On Tuesday 05 May 2020 23:55:21 Nicklas Karlsson wrote: > > I have a PMDC motor I’ve scavenged along with the MC-2100 motor > > control from a treadmill rated for 1.5 hp @ 90 volts. I’ve been > > testing it with LinuxCNC v2.7.15 in a mock-up environment I built > > for testing. I’m able to control the spindle speed via PWM pulses to > > the controller (HD2 pin 4). M3 S500 will get me somewhere between > > 520 and 580 rpm. You can hear the motor whine fluctuating with the > > RPM. I’ve also installed a CUI ATM 10 encoder on the back and seem > > to have it working with both an index and phase A signal. I have the > > jumpers on it set to 200 PPR but it can go all the way to 2048. I’m > > using a cheap china 5 axis BOB connected via parallel cable. > > > > Does anybody have any idea why I’m get so much flux on the rpm? > > Surely this isn’t normal? I know enough about the HAL to be > > dangerous. Is there some things I can check to smooth this out? > > Thanks. > > You are sure drive pwm signal outputs are constant duty cycle? > They probably aren't going to absolutely constant unless the math has no residual from a divide. And the higher the pwm rep rate, the more noticeable this variation will be, but it also going to vary at a high enough rate that the motor will average it. What its doing is adding or substracting one clock period here and there in order to give you on an average over a small fraction of a second, the exact speed requested. And its even pretty good at that in the pulse density mode at speeds less than 1% of the full on speed. What it does there is a 1% pulse, less and less often. So I believe the encoder is lieing. The question is why. If its accurate to .25 degrees, that's equ to microstepping the motor at 6x. In the real world microstepped steppers aren't any better. In any event there no real advantage to a pwn carrier well above the 1 kilohertz servo rate.
My two cents. > _______________________________________________ > 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
