Re: [Emc-users] Following Error Joint 2

[Peter C. Wallace]

On Wed, 3 Mar 2021, John Dammeyer wrote:


Date: Wed, 3 Mar 2021 16:42:25 -0800
From: John Dammeyer 
Reply-To: "Enhanced Machine Controller (EMC)"

To: "Enhanced Machine Controller (EMC)" 
Subject: [Emc-users] Following Error Joint 2


I made another video with the new 3D printed pulley.  Much better balanced as 
I made the inner hole and outside hub thicker and then bored and turned it to 
the correct diameter and concentric with each other. Now just shows the Z axis 
jogging up and down after homing.  I still get the occasional following error 
but it seems that's a LinuxCNC issue and not the motor.  Or it's electrical 
noise because the table is loaded down with two vices and a rotary table.  I 
think close to 200 lbs extra.  I'll have to weigh it. 
https://youtu.be/AJWI09C6h7U


I've read through this thread.  I'm using the MESA 7i92H which is Ethernet 
based and it's only the PC and the MESA on the network. 
https://forum.linuxcnc.org/10-advanced-configuration/27171-joint-2-following-error?start=10


Without all the extra weight on the table there is no following error.  If I 
remove BACKLASH compensation there is no following error.  It appears to go 
away if I make sure that the STEPGEN_MAXACCEL is set to double the 
MAX_ACCELERATION.


My parameters are
P = 1000.0
I = 0.0
D = 0.0
FF0 = 0.0
FF1 = 1.0
FF2 = 0.0
BIAS = 0.0
DEADBAND = 0.0

PCW on that forum stated that "For PID control of the stepgen, the stepgen is 
put into velocity mode and a basic velocity mode PID setting is used (FF1 = 
1.000, FF2 = .001 (servo period) P= ~150)"


My SERVO_PERIOD = 100 So should FF2 be set to that?  Or is the stepgen 
even in velocity mode and does it matter?


You need to double the stepgen acceleration settings if backlash
is enabled. That alone may be the reason for your following errors.


Normally FF2=0 is ok unless you are worried about following errors in the u 
region (FF2 should be set for the number of seconds between reading the stepgen 
position and writing the new velocity so normally a very small number)






What I don't understand is why extra weight made it show up. The AC Servo 
Drive is not showing an error and motor current rarely goes above 3.5A at 
220VAC or about 770W.


John


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Mesa Electronics

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Re: [Emc-users] Following Error Joint 2

[Gene Heskett]

On Wednesday 03 March 2021 19:42:25 John Dammeyer wrote:

> I made another video with the new 3D printed pulley.  Much better
> balanced as I made the inner hole and outside hub thicker and then
> bored and turned it to the correct diameter and concentric with each
> other. Now just shows the Z axis jogging up and down after homing.  I
> still get the occasional following error but it seems that's a
> LinuxCNC issue and not the motor.  Or it's electrical noise because
> the table is loaded down with two vices and a rotary table.  I think
> close to 200 lbs extra.  I'll have to weigh it.
> https://youtu.be/AJWI09C6h7U
>
> I've read through this thread.  I'm using the MESA 7i92H which is
> Ethernet based and it's only the PC and the MESA on the network.
> https://forum.linuxcnc.org/10-advanced-configuration/27171-joint-2-fol
>lowing-error?start=10
>
> Without all the extra weight on the table there is no following error.
>  If I remove BACKLASH compensation there is no following error.  It
> appears to go away if I make sure that the STEPGEN_MAXACCEL is set to
> double the MAX_ACCELERATION.
>
> My parameters are
> P = 1000.0
> I = 0.0
> D = 0.0
> FF0 = 0.0
> FF1 = 1.0
> FF2 = 0.0
> BIAS = 0.0
> DEADBAND = 0.0
>
> PCW on that forum stated that "For PID control of the stepgen, the
> stepgen is put into velocity mode and a basic velocity mode PID
> setting is used (FF1 = 1.000, FF2 = .001 (servo period) P= ~150)"
>
> My SERVO_PERIOD = 100
> So should FF2 be set to that?  Or is the stepgen even in velocity mode
> and does it matter?
>
> What I don't understand is why extra weight made it show up. The AC
> Servo Drive is not showing an error and motor current rarely goes
> above 3.5A at 220VAC or about 770W.
>
Put the halscope on it, trigger on the home switch, and watch the 
control, fb, and error sigs.

Adjust FF1 for zero error while its cruising, I think it will be higher 
than 1.0 Small amounts of FF2 and gain should be investigated.

> John
>
>
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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] Following Error Joint 2

[Gene Heskett]

On Wednesday 03 March 2021 20:18:44 Gene Heskett wrote:

> On Wednesday 03 March 2021 19:42:25 John Dammeyer wrote:
> > I made another video with the new 3D printed pulley.  Much better
> > balanced as I made the inner hole and outside hub thicker and then
> > bored and turned it to the correct diameter and concentric with each
> > other. Now just shows the Z axis jogging up and down after homing. 
> > I still get the occasional following error but it seems that's a
> > LinuxCNC issue and not the motor.  Or it's electrical noise because
> > the table is loaded down with two vices and a rotary table.  I think
> > close to 200 lbs extra.  I'll have to weigh it.
> > https://youtu.be/AJWI09C6h7U
> >
> > I've read through this thread.  I'm using the MESA 7i92H which is
> > Ethernet based and it's only the PC and the MESA on the network.
> > https://forum.linuxcnc.org/10-advanced-configuration/27171-joint-2-f
> >ol lowing-error?start=10
> >
> > Without all the extra weight on the table there is no following
> > error. If I remove BACKLASH compensation there is no following
> > error.  It appears to go away if I make sure that the
> > STEPGEN_MAXACCEL is set to double the MAX_ACCELERATION.
> >
> > My parameters are
> > P = 1000.0
> > I = 0.0
> > D = 0.0
> > FF0 = 0.0
> > FF1 = 1.0
> > FF2 = 0.0
> > BIAS = 0.0
> > DEADBAND = 0.0
> >
> > PCW on that forum stated that "For PID control of the stepgen, the
> > stepgen is put into velocity mode and a basic velocity mode PID
> > setting is used (FF1 = 1.000, FF2 = .001 (servo period) P= ~150)"
> >
> > My SERVO_PERIOD = 100
> > So should FF2 be set to that?  Or is the stepgen even in velocity
> > mode and does it matter?
> >
> > What I don't understand is why extra weight made it show up. The AC
> > Servo Drive is not showing an error and motor current rarely goes
> > above 3.5A at 220VAC or about 770W.
>
> Put the halscope on it, trigger on the home switch, and watch the
> control, fb, and error sigs.
>
> Adjust FF1 for zero error while its cruising, I think it will be
> higher than 1.0 Small amounts of FF2 and gain should be investigated.
>
That should have said "Dgain".
> > John
> >
> >
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>
> 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] Following Error Joint 2

[John Dammeyer]

> -Original Message-
> From: Gene Heskett [mailto:ghesk...@shentel.net]
> Sent: March-03-21 6:40 PM
> To: emc-users@lists.sourceforge.net
> Subject: Re: [Emc-users] Following Error Joint 2
> 
> On Wednesday 03 March 2021 20:18:44 Gene Heskett wrote:
> 
> > On Wednesday 03 March 2021 19:42:25 John Dammeyer wrote:
> > > I made another video with the new 3D printed pulley.  Much better
> > > balanced as I made the inner hole and outside hub thicker and then
> > > bored and turned it to the correct diameter and concentric with each
> > > What I don't understand is why extra weight made it show up. The AC
> > > Servo Drive is not showing an error and motor current rarely goes
> > > above 3.5A at 220VAC or about 770W.
> >
> > Put the halscope on it, trigger on the home switch, and watch the
> > control, fb, and error sigs.
> >
> > Adjust FF1 for zero error while its cruising, I think it will be
> > higher than 1.0 Small amounts of FF2 and gain should be investigated.
> >
> That should have said "Dgain".

The Following Error shows up a long way from the home switch.  It's the 
PageDown key for moving the Knee closer to the spindle that does it.  And 
flipping between the up/down keys with short knee movements with the 120 lbs on 
the table caused the issues.  

Recall this is open loop motion with no feedback from the servo other than if 
the servo faults which it doesn't.  So weight shouldn't matter.  Should it?  I 
removed the fault output from the servo drive so it can't fault the system.

The comment on the link about Ethernet latency is what interested me.  Again if 
electrical noise causes retries or delays in the Ethernet signalling then that 
could cause this sort of error under heavy load.

John




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Re: [Emc-users] Following Error Joint 2

[Jon Elson]

On 03/03/2021 09:17 PM, John Dammeyer wrote:


Recall this is open loop motion with no feedback from the 
servo other than if the servo faults which it doesn't. So 
weight shouldn't matter. Should it?
OK,this is EXTREMELY bizarre!  In open loop, how could 
LinuxCNC know anything about the load on the motor?  I think 
maybe it is some kind of electrical noise issue, the 
switching noise from the drive could well increase as motor 
current increases.  Possibly you could put some ferrite 
cores over the motor leads.


Jon


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Re: [Emc-users] Following Error Joint 2

[John Dammeyer]

> -Original Message-
> From: Jon Elson [mailto:el...@pico-systems.com]
> On 03/03/2021 09:17 PM, John Dammeyer wrote:
> > Recall this is open loop motion with no feedback from the
> > servo other than if the servo faults which it doesn't. So
> > weight shouldn't matter. Should it?

> OK,this is EXTREMELY bizarre!  In open loop, how could
> LinuxCNC know anything about the load on the motor?  I think
> maybe it is some kind of electrical noise issue, the
> switching noise from the drive could well increase as motor
> current increases.  Possibly you could put some ferrite
> cores over the motor leads.
> 
> Jon
Yes again my apologies for not being clear about that.   Step/dir from MESA 
7i92H 

I weighed the mass and it's 118 lbs or so.  I see the motor current climb to 
about 3.5A.  

I agree that I need to add some ferrites on the motor wires.  I've been playing 
with the new motor and a 26 pound vise on the table with no issues for the last 
few weeks.  And then add weight and now errors.   Might just add some ferrites 
to the network cable too.   The AC Servo drive is still sitting out away from 
everything else.  So if the motor itself is radiating it might be picked up by 
one of the other cables.

Baby steps...
John






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Re: [Emc-users] Following Error Joint 2

[Thaddeus Waldner]

That was my thinking. It would also need to be a smart motor driver that senses 
motor rotor position either via encoder or back emf and adjusts motor current 
based on load.

Thaddeus Waldner

From: Jon Elson 
Sent: Wednesday, March 3, 2021 9:57:00 PM
To: Enhanced Machine Controller (EMC) 
Subject: Re: [Emc-users] Following Error Joint 2

On 03/03/2021 09:17 PM, John Dammeyer wrote:
>
> Recall this is open loop motion with no feedback from the
> servo other than if the servo faults which it doesn't. So
> weight shouldn't matter. Should it?
OK,this is EXTREMELY bizarre!  In open loop, how could
LinuxCNC know anything about the load on the motor?  I think
maybe it is some kind of electrical noise issue, the
switching noise from the drive could well increase as motor
current increases.  Possibly you could put some ferrite
cores over the motor leads.

Jon


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Re: [Emc-users] Following Error Joint 2

[Gene Heskett]

On Wednesday 03 March 2021 22:17:35 John Dammeyer wrote:

> > -Original Message-
> > From: Gene Heskett [mailto:ghesk...@shentel.net]
> > Sent: March-03-21 6:40 PM
> > To: emc-users@lists.sourceforge.net
> > Subject: Re: [Emc-users] Following Error Joint 2
> >
> > On Wednesday 03 March 2021 20:18:44 Gene Heskett wrote:
> > > On Wednesday 03 March 2021 19:42:25 John Dammeyer wrote:
> > > > I made another video with the new 3D printed pulley.  Much
> > > > better balanced as I made the inner hole and outside hub thicker
> > > > and then bored and turned it to the correct diameter and
> > > > concentric with each What I don't understand is why extra weight
> > > > made it show up. The AC Servo Drive is not showing an error and
> > > > motor current rarely goes above 3.5A at 220VAC or about 770W.
> > >
> > > Put the halscope on it, trigger on the home switch, and watch the
> > > control, fb, and error sigs.
> > >
> > > Adjust FF1 for zero error while its cruising, I think it will be
> > > higher than 1.0 Small amounts of FF2 and gain should be
> > > investigated.
> >
> > That should have said "Dgain".
>
> The Following Error shows up a long way from the home switch.  It's
> the PageDown key for moving the Knee closer to the spindle that does
> it.  And flipping between the up/down keys with short knee movements
> with the 120 lbs on the table caused the issues.
>
> Recall this is open loop motion with no feedback from the servo other
> than if the servo faults which it doesn't.  So weight shouldn't
> matter.  Should it?  I removed the fault output from the servo drive
> so it can't fault the system.
>
> The comment on the link about Ethernet latency is what interested me. 
> Again if electrical noise causes retries or delays in the Ethernet
> signalling then that could cause this sort of error under heavy load.
>
> John

And this is what the high frequency gains do, FF2 and Dgain, giving a 
boost when the velocity changes. All this assumes that the actual power 
available is sufficient to achieve what the controller is asked to make 
it do. If the available power sags with the initial accell but the speed 
being asked is so high the power available cannot catch it up and is 
limiting you then following errors creep into long distance moves.

Currently, my plaything is down for mods, like a new cam to switch the 
home switch. I made a ring out of PETG that is about .4mm smaller than 
the flange diameter of this BS-1, to replace the narrow notch I cut in 
the flange for a home switch, and which it will sail right on by at 
search vels above 4 degrees a second. So now, when I get this mod 
finished, waiting the rest of the night for goop to set, but I may 
remake the cam thinner because a trial switch position shows its too 
thick, it 5mm thick and 2 will work the switch, leaving much more real 
estate to glue the switch to.

Take care John.

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 <http://geneslinuxbox.net:6309/gene>


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Re: [Emc-users] Following Error Joint 2

[John Dammeyer]

> >
> > The comment on the link about Ethernet latency is what interested me.
> > Again if electrical noise causes retries or delays in the Ethernet
> > signalling then that could cause this sort of error under heavy load.
> >
> > John
> 
> And this is what the high frequency gains do, FF2 and Dgain, giving a
> boost when the velocity changes. All this assumes that the actual power
> available is sufficient to achieve what the controller is asked to make
> it do. If the available power sags with the initial accell but the speed
> being asked is so high the power available cannot catch it up and is
> limiting you then following errors creep into long distance moves.
> 
Hi Gene,
My AC Servo is run open loop with step/dir.  It's not the Servo Driver that is 
calling out a following error.  It's LinuxCNC that also has no clue where the 
motor actually is unless the AC servo asserts a fault output.  And it can't do 
that because I disconnected it for this test.

I don't know how the Ethernet Communications with the MESA 7i92H works.  Page 8 
of the user manual says it's UDP which means launch and forget.  The sender has 
no way of knowing if the message was received although with only two devices 
perhaps there's a lower level that does verify that.

In either case Page 31 states there are error counters so if there is a packet 
error that is detected after a new motion command is issued; like change 
direction for example.  Then LinuxCNC might well decide to throw up a following 
error.

I will admit that I misread the HAL instructions and had the MAX_ACCELERATION 
parameter set to 125% higher.  But with Backlash it was supposed to be 200%.  
Once I changed that the problem went away.  So bad HAL info generates a 
following error?  Except that never happened without the extra 92 lbs on the 
table.

But if electrical noise from the higher load did cause a damaged UDP packet 
then there's the answer.  A quick change in direction to handle backlash and a 
missing message throws out the timing and results in a following error.
John




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Re: [Emc-users] Following Error Joint 2

[John Dammeyer]

The load part is interesting.  I wrote this Lazarus program to calculate force 
required based on what was going to be moved and leadscrew pitch etc.  It was 
never finished.  Don't know how accurate it is.
 
Might be worthwhile to add Step Rate and Max Acceleration conversions so the 
numbers could be compared with the INI file parameters in LinuxCNC.
 
I wrote this a while ago and I've forgotten what I was trying to achieve.
John
 
 

 
 
 
> -Original Message-
> From: Thaddeus Waldner [mailto:thadw...@gmail.com]
> Sent: March-03-21 8:19 PM
> To: Enhanced Machine Controller (EMC)
> Subject: Re: [Emc-users] Following Error Joint 2
> 
> That was my thinking. It would also need to be a smart motor driver that 
> senses motor rotor position either via encoder or back emf
> and adjusts motor current based on load.
> 
> Thaddeus Waldner
> 
> From: Jon Elson < <mailto:el...@pico-systems.com> el...@pico-systems.com>
> Sent: Wednesday, March 3, 2021 9:57:00 PM
> To: Enhanced Machine Controller (EMC) < 
> <mailto:emc-users@lists.sourceforge.net> emc-users@lists.sourceforge.net>
> Subject: Re: [Emc-users] Following Error Joint 2
> 
> On 03/03/2021 09:17 PM, John Dammeyer wrote:
> >
> > Recall this is open loop motion with no feedback from the
> > servo other than if the servo faults which it doesn't. So
> > weight shouldn't matter. Should it?
> OK,this is EXTREMELY bizarre!  In open loop, how could
> LinuxCNC know anything about the load on the motor?  I think
> maybe it is some kind of electrical noise issue, the
> switching noise from the drive could well increase as motor
> current increases.  Possibly you could put some ferrite
> cores over the motor leads.
> 
> Jon
> 
> 
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Re: [Emc-users] Following Error Joint 2

[Les Newell]

LinuxCNC is designed to run servos. The stepgens simulate servos and 
will throw a following error if they are unable to generate steps at the 
commanded rate or acceleration. As Peter says, you probably increase 
your stepgen acceleration.


Les

On 04/03/2021 03:17, John Dammeyer wrote:
The Following Error shows up a long way from the home switch. It's the 
PageDown key for moving the Knee closer to the spindle that does it. 
And flipping between the up/down keys with short knee movements with 
the 120 lbs on the table caused the issues.


Recall this is open loop motion with no feedback from the servo other 
than if the servo faults which it doesn't. So weight shouldn't matter. 
Should it? I removed the fault output from the servo drive so it can't 
fault the system.


The comment on the link about Ethernet latency is what interested me. 
Again if electrical noise causes retries or delays in the Ethernet 
signalling then that could cause this sort of error under heavy load.


John




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Re: [Emc-users] Following Error Joint 2

[Peter C. Wallace]

On Wed, 3 Mar 2021, John Dammeyer wrote:


Date: Wed, 3 Mar 2021 23:11:23 -0800
From: John Dammeyer 
Reply-To: "Enhanced Machine Controller (EMC)"

To: "'Enhanced Machine Controller (EMC)'" 
Subject: Re: [Emc-users] Following Error Joint 2



The comment on the link about Ethernet latency is what interested me.
Again if electrical noise causes retries or delays in the Ethernet
signalling then that could cause this sort of error under heavy load.

John


And this is what the high frequency gains do, FF2 and Dgain, giving a
boost when the velocity changes. All this assumes that the actual power
available is sufficient to achieve what the controller is asked to make
it do. If the available power sags with the initial accell but the speed
being asked is so high the power available cannot catch it up and is
limiting you then following errors creep into long distance moves.

Hi Gene, My AC Servo is run open loop with step/dir.  It's not the Servo 
Driver that is calling out a following error.  It's LinuxCNC that also has no 
clue where the motor actually is unless the AC servo asserts a fault output. 
And it can't do that because I disconnected it for this test.


I don't know how the Ethernet Communications with the MESA 7i92H works.  Page 
8 of the user manual says it's UDP which means launch and forget.  The sender 
has no way of knowing if the message was received although with only two 
devices perhaps there's a lower level that does verify that.


In either case Page 31 states there are error counters so if there is a packet 
error that is detected after a new motion command is issued; like change 
direction for example.  Then LinuxCNC might well decide to throw up a 
following error.


I will admit that I misread the HAL instructions and had the MAX_ACCELERATION 
parameter set to 125% higher.  But with Backlash it was supposed to be 200%. 
Once I changed that the problem went away.  So bad HAL info generates a 
following error?  Except that never happened without the extra 92 lbs on the 
table.


A following error is _expected_ if the stepgen maxaccel parameter is not at 
least 2x the joints maxaccel value (or if any stepgen constraint is lower

than what linuxCNC may command it to do) So HAL setup can absolutely cause
following errors.


But if electrical noise from the higher load did cause a damaged UDP packet 
then there's the answer.  A quick change in direction to handle backlash and a 
missing message throws out the timing and results in a following error. John


You can check this by plotting hm2_7i92.packet-error , but if setting the 
stepgen maxaccel value stops the following errors it does not seem likely they 
are caused by lost packets. Plotting the following error will also give you some 
insight into whats going on.










Peter Wallace
Mesa Electronics


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Re: [Emc-users] Following Error Joint 2

[John Dammeyer]

> From: Peter C. Wallace [mailto:p...@mesanet.com]
> On Wed, 3 Mar 2021, John Dammeyer wrote:
> 
> > Date: Wed, 3 Mar 2021 23:11:23 -0800
> > From: John Dammeyer 
> >>> The comment on the link about Ethernet latency is what interested me.
> >>> Again if electrical noise causes retries or delays in the Ethernet
> >>> signalling then that could cause this sort of error under heavy load.
> >>>
> >>> John
> > Hi Gene, My AC Servo is run open loop with step/dir.  It's not the Servo
> > Driver that is calling out a following error.  It's LinuxCNC that also has 
> > no
> > clue where the motor actually is unless the AC servo asserts a fault output.
> > And it can't do that because I disconnected it for this test.
> >
> > I don't know how the Ethernet Communications with the MESA 7i92H works.  
> > Page
> > 8 of the user manual says it's UDP which means launch and forget.  The 
> > sender
> > has no way of knowing if the message was received although with only two
> > devices perhaps there's a lower level that does verify that.
> >
> > In either case Page 31 states there are error counters so if there is a 
> > packet
> > error that is detected after a new motion command is issued; like change
> > direction for example.  Then LinuxCNC might well decide to throw up a
> > following error.
> >
> > I will admit that I misread the HAL instructions and had the 
> > MAX_ACCELERATION
> > parameter set to 125% higher.  But with Backlash it was supposed to be 200%.
> > Once I changed that the problem went away.  So bad HAL info generates a
> > following error?  Except that never happened without the extra 92 lbs on the
> > table.
> 
> A following error is _expected_ if the stepgen maxaccel parameter is not at
> least 2x the joints maxaccel value (or if any stepgen constraint is lower
> than what linuxCNC may command it to do) So HAL setup can absolutely cause
> following errors.
Should not the HAL driver code flag that error on start up?  Ie. Pseudo code
IF (BACKLASH <> 0.0) AND (STEPGEN_MAXACCEL < (MAX_ACCLERATION *2) THEN 
  ERROR in Parameter STEPGEN_MAXACCEL.

> >
> > But if electrical noise from the higher load did cause a damaged UDP packet
> > then there's the answer.  A quick change in direction to handle backlash 
> > and a
> > missing message throws out the timing and results in a following error. John
> 
> You can check this by plotting hm2_7i92.packet-error , but if setting the
> stepgen maxaccel value stops the following errors it does not seem likely they
> are caused by lost packets. Plotting the following error will also give you 
> some
> insight into whats going on.
> Peter Wallace
> Mesa Electronics

I'll try that but it doesn't explain why there were no following errors without 
the extra 92 lbs on the table and the incorrect STEPGEN_MAXACCEL.  I believe 
the Following Error Joint 2 message is incorrect.

Perhaps you can explain why that message shows up at all in an open loop 
situation?  What does the FPGA do that would cause that?  Is there a separate 
message for missing Ethernet or out of sequence Ethernet packets or is it 
lumped into Following Error on Joint?

Thanks
John




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Re: [Emc-users] Following Error Joint 2

[Thaddeus Waldner]

> 
> Perhaps you can explain why that message shows up at all in an open loop 
> situation?  What does the FPGA do that would cause that?  Is there a separate 
> message for missing Ethernet or out of sequence Ethernet packets or is it 
> lumped into Following Error on Joint?

A further question that I have; if lost ethernet packets raise a Following 
Error alarm and does NOT raise a Communication Error alarm, does that always 
mean Packet loss threshold is too lenient and/or FERROR, MIN_FERROR is too 
strict?

I actually had the same issue but more sporadically.. happened about once per 
month. I “fixed" it by commenting out the MIN_FERROR and FERROR . 
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Re: [Emc-users] Following Error Joint 2

[John Dammeyer]

> A following error is _expected_ if the stepgen maxaccel parameter is not at
> least 2x the joints maxaccel value (or if any stepgen constraint is lower
> than what linuxCNC may command it to do) So HAL setup can absolutely cause
> following errors.
> >
> > But if electrical noise from the higher load did cause a damaged UDP packet
> > then there's the answer.  A quick change in direction to handle backlash 
> > and a
> > missing message throws out the timing and results in a following error. John
> 
> You can check this by plotting hm2_7i92.packet-error , but if setting the
> stepgen maxaccel value stops the following errors it does not seem likely they
> are caused by lost packets. Plotting the following error will also give you 
> some
> insight into whats going on.
> 
Hi Peter,

One other thing about this.  From 
http://linuxcnc.org/docs/2.7/html/man/man9/hm2_eth.9.html#PACKET%20LOSS

"On the other hand, pid-stepper systems will run properly for extended periods 
of time with packet loss on the order of .01%, as long as following error is 
increased enough that having stale position feedback does not trigger a 
following error. Altering the HAL configuration so that during transient packet 
loss the pid and motion feedback value is equal to the command value, instead 
of the stale feedback value, appears to improve tuning. This can be 
accomplished with a mux2(9) component for each feedback signal, using 
packet−error as the mux2 sel input."

I have no idea from that paragraph how to program that into the HAL file.  An 
example would be handy.  Which feedback signal?  What does the mux output do?

From the same section:
"When a lost packet is detected, the packet−error pin is asserted in that 
cycle, the packet−error−level pin is increased, and if it reaches a threshold 
then a permanent low-level I/O error is signaled." 

I'm going to guess that low-level I/O error is a general 
_Following_Error_Joint_2_?

Going through the files at 
https://github.com/LinuxCNC/linuxcnc/tree/master/src/hal/drivers/mesa-hostmot2
I can find "packet_error_limit" but nothing that reports the following error.  
Still missing something.

John



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Re: [Emc-users] Following Error Joint 2

[Sam Sokolik]

sorry to throw something else into the mix... I was getting following
errors without realtime errors on the pie because the default internet time
sync (timesyncd) sucked..

timesyncd vs ntp

https://www.youtube.com/watch?v=RDKaFJmB254



On Thu, Mar 4, 2021 at 11:37 AM John Dammeyer 
wrote:

> > A following error is _expected_ if the stepgen maxaccel parameter is not
> at
> > least 2x the joints maxaccel value (or if any stepgen constraint is lower
> > than what linuxCNC may command it to do) So HAL setup can absolutely
> cause
> > following errors.
> > >
> > > But if electrical noise from the higher load did cause a damaged UDP
> packet
> > > then there's the answer.  A quick change in direction to handle
> backlash and a
> > > missing message throws out the timing and results in a following
> error. John
> >
> > You can check this by plotting hm2_7i92.packet-error , but if setting the
> > stepgen maxaccel value stops the following errors it does not seem
> likely they
> > are caused by lost packets. Plotting the following error will also give
> you some
> > insight into whats going on.
> >
> Hi Peter,
>
> One other thing about this.  From
> http://linuxcnc.org/docs/2.7/html/man/man9/hm2_eth.9.html#PACKET%20LOSS
>
> "On the other hand, pid-stepper systems will run properly for extended
> periods of time with packet loss on the order of .01%, as long as following
> error is increased enough that having stale position feedback does not
> trigger a following error. Altering the HAL configuration so that during
> transient packet loss the pid and motion feedback value is equal to the
> command value, instead of the stale feedback value, appears to improve
> tuning. This can be accomplished with a mux2(9) component for each feedback
> signal, using packet−error as the mux2 sel input."
>
> I have no idea from that paragraph how to program that into the HAL file.
> An example would be handy.  Which feedback signal?  What does the mux
> output do?
>
> From the same section:
> "When a lost packet is detected, the packet−error pin is asserted in that
> cycle, the packet−error−level pin is increased, and if it reaches a
> threshold then a permanent low-level I/O error is signaled."
>
> I'm going to guess that low-level I/O error is a general
> _Following_Error_Joint_2_?
>
> Going through the files at
>
> https://github.com/LinuxCNC/linuxcnc/tree/master/src/hal/drivers/mesa-hostmot2
> I can find "packet_error_limit" but nothing that reports the following
> error.  Still missing something.
>
> John
>
>
>
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Re: [Emc-users] Following Error Joint 2

[Les Newell]

I'm going to guess that low-level I/O error is a general 
_Following_Error_Joint_2_?


No. It is a different error. I can't remember the exact wording but I 
have seen it before.


The following error message is correct. With steppers you have two 
acceleration settings. There is the joint acceleration which is used by 
the trajectory planner and the stepgen acceleration. STEPGEN_MAXACCEL is 
used to simulate the physical limits of the stepper and it's load. It's 
a simulated equivalent to to a servo motor running out of torque. If the 
trajectory planner commands a higher acceleration than STEPGEN_MAXACCEL 
the stepgen will not be able to keep up and you get a following error in 
exactly the same way you would on a servo system that ran out of torque.


Les



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Re: [Emc-users] Following Error Joint 2

[Gene Heskett]

On Thursday 04 March 2021 12:59:28 Sam Sokolik wrote:

> sorry to throw something else into the mix... I was getting following
> errors without realtime errors on the pie because the default internet
> time sync (timesyncd) sucked..
>
> timesyncd vs ntp
>
> https://www.youtube.com/watch?v=RDKaFJmB254

This is moderately well known to pi users, Sam. ;-)

Why raspbian tolerates that is a puzzle.

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] Following Error Joint 2

[John Dammeyer]

Sam,
That little green machine of yours really hauls.   What pitch screws and motors 
(belts/pulley ratio) are you using on the XYZ axis?
John


> -Original Message-
> From: Sam Sokolik [mailto:samco...@gmail.com]
> Sent: March-04-21 9:59 AM
> To: Enhanced Machine Controller (EMC)
> Subject: Re: [Emc-users] Following Error Joint 2
> 
> sorry to throw something else into the mix... I was getting following
> errors without realtime errors on the pie because the default internet time
> sync (timesyncd) sucked..
> 
> timesyncd vs ntp
> 
> https://www.youtube.com/watch?v=RDKaFJmB254
> 
> 
> 
> On Thu, Mar 4, 2021 at 11:37 AM John Dammeyer 
> wrote:
> 
> > > A following error is _expected_ if the stepgen maxaccel parameter is not
> > at
> > > least 2x the joints maxaccel value (or if any stepgen constraint is lower
> > > than what linuxCNC may command it to do) So HAL setup can absolutely
> > cause
> > > following errors.
> > > >
> > > > But if electrical noise from the higher load did cause a damaged UDP
> > packet
> > > > then there's the answer.  A quick change in direction to handle
> > backlash and a
> > > > missing message throws out the timing and results in a following
> > error. John
> > >
> > > You can check this by plotting hm2_7i92.packet-error , but if setting the
> > > stepgen maxaccel value stops the following errors it does not seem
> > likely they
> > > are caused by lost packets. Plotting the following error will also give
> > you some
> > > insight into whats going on.
> > >
> > Hi Peter,
> >
> > One other thing about this.  From
> > http://linuxcnc.org/docs/2.7/html/man/man9/hm2_eth.9.html#PACKET%20LOSS
> >
> > "On the other hand, pid-stepper systems will run properly for extended
> > periods of time with packet loss on the order of .01%, as long as following
> > error is increased enough that having stale position feedback does not
> > trigger a following error. Altering the HAL configuration so that during
> > transient packet loss the pid and motion feedback value is equal to the
> > command value, instead of the stale feedback value, appears to improve
> > tuning. This can be accomplished with a mux2(9) component for each feedback
> > signal, using packet-error as the mux2 sel input."
> >
> > I have no idea from that paragraph how to program that into the HAL file.
> > An example would be handy.  Which feedback signal?  What does the mux
> > output do?
> >
> > From the same section:
> > "When a lost packet is detected, the packet-error pin is asserted in that
> > cycle, the packet-error-level pin is increased, and if it reaches a
> > threshold then a permanent low-level I/O error is signaled."
> >
> > I'm going to guess that low-level I/O error is a general
> > _Following_Error_Joint_2_?
> >
> > Going through the files at
> >
> > https://github.com/LinuxCNC/linuxcnc/tree/master/src/hal/drivers/mesa-hostmot2
> > I can find "packet_error_limit" but nothing that reports the following
> > error.  Still missing something.
> >
> > John
> >
> >
> >
> > ___
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> 
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Re: [Emc-users] Following Error Joint 2

[John Dammeyer]

> From: Les Newell [mailto:les.new...@fastmail.co.uk]
> > I'm going to guess that low-level I/O error is a general 
> > _Following_Error_Joint_2_?
> 
> No. It is a different error. I can't remember the exact wording but I
> have seen it before.
> 
> The following error message is correct. With steppers you have two
> acceleration settings. There is the joint acceleration which is used by
> the trajectory planner and the stepgen acceleration. STEPGEN_MAXACCEL is
> used to simulate the physical limits of the stepper and it's load. It's
> a simulated equivalent to to a servo motor running out of torque. If the
> trajectory planner commands a higher acceleration than STEPGEN_MAXACCEL
> the stepgen will not be able to keep up and you get a following error in
> exactly the same way you would on a servo system that ran out of torque.
> 
> Les
That doesn't explain why, if STEPGEN _MAXACCEL is set to 125% of 
MAX_ACCELERATION that the trajectory planner or Stepgen tries to use a number 
larger than that.

It's like saying I know you have a 1 gallon pail but because I have 1 gallon in 
my pail I'm going to pour it into yours.  Too bad it overflows when I pour two 
of my pails into one of yours.  You should have had a 2 gallon pail.

What the heck is the point of a parameter like STEPGEN_MAXACCEL or 
MAX_ACCELRATION if it can be broken so easily.

Just confused here.  
John





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Re: [Emc-users] Following Error Joint 2

[Todd Zuercher]

The trajectory planner obeys the MAX_ACCELERATION, the problem is when you 
throw backlash compensation in on top of it.  The Step generator then needs the 
extra headroom in STEPGEN _MAXACCEL to catch up with where the trajectory 
planner is commanding it to be plus the backlash take up move.  So the real 
problem is that the trajectory planner doesn't account for backlash, that is 
something added in on top of it's calculations.

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

-Original Message-
From: John Dammeyer  
Sent: Thursday, March 04, 2021 3:41 PM
To: 'Enhanced Machine Controller (EMC)' 
Subject: Re: [Emc-users] Following Error Joint 2

[EXTERNAL EMAIL] Be sure links are safe.

> From: Les Newell [mailto:les.new...@fastmail.co.uk]
> > I'm going to guess that low-level I/O error is a general 
> > _Following_Error_Joint_2_?
>
> No. It is a different error. I can't remember the exact wording but I 
> have seen it before.
>
> The following error message is correct. With steppers you have two 
> acceleration settings. There is the joint acceleration which is used 
> by the trajectory planner and the stepgen acceleration. 
> STEPGEN_MAXACCEL is used to simulate the physical limits of the 
> stepper and it's load. It's a simulated equivalent to to a servo motor 
> running out of torque. If the trajectory planner commands a higher 
> acceleration than STEPGEN_MAXACCEL the stepgen will not be able to 
> keep up and you get a following error in exactly the same way you would on a 
> servo system that ran out of torque.
>
> Les
That doesn't explain why, if STEPGEN _MAXACCEL is set to 125% of 
MAX_ACCELERATION that the trajectory planner or Stepgen tries to use a number 
larger than that.

It's like saying I know you have a 1 gallon pail but because I have 1 gallon in 
my pail I'm going to pour it into yours.  Too bad it overflows when I pour two 
of my pails into one of yours.  You should have had a 2 gallon pail.

What the heck is the point of a parameter like STEPGEN_MAXACCEL or 
MAX_ACCELRATION if it can be broken so easily.

Just confused here.
John





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Re: [Emc-users] Following Error Joint 2

[Peter C. Wallace]

On Thu, 4 Mar 2021, John Dammeyer wrote:


Date: Thu, 4 Mar 2021 12:40:34 -0800
From: John Dammeyer 
Reply-To: "Enhanced Machine Controller (EMC)"

To: "'Enhanced Machine Controller (EMC)'" 
Subject: Re: [Emc-users] Following Error Joint 2


From: Les Newell [mailto:les.new...@fastmail.co.uk]

I'm going to guess that low-level I/O error is a general 
_Following_Error_Joint_2_?


No. It is a different error. I can't remember the exact wording but I
have seen it before.

The following error message is correct. With steppers you have two
acceleration settings. There is the joint acceleration which is used by
the trajectory planner and the stepgen acceleration. STEPGEN_MAXACCEL is
used to simulate the physical limits of the stepper and it's load. It's
a simulated equivalent to to a servo motor running out of torque. If the
trajectory planner commands a higher acceleration than STEPGEN_MAXACCEL
the stepgen will not be able to keep up and you get a following error in
exactly the same way you would on a servo system that ran out of torque.

Les
That doesn't explain why, if STEPGEN _MAXACCEL is set to 125% of 
MAX_ACCELERATION that the trajectory planner or Stepgen tries to use a number 
larger than that.


The trajectory planner has no notion of what the stepgen/physical hardware 
limits are, it just obeys is maxaccel constraints (with the one exception:

if you have backlash compensation enabled, the maximum acceleration during
backlash compensation can be double the joint constraints)

If you set the stepgen maxaccel to 125% of the joint constraint, and you have 
backlash compensation enabled, the stepgen constraint will likely cause a 
following error during backlash compensation moves because the stepgen

cannot follow the requested motion.




It's like saying I know you have a 1 gallon pail but because I have 1 gallon 
in my pail I'm going to pour it into yours.  Too bad it overflows when I pour 
two of my pails into one of yours.  You should have had a 2 gallon pail. What 
the heck is the point of a parameter like STEPGEN_MAXACCEL or MAX_ACCELRATION 
if it can be broken so easily.


Well you cannot ask for more than the physical hardware can produce so there 
need to be bounds. Stepgen Maxaccel is useful for a couple of reasons:


1. If the stepgen is used alone, it be used to bound acceleration
(say for step/dir controlled VFD spindle)
2. It can improve robustness with regard to host servo thread jitter
(that is, it can bound velocity corrections to a value the mechanics can follow)





Just confused here.
John





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Peter Wallace
Mesa Electronics

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Re: [Emc-users] Following Error Joint 2

[John Dammeyer]

> From: Todd Zuercher [mailto:to...@pgrahamdunn.com]
> The trajectory planner obeys the MAX_ACCELERATION, the problem is when you 
> throw backlash compensation in on top of it.  The
> Step generator then needs the extra headroom in STEPGEN _MAXACCEL to catch up 
> with where the trajectory planner is
> commanding it to be plus the backlash take up move.  So the real problem is 
> that the trajectory planner doesn't account for
> backlash, that is something added in on top of it's calculations.

OK.  That makes sense then.  A short move in the opposite direction and then 
back in the other requires extra time for the backlash compensation but the 
trajectory planner doesn't have that information.  So it blindly assumes that 
the machine has 0 backlash.

Doesn't explain why I've been able to run with too low a setting for 
STEPGEN_MAXACCEL for so long without ever having a Following Error but add the 
weight and it's an instant failure.  Which still suggests Ethernet packets are 
probably also being corrupted.

I'll still change to a CAT7 or CAT8 shielded cable.  Just in case.

Thanks everyone.
John

> 
> Todd Zuercher
> P. Graham Dunn Inc.
> 630 Henry Street
> Dalton, Ohio 44618
> Phone:  (330)828-2105ext. 2031
> 
> -Original Message-
> From: John Dammeyer 
> Sent: Thursday, March 04, 2021 3:41 PM
> To: 'Enhanced Machine Controller (EMC)' 
> Subject: Re: [Emc-users] Following Error Joint 2
> 
> [EXTERNAL EMAIL] Be sure links are safe.
> 
> > From: Les Newell [mailto:les.new...@fastmail.co.uk]
> > > I'm going to guess that low-level I/O error is a general 
> > > _Following_Error_Joint_2_?
> >
> > No. It is a different error. I can't remember the exact wording but I
> > have seen it before.
> >
> > The following error message is correct. With steppers you have two
> > acceleration settings. There is the joint acceleration which is used
> > by the trajectory planner and the stepgen acceleration.
> > STEPGEN_MAXACCEL is used to simulate the physical limits of the
> > stepper and it's load. It's a simulated equivalent to to a servo motor
> > running out of torque. If the trajectory planner commands a higher
> > acceleration than STEPGEN_MAXACCEL the stepgen will not be able to
> > keep up and you get a following error in exactly the same way you would on 
> > a servo system that ran out of torque.
> >
> > Les
> That doesn't explain why, if STEPGEN _MAXACCEL is set to 125% of 
> MAX_ACCELERATION that the trajectory planner or Stepgen tries
> to use a number larger than that.
> 
> It's like saying I know you have a 1 gallon pail but because I have 1 gallon 
> in my pail I'm going to pour it into yours.  Too bad it
> overflows when I pour two of my pails into one of yours.  You should have had 
> a 2 gallon pail.
> 
> What the heck is the point of a parameter like STEPGEN_MAXACCEL or 
> MAX_ACCELRATION if it can be broken so easily.
> 
> Just confused here.
> John
> 
> 
> 
> 
> 
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Re: [Emc-users] Following error joint 2

[Jim Coleman]

I could be wrong, but I think the BDI is a REALLY old version of emc.  I
would try to download the newest version and go through the stepconf wizard
to set up your pins on the parport, and then try running the g code again.

On Thu, Aug 7, 2008 at 9:57 PM, Andi Frommel <[EMAIL PROTECTED]>wrote:

> hi folks
>
> i'm new to this...
> new to cnc
> new to emc2
> new to linux
>
> since i've almost finished a conversion of a desktop micro mill, i tried
> some of the example g-code files installed from the bdi.
>
> i use brushed dc motors together with whale2 drivers in
> step/dir mode.
> so far so good - but sometimes i get a following error joint 2
> (which is my z-axis).
>
> emc2 does not actually know the position of the axis in that
> mode (i assume)  'cos it continues anyway even if one of the drivers
> switches off due to a following error.
>
> that's why i want to ask you if you can help me with this nasty error
> which stops all movements.
> the error repeats every time when executing the same line in the g-code.
>
> thanks for your help
> andy
>
>
>
>
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Re: [Emc-users] Following error joint 2

[Jeff Epler]

When emc shows the "following error on joint" message for a
step&direction system, that means the system is misconfigured.  There
are two main causes for this error:

Cause 1: Insufficient "headroom" for acceleration and/or velocity.

Emc2 defines velocity and acceleration limits in both the trajectory
planner and in the step generator.  It's necessary to make the step
generator's limits just a bit higher than the trajectory planner's, or
you get a following error.

If you used stepconf to generate your configuration file, then you have
encountered a bug that will be fixed in the next release when you re-run
stepconf and regenerate your configuration files.

Until then, or if you did not use stepconf to generate your
configuration files, simply open up the .ini file in a text editor,
find the [AXIS_2] section, and for any line that starts "STEPGEN_MAXVEL"
or "STEPGEN_MAXACCEL", increase that number by 10%.  If this fixes the
problem, then you're done.  If not, maybe you have the second cause of
"following error"


Cause 2: Your step rate in steps per second is too high

There is a top limit to the number of steps per second that emc can
produce.  This is directly related to the BASE_PERIOD, which is the time
in nanoseconds between updates to the parallel port.  Unless you have
really large "step length" or "step space" values, then the maximum
number of steps per second is either 10/BASE_PERIOD or
5/BASE_PERIOD, depending whether the "doublestep" technique is
used.  (If you used stepconf to generate your configuration file, then
your configuration file uses the "doublestep" technique)

If you used stepconf to generate your configuration file, then you have
encountered a bug that will be fixed in the next release when you re-run
stepconf and regenerate your configuration files.

Until then, if you used stepconf, run it again and on the "basic machine
information" page note the value shown for "max step rate" in Hz.  On
the Z Axis Configuration page, note the value shown for "Pulse rate at
max speed".  Change the Maximum Velocity until this number is 10% below
the "max step rate" from the earlier page.

If you did not use stepconf, then in your inifile find the
[AXIS_2]MAX_VELOCITY line and decrease the value until you no longer
encounter the error.  Or you can do it based on the calculation 
MAX_VELOCITY = .90 * 5 / SCALE / BASE_PERIOD
using the SCALE value from the [AXIS_2] section and the BASE_PERIOD
value from the [EMCMOT] section.



The other problem you mention is that emc doesn't detect that the servo
amp has tripped out due to an error.  If your servo drive has a fault or
error output suitable for connection to a parall port input pin, you can
make emc aware of these errors.  For example, if you arrange to have a
HIGH logic level on parallel port pin 10 when the Z-axis amplifier is in
an error condition and a LOW logic level otherwise, then you can add a
line like the following to your .hal file:
net Zfault parport.0.pin-10-in => axis.2.amp-fault-in
If you generated your configuration file with stepconf, then put this in
your 'custom.hal' file.  When the fault signal is seen, emc will go to
"machine off" mode.

Jeff

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Re: [Emc-users] Following error joint 2

[Andi Frommel]

well, i don't think it's that old
if i'm not wrong, then it's this one:

# MD5 checksums generated by MD5summer (http://www.md5summer.org)
# Generated 10.07.2008 13:26:39
d2334dbba7313e9abc8c7c072d2af09c *ubuntu-7.10-desktop-i386.iso

i've downloaded the newest ubuntu-8.04-desktop-emc2-aj07-i386.iso but cannot 
install.
my controller has 256MB but the installer still denies with a memory error...
I've been thinking on trying the emc2.2.2-1-ubuntu6.06-desktop-i386.iso as a 
alternative.

could it be that my z-axis is too slow for a certain movement? i think the 
errors
happen on g0 commands after about 40mm of movement. if there is a time
constraint, the software could trap into a timeout and answer with a following
error - but, to be hounest, this sounds ridiculous to me...

on the other hand, can some high interrupt latency cause the problem?
i know i have one with that epia-v motherboard - but as long as i don't move 
any windows...
i've a new (old) vga card ready, this will be my next test for the latency 
problem tomorrow.

rgs andy


Ursprüngliche Nachricht
Von: [EMAIL PROTECTED]
Datum: 07.08.2008 23:35
An: <[EMAIL PROTECTED]>, "Enhanced Machine Controller 
(EMC)"
Betreff: Re: [Emc-users] Following error joint 2

I could be wrong, but I think the BDI is a REALLY old version of emc.  I
would try to download the newest version and go through the stepconf wizard
to set up your pins on the parport, and then try running the g code again.

On Thu, Aug 7, 2008 at 9:57 PM, Andi Frommel <[EMAIL PROTECTED]>wrote:

> hi folks
>
> i'm new to this...
> new to cnc
> new to emc2
> new to linux
>
> since i've almost finished a conversion of a desktop micro mill, i tried
> some of the example g-code files installed from the bdi.
>
> i use brushed dc motors together with whale2 drivers in
> step/dir mode.
> so far so good - but sometimes i get a following error joint 2
> (which is my z-axis).
>
> emc2 does not actually know the position of the axis in that
> mode (i assume)  'cos it continues anyway even if one of the drivers
> switches off due to a following error.
>
> that's why i want to ask you if you can help me with this nasty error
> which stops all movements.
> the error repeats every time when executing the same line in the g-code.
>
> thanks for your help
> andy



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Re: [Emc-users] Following error joint 2

[Jeff Epler]

On Thu, Aug 07, 2008 at 10:12:06PM +, Andi Frommel wrote:
> well, i don't think it's that old
> if i'm not wrong, then it's this one:
> 
> # MD5 checksums generated by MD5summer (http://www.md5summer.org)
> # Generated 10.07.2008 13:26:39
> d2334dbba7313e9abc8c7c072d2af09c *ubuntu-7.10-desktop-i386.iso

Ubuntu is different than BDI.  BDI is an older customized linux
distribution created before Ubuntu became popular.

We now encourage all new users to use Ubuntu 8.04 unless its minimum
requirements are too great; in that case, use 6.06 but be aware that it
won't receive updates as long as 8.04 will.

Jeff

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Re: [Emc-users] Following error joint 2

[Jon Elson]

Jeff Epler wrote:
> Ubuntu is different than BDI.  BDI is an older customized linux
> distribution created before Ubuntu became popular.
> 
> We now encourage all new users to use Ubuntu 8.04 unless its minimum
> requirements are too great; in that case, use 6.06 but be aware that it
> won't receive updates as long as 8.04 will.
He is using a recent EMC2 distro.  ONLY his TEST G-CODE file 
came from BDI, and that should work fine.  But, it may be asking 
for more velocity that his ini file max velocity and step pulse 
resolution allows.

Jon

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Re: [Emc-users] Following error joint 2

[Rob Jansen]

Andy,


> could it be that my z-axis is too slow for a certain movement? i think the
> errors
> happen on g0 commands after about 40mm of movement. if there is a time
> constraint, the software could trap into a timeout and answer with a
> following
> error - but, to be hounest, this sounds ridiculous to me...


Is the error signal output of the Whale2 connected back to EMC2?
If this is true then yes, you may detect that the Z-axis is too slow for
certain movement.

What happens if you use a G1 command with the same movement?
Try to increase the feed rate until you hit the max. velocity.

If the error output is fed back to EMC2, then on a G0 move the motor will
start and use the acceleration set in your ini file to reach the max.
velocity.
Now, if the max. velocity is too high the motor cannot follow the programmed
movement andthe error output of the Whale2 is pulled low and that triggers a
following error.
Also, if the acceleration is too high you run into the same situation.

on the other hand, can some high interrupt latency cause the problem?
> i know i have one with that epia-v motherboard - but as long as i don't
> move any windows...
> i've a new (old) vga card ready, this will be my next test for the latency
> problem tomorrow.
>


Ah, I tested with an EPIA board also - If I remember well a V1 (a 1 GHz
board).
I did not have much luck with that one,  after configuring it for my basic
mill (stepper motor drive, no encoders, position or error feedback) I had
lots of following errors. This is due to the fact that the embedded video is
snooping too much time of the processor and then EMC2 is not able to produce
the step pulses fast enough.
I do not remember if I tried this board with a VGA card, I do remember
trying an ASUS M2A-VM with both the embedded VGA and a PCI-VGA card but I
had no luck with that system.

If possible try another board. In the end I discovered that my older Compaq
(Athlon XP 2600+ with 768 MB) delivers almost the same real-time response as
my brand new Asus Striker-Extreme with Core Quad 6600 with 4 GB. There is of
course a difference when you start playing doom with EMC2 running (you're
doomed if you try ;-) )
Take any, almost any, board without embedded video to create a system being
more stable than the EPIA.

Rob

P.s: Don't get me wrong. The EPIA is a very good board, I have 2 EPIA boards
running web servers with scripting, SQL server and subversion server for 7
years now and they never failed on me (except for that one time where Typo3
went berserk ), it's just not "EMC friendly".
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Re: [Emc-users] Following error joint 2

[Ray Henry]

On Fri, 2008-08-08 at 08:04 +0200, Rob Jansen wrote:

> 
> Rob
> 
> P.s: Don't get me wrong. The EPIA is a very good
>  board, I have 2 EPIA boards running web servers
>  with scripting, SQL server and subversion server 
> for 7 years now and they never failed on me (except 
> for that one time where Typo3 went berserk ), it's 
> just not "EMC friendly".

I've found that some of the older MiniITX boards cause
occasional real-time delays.  The newer one's I've tested
are much better.  The Unichrome pro on-board hardware is 
really quite good.  I added test results to the wiki page
for one I use.

Rayh


  


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