Axis motor oscillates when its supposed to be idle

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14 Jul 2020 02:31 #174570 by M Sills
I am testing the drivers and steppers for my cnc lathe project. When I boot up linux cnc and try to jog an axis, the motor will constantly jitter back and forth about a quarter turn. The axis will move roughly the amount I told it to but it will constantly jitter while doing it. The coordinates that appear on the screen move with it. When I disable the machine, the jittering stops. When the machine is enabled, it only happens once I tell an axis to move.

I went to change the timings for the stepper driver in pncconf but while testing, once the motors were told to move, they would move the correct direction and then slowly rotate in a direction unless I told the program to disable the axis.
I should note that the enable/disable connection is not currently connected as the manual said it isn't necessary. I do plan to connect them in the future.

I am using a 7i76e connected to an Rpi 4 running 32 bit Buster. I am using the image that spacehitchhiker42 posted here. www.forum.linuxcnc.org/18-computer/36879...berry-pi-4?start=130

The stepper drivers I am using are CL57Ts. I am using timings of 2500, 2500, 5000, 5000. That's something like the signal on time, signal off time, direction hold and direction off or what ever they are called in pncconf.
I could not test values higher than 5000 for my directions in pncconf tuning due to the program resetting the value but I could set it high. I have tried to save 6000 as my direction but linuxcnc behaves in the same manner when booted.

It has something like a 10hz oscillation for the motor's jitter.

The stepper manual can be found here. It's a link to a pdf so it might auto download.
www.omc-stepperonline.com/download/CL57T.pdf

A quick run through if my system.
Rpi 4 as the computer
7i76e mesa card
2 cl57t closed loop stepper drivers
2 closed loop stepper motors
Taigturn lathe
12v server power supply to run the 7i76e from the field power connector
2 36v mean well power supplies for the steppers

Any help will be appreciated
If I need to clarify anything, please let me know.

If needed, I should be able to attach a video or two tommorow to help show my issue

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14 Jul 2020 03:38 #174577 by PCW
Can you post your hal and ini files?

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14 Jul 2020 04:39 #174579 by M Sills
I wasn't sure what files you need to I added every .hal and .ini file I had in my generated file.
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14 Jul 2020 08:02 #174584 by tommylight
Delete this line in the HAL file for all axis:
setp pid.x.maxerror .0005

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14 Jul 2020 14:45 #174639 by PCW
The P values are wrong, they should all be 1000 for a 1 ms servo thread

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14 Jul 2020 17:45 #174650 by M Sills
So I tried Tommylights suggested solution and it still behaved the same.
It also would still drift when I was in the tuning tab for pconf.

As for PCW, what is a P value and how do I change it.

I should also mention that I am running my stepper motors at 2000 steps a revolution using micro steps.

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14 Jul 2020 17:58 - 14 Jul 2020 18:03 #174651 by PCW
The P value is the P term for the PID, its in the ini file
I assumed you knew what it was since you changed it from the default 1000
Last edit: 14 Jul 2020 18:03 by PCW.

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14 Jul 2020 18:14 #174653 by M Sills
I'll try modifying it when ever I get back and see if that fixes it.

Is the p value generated in the pncconf utility or is it pulled from another location on the machine?

I should mention that I personally didn't change the file.
Unless I clicked the wrong option in pncconf or the image I had downloaded already had it auto to that, then I have no clue how it happened. I am running 2.9 so it could be a small bug.

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14 Jul 2020 18:25 #174654 by PCW
pncconfs defaults for P values is 1/servo_thread_period = 1000 at the default
1 ms servo thread.

Its possible you changed the servo thread period which would change the values
or you accidentally changed them in pncconf.

It any case the values you had were 10000 for one axis and 7142.85714286 ???
for the other, these values are guaranteed to cause oscillation.

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14 Jul 2020 19:11 #174656 by M Sills
Changing the values worked. I no longer have the annoying oscillations.

I still have a small issue, when I rerun pncconf on the file, it defaults to the weird values.
When I set this file up originally, I had removed a zero from the servo thread period. I have since fixed this issue but it still sets it to this weird value.

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