On Tuesday 08 December 2020 19:05:52 Chris Albertson wrote: > What next? You have set P-gain but what about I and D gains? > That has been tried, gently, but doesn't seem to have the desired effect.
> 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 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
