John Payson wrote:
>
> One thing I was wondering about but didn't really see mentioned: if one is PWM
'ing a motor while
> trying to measure its speed (via back EMF) what is the preferred way of handli
ng inductive kick-
> back from the motor?

This could be done by a short delay preceding the measurement.

But I4ve 2 more problems:

The Moror is a series-wound-type ( mdrklin ) so how to get backemf
without a constant field.
A much bigger problem is the realy unsteady behavior at low speeds.

 I'm particularly curious about a model-railroading application where
there
> is an unknown and variable amount of resistance between the supply unit and th
e motor.  If the
> PWM outputs a constant current when on, and if inductive kickback can be filte
red out so as not
> to skew the measurements, it would seem that gunk on the rails would be a 99.4
4% non-issue with
> regard to maintaining constant speed provided only that the current supply had
 adequate compliance
> voltage.
>
> Is such a design practical/feasible?

Well, is practically already done, but with a true DC-Motor.

Any ideas how to adress the behavior at realy low speeds ? Thought about
a reflex-sensor sfh 900 to do real speed regulation.

WBR Stefan