On Wed, 2010-01-06 at 18:45 -0800, Flying Electron wrote: ... snip > switched on and off 3 times per rev. But if this is correct, wouldn't > stopping and holding the position of the motor somewhere between the > poles be like how microstepping works on stepper motors and it wouldn't > be that accurate? ... snip
No, because the servo joint position encoder will feed the position back to EMC2 which calculates an error value. The error value is used to send a forward or reverse command to the motor driver. I suppose a micro stepper drive could do the same thing, but then you would have to add a commutator system of some sort to the driver, and then you would have a slow brushless motor. Brushless DC motors really should be thought of as brushed DC motors with solid state commutation. The motor drive gets a forward or reverse command based on the position feedback, then the drive sends current to the motor coil that is indicated by the commutator. Also remember that the feedback is only good for about a millisecond until the next servo cycle creates another command. It might be considered normal to have the drive cycle two coils on successive cycles against each other even though the overall result is no change in position. On the surface, the differences can be subtle, but steppers and brushless motors really are different. Even DC brushless and AC brushless motors are different. (Beware, I am not an expert) -- Kirk Wallace http://www.wallacecompany.com/machine_shop/ http://www.wallacecompany.com/E45/index.html California, USA ------------------------------------------------------------------------------ This SF.Net email is sponsored by the Verizon Developer Community Take advantage of Verizon's best-in-class app development support A streamlined, 14 day to market process makes app distribution fast and easy Join now and get one step closer to millions of Verizon customers http://p.sf.net/sfu/verizon-dev2dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
