joint 2 following error

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12 Dec 2020 09:43 - 12 Dec 2020 09:43 #191718 by zu4lu
Replied by zu4lu on topic joint 2 following error
I had joint-errors on joint3, the z-axis, mesa 7i96. With your proposal:

>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)

i got it working with no more joint errors.
thanks
Last edit: 12 Dec 2020 09:43 by zu4lu.

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25 Sep 2021 08:40 #221535 by Markyd
Replied by Markyd on topic joint 2 following error

I have done some experimentation and have found that you can get better
stepgen following performance on systems with moderate jitter by using a
PID loop for position control instead of the stepgen drivers built-in position control loop.
The problem with the built in driver position control is that its tends to overcorrect
for measured position errors cause by sampling jitter.

Here is an example hal /ini file setup:

freeby.mesanet.com/hm2-pidstepper.zip

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)

This seems to work well for Ethernet systems which have large jitter (>100 usec)

I've just tried to download this example (the .zip file) but it doesn't seem to be there anymore? 
I'm having following errors on my system (RPI4, 7i96, 7i85, 7i73 with steppers) and I'm wondering what the best process is to find the source of the issue?
 

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27 Sep 2021 12:53 - 27 Sep 2021 12:53 #221700 by Todd Zuercher
We would need to know more about exactly how you have your system configured.
Do you have position feedback set up from encoders into Linuxcnc?
Are you using that as the position feedback for each joint?
Are your using step motors or servos?
Posting copies of your config files would help clear up some of these questions.
Hal Scope is a very useful tool for tracking down problems like this, try plotting the velocity command vs velocity feedback and f-error for the joint in question.
But if the source of the problem is bad latency in your pc (pi) all bets are off.
Last edit: 27 Sep 2021 12:53 by Todd Zuercher.

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10 Oct 2021 06:34 #222715 by Markyd
Replied by Markyd on topic joint 2 following error
i ended up starting a new thread about my latency (forum.linuxcnc.org/38-general-linuxcnc-q...s-this-normal#222714) thinking that was the issue. Turns out is was probably just the following error (Thanks PCW). The hal and ini are posted at that link.

Its a raspberry pi. Steppers, and it is not currently using the linear encoder position feedback, although it is being fed in via a 7i85.

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