Re: [CAD_CAM_EDM_DRO] Re: Going home / more stepper speed!

mariss92705@... wrote:

> Alan,
>
> I respectfully disagree with Jon. You cannot see ringing with either
> a voltage probe or a current probe when the motor windings are driven
> with a full bridge at low speed. This is because any back-EMF signal
> is completely washed out by the motor's inductive current and the low
> impedence voltage source that constitutes the bridge.

Yup, I realized you are right!

> I have tried very hard to come up with differential canceling circuit
> schemes to accomplish this because a real breakthrough would be the
> result.
>
> If it were possible to reliably retrieve this signal then it would be
> very simple to use it to use it to actively damp the ringing and also
> have direct missed step feedback.

I think this can be done with some motors with split windings that are
on different poles of the stator. (Obviously, windings that are distributed
over the same stator poles would couple the same flux.)

> The signal is there alright, at higher speeds (>100 full steps per
> sec), it is easy to find. Unfortunately as speed approaches zero, so
> does the back EMF.

Yes, right there, too.

Jon