it doesn't seem 
> to do what expected.
>> 
>> PWM uses a constant square wave rate like that is always between 60 Hz and
>> maybe up to 1,000 Hz.  What changes is the "duty cycle" or the ratio of
>> "on" to "off".  But it just runs at about 60Hz.  PWM uses just one wire.
> 
> Right,  and some hardware let's you pick the frequency, up front..  and then 
> change the duty cycles.  that is what I figured. However, I saw in the 
> manual,  the "high" side of the pulse in the duty cycle" lasts always 2.5usec 
> and you change the length of the cycle. To me that just seems that you change 
> the duty cycle, relative to the frequency...   as in the frequency is 
> determined by how you build the cycles..   which is what I see happening.
> 
> 
>> 
>> Pulse/Direction uses two wires.  One sends a single pulse each time the
>> motor needs to move a step and the other wire is either "1" or "0" to
>> indicate the direction, either backward or forward.
> 
> correct,  direction is either constantly high, or constantly low..  for how 
> long you want it...   and that works perfectly
> 
> 
>> 
>> With this type of system I don't think you worry about minor things like
>> atmospheric refraction of structural flex.  You can just run at a constant
>> rate.
> 
> Yes ..  at this point I am not worried about that. I want to make a 
> "mechanical" precise contraption.
> 
> 
>> 
>> I am wondering why you selected a Raspberry Pi and not some micro
>> controller.  Perhaps you are planning a user interface that is complex?
> 
> well..  sort of.  I am planning on one that does the "positioning,  one that 
> does the imagng  and if needed one that does that "positioning"
> 
> I use them because they are easy to use,  run Linux, I know Linux, hardware.. 
>  I can hook it up to a network,  and see if I canhave Stellarium" send 
> coordinates to it at some point. It is more a "olution" that I can build on 
> and expand   if I wanted to.   There are very compact  solutions to use,  
> that are cheaper, easier etc..   BUT  I want o build my own my way,.
> 
> I built a seismograph like that, could be done easier/cheaper, but I wanted 
> to build an online one and do it myself ...   just because I can ..   and 
> because I think it can be done.
> 
> I'm a researcher/scientist,  I like to build things so I can figure out how 
> it works...
> 
>> 
>> All you software needs to do is generate  plusle each time the motr needs
>> to step.   For the motor that runs the EQ platform this step rate is fixed
>> forever.  For the other two they can step at whatever rate do want.
> 
> Yes exactly,  that is what I noticed.  I can move the stepper at pretty much 
> any desired rate/speed I want,  pretty precise, and.. if it runs at the exact 
> right speed.  that would be cool.
> 
> BUT,  I want to know how to figure out how to run it at the exact right 
> speed, with the exact right power, optimally, as best as I can ..   and not 
> by trial and error and decide "yeah good enough",  I want to calculate it.
> 
> So that is why I want to understand w

Re: [Emc-users] off topic: pwm with a stepper driver/motor

[R C]

On 7/9/20 6:47 PM, Chris Albertson wrote:

OK, got it a "Dob, on a Ea, platform and the platform on an Az, El mount.



Yup.



Again PWM is "Pisle Width Modulation"  Steppers and stepper drivers don't
use PWM.  They use what we cal "Pulse/Direction"
I didn't know that,  I read the product manual, it mentioned PWM, with 
some specs, I tried that, seems to kinda work   well work as in a  
okcupid profile that says "I don't like drama and games" but some how it 
doesn't seem to do what expected.


PWM uses a constant square wave rate like that is always between 60 Hz and
maybe up to 1,000 Hz.  What changes is the "duty cycle" or the ratio of
"on" to "off".  But it just runs at about 60Hz.  PWM uses just one wire.


Right,  and some hardware let's you pick the frequency, up front..  and 
then change the duty cycles.  that is what I figured. However, I saw in 
the manual,  the "high" side of the pulse in the duty cycle" lasts 
always 2.5usec and you change the length of the cycle. To me that just 
seems that you change the duty cycle, relative to the frequency...   as 
in the frequency is determined by how you build the cycles..   which is 
what I see happening.





Pulse/Direction uses two wires.  One sends a single pulse each time the
motor needs to move a step and the other wire is either "1" or "0" to
indicate the direction, either backward or forward.


correct,  direction is either constantly high, or constantly low..  for 
how long you want it...   and that works perfectly





With this type of system I don't think you worry about minor things like
atmospheric refraction of structural flex.  You can just run at a constant
rate.


Yes ..  at this point I am not worried about that. I want to make a 
"mechanical" precise contraption.





I am wondering why you selected a Raspberry Pi and not some micro
controller.  Perhaps you are planning a user interface that is complex?


well..  sort of.  I am planning on one that does the "positioning,  one 
that does the imagng  and if needed one that does that "positioning"


I use them because they are easy to use,  run Linux, I know Linux, 
hardware..  I can hook it up to a network,  and see if I canhave 
Stellarium" send coordinates to it at some point. It is more a "olution" 
that I can build on and expand   if I wanted to.   There are very 
compact  solutions to use,  that are cheaper, easier etc..   BUT  I want 
o build my own my way,.


I built a seismograph like that, could be done easier/cheaper, but I 
wanted to build an online one and do it myself ...   just because I can 
..   and because I think it can be done.


I'm a researcher/scientist,  I like to build things so I can figure out 
how it works...




All you software needs to do is generate  plusle each time the motr needs
to step.   For the motor that runs the EQ platform this step rate is fixed
forever.  For the other two they can step at whatever rate do want.


Yes exactly,  that is what I noticed.  I can move the stepper at pretty 
much any desired rate/speed I want,  pretty precise, and.. if it runs at 
the exact right speed.  that would be cool.


BUT,  I want to know how to figure out how to run it at the exact right 
speed, with the exact right power, optimally, as best as I can ..   and 
not by trial and error and decide "yeah good enough",  I want to 
calculate it.


So that is why I want to understand what the best way is , software 
wise, to drive those steppers,  to run those motors, algorithm wise.





Why encoders?  If the motors are proerly sized they will never skip steps
and you can count steps to know where you are.  If you put on encoders you
just need to  encoder steps


The encoders are just there to check,  and fun to play with..  or more 
seriously...


I use the encoders similar to a prenup,  hope I don't need it/them to 
correct  mis-steps...  but it doesn't hurt to have






On Thu, Jul 9, 2020 at 1:48 PM R C  wrote:


there will be worm gears, and those will just gear all the axis/axes
down down.

On 7/9/20 1:23 PM, Chris Albertson wrote:

Telescopes are something I know a little about, What you don't tell us

and

what matters quite a lot is the mechanical gearing.  How are the
motors connected to the mount?

there will be worm gears, and those will just gear all the axis/axes
down down. the 3 motors are going to be connected to a stepperdriver
(DM542 or so) and the stepper drivers are 'driven' by an raspberry pi
(mounted in the mount) and I am using a quadrature encoder on  all 3, on
the shaft that drives the main gear on each motor.


If this is an equatorial mount what are there three motors?  and why care
much about if declination moves smoothing as it is only for slewing to a
new target.


It is not exactly an equatorial mount, it is an equatorial platform,
aligned with polaris (northern star) and it turn oposite the rotation of
the earth, to compensate for rotation.

it only has one motor, because it only has to tilt to compensate for
rotation, at a

Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Gene Heskett]

On Thursday 09 July 2020 20:32:42 Gene Heskett wrote:


> > > Steppers aren't pwm driven, so ignore that. But a 48 volt supply
> > > is pushing the ratings of a DM542 which is 50 volts max, and you
> > > would be wise to adjust it a few volts lower. I have a pair of 7.5
> > > amp 48 volt supplies running my 11x56 Sheldon lathe, but they are
> > > turned down to 42.5 volts, much safer, and it still marches at way
> > > faster speeds than needed for a good cut.
> >
> > I can do that, I can put a voltage regulator between them.   What do
> > you mean by "safer" btw?

I didn't see this during my previous reply.

Don't do that, you'll find a teeny knob near the output strip that when 
adjusted, will set its output voltage. Don't assume that turning it CCW 
turns it down, so use a meter. Stepper drivers regulate the motors 
current by switching it on and off at ultrasonic speeds. The surplus 
current gets pushed back into the power supply and is used for makeup on 
the next cycle, so its got to pass current both ways in and out of the 
supply. This creates noise spikes that can easily overvoltage a 50 volt 
part, eventually blowing it, so always figure on about 5 volts less than 
the drivers voltage rating just so this microsecond spike won't 
eventually punch thru one of the outputs switching transistors. That 
will let out the smoke and break the mirror that makes all this stuff 
work. ;-)
[...]
>
> One thing I might consider is belt drives, using very fine toothed
> pulleys like a 3d printer uses, but since your motions are under 180
> degrees, I'd use smooth turned wheels, fastening the belt in slots in
> the far side of a good sized wheel. Cheap, zero backlash, unlike an
> expen$ive worm drive.  Those belts are generally kevlar or dacron
> backed, and zero stretch under long term tension. Buy them by the
> foot. Use the money you save to buy your suds come your birthday. ;-)

If this idea still moves it too coarsely, 3d print another 20/1 geardown 
to put between the motor and the big wheel.  But because its slower 
sprocket will be turning several turns, it will need a continuous belt 
and real sprockets. Up to about 6" sprockets can be done on an Ender 3 
printer.

> > Ron
> >
> > >> thanks,
> > >>
> > >>
> > >> Ron
> > >>
> > >>
> > >>
> > >> ___
> > >> Emc-users mailing list
> > >> Emc-users@lists.sourceforge.net
> > >> https://lists.sourceforge.net/lists/listinfo/emc-users
> > >
> > > Cheers, Gene Heskett
> >
> > ___
> > Emc-users mailing list
> > Emc-users@lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/emc-users
>
> Cheers, Gene Heskett


Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.
 - Louis D. Brandeis
Genes Web page 


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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Chris Albertson]

Gene,

Belts are a good idea for the Ax and El axis but in the Eq axis he needs
something on the order of 100:1 reduction

The time tested traditional method is a synchronous AC moter and a VFD that
can do 60 Hz +/- about 5 percent.  This axis turns only 1 rev per day but
the step need to be less then the eye can see

Belts can go to about 6:1 at best a double belt reduction only goes to 36:1
wich would be about right for Az, El.

We don't know if he is doing photography

One more thing:  I think I read he is using 48 volts.   That is the wrong
voltage for this use case.  I'd go down to half that.  He is doing only
about 10 Hz.

On Thu, Jul 9, 2020 at 5:35 PM Gene Heskett  wrote:

> On Thursday 09 July 2020 19:05:45 R C wrote:
>
> > Hello Gene,
> >
> >
> > To start with the end of your reply,  I actually am a mathematician
> > :)
> >
> > On 7/9/20 4:24 PM, Gene Heskett wrote:
> > > On Thursday 09 July 2020 14:23:57 R C wrote:
> > >> Hello,
> > >>
> > >> this is (probably) off topic, been seen that happen.  If it is
> > >> please ignore it.
> > >>
> > >>
> > >> I am building a "motorized"  telescope mount (dobsonian) with what
> > >> is called an equatorial platform, it has 3 axis which I am going to
> > >> drive with stepper motors.
> > >>
> > >>
> > >> The stepper motors I use with a stepper driver, those common DM542
> > >> ones, the stepper motors themselves are 2A and 1.8 degrees per
> > >> step.
> > >>
> > >>
> > >> What I want to accomplish with the equatorial platform)  (it
> > >> compensates for the rotation of the earth) is that,  the start and
> > >> end position accuracy is not that important,  smooth and
> > >> constant/consistent movement is.  for the azimuth/altitude
> > >> precision is not a really big deal, but you'd want to move these 2
> > >> axis somewhat swift.
> > >>
> > >>
> > >> So there are a few factors to decide.
> > >>
> > >>
> > >> I probably want micro stepping,  what settings on the driver for
> > >> pulses per rev, is best to use (or is that just trial and error?)
> > >
> > > I think the gear ratio is as important as the microstepping ratio
> > > which I would probably set to 8 or 16 with the dip switches on the
> > > dm542's. Any higher than that and the higher speeds need stepper
> > > pulses faster than the opto's in the DM542 inputs which will limit
> > > your top speed to just north of 200 kilohertz for a step rate.
> >
> > Correct, the  gear ratio and stepper resolution are important, so is
> > leverage/torque..  and well..  space to put it.   To move the mount
> >
> > on it's vertical axis, azimuth,  and to move the  newtonian tube, the
> > latitude, U use 360 teeth gears, because they are bigger and have more
> > "leverage", so
> >
> > I can move  them easier/faster (somewhat, that is a trade off too).
> >
> > > Next is the resolution of your mirror, so you would want it to move
> > > about 4 microsteps to see it visibly move in the eyepiece.
> >
> > The one I am doing this with is not that big,  it is an 8" main
> > mirror.
> >
> > > Then if you are well balanced and running on ball bearings for low
> > > friction on all 3 axis's, you may want to experiment with the motor
> > > current to see if a certain current gets you a more even movement,
> > > some drivers, and I haven't asked, nor tried to prove that 1/8th or
> > > 1/16 step gives the same movement as it depends both on the currant
> > > mapping used by the DM542 driver and the magnetic (iron) properties
> > > of the motor.
> >
> > Yes they all have ball bearings,  a big "lazy susan" style one betwen
> > platform and mount,  pillow/pocket bearings for the
> >
> > elliptical friction "runners".  However, kepping the Azimuth
> > bearing/joint and latitude bearing/joint steady for a dobsonian is
> > more important..  they kinda need to be "locked"  when on a target.
> >
> > The equatorial platform needs to run smoothly and steady, no or little
> > "jerking"
> >
> >
> > That is something I want to experiment/try/figure-out   if there is a
> > micro stepping setting that  would be best to use. The
> > smoother/constant/consistent I mover the EQ
> >
> > platform the better. That is where micro stepping and speed comes in I
> > think. If I can continuously can keep moving without stopping, slowing
> > down, speed up, the better it is probably.
> >
> > >> As with PWM itself, I am probably just not too familiar with it.
> > >> From what I understand, the voltage I use for the motors determines
> > >> how fast I can go (I am going to use a 48V switching power supply).
> > >
> > > Steppers aren't pwm driven, so ignore that. But a 48 volt supply is
> > > pushing the ratings of a DM542 which is 50 volts max, and you would
> > > be wise to adjust it a few volts lower. I have a pair of 7.5 amp 48
> > > volt supplies running my 11x56 Sheldon lathe, but they are turned
> > > down to 42.5 volts, much safer, and it still marches at way faster
> > > speeds than needed for a good cut.
> >
> > I can do that, I can put a voltage reg

Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Chris Albertson]

OK, got it a "Dob, on a Ea, platform and the platform on an Az, El mount.

Again PWM is "Pisle Width Modulation"  Steppers and stepper drivers don't
use PWM.  They use what we cal "Pulse/Direction"

PWM uses a constant square wave rate like that is always between 60 Hz and
maybe up to 1,000 Hz.  What changes is the "duty cycle" or the ratio of
"on" to "off".  But it just runs at about 60Hz.  PWM uses just one wire.

Pulse/Direction uses two wires.  One sends a single pulse each time the
motor needs to move a step and the other wire is either "1" or "0" to
indicate the direction, either backward or forward.

With this type of system I don't think you worry about minor things like
atmospheric refraction of structural flex.  You can just run at a constant
rate.

I am wondering why you selected a Raspberry Pi and not some micro
controller.  Perhaps you are planning a user interface that is complex?

All you software needs to do is generate  plusle each time the motr needs
to step.   For the motor that runs the EQ platform this step rate is fixed
forever.  For the other two they can step at whatever rate do want.

Why encoders?  If the motors are proerly sized they will never skip steps
and you can count steps to know where you are.  If you put on encoders you
just need to  encoder steps



On Thu, Jul 9, 2020 at 1:48 PM R C  wrote:

> there will be worm gears, and those will just gear all the axis/axes
> down down.
>
> On 7/9/20 1:23 PM, Chris Albertson wrote:
> > Telescopes are something I know a little about, What you don't tell us
> and
> > what matters quite a lot is the mechanical gearing.  How are the
> > motors connected to the mount?
>
> there will be worm gears, and those will just gear all the axis/axes
> down down. the 3 motors are going to be connected to a stepperdriver
> (DM542 or so) and the stepper drivers are 'driven' by an raspberry pi
> (mounted in the mount) and I am using a quadrature encoder on  all 3, on
> the shaft that drives the main gear on each motor.
>
> >
> > If this is an equatorial mount what are there three motors?  and why care
> > much about if declination moves smoothing as it is only for slewing to a
> > new target.
>
>
> It is not exactly an equatorial mount, it is an equatorial platform,
> aligned with polaris (northern star) and it turn oposite the rotation of
> the earth, to compensate for rotation.
>
> it only has one motor, because it only has to tilt to compensate for
> rotation, at a steady speed. The telescope, with a dobsonian mount is
> standing on top of that ...  and
>
> it has an  azimuth (rotate horizontally, with respect to the platform)
> and  and an elevation mount, to tilt the telescope.
>
>
> So one motor for the platform,  one for  rotating it (azimuth) and one
> motor for altitude, tilting the tube.. (the latter two are for
> "convenience"  just to point the telescope at an object and precission
> is not "that" big a deal because once the object is in sight, those two
> motors 'hold'.  after that the plaform is tilting, to compensate for
> rotation of the earth).
>
>
> >
> > But if this is Az, El then yes I see why three motors,  You have Az, El
> and
> > Feild rotation and all most move smoothly and in exact synchonized
> motion.
> >But an equatorial drive needs only one moer to move smooth.
>
>
> Exactly..  you got the idea there.  once the object is "locked in" only
> the equatorial platform has to  precisely move, without "jerking"
>
>
> >
> > As for PWM.  PWM is nothing at all to do with stepper motors. You can
> > forget about it.Unless you decide to not use steppers.
>
>
> I am using stepperdrivers,  which are running the stepper motors,  and
> the stepperdrivers use PWM to tell them what to do?
>
>
> >
> >
> > The way to work this is to choose a gear ratio, typically a very large
> > reduction, andchoose a step size that is literally "invisable" given you
> > angular resolution.   Of course angular resolution depends on aperture or
> > maybe the pixel size and focal length if this is purly a photographic
> > 'scope.   The steps need to be smaller then 1/2 the angular resolution
> and
> > conservative designers might go even smaller,   Hence the use of really
> big
> > worm/wheel reduction systems
>
>
> I already have figured out the mechanical part so that even with full
> steps, I can still accurately move t=it  and track rotation of "the
> field"  aka rotation of the earth.
>
>
> >
> > Example.   (1) You have a 180 tooth gear and a 1.8 degree step size.
>  That
> > works out to 36 arc seconds per step.  This might be good enough for a
> > small scope used in poor seeing condidtions.
> > (2) 360 tooth gear and 1/8th microstepping now you are at roughly 2
> > arcseconds per step.  This is much better
>
> I have two 360 gear sets (for alt/azi)  but they are big..   and a 60
> teeth  gear/work set.  ratio 60:1
>
> (one rotation of the gear needs 60 rotations of the worm, with full
> stepping that means 12,000 steps for
>
> one rotatio

Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Gene Heskett]

On Thursday 09 July 2020 19:05:45 R C wrote:

> Hello Gene,
>
>
> To start with the end of your reply,  I actually am a mathematician 
> :)
>
> On 7/9/20 4:24 PM, Gene Heskett wrote:
> > On Thursday 09 July 2020 14:23:57 R C wrote:
> >> Hello,
> >>
> >> this is (probably) off topic, been seen that happen.  If it is
> >> please ignore it.
> >>
> >>
> >> I am building a "motorized"  telescope mount (dobsonian) with what
> >> is called an equatorial platform, it has 3 axis which I am going to
> >> drive with stepper motors.
> >>
> >>
> >> The stepper motors I use with a stepper driver, those common DM542
> >> ones, the stepper motors themselves are 2A and 1.8 degrees per
> >> step.
> >>
> >>
> >> What I want to accomplish with the equatorial platform)  (it
> >> compensates for the rotation of the earth) is that,  the start and
> >> end position accuracy is not that important,  smooth and
> >> constant/consistent movement is.  for the azimuth/altitude
> >> precision is not a really big deal, but you'd want to move these 2
> >> axis somewhat swift.
> >>
> >>
> >> So there are a few factors to decide.
> >>
> >>
> >> I probably want micro stepping,  what settings on the driver for
> >> pulses per rev, is best to use (or is that just trial and error?)
> >
> > I think the gear ratio is as important as the microstepping ratio
> > which I would probably set to 8 or 16 with the dip switches on the
> > dm542's. Any higher than that and the higher speeds need stepper
> > pulses faster than the opto's in the DM542 inputs which will limit
> > your top speed to just north of 200 kilohertz for a step rate.
>
> Correct, the  gear ratio and stepper resolution are important, so is
> leverage/torque..  and well..  space to put it.   To move the mount
>
> on it's vertical axis, azimuth,  and to move the  newtonian tube, the
> latitude, U use 360 teeth gears, because they are bigger and have more
> "leverage", so
>
> I can move  them easier/faster (somewhat, that is a trade off too).
>
> > Next is the resolution of your mirror, so you would want it to move
> > about 4 microsteps to see it visibly move in the eyepiece.
>
> The one I am doing this with is not that big,  it is an 8" main
> mirror.
>
> > Then if you are well balanced and running on ball bearings for low
> > friction on all 3 axis's, you may want to experiment with the motor
> > current to see if a certain current gets you a more even movement,
> > some drivers, and I haven't asked, nor tried to prove that 1/8th or
> > 1/16 step gives the same movement as it depends both on the currant
> > mapping used by the DM542 driver and the magnetic (iron) properties
> > of the motor.
>
> Yes they all have ball bearings,  a big "lazy susan" style one betwen
> platform and mount,  pillow/pocket bearings for the
>
> elliptical friction "runners".  However, kepping the Azimuth
> bearing/joint and latitude bearing/joint steady for a dobsonian is
> more important..  they kinda need to be "locked"  when on a target.
>
> The equatorial platform needs to run smoothly and steady, no or little
> "jerking"
>
>
> That is something I want to experiment/try/figure-out   if there is a
> micro stepping setting that  would be best to use. The
> smoother/constant/consistent I mover the EQ
>
> platform the better. That is where micro stepping and speed comes in I
> think. If I can continuously can keep moving without stopping, slowing
> down, speed up, the better it is probably.
>
> >> As with PWM itself, I am probably just not too familiar with it.
> >> From what I understand, the voltage I use for the motors determines
> >> how fast I can go (I am going to use a 48V switching power supply).
> >
> > Steppers aren't pwm driven, so ignore that. But a 48 volt supply is
> > pushing the ratings of a DM542 which is 50 volts max, and you would
> > be wise to adjust it a few volts lower. I have a pair of 7.5 amp 48
> > volt supplies running my 11x56 Sheldon lathe, but they are turned
> > down to 42.5 volts, much safer, and it still marches at way faster
> > speeds than needed for a good cut.
>
> I can do that, I can put a voltage regulator between them.   What do
> you mean by "safer" btw?
>
> >> as for PWM,  I can of course  change the length of the pulse itself
> >> and, independently, change the time between two pulses. What is the
> >> relation ship there?  WHat does a longer  width of the pulse itself
> >> do?  and what exactly does a longer gap between the pulses do (of
> >> course the wider the gap between two pulses the slower the motor
> >> turns).
> >>
> >>
> >> for, especially, the equatorial platform, I want to avoid "jerking"
> >> it,  meaning  starting and stopping the stepper motor as little as
> >> possible and just go at a 'slow' constant speed.
> >
> > LinuxCNC has "adjustment knobs" for that, but are set with a text
> > editor and forgotten once done.  Slewing to another star can be done
> > with a second or more to get to speed, and a slowdown in approaching
> > the new target so "jer

Re: [Emc-users] off topic: pwm with a stepper driver/motor

[R C]

I am not using linux cnc,  I am just  'driving'  the stepper drivers 
with a raspberry pi



I figured,  same hardware (drivers, motors),  "Linux CNC" can use it, so 
thought I'd just ask here about the internals/specifics and how to use it.



On 7/9/20 1:44 PM, andy pugh wrote:

On Thu, 9 Jul 2020 at 19:26, R C  wrote:


The stepper motors I use with a stepper driver, those common DM542 ones,
the stepper motors themselves are 2A and 1.8 degrees per step.

...

As with PWM itself, I am probably just not too familiar with it.

Do you mean PWM?

Stepper drivers take step and direction, not PWM.

I think this is a job for an Arduino, rather than LinuxCNC.
Especially as I assume that an equatorial mount runs at an absolutely
constant rate anywhere in the world?




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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[R C]

Hello Gene,


To start with the end of your reply,  I actually am a mathematician  :)


On 7/9/20 4:24 PM, Gene Heskett wrote:

On Thursday 09 July 2020 14:23:57 R C wrote:


Hello,

this is (probably) off topic, been seen that happen.  If it is please
ignore it.


I am building a "motorized"  telescope mount (dobsonian) with what is
called an equatorial platform, it has 3 axis which I am going to drive
with stepper motors.


The stepper motors I use with a stepper driver, those common DM542
ones, the stepper motors themselves are 2A and 1.8 degrees per step.


What I want to accomplish with the equatorial platform)  (it
compensates for the rotation of the earth) is that,  the start and end
position accuracy is not that important,  smooth and
constant/consistent movement is.  for the azimuth/altitude precision
is not a really big deal, but you'd want to move these 2 axis
somewhat swift.


So there are a few factors to decide.


I probably want micro stepping,  what settings on the driver for
pulses per rev, is best to use (or is that just trial and error?)


I think the gear ratio is as important as the microstepping ratio which I
would probably set to 8 or 16 with the dip switches on the dm542's. Any
higher than that and the higher speeds need stepper pulses faster than
the opto's in the DM542 inputs which will limit your top speed to just
north of 200 kilohertz for a step rate.


Correct, the  gear ratio and stepper resolution are important, so is 
leverage/torque..  and well..  space to put it.   To move the mount


on it's vertical axis, azimuth,  and to move the  newtonian tube, the 
latitude, U use 360 teeth gears, because they are bigger and have more 
"leverage", so


I can move  them easier/faster (somewhat, that is a trade off too).




Next is the resolution of your mirror, so you would want it to move about
4 microsteps to see it visibly move in the eyepiece.


The one I am doing this with is not that big,  it is an 8" main mirror.


Then if you are well balanced and running on ball bearings for low
friction on all 3 axis's, you may want to experiment with the motor
current to see if a certain current gets you a more even movement, some
drivers, and I haven't asked, nor tried to prove that 1/8th or 1/16 step
gives the same movement as it depends both on the currant mapping used
by the DM542 driver and the magnetic (iron) properties of the motor.


Yes they all have ball bearings,  a big "lazy susan" style one betwen 
platform and mount,  pillow/pocket bearings for the


elliptical friction "runners".  However, kepping the Azimuth 
bearing/joint and latitude bearing/joint steady for a dobsonian is more 
important..  they kinda need to be "locked"  when on a target.


The equatorial platform needs to run smoothly and steady, no or little 
"jerking"



That is something I want to experiment/try/figure-out   if there is a 
micro stepping setting that  would be best to use. The 
smoother/constant/consistent I mover the EQ


platform the better. That is where micro stepping and speed comes in I 
think. If I can continuously can keep moving without stopping, slowing 
down, speed up, the better it is probably.





As with PWM itself, I am probably just not too familiar with it. From
what I understand, the voltage I use for the motors determines how
fast I can go (I am going to use a 48V switching power supply).

Steppers aren't pwm driven, so ignore that. But a 48 volt supply is
pushing the ratings of a DM542 which is 50 volts max, and you would be
wise to adjust it a few volts lower. I have a pair of 7.5 amp 48 volt
supplies running my 11x56 Sheldon lathe, but they are turned down to
42.5 volts, much safer, and it still marches at way faster speeds than
needed for a good cut.


I can do that, I can put a voltage regulator between them.   What do you 
mean by "safer" btw?



as for PWM,  I can of course  change the length of the pulse itself
and, independently, change the time between two pulses. What is the
relation ship there?  WHat does a longer  width of the pulse itself
do?  and what exactly does a longer gap between the pulses do (of
course the wider the gap between two pulses the slower the motor
turns).


for, especially, the equatorial platform, I want to avoid "jerking"
it,  meaning  starting and stopping the stepper motor as little as
possible and just go at a 'slow' constant speed.


LinuxCNC has "adjustment knobs" for that, but are set with a text editor
and forgotten once done.  Slewing to another star can be done with a
second or more to get to speed, and a slowdown in approaching the new
target so "jerk" can be very low.


I am not too worried about that part,  zooming in on an object, that is 
fine,  I could do that  manually, well remotely.  and once "locked in"  
keep it steady and start the EQ platform.


I am also terribly worried about the "Go To" features of the telescope.  
I am planning on a good camera on the telescope,  and a "cheap" camera 
on the finder scope. Ultimately 

Re: [Emc-users] off topic: pwm with a stepper driver/motor

[R C]

On 7/9/20 1:44 PM, andy pugh wrote:

On Thu, 9 Jul 2020 at 19:26, R C  wrote:


The stepper motors I use with a stepper driver, those common DM542 ones,
the stepper motors themselves are 2A and 1.8 degrees per step.

...

As with PWM itself, I am probably just not too familiar with it.

Do you mean PWM?


yes




Stepper drivers take step and direction, not PWM.


correct,  but the direction is either high or low,  while the PUL (step) 
ping/port takes PWM signals, which you can easily create with a RPI,  I 
have that part working.  I have the impression that on the 
stepperdriver, the pulswidth is constant a table in the docs shows that 
, so the duty cycle is always  2.5us of power and then some delay   so 
if a cycle iis 2.5us hi,  2.5us low and then 5us low, the duty cycle is 
10us at 50%..    and if   hi is 2.5 us, the low is 2.5us, the duty cycle 
is5us, at 100%   etc.


That is what I wanted to ask,  if that is correct   because 
typically you would set the input frequency,  and that gives you a duty 
cycle length,  and  the width of the pulse (plus the voltage) would 
dictate the power.  but  with these drivers,  the  pule width seems 
fixed ??   and the frequency can pretty much can be anything less then 200k




I think this is a job for an Arduino, rather than LinuxCNC.
Especially as I assume that an equatorial mount runs at an absolutely
constant rate anywhere in the world?

well, I am not using CNC  (that is why I called it off topic) unless 
anyone would ever like to build that into it... (instead of a mill and 
lathe, add a telescope.. *lol* )...   an Arduino wouldn't do anything 
different than the RPI does. I can make the motor run at different 
speeds etc..   just want to know the relation between dutu cycle and 
pulse length ..



Ron

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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Gene Heskett]

On Thursday 09 July 2020 14:23:57 R C wrote:

> Hello,
>
> this is (probably) off topic, been seen that happen.  If it is please
> ignore it.
>
>
> I am building a "motorized"  telescope mount (dobsonian) with what is
> called an equatorial platform, it has 3 axis which I am going to drive
> with stepper motors.
>
>
> The stepper motors I use with a stepper driver, those common DM542
> ones, the stepper motors themselves are 2A and 1.8 degrees per step.
>
>
> What I want to accomplish with the equatorial platform)  (it
> compensates for the rotation of the earth) is that,  the start and end
> position accuracy is not that important,  smooth and
> constant/consistent movement is.  for the azimuth/altitude precision
> is not a really big deal, but you'd want to move these 2 axis 
> somewhat swift.
>
>
> So there are a few factors to decide.
>
>
> I probably want micro stepping,  what settings on the driver for
> pulses per rev, is best to use (or is that just trial and error?)
>
I think the gear ratio is as important as the microstepping ratio which I 
would probably set to 8 or 16 with the dip switches on the dm542's. Any 
higher than that and the higher speeds need stepper pulses faster than 
the opto's in the DM542 inputs which will limit your top speed to just 
north of 200 kilohertz for a step rate.

Next is the resolution of your mirror, so you would want it to move about 
4 microsteps to see it visibly move in the eyepiece.

Then if you are well balanced and running on ball bearings for low 
friction on all 3 axis's, you may want to experiment with the motor 
current to see if a certain current gets you a more even movement, some 
drivers, and I haven't asked, nor tried to prove that 1/8th or 1/16 step 
gives the same movement as it depends both on the currant mapping used 
by the DM542 driver and the magnetic (iron) properties of the motor.

> As with PWM itself, I am probably just not too familiar with it. From
> what I understand, the voltage I use for the motors determines how
> fast I can go (I am going to use a 48V switching power supply).

Steppers aren't pwm driven, so ignore that. But a 48 volt supply is 
pushing the ratings of a DM542 which is 50 volts max, and you would be 
wise to adjust it a few volts lower. I have a pair of 7.5 amp 48 volt 
supplies running my 11x56 Sheldon lathe, but they are turned down to 
42.5 volts, much safer, and it still marches at way faster speeds than 
needed for a good cut.
>
> as for PWM,  I can of course  change the length of the pulse itself 
> and, independently, change the time between two pulses. What is the
> relation ship there?  WHat does a longer  width of the pulse itself
> do?  and what exactly does a longer gap between the pulses do (of
> course the wider the gap between two pulses the slower the motor
> turns).
>
>
> for, especially, the equatorial platform, I want to avoid "jerking"
> it,  meaning  starting and stopping the stepper motor as little as
> possible and just go at a 'slow' constant speed.
>
LinuxCNC has "adjustment knobs" for that, but are set with a text editor 
and forgotten once done.  Slewing to another star can be done with a 
second or more to get to speed, and a slowdown in approaching the new 
target so "jerk" can be very low.

The problem I see in moving a Dob is in the kinematics conversion because 
its axis's for az-el need to be mapped to the location on the planet for 
the base motors movements. A newtonian on a polar mount cancels 99.99% 
of that because the 2 axis's are 90 degrees to each other, the Dob mount 
is not.
>
>
> sorry if totally of topic

Not totally.  Might be an interesting diversion. :)  But I'll let some of 
our better maths people comment on the kinematics.

>
> thanks,
>
>
> Ron
>
>
>
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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[R C]

there will be worm gears, and those will just gear all the axis/axes 
down down.


On 7/9/20 1:23 PM, Chris Albertson wrote:

Telescopes are something I know a little about, What you don't tell us and
what matters quite a lot is the mechanical gearing.  How are the
motors connected to the mount?


there will be worm gears, and those will just gear all the axis/axes 
down down. the 3 motors are going to be connected to a stepperdriver 
(DM542 or so) and the stepper drivers are 'driven' by an raspberry pi 
(mounted in the mount) and I am using a quadrature encoder on  all 3, on 
the shaft that drives the main gear on each motor.




If this is an equatorial mount what are there three motors?  and why care
much about if declination moves smoothing as it is only for slewing to a
new target.



It is not exactly an equatorial mount, it is an equatorial platform, 
aligned with polaris (northern star) and it turn oposite the rotation of 
the earth, to compensate for rotation.


it only has one motor, because it only has to tilt to compensate for 
rotation, at a steady speed. The telescope, with a dobsonian mount is 
standing on top of that ...  and


it has an  azimuth (rotate horizontally, with respect to the platform)  
and  and an elevation mount, to tilt the telescope.



So one motor for the platform,  one for  rotating it (azimuth) and one 
motor for altitude, tilting the tube.. (the latter two are for 
"convenience"  just to point the telescope at an object and precission 
is not "that" big a deal because once the object is in sight, those two 
motors 'hold'.  after that the plaform is tilting, to compensate for 
rotation of the earth).





But if this is Az, El then yes I see why three motors,  You have Az, El and
Feild rotation and all most move smoothly and in exact synchonized motion.
   But an equatorial drive needs only one moer to move smooth.



Exactly..  you got the idea there.  once the object is "locked in" only 
the equatorial platform has to  precisely move, without "jerking"





As for PWM.  PWM is nothing at all to do with stepper motors. You can
forget about it.Unless you decide to not use steppers.



I am using stepperdrivers,  which are running the stepper motors,  and 
the stepperdrivers use PWM to tell them what to do?






The way to work this is to choose a gear ratio, typically a very large
reduction, andchoose a step size that is literally "invisable" given you
angular resolution.   Of course angular resolution depends on aperture or
maybe the pixel size and focal length if this is purly a photographic
'scope.   The steps need to be smaller then 1/2 the angular resolution and
conservative designers might go even smaller,   Hence the use of really big
worm/wheel reduction systems



I already have figured out the mechanical part so that even with full 
steps, I can still accurately move t=it  and track rotation of "the 
field"  aka rotation of the earth.





Example.   (1) You have a 180 tooth gear and a 1.8 degree step size.   That
works out to 36 arc seconds per step.  This might be good enough for a
small scope used in poor seeing condidtions.
(2) 360 tooth gear and 1/8th microstepping now you are at roughly 2
arcseconds per step.  This is much better


I have two 360 gear sets (for alt/azi)  but they are big..   and a 60 
teeth  gear/work set.  ratio 60:1


(one rotation of the gear needs 60 rotations of the worm, with full 
stepping that means 12,000 steps for


one rotation of the shaft that turns the platform.  and I only need to 
tilt the platform 15 degrees in an hour


which should be doable.   I would only need 14-15 arc second precision 
really,  per second.





How fast do you need to step?   Assume the Earth turns once per day ;-)
  That is 1,300,000 arc seconds per 86,000 seconds.   Or about 15 arcseconds
per second.  So the motor in case number two steps only about 7 or 8 times
per second.  So it looks like you could do 1/16th step or even more.



I need to tilt the platform 15 degrees per hour,  earth rotates 360 
degrees in 24 hours,  that is 15 degrees per hour,  or 15 arc mins per 
minute  which is 15 arc secs per second. ..  which is pretty slow, but 
the need it to do it smoothly.





But you trade off slewing speed if the microsteps are too small.  So you
want them to be invisible at your optical resolution but no smaller.  This
depends on the aperture of the scope and the camera's angular pixel size


right, like that   and yes,  taking lot's of pics,  so vibration is a no 
no (although that can be fixed afterwards) but ideally, smooth  moving 
and accurate, for compensation, would be best.




But is this az, el or equatorial?   And what is the gearing?  I just made
up those examples from thin air.


equatorial,  the equatorial platform is most important.


The idea is. set the platform ready (at 15 degrees "towards" rotation.  
then move the scope to the object and keep it there. so AZ and Alt are 
holding.  the EQ starts moving, in orde

Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Chris Albertson]

On Thu, Jul 9, 2020 at 12:47 PM andy pugh  wrote:

> On Thu, 9 Jul 2020 at 19:26, R C  wrote:
>
> > The stepper motors I use with a stepper driver, those common DM542 ones,
> > the stepper motors themselves are 2A and 1.8 degrees per step.
> ...
> > As with PWM itself, I am probably just not too familiar with it.
>
> Do you mean PWM?
>
> Stepper drivers take step and direction, not PWM.
>
> I think this is a job for an Arduino, rather than LinuxCNC.
> Especially as I assume that an equatorial mount runs at an absolutely
> constant rate anywhere in the world?
>

Almost,
1) the atmosphere refracts light more near the horizon than at zenith and
2) most telescope mounts flex as they move and
3) every worm and wheel system has at least some periodic error

I worked on an astrometry (yes the spelling is correct) project where the
units are "mas" or "milliarcseconds"  At that level nothing is straight,
square or constant.  Today even amateurs on a personal budget can work at
this level and it does matter if doing photography of planets.

I'd recommend a microcontroller that has built-in floating point and it
REALLY helps if it can run NTP off a GPS receiver so you get at least
millisecond level time.   Arduinos are not up to this unless they are
connected to a PC

So the design depends of if you want ot be dependent on a computer.   Most
users will have a PC or even a couple of them if doing photography

That said, for casual visual use, a constant pusle generator is all you
need, even the Arduino is overkill.  You could use a 555 chip.

But this person said THREE motors.So I think maybe it is an az, el
system with field de-rotation.  None of those rates would be constant.

>
> --
> atp
> "A motorcycle is a bicycle with a pandemonium attachment and is
> designed for the especial use of mechanical geniuses, daredevils and
> lunatics."
> — George Fitch, Atlanta Constitution Newspaper, 1912
>
>
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-- 

Chris Albertson
Redondo Beach, California

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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[andy pugh]

On Thu, 9 Jul 2020 at 19:26, R C  wrote:

> The stepper motors I use with a stepper driver, those common DM542 ones,
> the stepper motors themselves are 2A and 1.8 degrees per step.
...
> As with PWM itself, I am probably just not too familiar with it.

Do you mean PWM?

Stepper drivers take step and direction, not PWM.

I think this is a job for an Arduino, rather than LinuxCNC.
Especially as I assume that an equatorial mount runs at an absolutely
constant rate anywhere in the world?

-- 
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1912


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Re: [Emc-users] off topic: pwm with a stepper driver/motor

[Chris Albertson]

Telescopes are something I know a little about, What you don't tell us and
what matters quite a lot is the mechanical gearing.  How are the
motors connected to the mount?

If this is an equatorial mount what are there three motors?  and why care
much about if declination moves smoothing as it is only for slewing to a
new target.

But if this is Az, El then yes I see why three motors,  You have Az, El and
Feild rotation and all most move smoothly and in exact synchonized motion.
  But an equatorial drive needs only one moer to move smooth.

As for PWM.  PWM is nothing at all to do with stepper motors. You can
forget about it.Unless you decide to not use steppers.


The way to work this is to choose a gear ratio, typically a very large
reduction, andchoose a step size that is literally "invisable" given you
angular resolution.   Of course angular resolution depends on aperture or
maybe the pixel size and focal length if this is purly a photographic
'scope.   The steps need to be smaller then 1/2 the angular resolution and
conservative designers might go even smaller,   Hence the use of really big
worm/wheel reduction systems

Example.   (1) You have a 180 tooth gear and a 1.8 degree step size.   That
works out to 36 arc seconds per step.  This might be good enough for a
small scope used in poor seeing condidtions.
(2) 360 tooth gear and 1/8th microstepping now you are at roughly 2
arcseconds per step.  This is much better

How fast do you need to step?   Assume the Earth turns once per day ;-)
 That is 1,300,000 arc seconds per 86,000 seconds.   Or about 15 arcseconds
per second.  So the motor in case number two steps only about 7 or 8 times
per second.  So it looks like you could do 1/16th step or even more.

But you trade off slewing speed if the microsteps are too small.  So you
want them to be invisible at your optical resolution but no smaller.  This
depends on the aperture of the scope and the camera's angular pixel size

But is this az, el or equatorial?   And what is the gearing?  I just made
up those examples from thin air.

One thing you really want is FEEDBACK from a guide star or even from the
main camera.  A guid camera can detect feild drife and change the speed of
the motor compensate. Drift is caused by (1) changes in
atmospheric refraction as the target moves and (2) the telescope mount
flexing as the scope moves.   Some sophisticated software tries to model
this and calculate the effect but a close loop is best and now days cheap
to do.

Last time I did this we used NTP to keep the controller's clock
synchronized to actual time.  We used a local GPS receiver to create a
local NTP server

Yes, one could use LinuxCNC to drive the motors it might be easier to just
use a microcontroller.


On Thu, Jul 9, 2020 at 11:26 AM R C  wrote:

> Hello,
>
> this is (probably) off topic, been seen that happen.  If it is please
> ignore it.
>
>
> I am building a "motorized"  telescope mount (dobsonian) with what is
> called an equatorial platform, it has 3 axis which I am going to drive
> with stepper motors.
>
>
> The stepper motors I use with a stepper driver, those common DM542 ones,
> the stepper motors themselves are 2A and 1.8 degrees per step.
>
>
> What I want to accomplish with the equatorial platform)  (it compensates
> for the rotation of the earth) is that,  the start and end position
> accuracy is not that important,  smooth and constant/consistent movement
> is.  for the azimuth/altitude precision is not a really big deal, but
> you'd want to move these 2 axis  somewhat swift.
>
>
> So there are a few factors to decide.
>
>
> I probably want micro stepping,  what settings on the driver for pulses
> per rev, is best to use (or is that just trial and error?)
>
>
> As with PWM itself, I am probably just not too familiar with it. From
> what I understand, the voltage I use for the motors determines how fast
> I can go (I am going to use a 48V switching power supply).
>
>
> as for PWM,  I can of course  change the length of the pulse itself
> and, independently, change the time between two pulses. What is the
> relation ship there?  WHat does a longer  width of the pulse itself do?
> and what exactly does a longer gap between the pulses do (of course the
> wider the gap between two pulses the slower the motor turns).
>
>
> for, especially, the equatorial platform, I want to avoid "jerking" it,
> meaning  starting and stopping the stepper motor as little as possible
> and just go at a 'slow' constant speed.
>
>
>
> sorry if totally of topic
>
>
> thanks,
>
>
> Ron
>
>
>
> ___
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-- 

Chris Albertson
Redondo Beach, California

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[Emc-users] off topic: pwm with a stepper driver/motor

[R C]

Hello,

this is (probably) off topic, been seen that happen.  If it is please 
ignore it.



I am building a "motorized"  telescope mount (dobsonian) with what is 
called an equatorial platform, it has 3 axis which I am going to drive 
with stepper motors.



The stepper motors I use with a stepper driver, those common DM542 ones, 
the stepper motors themselves are 2A and 1.8 degrees per step.



What I want to accomplish with the equatorial platform)  (it compensates 
for the rotation of the earth) is that,  the start and end position 
accuracy is not that important,  smooth and constant/consistent movement 
is.  for the azimuth/altitude precision is not a really big deal, but 
you'd want to move these 2 axis  somewhat swift.



So there are a few factors to decide.


I probably want micro stepping,  what settings on the driver for pulses 
per rev, is best to use (or is that just trial and error?)



As with PWM itself, I am probably just not too familiar with it. From 
what I understand, the voltage I use for the motors determines how fast 
I can go (I am going to use a 48V switching power supply).



as for PWM,  I can of course  change the length of the pulse itself  
and, independently, change the time between two pulses. What is the 
relation ship there?  WHat does a longer  width of the pulse itself do?  
and what exactly does a longer gap between the pulses do (of course the 
wider the gap between two pulses the slower the motor turns).



for, especially, the equatorial platform, I want to avoid "jerking" it,  
meaning  starting and stopping the stepper motor as little as possible 
and just go at a 'slow' constant speed.




sorry if totally of topic


thanks,


Ron



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