Spindle PID troubleshooting -- solved

Found the problem. Posting so that other people can find it as well (like me, a year from now!).

Basically, changed
(which is now commented out)
to
Hope this is helpful for someone else.

Paul Tan.

filtered rpm is usually for a more steady display of RPM.

I still wonder about your scaling - IIRC you VFD is 0-5 Volt and your RPM is 0-5000

but your scaling doesn't reflect this:

OUTPUT_SCALE = 4700
OUTPUT_MIN_LIMIT = 0
OUTPUT_MAX_LIMIT = 4700

This defines the scaling as 0-10 volts 0-4700 RPM
That could definitely throw off the proper spindle speed.

Chris

I think there are two things.

First - the actual speed is lagging, You command 16.667 rps and only get 13.947 rps. This error can be reduced by the pid controller. Bring up halscope and look at pid.s.command, pid.s.feedback and pid.s.error. Make sure the nominal scaling is right (4700 vs 5000 rpm as indicated above), you can also compensate for scaling errors with FF0. It is always best to have the scaling set as good as it reasonably gets, the smaller the error the pid controller need to adjust for the better. Then it is basically a servo tuning exercise for which there are many guides out there. But the easy way is to work with P parameter. In the first screenshot you use halshow to view signals. Instead view the pins for the pid.s component in halshow.

Second - The rpm value in gmoccapy does not show the real speed value (pid.s.feedback). Isn't that what you got better by using the filtered data.