Tuesday, October 04, 2016

Spinning a motor is hard

I'm trying to spin a 3 phase motor really, really slow.   For this I have chosen Sinusoidal Commutation.  Just a few sine calculations and I'm good, right?


Sinusoidal commutation of BLDC motors is hard.  Even so-called "open loop" commutation (which still expects feedback -- is it still really "open"?) is difficult.

You can find a google load of papers on how to perform (6 step) trapezoidal commutation and then some that kind of talk about sinusoidal.

It's all maddening and the reason why motors are its own field of study.  Lots of physics. Lots of math. Lots of stuff you can't shortcut.  Jerk, torque ripple, back EMF.  Don't get me started on rotors and pole count.  How about Phase finding?  Know how to do that?

To spin, you must have feedback!  Don't Hall effect sensors? How about with angular magnetic encoders? If you are man (or woman) enough, you venture into FOC.

I'm spending weekends and some weeknights learning how to spin a motor so me and my partners can build a killer robotic application. (Killer may be a bad choice of words....)

I'm really learning how much I don't really know.

Spinning a motor is hard...