Re: z axis drive question

Jon Elson wrote:

> A properly designed servo motor has no detectable "cogging" due to
> individual
> windings, commutator segments and pole pieces. (Yes, badly designed
> motors, or those for high-speed operation only, may have significant
> torque ripple, velocity ripple or reluctance cogging, but these are

NOT

> servo motors.)
>
> Jon

Can one detect cogging by turning the motor by hand? The reason I ask
is that I recently bought a used servo motor, and when I rotate the
motor by hand I can clearly feel a "stepping" sensation; that is, the
motor favors some positions over others. I think it has 8 steps/rev,
and some steps are a bit weaker than the others. They are not very
distinct (nothing like a stepper), but quite strong - when left in
the middle of a step the motor turns so that it sits between steps...
if you get what I mean.

This is the same 3-ph PM Yaskawa servo motor I asked about in an
earlier message.

Thanks for all help!

Arvid