Gene is getting good results with his 3-phase steppers and no PID control in LCNC because the 3-phase steppers have internal PID position control loops in the motor driver electronics. These motors have an encoder wheel for feedback. So these steppers are basically the same as a servo with feedback implemented on the servo driver.
>From my experience with motion control (robots), the BEST place to run the control loop is in hardware attached to the motor. Typically, this is a microcontroller There, the loop can run as fast as it needs to and the timing jitter is a non-issue. On Thu, Oct 28, 2021 at 11:14 AM Sam Sokolik <samco...@gmail.com> wrote: > This is a quote from peter on the forum.. > > 'I have done some experimentation and have found that you can get better > stepgen following performance on systems with moderate jitter by using a > PID loop for position control instead of the stepgen drivers built-in > position control loop. > The problem with the built in driver position control is that its tends to > overcorrect > for measured position errors cause by sampling jitter.' > > On Thu, Oct 28, 2021 at 12:35 PM Gene Heskett <ghesk...@shentel.net> > wrote: > > > On Thursday 28 October 2021 11:45:49 Sam Sokolik wrote: > > > > > All my machines - steppers and servos are running pid. I think > > > Peter forgot to mention - The reason PID is recommended is because it > > > handles latency spikes way better. We have seen situations where a > > > latency spike confuses the hell out of position mode stepgens. > > > (ymmv) > > > > But thats why we run preempt-rt kernels Sam. Even on the pi, the maximum > > spike is 200 microseconds while FF is initializing. W/O FF, 4 to 50 > > u-secs. And the big lathe has never noticed that. The little mill, > > before it commited suicide by spitting out all the balls of the y nut, > > was running sw steppers, and they did notice occasionally. It also > > severely limited that machines rapids, to around 8 or 9" a minute. > > Putting a 5i25 in it and it ran about 50 ipm w/o any stutters. > > > > > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > _______________________________________________ > 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
