On 10/08/2015 01:18 AM, Marshland Engineering wrote: > Apparently DC Brushless cog but not AC ? > Anyway I'm about to order a 6N.m 1.8KW AC motor and drive for $340. It's > worth a try. > > Brushes ?? My South Western Industries mill has run 20+ hours a week for + 10 > years and I have never changed a brush. Maybe I should check sometime.
My understanding of motor cogging is that it is the torque or speed variation due to the layout of the magnetic poles. https://en.wikipedia.org/wiki/Cogging_torque This has been an issue with DC brushed motors when driven by a simple voltage source. Generally, half the rotor coils are energized South and half North. As the rotor turns the brushes change the polarity of a coil in order to shift the magnetic phase of the rotor away from the stator in order to create torque. This is a one coil quantum change, so the torque is also a step change, therefore not smooth. One way to smooth the torque is to twist the rotor coil layout the adjust the torque profile relative to the rotor/stator position. This still is in the context of driving a motor with a simple power source. When speed, position or other feedback is added to control the source, cogging does not apply. Cogging could be an issue for AC or DC brushless and AC induction motors if they are driven by a simple power source that matches the type of motor -- AC induction needing AC mains power with properly phased legs, AC brushless needing three phase AC sinusoidal power, and DC brushless needing three phase trapezoidal power. -- Kirk Wallace http://www.wallacecompany.com/machine_shop/ http://www.wallacecompany.com/E45/ ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
