Re: brushless servos without hall commutation

All of the Microchip app notes that I have seen were written for DC
brushless motors. They have trapeziodal back EMF and are commutated
differently than AC brushless motors which have sinusoidal back EMF.
The DC brushless motors are driven on two of the three leads at a
time, while the AC motors are driven on all three leads
simultaneously with waveforms that approximate 3 phase sinusoidal
current when smoothed by the motors inductance.

~petev

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "bluecoast1" <bluecoast@h...>
wrote:

>
>
> Hey,
>
> actually I read a microchip appnote (one of the originals on

brushless

> control) and they optionally ran it on back-emf sensing, and they
> blipped the motor or something to get the initial position via
> back-emf before starting up (I think).
>
> This seems like it might be okay for speed control but maybe not so
> good for position control.