Re: brushless servos without hall commutation

bluecoast says:

>I have a number of brushless servos I've collected to
>build some cnc
>machines. All of them have optical encoders of some
>resolution, but
>none have hall-effect sensors for commutation.

snip

>Has anyone faked the hall-sensor arrangement somehow?

bluecoast

I can't imagine how you would fake halls. Your best
bet may be to put halls on. I have never seen a
brushless motor with an encoder but without halls, for
my education could you give a brand and model? There
are quite a few encoders with simulated hall tracks,
you sure you don't have one of those?

If you were building a drive, the way to do this is to
sense the current in the windings. I just saw an app
note at Motorola, I mean Freescale, that talks about
sensing the current. The winding current will tell
you where you are just like the halls. This is called
a sensorless drive. AMC has some drives that do this.
AMC also has some drives that will work open-loop if
I'm reading the manuals correctly.

Eric






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