Re: [CAD_CAM_EDM_DRO] Re: Allegro 2961 uptdate

lonnietoons@... wrote:

> I have got the 540 oz/in motors up to 5800 steps/sec, but usually
> they stall out before 3000.
> I have some smaller 140 oz/in 6 wire motors(half connected) that
> stall out around 1300. If I carefully accelerate thru 1300 then it
> goes on up to 8000.

This is obviously a resonance. Are you doing this with the motor just
sitting on the bench? You will always get resonance that way. When the
motor is connected to a machine, it should do much better, as the machine
provides damping. There are viscous dampers used in cases where the
machine doesn't provide enough damping. It is basically a disc shaped
chamber with a free-floating steel or lead "washer" inside, and filled with
a thick oil or grease. There are more primitive versions that have a
free floating steel plate held loosely between steel plates that are
attached to the shaft. There is a rubber sheet between the floating plate
and the driven plates. The concept is the same. When resonance ocurrs,
there is a rapid rotational vibration in the motor shaft, and the
free floating plate doesn't follow that vibration, just the steady
rotation of the motor. The friction between the disc and chamber
or plates dissipates the resonance, preventing it from building to a
level that could cause steps to be lost.

> I have tried changing some things but no help.
> Does anybody know any tricks that help with this mid-range
> instability?

If you are doing this with the motor free, install it in something. If the
problem persists, then you can think about dampers. Driving the leadscrews
with toothed belts also seems to provide just a little extra damping.

Jon