Re: Is this servo usable for position control?

--- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:

> grantfair2001 wrote:
>
> > --- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:
> > > grantfair2001 wrote:
> > >
> > > > I have 3 Japan Servo DC servomotors . . . If I count the tach
> > pulses can I
> > > > use this to establish positions reliably?
> > >Are these brush motors or brushless DC. If 2-wire brushless DC,
> > > then it will only turn
> > > one direction, so that is also useless for positioning

> > Is there an easy way to determine if it has brushes?
>
> Hmmm, not so easy. You might try using a DVM in ohmmeter mode
> across the wires. if you get very low readings (10 Ohms or less)
> with both polarities, it is almost certainly a brush motor. If you

get

> high reading one or both ways, then it is a brushless DC motor, and
> cannot be reversed (without changing circuit wiring inside the

motor).

I got about 200 ohms with both ohmmeter polarities.

I connected it to 15 volts and then reversed power supply polarity,
and it worked both ways. Does this mean it is a brush motor?

The tach put out a nice sine wave, about 1 V p-p.

Assuming it is usable forward and reverse, then I can tell which
direction it is going depending on what polarity voltage I am telling
it to use. Obviously I can't use the controller board as is, but
perhaps a simple addition might do the trick (I'm not sure how the
variable pulse width input which controls speed actually does this,
with PWM or what? Anyway, this brings me back to my original
question, could I use it for position control?

Thanks for your assistance.

Grant