Andy Pugh wrote: > I _think_ what you would have in such a dual PID loop would be a loop > closed by velocity but controlled by duty-cycle (and motor torque is > at least approximately directly proportional to PWM duty cycle) driven > by a loop closed by position and controlled by velocity. > > If the motor had high resistance and no back-EMF, this might be true, where voltage out of the drive is proportional to current. In general, the motors have fairly low resistance, and the motor's back-EMF is pretty dominant, so voltage out is closely proportional to SPEED, not torque. This totally changes the way the servo loop operates. So, current is proportional to the difference between back-EMF and applied voltage. I = (Vout - bEMF) / R
Jon ------------------------------------------------------------------------------ This SF.net email is sponsored by Sprint What will you do first with EVO, the first 4G phone? Visit sprint.com/first -- http://p.sf.net/sfu/sprint-com-first _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
