On 08/26/2017 12:39 PM, Eric H. Johnson wrote:
Andy,
Yes, as TYPE = ANGULAR in the joint section.
As for P, yes that would seem to agree with what I am seeing.
I made some headway by starting at 24000 counts per degree (actual counts per
revolution). Tuned that in, then did the same at 1000, 500, 250 and 125. Still
struggling at 66.6666. Can get it to run slowly, but goes unstable at speed and
sometimes when nearing the end point.
Yes, the problem with the PID is that when the scale value
going in is very low, the jumps in the user units when the
encoder or step count changes by one is much larger. Since
position is quantized by either step count or encoder
counts, there isn't a whole lot you can do about this. The
best is to set the FF1 as closely as you possibly can with P
and D very low, use FF2 (with real servos only) in tiny
increments to help with acceleration, and then raise P until
the error is acceptable. D should be at the minimum you can
live with, as increasing D just amplifies the encoder count
jumps.
Some systems have velocity estimation that tries to smooth
out the velocity jumps caused by this. If you are NOT using
velocity estimation where it is available, I think you will
find it helpful.
Jon
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