Jogging wobble/hunting

26 Apr 2024 00:08 #299088 by sirbrialliance
When I jog with my CNC setup (via a WHB04B-6), sometimes instead of going to the commanded position it sort of "wiggles" around the target position back and forth in a sort of sine wave until it eventually settles on the correct location. It's not a mechanics issues, LinuxCNC is commanding my (no feedback) steppers to move like this.


Additionally, if the sine wave tries to violate soft bounds everything faults and errors out.

What do I need to do to make it track my jogging exactly and not do weird things like this? I understand if it overshoots a bit if I suddenly switch directions, but it shouldn't have trouble tracking normal forward movement.

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26 Apr 2024 01:04 - 26 Apr 2024 04:03 #299089 by PCW
Replied by PCW on topic Jogging wobble/hunting
It looks to be an issue in the step generator.
I wonder if you have run into clipping of the feedback loop
because the step lengths and step space are so close
to bounding the maximum velocity.

I would first try setting the step lengths to say 30000,30000
so you have lots of margin.

Also there is no DPLL enabled, so you need a couple  statements like:

setp hm2_7i96s.0.dpll.01.timer-us -100
setp hm2_7i96s.0.stepgen.timer-number 1

in the hal file


Actually, looking at the plot more carefully, it looks like
there is an acceleration constraint violation that starts
the oscillation. That seems more like a  LinuxCNC bug.
Last edit: 26 Apr 2024 04:03 by PCW.
The following user(s) said Thank You: sirbrialliance

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29 May 2024 01:01 #301714 by sirbrialliance
Thanks for taking a look and sharing your wisdom!

Adding the DPLL settings you suggested fixed it. Additionally, I'm not longer getting random "Joint x Following error" errors even while jogging completely within bounds.

Thanks a bunch!

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