I agree with Gerhard. I made something like this using a nice pot on the
output shaft of the motor and it worked great after I got it tweaked.
 James

 On 10/16/05, Gerhard Fiedler <lists@connectionbrazil.com> wrote:
>
> Neil Baylis wrote:
>
> > This is a brush commutated DC servo, and has a built in DC tachometer.
> In
> > addition, someone has atached an optical encoder on the back. The
> > encoder has only moderate resolution as far as I can tell by visually
> > inspecting. Maybe 100 pulses per rev. Also, the encoder has only 3
> > wires, so no direction info in there.
>
> > I want to begin by building a simple servo controller that will use thi=
s
> > encoder for position feedback, and use the tach for velocity. I would
> > obtain direction info by sampling the tach output voltage on every
> > transition of the encoder signal. Obviously, the direction is the sign
> > of the tacho signal.
> >
> > Will this work?
>
> For a servo controller, I would very much like a better direction signal,
> and also an absolute position signal. The way this sounds, the controller
> doesn't have a clue where the shaft position is on power-up.
>
> Gerhard
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