subject:"\[Emc\-users\] Calculating table acceleration. Was\: Need help with Bostomatic BD18\-2 to linuxcnc"

On Thu, 23 Jul 2020 at 18:05, John Dammeyer  wrote:

> In my case the Motor inertia is 3.4kg/cm^2.

> However, I suspect that the energy required to spin the pulleys and lead 
> screw (1000 RPM for the lead screw with 3:1 on the motor) is a small part of 
> moving a 220 lb (100kg) table with a motor rated at 226 oz.in (x3 with 
> reduction = 678 oz-in or 4.8Nm on lead screw).

Try calculating the equivalent moment of inertia using the formula I derived.
(But check my work to make sure  that the 2pi is in the right place, I
think we end up with too many of them)

-- 
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] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-23 Thread Thaddeus Waldner

I think the answer to your question is, you need to stay with a unit of g 
because that is what you started out with.
Imperial units for torque, oz-in, lb-in, lb-ft, are defined by the force of 
gravity on a mass of one lb (or oz).

Si unit of torque is Newton-meters. No need to involve g when using those.

> On Jul 23, 2020, at 12:05 PM, John Dammeyer  wrote:
> 
> And the magic number in the math is the assumption that the units are G.

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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-23 Thread John Dammeyer

> -Original Message-
> From: Jon Elson [mailto:el...@pico-systems.com]
> Sent: July-23-20 9:00 AM
> To: Enhanced Machine Controller (EMC)
> Subject: Re: [Emc-users] Calculating table acceleration. Was: Need help with 
> Bostomatic BD18-2 to linuxcnc
> 
> On 07/23/2020 05:09 AM, andy pugh wrote:
> > On Thu, 23 Jul 2020 at 09:22, John Dammeyer  wrote:
> >
> >> Not ignoring you at all.  Just waiting for an idea for the math that leads 
> >> to calculating MAX_ACCELERATION in the ini file given
> the parameters I've mentioned before.
> > I think that the problem is treating the motor as an ideal torque
> > source. It has inertia, it has inductance, it has a non-linear
> > current-torque graph and it has back-emf.
> While the inductance is visible at PWM frequencies, for the
> size motors we are dealing with, it really has little effect
> at the frequencies and bandwidth involved in CNC motion control.
> 
> Rotational inertia, however, is a BIG issue.  The leadscrew
> can be thought of as a torsion spring, the length of the
> active spring changes as the ball nut progresses down the
> screw, and the motor angular momentum turns it all into a
> spring and mass system.  I have this issue on my Bridgeport,
> the leadscrews are too small diameter for such a massive
> system, and I get a resonance that varies between 20 - 40 Hz.
> 
> Applying a voltage to a motor leads to reduced current as
> the motor speed increases, due to the back EMF generated.
> That's why it would be good to put a resistance in the
> circuit to get more constant current if trying to test
> practical acceleration limits.  Motor torque will be quite
> linear with respect to current over a wide range of currents
> within the motor's rating envelope.
> 
> Your extensive calculations are appreciated, but without
> knowing a few key parameters it can be hard to get started.
> I have the gear here to measure inductance, but not
> everybody does.  I guess with an encoder connected to a
> motor, and a constant-current source, rotor inertia could be
> obtained.
> 
> Jon

In my case the Motor inertia is 3.4kg/cm^2.  And I agree. I still even have 
alignment issues that result in different sounds depending on where the lead 
screw and table are.  And my acme screw is 1"diameter.  (25.4mm)

However, I suspect that the energy required to spin the pulleys and lead screw 
(1000 RPM for the lead screw with 3:1 on the motor) is a small part of moving a 
220 lb (100kg) table with a motor rated at 226 oz.in (x3 with reduction = 678 
oz-in or 4.8Nm on lead screw).

The HP_UHU servo has two comparators for current limit and two trim pots for 
adjustment.  One sets high speed and the signal is filtered with a RC 820 Ohm 
and 470pF cap.  The other sets low speed continuous stall current with 330K and 
220uF.   I imagine your servo drives have something similar.   I guess 
theoretically you set the high speed for the Peak Current of 40A and the 
Continuous for 7.8A.

Those two settings will probably have far more to do with the MAX_ACCELERATION 
value than lead screw or pulley inertia.  But none of that changes the math I 
did that suggested the acceleration with this motor could be set at 100x of 
what actually works.   And the magic number in the math is the assumption that 
the units are G.

I have to leave this alone for a while.  When I have some room and access with 
my 4 channel scope I'll take a look at the current limit signals relative to 
encoder pulses to see what's going on.  As I said earlier, my little Lazarus 
program at the moment is junk because it makes an assumption on units of 
gravity that I don't think are valid.

John Dammeyer

> 
> 
> 
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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-23 Thread Todd Zuercher

Agreed, it generally isn't much different working in US vs metric, you just 
have to make sure ALL of your units always jive. (and I don't think you have to 
use slugs)  You can still have the same problems in metric, but there those 
mistakes often only results in a decimal point miss placement, but it doesn't 
make the result any less wrong.  So it is a very good idea to write out all 
your units used as you go, to help prevent these mistakes.

Also it isn't always easy to gather all of the pertinent significant variables, 
such as the motor rotor inertia, screw's rotating inertia, table mass (plus 
theoretical max table load) plus all the related frictions (which may not be 
insignificant), and I don't have any knowledge of the electrical inefficiencies 
of the servo or stepper motor.  Step testing sounds the more logical way to 
come to an accurate conclusion.

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

-Original Message-
From: Bari  
Sent: Thursday, July 23, 2020 10:54 AM
To: emc-users@lists.sourceforge.net
Subject: Re: [Emc-users] Calculating table acceleration. Was: Need help with 
Bostomatic BD18-2 to linuxcnc

[EXTERNAL EMAIL] Be sure links are safe.

It's really not a big deal. Engineering and science is full of math operations 
that you have to jump to all the time. If it is too difficult find someone else 
that is not a complainer to help you.

On 7/23/20 12:34 AM, Chris Albertson wrote:

> Why on Earth do people still use US units?   OK if your final result must
> be expressed that way, but do the math in metric then convert at the end.

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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-23 Thread Jon Elson


On 07/23/2020 05:09 AM, andy pugh wrote:

On Thu, 23 Jul 2020 at 09:22, John Dammeyer  wrote:


Not ignoring you at all.  Just waiting for an idea for the math that leads to 
calculating MAX_ACCELERATION in the ini file given the parameters I've 
mentioned before.

I think that the problem is treating the motor as an ideal torque
source. It has inertia, it has inductance, it has a non-linear
current-torque graph and it has back-emf.
While the inductance is visible at PWM frequencies, for the 
size motors we are dealing with, it really has little effect 
at the frequencies and bandwidth involved in CNC motion control.


Rotational inertia, however, is a BIG issue.  The leadscrew 
can be thought of as a torsion spring, the length of the 
active spring changes as the ball nut progresses down the 
screw, and the motor angular momentum turns it all into a 
spring and mass system.  I have this issue on my Bridgeport, 
the leadscrews are too small diameter for such a massive 
system, and I get a resonance that varies between 20 - 40 Hz.


Applying a voltage to a motor leads to reduced current as 
the motor speed increases, due to the back EMF generated.  
That's why it would be good to put a resistance in the 
circuit to get more constant current if trying to test 
practical acceleration limits.  Motor torque will be quite 
linear with respect to current over a wide range of currents 
within the motor's rating envelope.


Your extensive calculations are appreciated, but without 
knowing a few key parameters it can be hard to get started.  
I have the gear here to measure inductance, but not 
everybody does.  I guess with an encoder connected to a 
motor, and a constant-current source, rotor inertia could be 
obtained.


Jon



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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-23 Thread Jon Elson


On 07/23/2020 02:00 AM, John Dammeyer wrote:

Hi Tomp,

I understand the process and the step response.   One thing in the mix that we 
haven't discussed, and I really was hoping Jon Elson would chime in again, is 
exactly how much impact the servo drive has on all this.
Well, both the motor and the drive have current limits.  
Often the drive has a lower limit than the motor, so it is 
the dominant one. Current in the motor equals torque, and 
torque is proportional to linear force on the axis.  So, the 
drive (or motor) current limit absolutely sets the 
acceleration that can be achieved.
You can crank up the MAX_ACCELERATION parameter in the .ini 
file and watch the error with Halscope (on machines equipped 
with encoders) and see when the servo drive "runs out of 
juice".  Then, back off on the accel parameter by 10 - 15 % 
to account for cutting forces, and you should be at the optimum.

The application of DC voltage to a motor and then measuring up to speed brings 
up the question as to how you know the motor is up to speed.  But anyway.  
Could do it with the scope monitoring step pulses and using evenly spaced 
pulses as the up to speed indication.


Well, actually, it isn't voltage, but current, that should 
be applied to the motor.  Using a small resistance in series 
would approximate a constant current source, and give 
constant acceleration.


Jon


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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-23 Thread Jon Elson


On 07/22/2020 11:52 PM, John Dammeyer wrote:
  
But does the accel value in F=ma have to be gravity?  And if not, what then?
  

No!  G and weight in Lbs are convenient units because we 
live on earth.  They are useless anywhere else.

But, they are familiar to anyone who lives here.

mass is a constant property of matter, anywhere in the 
universe, at least as long as you stay away from 
relativistic velocities.  And, the same for acceleration.  G 
is just a unit conversion to other units.
m/s^2 is a universal unit.  So, the acceleration on a 
machine part can be measured and expressed completely 
without reference to the earth.


Jon


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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-23 Thread Mark Wendt

On Thu, Jul 23, 2020 at 11:35 AM dave engvall  wrote:

>
>
> On 7/23/20 7:53 AM, Bari wrote:
> > It's really not a big deal. Engineering and science is full of math
> > operations that you have to jump to all the time. If it is too
> > difficult find someone else that is not a complainer to help you.
> >
> >
> > On 7/23/20 12:34 AM, Chris Albertson wrote:
> >
> >> Why on Earth do people still use US units?   OK if your final result
> >> must
> >> be expressed that way, but do the math in metric then convert at the
> >> end.
> >
> > Careful Chris ... you are being  logical. ;-) Politics and logic are
> > rarely in the same room. But then I'm an old grump. We had our chance
> > to convert when we build the interstate hwy system. If we had
> > converted to Km and liters at that time we might be metric by now. Any
> > manufacturing that competes internationally converted long ago. The
> > military converted long ago but in the '60's the grid was metric but
> > the heights were still in feet.
> Dave
>

And yet, global navigation is still done in terms of latitude and
longitude, using nautical miles.  In the age of computers and calculators,
who cares what units are being used?  it's not like anybody is doing
calculations longhand anymore.

Mark

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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-23 Thread dave engvall




On 7/23/20 7:53 AM, Bari wrote:
It's really not a big deal. Engineering and science is full of math 
operations that you have to jump to all the time. If it is too 
difficult find someone else that is not a complainer to help you.



On 7/23/20 12:34 AM, Chris Albertson wrote:

Why on Earth do people still use US units?   OK if your final result 
must
be expressed that way, but do the math in metric then convert at the 
end.


Careful Chris ... you are being  logical. ;-) Politics and logic are 
rarely in the same room. But then I'm an old grump. We had our chance 
to convert when we build the interstate hwy system. If we had 
converted to Km and liters at that time we might be metric by now. Any 
manufacturing that competes internationally converted long ago. The 
military converted long ago but in the '60's the grid was metric but 
the heights were still in feet.

   Dave

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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-23 Thread Bari

It's really not a big deal. Engineering and science is full of math 
operations that you have to jump to all the time. If it is too difficult 
find someone else that is not a complainer to help you.



On 7/23/20 12:34 AM, Chris Albertson wrote:


Why on Earth do people still use US units?   OK if your final result must
be expressed that way, but do the math in metric then convert at the end.



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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-23 Thread Nicklas SB Karlsson

> On Thu, 23 Jul 2020 at 09:22, John Dammeyer  wrote:
> 
> > Not ignoring you at all.  Just waiting for an idea for the math that leads 
> > to calculating MAX_ACCELERATION in the ini file given the parameters I've 
> > mentioned before.
> 
> I think that the problem is treating the motor as an ideal torque
> source. It has inertia, it has inductance, it has a non-linear
> current-torque graph and it has back-emf.

Agree but think current-torque graph usually is rather linear for electric 
motors used for servos. It will be non linear then stator iron start to 
saturate due to high flux density.

> I think that the approach most likely to yield success here is a
> discrete time-stepping approach, starting with calculating the motor
> current.
> 
> At any time dI/dt = (Vs - Vb) / L where Vs is supply voltage, Vb is
> back-emf and L is the motor inductance.
> We can calculate Vb from the nameplate:  Vb = rated-voltage * (
> actual-rpm / rated-rpm )
> 
> Start from time=0:
> Time (t) = 0, current (I) = 0, Vi = 180, motor speed, revs per sec(R)
> = 0, Vb = 0, torque (T) = 0
> 
> I += L * (Vs - Vb) dt

Agree. Vs could be changed instantly so jerk could be changed instantly and 
then there are limitations on all variables.

> Use the motor torque rating graph to calculate torque for the new I.
> Or calculate proportionally from rated torque / rated current.
> 
> We now know the instantaneous torque from the motor. Part of this goes
> to overcome rotary inertia, part goes to overcome linear inertia.
> Ideally you match these (which is why servo motors come in low, medium
> and high inertia variants)
> 
> Generally speaking, with W = speed in radians/sec
> (1) dW/dt = 2pi dR/dt =  T/J, so we need an equivalent J (moment of
> inertia) for the table linear motion. for a table speed V and
> leadscrew pitch P (in mm or in, not tpi):
> 
> (2) dR/dt =  dV/dt / P
> Inertial force = M.dV/dt
> As already derived F/T = 2pi/P
> (https://en.wikipedia.org/wiki/Screw_(simple_machine)#Frictionless_mechanical_advantage)
> So
> M dV/dt / T  = 2pi/P
> Substitute dV/dt (2) => M P dR/dt = 2pi T / P
> Re-arrange to look like (1)
> M P dW/dt / 2pi = 2pi T / P
> dW/dt = T (4 pi^2 / M P^2)  => T / (M P^2 / 4 pi^2)   ... I am
> unhappy with this, you rarely see a pi^2 term.
> 
> So now we can say that the equivalent moment of inertia of the table
> (Je) = M P^2 / 4pi^2
> 
> Combining motor inertia (Jm) and table inertia (Je)
> 
> dW / dt = T / (Jm + Je)
> 
> R += (T / 2pi(Jm + Je) ) dt .. There is an 8 pi ^ 3 in there
> now, I think I got something wrong...
> 
> V = PR
> 
> And loop back, calculating the new Vb, the new I, new T and so on.
> 
> I am confident in the physics here, less so in my algebraic
> manipulations, specifically the 2pi which I feel should have cancelled
> rather than squared somewhere. It might be better to re-work in
> radians/sec throughout.
> I am a little surprised to see P^2, but that has to be a factor. I had
> that cancel and re-thought (2) Consider a pitch of zero.
> 
> -- 
> 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] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-23 Thread Nicklas SB Karlsson

> On Thu, 23 Jul 2020 at 05:55, John Dammeyer  wrote:
> >
> > I've asked a retired physics professor friend for some enlightenment.
> 
> I have a PhD in Physics, but seem to be being ignored.

Maybe I missed what you said?


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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

On Thu, 23 Jul 2020 at 11:09, andy pugh  wrote:

> I += L * (Vs - Vb) dt

Oops!

V = L di/dt

di = (V / L) dt

So that should be

I += (Vs-Vb)/L dt

-- 
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] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

On Thu, 23 Jul 2020 at 09:22, John Dammeyer  wrote:

> Not ignoring you at all.  Just waiting for an idea for the math that leads to 
> calculating MAX_ACCELERATION in the ini file given the parameters I've 
> mentioned before.

I think that the problem is treating the motor as an ideal torque
source. It has inertia, it has inductance, it has a non-linear
current-torque graph and it has back-emf.

I think that the approach most likely to yield success here is a
discrete time-stepping approach, starting with calculating the motor
current.

At any time dI/dt = (Vs - Vb) / L where Vs is supply voltage, Vb is
back-emf and L is the motor inductance.
We can calculate Vb from the nameplate:  Vb = rated-voltage * (
actual-rpm / rated-rpm )

Start from time=0:
Time (t) = 0, current (I) = 0, Vi = 180, motor speed, revs per sec(R)
= 0, Vb = 0, torque (T) = 0

I += L * (Vs - Vb) dt

Use the motor torque rating graph to calculate torque for the new I.
Or calculate proportionally from rated torque / rated current.

We now know the instantaneous torque from the motor. Part of this goes
to overcome rotary inertia, part goes to overcome linear inertia.
Ideally you match these (which is why servo motors come in low, medium
and high inertia variants)

Generally speaking, with W = speed in radians/sec
(1) dW/dt = 2pi dR/dt =  T/J, so we need an equivalent J (moment of
inertia) for the table linear motion. for a table speed V and
leadscrew pitch P (in mm or in, not tpi):

(2) dR/dt =  dV/dt / P
Inertial force = M.dV/dt
As already derived F/T = 2pi/P
(https://en.wikipedia.org/wiki/Screw_(simple_machine)#Frictionless_mechanical_advantage)
So
M dV/dt / T  = 2pi/P
Substitute dV/dt (2) => M P dR/dt = 2pi T / P
Re-arrange to look like (1)
M P dW/dt / 2pi = 2pi T / P
dW/dt = T (4 pi^2 / M P^2)  => T / (M P^2 / 4 pi^2)   ... I am
unhappy with this, you rarely see a pi^2 term.

So now we can say that the equivalent moment of inertia of the table
(Je) = M P^2 / 4pi^2

Combining motor inertia (Jm) and table inertia (Je)

dW / dt = T / (Jm + Je)

R += (T / 2pi(Jm + Je) ) dt .. There is an 8 pi ^ 3 in there
now, I think I got something wrong...

V = PR

And loop back, calculating the new Vb, the new I, new T and so on.

I am confident in the physics here, less so in my algebraic
manipulations, specifically the 2pi which I feel should have cancelled
rather than squared somewhere. It might be better to re-work in
radians/sec throughout.
I am a little surprised to see P^2, but that has to be a factor. I had
that cancel and re-thought (2) Consider a pitch of zero.

-- 
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] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-23 Thread Mark

A G is a G is a G. As a unit of acceleration, it doesn't matter what
vector that unit of acceleration takes. I flew fighters for the USAF
for years. I've pulled G's in just about any direction possible.

On 7/23/20 12:52 AM, John Dammeyer wrote:

I've asked a retired physics professor friend for some enlightenment.

Jon Elson has stated that with T = r x Fsin(theta) and F=ma that the acceleration is Gravity because it's equivalent to dropping the X axis table and letting the earth accelerate it.

But F=mg is the force due to gravity. I might well be that since we're dealing with horizontal motion here that the acceleration value is different so we're talking about F=ma.

We know the Force because we know the torque and the effective radius and that the force is perpendicular so sin(theta) is 1 and can be ignored. We know the mass.

When we set up MAX_VELOCITY and MAX_ACCELERATION in the ini file the velocity is in in/sec. The acceleration we don't know. We can keep trying values until the servo drive reports a following error because the step pulses have exceeded the encoder pulses by the preprogramed alarm point. Then back off until we are comfortable. And if the motor isn't connected then it spins up way faster than when it has to move the table.

But does the accel value in F=ma have to be gravity? And if not, what then?

John Dammeyer

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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-23 Thread Gene Heskett

On Thursday 23 July 2020 01:57:46 John Dammeyer wrote:

> Hi Chris,
>
> > -Original Message-
> > From: Chris Albertson [mailto:albertson.ch...@gmail.com]
> >
> > Why on Earth do people still use US units?   OK if your final result
> > must be expressed that way, but do the math in metric then convert
> > at the end.
>
> 
>
> > I taught high school science for a while and never once would ever
> > talk about US units like feet or pints or pounds. The students had
> > no problems with this as their middle school teachers did the same. 
> >  No one who is educated in the last few decades would know how to
> > work with "feet per second squared"
>
> Appreciate the comments.  But even if I used the servo motor 1.6Nm the
> pitch of the lead screw is 0.2" so I could easily convert that to
> 5.08mm  or 0.00508m for that matter.  In Canada much of what we do is
> metric.   And my program has a check box that lets a user switch along
> with converting all the imperial units to metric and back.
>
> But that's beside the point I think.  None of what you said explains
> how to calculate the MAX_ACCELERATION in the INI file given parameters
> like motor/leadscrew torque, leadscrew pitch, max speed and table
> weight (mass).
>
> Any ideas?
> John
>
I think its difficult, if not impossible, to accurately predict what 
performance you get just because there are so many variables.  Take the 
x axis of my sheldon as a furinstance. With both axises running on 
honking big toroid supplies, making about 43 volts in the case of the x 
axis, it could not move at more than 30 ipm without stalling. Should be 
unrelated changing the z motor from a 1600 oz/in nema 34 that could move 
the Z at 72 ipm, on a 65 volt supply, out for a 3 phase, 3NM nema-23 
running on a now 42.5 volt switcher, but because of the length of the 
7.5 amp switcher, I had to remove both big toroids and install 2 of the 
7.5 amp supplies. So x, still running on virtually the same voltage, one 
would think it would still run the same.

Guess again. I have a new X speed limit of 120 ipm!  Actually thats 
above, but the motor doesn't stall, it trips off the driver decelerating 
from 120 ipm, but doesn't trip that 2M542 at 110 ipm.  The newer 3 phase 
z driver can now do 120 ipm w/o any problems.  The x difference is only 
the better regulation of the now switchmode supply thats within a volt 
of the supply removed.

So I'll submit that only by building it and trying it, will you find the 
limits. Accel limits were able to be raised from 3.75 to near 20 at the 
same time. Results are so good that I may swap the nema-24 in the apron 
out for a 2NM version of the 3 phase as its short enough to fit whereas 
the 3NM is about 5mm too long and its rear would hit the bed.  OTOH, a 
4x improvement in both speed AND accel, just by swapping its power 
supply was a very pleasant surprise.

But I'll put some time on it as is. The main problem with the full 120 
ipm movements is that the 2M542's don't have a fault output. So LCNC 
keeps on blindly sending movements to a faulted driver.  Thats not good 
when it happens, so I'll slow it back down a wee bit.

Anyway, have fun finding the limits, stay safe and well, all of you.

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] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-23 Thread John Dammeyer



> -Original Message-
> From: andy pugh [mailto:bodge...@gmail.com]
> Sent: July-23-20 1:03 AM
> To: Enhanced Machine Controller (EMC)
> Subject: Re: [Emc-users] Calculating table acceleration. Was: Need help with 
> Bostomatic BD18-2 to linuxcnc
> 
> On Thu, 23 Jul 2020 at 05:55, John Dammeyer  wrote:
> >
> > I've asked a retired physics professor friend for some enlightenment.
> 
> I have a PhD in Physics, but seem to be being ignored.
> 
Not ignoring you at all.  Just waiting for an idea for the math that leads to 
calculating MAX_ACCELERATION in the ini file given the parameters I've 
mentioned before.

John


> --
> 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] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

On Thu, 23 Jul 2020 at 05:55, John Dammeyer  wrote:
>
> I've asked a retired physics professor friend for some enlightenment.

I have a PhD in Physics, but seem to be being ignored.

-- 
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] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-23 Thread John Dammeyer

Hi Tomp,

I understand the process and the step response.   One thing in the mix that we 
haven't discussed, and I really was hoping Jon Elson would chime in again, is 
exactly how much impact the servo drive has on all this.  

The application of DC voltage to a motor and then measuring up to speed brings 
up the question as to how you know the motor is up to speed.  But anyway.  
Could do it with the scope monitoring step pulses and using evenly spaced 
pulses as the up to speed indication.

But that's all empirical tested until it works.  I want the starting point.

John



> -Original Message-
> From: Thomas J Powderly [mailto:tjt...@gmail.com]
> Sent: July-22-20 11:19 PM
> To: emc-users@lists.sourceforge.net
> Subject: Re: [Emc-users] Calculating table acceleration. Was: Need help with 
> Bostomatic BD18-2 to linuxcnc
> 
> John
> 
> We used to measure the acceleration rather than calculate it.
> 
> 
> We loaded the axis with whatever tooling and 'normal' work piece,
> 
> then,� in open loop,
> 
> we applied a voltage that would achieve the max velocity, very briefly.
> 
> just a bit longer than necc to get to the max velocity ( some hundred of
> millisecond, not whole seconds )
> 
> then we measured how long it took to get to the max velocity
> 
> _that_ is your practical acceleration in one direction
> 
> the test is called a ';step' response
> 
> it has nothing to do with stepper motors
> 
> it has to do with the immediate 0 to max velocity command
> 
> that's the 'step'
> 
> on a dual trace storage scope you should monitor the velocity command
> and the velocity.
> 
> hth
> 
> tomp
> 
> ( this acc will be greater than the whole machine can achieve turning
> sharp corners and reversing
> 
>  �but its a real, practical start value )
> 
> 
> On 7/23/20 12:57 PM, John Dammeyer wrote:
> > Hi Chris,
> >
> >> -Original Message-
> >> From: Chris Albertson [mailto:albertson.ch...@gmail.com]
> >>
> >> Why on Earth do people still use US units?   OK if your final result must
> >> be expressed that way, but do the math in metric then convert at the end.
> > 
> >> I taught high school science for a while and never once would ever talk
> >> about US units like feet or pints or pounds. The students had no problems
> >> with this as their middle school teachers did the same.   No one who is
> >> educated in the last few decades would know how to work with "feet per
> >> second squared"
> >>
> > Appreciate the comments.  But even if I used the servo motor 1.6Nm the 
> > pitch of the lead screw is 0.2" so I could easily convert
> that to 5.08mm  or 0.00508m for that matter.  In Canada much of what we do is 
> metric.   And my program has a check box that lets
> a user switch along with converting all the imperial units to metric and back.
> >
> > But that's beside the point I think.  None of what you said explains how to 
> > calculate the MAX_ACCELERATION in the INI file given
> parameters like motor/leadscrew torque, leadscrew pitch, max speed and table 
> weight (mass).
> >
> > Any ideas?
> > John
> >
> >
> >
> >
> >> Chris Albertson
> >> Redondo Beach, California
> >>
> >> ___
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> >
> >
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> 
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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-22 Thread Thomas J Powderly


John

We used to measure the acceleration rather than calculate it.


We loaded the axis with whatever tooling and 'normal' work piece,

then,  in open loop,

we applied a voltage that would achieve the max velocity, very briefly.

just a bit longer than necc to get to the max velocity ( some hundred of 
millisecond, not whole seconds )


then we measured how long it took to get to the max velocity

_that_ is your practical acceleration in one direction

the test is called a ';step' response

it has nothing to do with stepper motors

it has to do with the immediate 0 to max velocity command

that's the 'step'

on a dual trace storage scope you should monitor the velocity command 
and the velocity.


hth

tomp

( this acc will be greater than the whole machine can achieve turning 
sharp corners and reversing


 but its a real, practical start value )


On 7/23/20 12:57 PM, John Dammeyer wrote:

Hi Chris,


-Original Message-
From: Chris Albertson [mailto:albertson.ch...@gmail.com]

Why on Earth do people still use US units?   OK if your final result must
be expressed that way, but do the math in metric then convert at the end.



I taught high school science for a while and never once would ever talk
about US units like feet or pints or pounds. The students had no problems
with this as their middle school teachers did the same.   No one who is
educated in the last few decades would know how to work with "feet per
second squared"


Appreciate the comments.  But even if I used the servo motor 1.6Nm the pitch of the 
lead screw is 0.2" so I could easily convert that to 5.08mm  or 0.00508m for 
that matter.  In Canada much of what we do is metric.   And my program has a check 
box that lets a user switch along with converting all the imperial units to metric 
and back.

But that's beside the point I think.  None of what you said explains how to 
calculate the MAX_ACCELERATION in the INI file given parameters like 
motor/leadscrew torque, leadscrew pitch, max speed and table weight (mass).

Any ideas?
John





Chris Albertson
Redondo Beach, California

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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

Hi Chris,

> -Original Message-
> From: Chris Albertson [mailto:albertson.ch...@gmail.com]
> 
> Why on Earth do people still use US units?   OK if your final result must
> be expressed that way, but do the math in metric then convert at the end.

> 
> I taught high school science for a while and never once would ever talk
> about US units like feet or pints or pounds. The students had no problems
> with this as their middle school teachers did the same.   No one who is
> educated in the last few decades would know how to work with "feet per
> second squared"
> 
Appreciate the comments.  But even if I used the servo motor 1.6Nm the pitch of 
the lead screw is 0.2" so I could easily convert that to 5.08mm  or 0.00508m 
for that matter.  In Canada much of what we do is metric.   And my program has 
a check box that lets a user switch along with converting all the imperial 
units to metric and back.  

But that's beside the point I think.  None of what you said explains how to 
calculate the MAX_ACCELERATION in the INI file given parameters like 
motor/leadscrew torque, leadscrew pitch, max speed and table weight (mass).

Any ideas?
John




> 
> Chris Albertson
> Redondo Beach, California
> 
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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

Why on Earth do people still use US units?   OK if your final result must
be expressed that way, but do the math in metric then convert at the end.

Using US units is like doing long division in Roman numerals.  It can be
done but is way-hard so is it far easier to convert to Arabic number do the
division that converts back to Roman. In Rome a simple problem like
MCXXVI / VII requited the equivalent of graduate-level education.  But
today with our better number system, we teach 10-year-olds to do this with
paper and pencil.

The US system is like using Roman numbers.  It is so hard that most people
get wrong answers.   The proof is in this thread.   So far EVERY
calculation is wrong

One huge mistake I saw is confusing mass and force.  there is no such thing
as a 200-pound mass.  The US unit of mass is the "slug" Your calculations
are off by a factor of about 32 if you try and use pound as mass units.

Doing Physics using US customary units is so horrible that they have not
taught this in schools for the last 40 years.  No one but old folks would
even know this stuff.   I remember my Physics professor at UCLA in the late
1970s saying "just don't bother with feet, slugs and BTUs and miles"   In
high school, we did have to do a few of the problems using feet per second
and slugs of mass.

I think I was of the generation who saw the switch.  We had to use slide
rules in 10th grade but in 11th the decision was made to use calculators
and very soon after that all science education was metric only.

I taught high school science for a while and never once would ever talk
about US units like feet or pints or pounds. The students had no problems
with this as their middle school teachers did the same.   No one who is
educated in the last few decades would know how to work with "feet per
second squared"

Here is a great explanation of US units for mass and force, after reading
it you will see why no one should ever bother with this
https://en.wikipedia.org/wiki/Slug_(unit)

I think the advice I got at UCLA was the best "don't even bother learning
this"

On Wed, Jul 22, 2020 at 9:22 PM Bari  wrote:

>
> On 7/22/20 11:04 PM, Bruce Layne wrote:
> >
> > On 7/22/20 11:43 PM, Thaddeus Waldner wrote:
> >> 1g = roughly 32in/s^2
> > 1 g is 32 ft/sec^2
> >
> > Feet, not inches.
> >
>
> Comparing Standard Gravity to Other Acceleration Units
>
> Standard Gravity1 G's
> Meters per Second per Second9.81
> Feet per Second per Second32.174
> Inches per Second per Second386.09
>
>
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-- 

Chris Albertson
Redondo Beach, California

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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

I've asked a retired physics professor friend for some enlightenment. 

Jon Elson has stated that with T = r x Fsin(theta) and  F=ma that the 
acceleration is Gravity because it's equivalent to dropping the X axis table 
and letting the earth accelerate it.

But F=mg is the force due to gravity.  I might well be that since we're dealing 
with horizontal motion here that the acceleration value is different so we're 
talking about F=ma.  

We know the Force because we know the torque and the effective radius and that 
the force is perpendicular so sin(theta) is 1 and can be ignored.   We know the 
mass.

When we set up MAX_VELOCITY and MAX_ACCELERATION in the ini file the velocity 
is in in/sec.  The acceleration we don't know.  We can keep trying values until 
the servo drive reports a following error because the step pulses have exceeded 
the encoder pulses by the preprogramed alarm point.  Then back off until we are 
comfortable.  And if the motor isn't connected then it spins up way faster than 
when it has to move the table.

But does the accel value in F=ma have to be gravity?  And if not, what then?

John Dammeyer

> -Original Message-
> From: Bari [mailto:bari00...@gmail.com]
> Sent: July-22-20 9:21 PM
> To: emc-users@lists.sourceforge.net
> Subject: Re: [Emc-users] Calculating table acceleration. Was: Need help with 
> Bostomatic BD18-2 to linuxcnc
> 
> 
> On 7/22/20 11:04 PM, Bruce Layne wrote:
> >
> > On 7/22/20 11:43 PM, Thaddeus Waldner wrote:
> >> 1g = roughly 32in/s^2
> > 1 g is 32 ft/sec^2
> >
> > Feet, not inches.
> >
> 
> Comparing Standard Gravity to Other Acceleration Units
> 
> Standard Gravity��� 1 G's
> Meters per Second per Second��� 9.81
> Feet per Second per Second��� 32.174
> Inches per Second per Second��� 386.09
> 
> 
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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-22 Thread Thaddeus Waldner

Yes!  Thank you. 


> On Jul 22, 2020, at 11:07 PM, John Dammeyer  wrote:
> 
> 
>> -Original Message-
>> From: Thaddeus Waldner [mailto:thadw...@gmail.com]
>> Sent: July-22-20 8:43 PM
>> To: Enhanced Machine Controller (EMC)
>> Subject: Re: [Emc-users] Calculating table acceleration. Was: Need help with 
>> Bostomatic BD18-2 to linuxcnc
>> 
>> Start with a 226 oz in
>> 
>> / 16 = 14.125 lb in
>> 
>> 5 threads per inch is the same as a belt pulley with a circumference of 0.2
>> inches
>> 
>> since our unit is in lb in, we need to go from a pulley with diameter of
>> Pi, to diameter of .2
>> 
>> thus our final force is 14.125 * (pi/0.2) = 221.875 pounds (poundal?) force
>> 
>> divide that by your mass of 200lb and you get
>> 
>> 1.109 g
>> 
>> 1g = roughly 32in/s^2 so
>> 
>> 35.69 in/s^2
>> 
>> This is close to your ballpark guess of 40
>> 
>> Did I make a mistake anywhere?
>> 
> 
> 1 G is 32 ft/sec^2 or 384 in/sec^2 and that's where it falls apart.  Based on 
> real life the acceleration value is out by a factor of about 100.
> 
> And I don't understand why
> " since our unit is in lb in, we need to go from a pulley with diameter of  
> Pi, to diameter of .2"
> 
> It could well be that Jon Elson's explanation of linear force is incorrect.  
> 
> John
> 
> 
>> 
>> 
>>> On Wed, Jul 22, 2020 at 5:24 PM Nicklas SB Karlsson <
>>> nicklas.karlsso...@gmail.com> wrote:
>>> 
>>> On Wed, 22 Jul 2020 11:29:36 -0700
>>> Chris Albertson  wrote:
>>> 
>>>> I don't see any relation between max acceleration and max speed.
>>>> Acceleration is determined by (1) the mass of the table and (2) the
>>>> torque the motor can produce while speed is determined by the max RPM
>>>> of the motor.
>>> 
>>> Mostly agree though as torque usually depend mostly on current there will
>>> be a resistive voltage drop at higher torque which will reduce speed at
>>> higher torque, speed reduction is usually small. For example series
>>> connected DC motors and induction motors made for direct will reduce speed
>>> so there are exceptions but do not expect these are used as servo motors
>>> anyway.
>>> 
>>> Change gear ratio and use motor with same power different speed may change
>>> acceleration due to rotor inertia.
>>> 
>>>> It is very easy to buy a tiny motor with low torque that spins very
>>>> fast.  Or you can find powerful but slow motors.   Multiplying the
>>>> speed by three to find acceleration, if it works is just a
>>>> coincidence.  The factor could be 0.5 or 10.
>>> 
>>> High torque motors usually need a gear box or will become heavy. This is
>>> because flux and current is multiplied to get force while there is choice
>>> between current or flux in electric motor air gap, there is an optimal
>>> choice then either air gap area or diameter need to be increased. Magnetic
>>> materials will saturate then flux get high enough while conductor losses
>>> increase with current.
>>> 
>>>> There are two whys to go.  A mechanical engineer would start with a
>>>> requirement for a certain speed and a certain acceleration.  His boss
>>>> would give him those goals and then he would select a motor and drive.
>>>>  The other way used by most amateurs is to just buy a motor that
>>>> "seems right" and then test it to see what speed and a certain
>>>> acceleration you can get from it.
>>> 
>>> Not sure the boss will ask mechanical engineer about speed and a certain
>>> acceleration and then give these as a goal to the engineer. It is common
>>> boss read economics and contract but then it come to technical details odd
>>> things may happen.
>>> 
>>> 
>>> Nicklas SB Karlsson
>>> 
>>> 
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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

BTW, it looks like the numbers that Jon came up with match with this site.  
I've used their motors.  Nice stuff.
https://www.kollmorgen.com/en-us/developer-network/calculating-linear-force-and-torque-ballscrew/

Using the 
F2 = T x 2 x PI / L

I get the exact same value in oz-in and when converted to lbs matches my 
program.

But as yet I've not figured out how to turn that into a LinuxCNC 
MAX_ACCELERATION value that is useful.

John


> -Original Message-
> From: John Dammeyer [mailto:jo...@autoartisans.com]
> Sent: July-22-20 9:05 PM
> To: 'Enhanced Machine Controller (EMC)'
> Subject: Re: [Emc-users] Calculating table acceleration. Was: Need help with 
> Bostomatic BD18-2 to linuxcnc
> 
> 
> > -Original Message-
> > From: Thaddeus Waldner [mailto:thadw...@gmail.com]
> > Sent: July-22-20 8:43 PM
> > To: Enhanced Machine Controller (EMC)
> > Subject: Re: [Emc-users] Calculating table acceleration. Was: Need help 
> > with Bostomatic BD18-2 to linuxcnc
> >
> > Start with a 226 oz in
> >
> > / 16 = 14.125 lb in
> >
> > 5 threads per inch is the same as a belt pulley with a circumference of 0.2
> > inches
> >
> > since our unit is in lb in, we need to go from a pulley with diameter of
> > Pi, to diameter of .2
> >
> > thus our final force is 14.125 * (pi/0.2) = 221.875 pounds (poundal?) force
> >
> > divide that by your mass of 200lb and you get
> >
> > 1.109 g
> >
> > 1g = roughly 32in/s^2 so
> >
> > 35.69 in/s^2
> >
> > This is close to your ballpark guess of 40
> >
> > Did I make a mistake anywhere?
> >
> 
> 1 G is 32 ft/sec^2 or 384 in/sec^2 and that's where it falls apart.  Based on 
> real life the acceleration value is out by a factor of about
> 100.
> 
> And I don't understand why
> " since our unit is in lb in, we need to go from a pulley with diameter of  
> Pi, to diameter of .2"
> 
> It could well be that Jon Elson's explanation of linear force is incorrect.
> 
> John
> 
> 
> >
> >
> > On Wed, Jul 22, 2020 at 5:24 PM Nicklas SB Karlsson <
> > nicklas.karlsso...@gmail.com> wrote:
> >
> > > On Wed, 22 Jul 2020 11:29:36 -0700
> > > Chris Albertson  wrote:
> > >
> > > > I don't see any relation between max acceleration and max speed.
> > > > Acceleration is determined by (1) the mass of the table and (2) the
> > > > torque the motor can produce while speed is determined by the max RPM
> > > > of the motor.
> > >
> > > Mostly agree though as torque usually depend mostly on current there will
> > > be a resistive voltage drop at higher torque which will reduce speed at
> > > higher torque, speed reduction is usually small. For example series
> > > connected DC motors and induction motors made for direct will reduce speed
> > > so there are exceptions but do not expect these are used as servo motors
> > > anyway.
> > >
> > > Change gear ratio and use motor with same power different speed may change
> > > acceleration due to rotor inertia.
> > >
> > > > It is very easy to buy a tiny motor with low torque that spins very
> > > > fast.  Or you can find powerful but slow motors.   Multiplying the
> > > > speed by three to find acceleration, if it works is just a
> > > > coincidence.  The factor could be 0.5 or 10.
> > >
> > > High torque motors usually need a gear box or will become heavy. This is
> > > because flux and current is multiplied to get force while there is choice
> > > between current or flux in electric motor air gap, there is an optimal
> > > choice then either air gap area or diameter need to be increased. Magnetic
> > > materials will saturate then flux get high enough while conductor losses
> > > increase with current.
> > >
> > > > There are two whys to go.  A mechanical engineer would start with a
> > > > requirement for a certain speed and a certain acceleration.  His boss
> > > > would give him those goals and then he would select a motor and drive.
> > > >   The other way used by most amateurs is to just buy a motor that
> > > > "seems right" and then test it to see what speed and a certain
> > > > acceleration you can get from it.
> > >
> > > Not sure the boss will ask mechanical engineer about speed and a certain
> > > acceleration and then give these as a goal to the engineer. It is common
> > > boss read economics and

Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-22 Thread Bari



On 7/22/20 11:04 PM, Bruce Layne wrote:


On 7/22/20 11:43 PM, Thaddeus Waldner wrote:

1g = roughly 32in/s^2

1 g is 32 ft/sec^2

Feet, not inches.



Comparing Standard Gravity to Other Acceleration Units

Standard Gravity    1 G's
Meters per Second per Second    9.81
Feet per Second per Second    32.174
Inches per Second per Second    386.09


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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc



> -Original Message-
> From: Thaddeus Waldner [mailto:thadw...@gmail.com]
> Sent: July-22-20 8:43 PM
> To: Enhanced Machine Controller (EMC)
> Subject: Re: [Emc-users] Calculating table acceleration. Was: Need help with 
> Bostomatic BD18-2 to linuxcnc
> 
> Start with a 226 oz in
> 
> / 16 = 14.125 lb in
> 
> 5 threads per inch is the same as a belt pulley with a circumference of 0.2
> inches
> 
> since our unit is in lb in, we need to go from a pulley with diameter of
> Pi, to diameter of .2
> 
> thus our final force is 14.125 * (pi/0.2) = 221.875 pounds (poundal?) force
> 
> divide that by your mass of 200lb and you get
> 
> 1.109 g
> 
> 1g = roughly 32in/s^2 so
> 
> 35.69 in/s^2
> 
> This is close to your ballpark guess of 40
> 
> Did I make a mistake anywhere?
> 

1 G is 32 ft/sec^2 or 384 in/sec^2 and that's where it falls apart.  Based on 
real life the acceleration value is out by a factor of about 100.

And I don't understand why
" since our unit is in lb in, we need to go from a pulley with diameter of  Pi, 
to diameter of .2"

It could well be that Jon Elson's explanation of linear force is incorrect.  

John


> 
> 
> On Wed, Jul 22, 2020 at 5:24 PM Nicklas SB Karlsson <
> nicklas.karlsso...@gmail.com> wrote:
> 
> > On Wed, 22 Jul 2020 11:29:36 -0700
> > Chris Albertson  wrote:
> >
> > > I don't see any relation between max acceleration and max speed.
> > > Acceleration is determined by (1) the mass of the table and (2) the
> > > torque the motor can produce while speed is determined by the max RPM
> > > of the motor.
> >
> > Mostly agree though as torque usually depend mostly on current there will
> > be a resistive voltage drop at higher torque which will reduce speed at
> > higher torque, speed reduction is usually small. For example series
> > connected DC motors and induction motors made for direct will reduce speed
> > so there are exceptions but do not expect these are used as servo motors
> > anyway.
> >
> > Change gear ratio and use motor with same power different speed may change
> > acceleration due to rotor inertia.
> >
> > > It is very easy to buy a tiny motor with low torque that spins very
> > > fast.  Or you can find powerful but slow motors.   Multiplying the
> > > speed by three to find acceleration, if it works is just a
> > > coincidence.  The factor could be 0.5 or 10.
> >
> > High torque motors usually need a gear box or will become heavy. This is
> > because flux and current is multiplied to get force while there is choice
> > between current or flux in electric motor air gap, there is an optimal
> > choice then either air gap area or diameter need to be increased. Magnetic
> > materials will saturate then flux get high enough while conductor losses
> > increase with current.
> >
> > > There are two whys to go.  A mechanical engineer would start with a
> > > requirement for a certain speed and a certain acceleration.  His boss
> > > would give him those goals and then he would select a motor and drive.
> > >   The other way used by most amateurs is to just buy a motor that
> > > "seems right" and then test it to see what speed and a certain
> > > acceleration you can get from it.
> >
> > Not sure the boss will ask mechanical engineer about speed and a certain
> > acceleration and then give these as a goal to the engineer. It is common
> > boss read economics and contract but then it come to technical details odd
> > things may happen.
> >
> >
> > Nicklas SB Karlsson
> >
> >
> > ___
> > Emc-users mailing list
> > Emc-users@lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/emc-users
> >
> 
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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-22 Thread Bruce Layne




On 7/22/20 11:43 PM, Thaddeus Waldner wrote:
> 1g = roughly 32in/s^2

1 g is 32 ft/sec^2

Feet, not inches.



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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-22 Thread Thaddeus Waldner

Ah yes

In lb is radius, so the ballscrew factor is 2pi*threads per inch

Which would double the acceleration from my earlier numbers.


> On Jul 22, 2020, at 10:43 PM, Thaddeus Waldner  wrote:
> 
> 
> 
> 
> Start with a 226 oz in
> 
> / 16 = 14.125 lb in
> 
> 5 threads per inch is the same as a belt pulley with a circumference of 0.2 
> inches
> 
> since our unit is in lb in, we need to go from a pulley with diameter of Pi, 
> to diameter of .2
> 
> thus our final force is 14.125 * (pi/0.2) = 221.875 pounds (poundal?) force
> 
> divide that by your mass of 200lb and you get  
> 
> 1.109 g
> 
> 1g = roughly 32in/s^2 so 
> 
> 35.69 in/s^2
> 
> This is close to your ballpark guess of 40
> 
> Did I make a mistake anywhere?
> 
> 
> 
> 
>> On Wed, Jul 22, 2020 at 5:24 PM Nicklas SB Karlsson 
>>  wrote:
>> On Wed, 22 Jul 2020 11:29:36 -0700
>> Chris Albertson  wrote:
>> 
>> > I don't see any relation between max acceleration and max speed.
>> > Acceleration is determined by (1) the mass of the table and (2) the
>> > torque the motor can produce while speed is determined by the max RPM
>> > of the motor.
>> 
>> Mostly agree though as torque usually depend mostly on current there will be 
>> a resistive voltage drop at higher torque which will reduce speed at higher 
>> torque, speed reduction is usually small. For example series connected DC 
>> motors and induction motors made for direct will reduce speed so there are 
>> exceptions but do not expect these are used as servo motors anyway.
>> 
>> Change gear ratio and use motor with same power different speed may change 
>> acceleration due to rotor inertia.
>> 
>> > It is very easy to buy a tiny motor with low torque that spins very
>> > fast.  Or you can find powerful but slow motors.   Multiplying the
>> > speed by three to find acceleration, if it works is just a
>> > coincidence.  The factor could be 0.5 or 10.
>> 
>> High torque motors usually need a gear box or will become heavy. This is 
>> because flux and current is multiplied to get force while there is choice 
>> between current or flux in electric motor air gap, there is an optimal 
>> choice then either air gap area or diameter need to be increased. Magnetic 
>> materials will saturate then flux get high enough while conductor losses 
>> increase with current.
>> 
>> > There are two whys to go.  A mechanical engineer would start with a
>> > requirement for a certain speed and a certain acceleration.  His boss
>> > would give him those goals and then he would select a motor and drive.
>> >   The other way used by most amateurs is to just buy a motor that
>> > "seems right" and then test it to see what speed and a certain
>> > acceleration you can get from it.
>> 
>> Not sure the boss will ask mechanical engineer about speed and a certain 
>> acceleration and then give these as a goal to the engineer. It is common 
>> boss read economics and contract but then it come to technical details odd 
>> things may happen.
>> 
>> 
>> Nicklas SB Karlsson
>> 
>> 
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>> Emc-users@lists.sourceforge.net
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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-22 Thread Thaddeus Waldner

Start with a 226 oz in

/ 16 = 14.125 lb in

5 threads per inch is the same as a belt pulley with a circumference of 0.2
inches

since our unit is in lb in, we need to go from a pulley with diameter of
Pi, to diameter of .2

thus our final force is 14.125 * (pi/0.2) = 221.875 pounds (poundal?) force

divide that by your mass of 200lb and you get

1.109 g

1g = roughly 32in/s^2 so

35.69 in/s^2

This is close to your ballpark guess of 40

Did I make a mistake anywhere?




On Wed, Jul 22, 2020 at 5:24 PM Nicklas SB Karlsson <
nicklas.karlsso...@gmail.com> wrote:

> On Wed, 22 Jul 2020 11:29:36 -0700
> Chris Albertson  wrote:
>
> > I don't see any relation between max acceleration and max speed.
> > Acceleration is determined by (1) the mass of the table and (2) the
> > torque the motor can produce while speed is determined by the max RPM
> > of the motor.
>
> Mostly agree though as torque usually depend mostly on current there will
> be a resistive voltage drop at higher torque which will reduce speed at
> higher torque, speed reduction is usually small. For example series
> connected DC motors and induction motors made for direct will reduce speed
> so there are exceptions but do not expect these are used as servo motors
> anyway.
>
> Change gear ratio and use motor with same power different speed may change
> acceleration due to rotor inertia.
>
> > It is very easy to buy a tiny motor with low torque that spins very
> > fast.  Or you can find powerful but slow motors.   Multiplying the
> > speed by three to find acceleration, if it works is just a
> > coincidence.  The factor could be 0.5 or 10.
>
> High torque motors usually need a gear box or will become heavy. This is
> because flux and current is multiplied to get force while there is choice
> between current or flux in electric motor air gap, there is an optimal
> choice then either air gap area or diameter need to be increased. Magnetic
> materials will saturate then flux get high enough while conductor losses
> increase with current.
>
> > There are two whys to go.  A mechanical engineer would start with a
> > requirement for a certain speed and a certain acceleration.  His boss
> > would give him those goals and then he would select a motor and drive.
> >   The other way used by most amateurs is to just buy a motor that
> > "seems right" and then test it to see what speed and a certain
> > acceleration you can get from it.
>
> Not sure the boss will ask mechanical engineer about speed and a certain
> acceleration and then give these as a goal to the engineer. It is common
> boss read economics and contract but then it come to technical details odd
> things may happen.
>
>
> Nicklas SB Karlsson
>
>
> ___
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> Emc-users@lists.sourceforge.net
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>

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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-22 Thread Nicklas SB Karlsson

On Wed, 22 Jul 2020 11:29:36 -0700
Chris Albertson  wrote:

> I don't see any relation between max acceleration and max speed.
> Acceleration is determined by (1) the mass of the table and (2) the
> torque the motor can produce while speed is determined by the max RPM
> of the motor.

Mostly agree though as torque usually depend mostly on current there will be a 
resistive voltage drop at higher torque which will reduce speed at higher 
torque, speed reduction is usually small. For example series connected DC 
motors and induction motors made for direct will reduce speed so there are 
exceptions but do not expect these are used as servo motors anyway.

Change gear ratio and use motor with same power different speed may change 
acceleration due to rotor inertia.

> It is very easy to buy a tiny motor with low torque that spins very
> fast.  Or you can find powerful but slow motors.   Multiplying the
> speed by three to find acceleration, if it works is just a
> coincidence.  The factor could be 0.5 or 10.

High torque motors usually need a gear box or will become heavy. This is 
because flux and current is multiplied to get force while there is choice 
between current or flux in electric motor air gap, there is an optimal choice 
then either air gap area or diameter need to be increased. Magnetic materials 
will saturate then flux get high enough while conductor losses increase with 
current.

> There are two whys to go.  A mechanical engineer would start with a
> requirement for a certain speed and a certain acceleration.  His boss
> would give him those goals and then he would select a motor and drive.
>   The other way used by most amateurs is to just buy a motor that
> "seems right" and then test it to see what speed and a certain
> acceleration you can get from it.

Not sure the boss will ask mechanical engineer about speed and a certain 
acceleration and then give these as a goal to the engineer. It is common boss 
read economics and contract but then it come to technical details odd things 
may happen.

Nicklas SB Karlsson

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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

I have to get back to other projects for a while.  I've disabled the metric 
checkbox and made it invisible since the conversion to metric and back isn't 
complete yet.  And since the value to use for MAX_ACCELERATION in the INI file 
is suspect perhaps the whole project is a joke.

I've attached the zip with the Lazarus Source Code.  I've compiled and run this 
on a PC with Windows, BeagleBone and Raspberry Pi.  If you are running Linux 
sudo apt install lazarus 
should be enough.

My first attempt at putting something on GitHub.
https://github.com/jcdammeyer/LinuxCNC

John Dammeyer


> -Original Message-
> From: John Dammeyer [mailto:jo...@autoartisans.com]
> Sent: July-22-20 12:53 PM
> To: 'Enhanced Machine Controller (EMC)'
> Subject: Re: [Emc-users] Calculating table acceleration. Was: Need help with 
> Bostomatic BD18-2 to linuxcnc
> 
> > -Original Message-
> > From: andy pugh [mailto:bodge...@gmail.com]
> >
> > On Wed, 22 Jul 2020 at 19:33, Chris Albertson < 
> > <mailto:albertson.ch...@gmail.com> albertson.ch...@gmail.com> wrote:
> >
> > > That said acceleration is related to speed.   (acceleration) x (time) = 
> > > (speed)
> > > example:  (10 inch per second squared) x ( 0.5 seconds) = (5 inches per 
> > > second)
> >
> > Also bear in mind that speed x acceleration x mass = power
> >
> > --
> > atp
> 
> Let's take step back to the original question
> 
> One has a motor with a plate that says 3000 RPM, 226 oz-in, 7.8A continuous 
> at 90V.   The mill has a 5 TPI lead screw and a table that
> weighs 200 lbs.
> 
> So the questions that I think were asked or what the discussion was about was:
> 
> 1. Can you run this table lead screw at 3000 RPM if the Servo Drive can 
> handle 7.8A at 90V.
> 2. If not what reduction ratio is required between motor and lead screw to 
> run the motor at full speed.
> 
> Jon Elson provided the numbers for linear force created by the lead screw 
> pitch. (with some guessing at friction) and the form I
> created and attached  with 1:1 ratio shows 600 ipm and and 2.2G acceleration.
> 
> 
> 
> In real life I have the second screen shot with 3:1 belt reduction and as is 
> logical, speed drops by 1/3, Torque is multiplied by 3 so
> Acceleration also increased by 3 to 6.66G.
> 
> 
> If we divided 200 by 60 we get a speed of 3.33 in/sec which, if the 
> LinuxCNC ini file has LINEAR=inches, is used for
> MAX_VELOCITY.  From the ini file documentation  
> http://linuxcnc.org/docs/2.6/html/config/ini_config.html#sub:ini-variables
> 
> However the document also says "The maximum acceleration for any axis or 
> coordinated axis move, in machine units per second
> per second."
> 
> There is no way that my motor can do 2556 in/sec^2.  In fact 40 is a more 
> reasonable number. So we can do as Andy suggests and
> just get to it by trial and error.  But what's the point of any of this math 
> if all we do is configure by mucking around until it sort of
> works.
> 
> So either Jon Elson is horribly wrong with the constant linear force 
> calculation to determine force required to accelerate or
> something else is wrong.  I'm just trying to figure out how to calculate, 
> knowing only the above parameters, what you'd plug into
> MAX_ACCELERATION as a starting point.  I realize it needs to be tweaked since 
> ball screw verses acme screw makes a difference.
> Static verses Kinetic friction makes a difference.
> 
> So is Jon's calculation of Continuous Linear force correct?  Something's 
> missing but I can't put my finger on it.
> John Dammeyer
> 
> 
> 
> 



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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

> -Original Message-
> From: andy pugh [mailto:bodge...@gmail.com]
> 
> On Wed, 22 Jul 2020 at 19:33, Chris Albertson < 
>  albertson.ch...@gmail.com> wrote:
> 
> > That said acceleration is related to speed.   (acceleration) x (time) = 
> > (speed)
> > example:  (10 inch per second squared) x ( 0.5 seconds) = (5 inches per 
> > second)
> 
> Also bear in mind that speed x acceleration x mass = power
> 
> --
> atp

Let's take step back to the original question

One has a motor with a plate that says 3000 RPM, 226 oz-in, 7.8A continuous at 
90V.   The mill has a 5 TPI lead screw and a table that weighs 200 lbs.

So the questions that I think were asked or what the discussion was about was:

1. Can you run this table lead screw at 3000 RPM if the Servo Drive can handle 
7.8A at 90V.
2. If not what reduction ratio is required between motor and lead screw to run 
the motor at full speed.

Jon Elson provided the numbers for linear force created by the lead screw 
pitch. (with some guessing at friction) and the form I created and attached  
with 1:1 ratio shows 600 ipm and and 2.2G acceleration.

In real life I have the second screen shot with 3:1 belt reduction and as is 
logical, speed drops by 1/3, Torque is multiplied by 3 so Acceleration also 
increased by 3 to 6.66G.

If we divided 200 by 60 we get a speed of 3.33 in/sec which, if the 
LinuxCNC ini file has LINEAR=inches, is used for MAX_VELOCITY.  From the ini 
file documentation  
http://linuxcnc.org/docs/2.6/html/config/ini_config.html#sub:ini-variables

However the document also says "The maximum acceleration for any axis or 
coordinated axis move, in machine units per second per second."

There is no way that my motor can do 2556 in/sec^2.  In fact 40 is a more 
reasonable number. So we can do as Andy suggests and just get to it by trial 
and error.  But what's the point of any of this math if all we do is configure 
by mucking around until it sort of works.

So either Jon Elson is horribly wrong with the constant linear force 
calculation to determine force required to accelerate or something else is 
wrong.  I'm just trying to figure out how to calculate, knowing only the above 
parameters, what you'd plug into MAX_ACCELERATION as a starting point.  I 
realize it needs to be tweaked since ball screw verses acme screw makes a 
difference.  Static verses Kinetic friction makes a difference.

So is Jon's calculation of Continuous Linear force correct?  Something's 
missing but I can't put my finger on it.
John Dammeyer

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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

Hi Sam,
> From: Sam Sokolik [mailto:samco...@gmail.com]
> Is this stepper torque?  The peak torque is only at 0 rpm and drops off
> substantially as you increase rpm.  You  would need to look a the torque
> curve of the stepper and decide what top rpm you are looking for and
> calculate accordingly..

The discussion started with what sort of values and driver to install for a 
specific Servo.  Jon became involved because he sells servo drivers.  And then 
he made a mistake with scaling units and then I made a mistake with scaling 
units and it's really clear a tool to figure this out would be handy.  At least 
as a starting point and then tweaking the actual values still might be 
required.  

For example someone might not take apart their entire XY table assembly to 
weigh it to figure out how big a servo or stepper they need.  Mostly they will 
look at what's out there, listen to feedback and then decide.

My issue is the math still doesn't make sense.   If I try 1700in/Sec^2 the 
servo faults instantly.   MAX_ACCELERATION that works is about 40 in/sec^2 
without faults.  And Actually I run 20 for MAX_ACCELERATION and 
STEPGEN_MAXACCEL at 40 because I use backlash and it's supposed to be 100% 
larger.

So with Jon being the Servo designer I thought perhaps he could answer why 
there's such a large disparity.  Or is there still a math conversion problem 
here?

John



> 
> > Ho Jon,
> >
> > I've changed the subject line to be more relevant and corrected the
> > gravity value.
> >
> > Now we have 1703 In/Sec^2 for maximum possible acceleration given the load
> > and torque ratings.
> >
> > On my system in imperial units I have 2.5 inches/second and I randomly
> > picked the accel as 3x that.  Does that mean I could set MAX_ACCEL to say
> > 1700 and get away with that or is that number abnormally high?  I know I
> > can try it but I'd like to know if the math is accurate.
> >
> > MAX_VELOCITY = 2.5
> > MAX_ACCELERATION = 7.5
> > What I'm trying to do with this tool is to take out some of the guesswork
> > or the accidental divide instead of multiply.
> >
> > And second question. If someone is using metric units for their system
> > what units are used to describe MAX_VELOCITY and ACCEL?
> > Is it mm/minute? Or mm/second?  Or meters/second?   Is the weight
> > specified in grams or kg?
> >
> > I want to be able to make the checkbox convert the imperial < = > metric
> > correctly.
> >
> >
> >
> > Thanks
> > John Dammeyer
> >
> > ___
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> > https://lists.sourceforge.net/lists/listinfo/emc-users
> >
> 
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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-22 Thread Peter C. Wallace

On Wed, 22 Jul 2020, John Dammeyer wrote:

Date: Wed, 22 Jul 2020 09:06:38 -0700
From: John Dammeyer 
Reply-To: "Enhanced Machine Controller (EMC)"

To: "'Enhanced Machine Controller (EMC)'" 
Subject: [Emc-users] Calculating table acceleration. Was: Need help with
    Bostomatic BD18-2 to linuxcnc

Ho Jon,

I've changed the subject line to be more relevant and corrected the gravity 
value.

Now we have 1703 In/Sec^2 for maximum possible acceleration given the load and 
torque ratings.

Is this including the ballscrew+motor inertia? this may be larger than the 
linear motions reflected inertia

On my system in imperial units I have 2.5 inches/second and I randomly picked 
the accel as 3x that.  Does that mean I could set MAX_ACCEL to say 1700 and 
get away with that or is that number abnormally high?  I know I can try it but 
I'd like to know if the math is accurate.

Probably not because of the drop in motor torque with speed as Sam mentioned
plus 1700 IPS/S and 2.5 IPS means full speed in about 1.5 ms. I doubt the bare 
step motor could do that...

MAX_VELOCITY = 2.5 MAX_ACCELERATION = 7.5 What I'm trying to do with this tool 
is to take out some of the guesswork or the accidental divide instead of 
multiply.

And second question. If someone is using metric units for their system what 
units are used to describe MAX_VELOCITY and ACCEL?
Is it mm/minute? Or mm/second?  Or meters/second?   Is the weight specified in 
grams or kg?

I want to be able to make the checkbox convert the imperial < = > metric 
correctly.

Thanks
John Dammeyer

Peter Wallace
Mesa Electronics

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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-22 Thread Mark Wendt

Yup, speed is distance/time, as long as a constant velocity is held.  Speed
is constantly increasing as long as your acceleration is constant.
Changing accelerations are a bit more complicated to deal with.

Mark

On Wed, Jul 22, 2020 at 3:13 PM Chris Albertson 
wrote:

> Yes, you technically correct.   I should have written
>
> ...acceleration is related to speed.   (acceleration) x (time) =
> (change in speed)
>
>
> On Wed, Jul 22, 2020 at 12:05 PM Mark Wendt  wrote:
> >
> > On Wed, Jul 22, 2020 at 2:33 PM Chris Albertson <
> albertson.ch...@gmail.com>
> > wrote:
> >
> > >
> > > That said acceleration is related to speed.   (acceleration) x (time) =
> > > (speed)
> > > example:  (10 inch per second squared) x ( 0.5 seconds) = (5 inches per
> > > second)
> > >
> >
> > That's true only if your initial velocity is zero.
> >
> > Mark
> >
> > ___
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>
>
>
> --
>
> Chris Albertson
> Redondo Beach, California
>
>
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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

Yes, you technically correct.   I should have written

...acceleration is related to speed.   (acceleration) x (time) =
(change in speed)


On Wed, Jul 22, 2020 at 12:05 PM Mark Wendt  wrote:
>
> On Wed, Jul 22, 2020 at 2:33 PM Chris Albertson 
> wrote:
>
> >
> > That said acceleration is related to speed.   (acceleration) x (time) =
> > (speed)
> > example:  (10 inch per second squared) x ( 0.5 seconds) = (5 inches per
> > second)
> >
>
> That's true only if your initial velocity is zero.
>
> Mark
>
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Redondo Beach, California


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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

> Also bear in mind that speed x acceleration x mass = power

That is actually informative here.  It shows that after you have
guessed and bought some motor that has some given power like say 1/2
HP or 400W or whatever, the power is now fixed.   Also, the mass of
the table is fixed.

So by the above equation, you see that the product of speed and
acceleration is fixed (for you machine or motor) but you can trade
speed for acceleration by changing the gear ratio or lead screw pitch.
You can choose to go twice as fast if you accept 1/2 the acceleration.
Or vice versa.

So if you like for acceleration to be 3X speed there is some gear
ratio or screw pitch the will do just that.

But so far we are only talking about jogs and ignoring cutting force


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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-22 Thread Mark Wendt

On Wed, Jul 22, 2020 at 2:33 PM Chris Albertson 
wrote:

>
> That said acceleration is related to speed.   (acceleration) x (time) =
> (speed)
> example:  (10 inch per second squared) x ( 0.5 seconds) = (5 inches per
> second)
>

That's true only if your initial velocity is zero.

Mark

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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-22 Thread andy pugh

On Wed, 22 Jul 2020 at 19:33, Chris Albertson  wrote:

> That said acceleration is related to speed.   (acceleration) x (time) = 
> (speed)
> example:  (10 inch per second squared) x ( 0.5 seconds) = (5 inches per 
> second)

Also bear in mind that speed x acceleration x mass = power

-- 
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] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

I don't see any relation between max acceleration and max speed.
Acceleration is determined by (1) the mass of the table and (2) the
torque the motor can produce while speed is determined by the max RPM
of the motor.

It is very easy to buy a tiny motor with low torque that spins very
fast.  Or you can find powerful but slow motors.   Multiplying the
speed by three to find acceleration, if it works is just a
coincidence.  The factor could be 0.5 or 10.

There are two whys to go.  A mechanical engineer would start with a
requirement for a certain speed and a certain acceleration.  His boss
would give him those goals and then he would select a motor and drive.
  The other way used by most amateurs is to just buy a motor that
"seems right" and then test it to see what speed and a certain
acceleration you can get from it.

It both cases you end up iterating to the solution.  The engineer has
to tell his boss "Going that fast is going to make the machine very
expensive.  Are you sure you want those performance numbers?"  The
amateur looks at the results of testing and asking himself "Is it with
it to make otherguess and try another motors or do I live with this
one?"

That said acceleration is related to speed.   (acceleration) x (time) = (speed)
example:  (10 inch per second squared) x ( 0.5 seconds) = (5 inches per second)

In theory, if you had enough time the speed could be anything but
typically the motor only spins so fast and you hit some real-world
limit.

The bottom line is to test, find where it stops working reliably than
to be conservative cut those test results in half, and use that as
your limit.

On Wed, Jul 22, 2020 at 9:09 AM John Dammeyer  wrote:
>
> Ho Jon,
>
> I've changed the subject line to be more relevant and corrected the gravity 
> value.
>
> Now we have 1703 In/Sec^2 for maximum possible acceleration given the load 
> and torque ratings.
>
> On my system in imperial units I have 2.5 inches/second and I randomly picked 
> the accel as 3x that.  Does that mean I could set MAX_ACCEL to say 1700 and 
> get away with that or is that number abnormally high?  I know I can try it 
> but I'd like to know if the math is accurate.
>
> MAX_VELOCITY = 2.5
> MAX_ACCELERATION = 7.5
> What I'm trying to do with this tool is to take out some of the guesswork or 
> the accidental divide instead of multiply.
>
> And second question. If someone is using metric units for their system what 
> units are used to describe MAX_VELOCITY and ACCEL?
> Is it mm/minute? Or mm/second?  Or meters/second?   Is the weight specified 
> in grams or kg?
>
> I want to be able to make the checkbox convert the imperial < = > metric 
> correctly.
>
>
>
> Thanks
> John Dammeyer
>
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Re: [Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc

2020-07-22 Thread Sam Sokolik

Is this stepper torque?  The peak torque is only at 0 rpm and drops off
substantially as you increase rpm.  You  would need to look a the torque
curve of the stepper and decide what top rpm you are looking for and
calculate accordingly..

On Wed, Jul 22, 2020, 11:09 AM John Dammeyer  wrote:

> Ho Jon,
>
> I've changed the subject line to be more relevant and corrected the
> gravity value.
>
> Now we have 1703 In/Sec^2 for maximum possible acceleration given the load
> and torque ratings.
>
> On my system in imperial units I have 2.5 inches/second and I randomly
> picked the accel as 3x that.  Does that mean I could set MAX_ACCEL to say
> 1700 and get away with that or is that number abnormally high?  I know I
> can try it but I'd like to know if the math is accurate.
>
> MAX_VELOCITY = 2.5
> MAX_ACCELERATION = 7.5
> What I'm trying to do with this tool is to take out some of the guesswork
> or the accidental divide instead of multiply.
>
> And second question. If someone is using metric units for their system
> what units are used to describe MAX_VELOCITY and ACCEL?
> Is it mm/minute? Or mm/second?  Or meters/second?   Is the weight
> specified in grams or kg?
>
> I want to be able to make the checkbox convert the imperial < = > metric
> correctly.
>
>
>
> Thanks
> John Dammeyer
>
> ___
> Emc-users mailing list
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>

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[Emc-users] Calculating table acceleration. Was: Need help with Bostomatic BD18-2 to linuxcnc