What next? You have set P-gain but what about I and D gains?
On Tue, Dec 8, 2020 at 12:49 PM Gene Heskett <ghesk...@shentel.net> wrote: > Lo all; > > I'm back to playing with the servo again, following John Thorntons > instructs from the wiki article. And I note a couple things. > > 1. The pid_a.FF1 value has little or no effect on the amplitude of the > error. So that probably needs addressed by educating me on how its > calculated. > > 2.pid_a.FF2 isn't working as that article says it should, a little effect > on the shape but zero effect that would lead to a zero error when cruising > > 3. pid_a.Pgain effects the amplitude of the error signal, with about > 350000 being the onset of a low level oscillation, about 10% when > cruising. But its also the lowest error at 15 to 20 millivolts. > > 4. I am getting some improvement. but nothing like the pix on that wiki > article. > > It explains that pid_a.FF1 should be 10/velocity@10V (velocity is in > machine units per second). Since I do not yet have the motor actually > moving the BS-1 clone, nor have I managed to get a home switch set up so I > can actually measure the scale, the scale temporarily set is likely wrong. > Since I've 2 worms in series, for playing I've a high value set for scale, > 5000. With the encoder on the back of the motor it could well be higher > than that. > > But no combination of numbers results in a cruising error of zero, its > alway plus at cruise speed. > > And if I go at more than about 30% high pwm, motor inertia causes the > servo to use reverse to stop if I ask for more than 60 degrees a second. > This use of reverse causes the supply, a 350 watt 24 volt switcher, to do a > shutdown because it thinks is been crowbarred, and the powerdown to recover > is around 3 minutes. > > I think I might have a way that will fix that as this driver can do > crowbar the motor braking if the signals are re-arranged and fast enough. > If I setup a hardware timer in the form of a a retriggerable ooneshot > drive from the pwm signal, which is running at 4 kilohertz, or 250u-secs > pulse is a 100% signal, but the timer timesout in 200 microseconds, it will > time out and apply the brakes for whats left of the 250 microsecond pwm > cycle if the pwn drops below 20%. This should slow the motor fast enough it > will never actually use reverse to stop. And that mode will never effect > the psu. > > But first, what can I do about the ineffectiveness of setting FF1 anyplace > between .5 and 25. I think its effecting the motors cruising speed but has > zero effect on the amplitude or shape of the error if enough Pgain is used > to make it follow well. > > With Pgain at 250000 it cruises stably, with a reasonably flat top to the > error, about 20 millivolts of error, but FF2 seems to have little effect on > the initial overshoot, or the overshoot when stopping, and its the > overshoot when stopping that is shutting down the supply unless I set max > jog to below 60 so friction stops it. That 60 is about 1/3rd of what the > motor can do in terms of output shaft rpms if fed its normal 24 volts. > > Anybody know what I should look at next? > > Thank you. > > Cheers, Gene Heskett > > > -- > "There are four boxes to be used in defense of liberty: > soap, ballot, jury, and ammo. Please use in that order." > -Ed Howdershelt (Author) > If we desire respect for the law, we must first make the law respectable. > - Louis D. Brandeis > Genes Web page <http://geneslinuxbox.net:6309/gene> > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
