Servo PID Tuning - can't clamp down on overshoot

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29 Dec 2016 21:20 #84875 by SRDC
Here are more screenshots
  • same acceleration (10in/s^2)
  • no FF2
  • just dropping P from 20 to 15 to 10 to 5 to 3 (see the file names)

I was able to recenter before & after with Igain after these screenshots, but nothing seems to really help the initial lag at all.
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29 Dec 2016 21:24 #84876 by PCW
Hmm if accceleration doesn't affect the overshoot then its not likely to be lag in the resolver
mechanical?

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29 Dec 2016 21:32 #84878 by SRDC
Just to make sure the acceleration wasn't a problem at all, we dropped the acceleration down to 3 in/s^2. Halscope screenshot is attached -- no real change. The initial lag is still around 0.002-0.003 inches.

It exactly matches the acceleration time period, and then jumps into position almost vertically. It's almost like something is holding the motors back during acceleration.
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29 Dec 2016 21:56 #84879 by PCW
You might try increasing the drives velocity loop gain (increase till it oscillates then back off 20% or so)
while linuxCNCs P term is low to see if that helps the lag.

the fact that its unaffected by acceleration does suggest mechanical issues though

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29 Dec 2016 22:09 #84882 by SRDC
Just tried increasing "speed loop gain adjustment volume." It did help a teeny bit. We increased it 2 'gradations.' On the 3rd gradation, it started buzzing as soon as the drive was enabled, so we backed it back down to 2 gradations.

Still not changing the basic problem.

What mechanical issues would you look at?
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