Re: [CAD_CAM_EDM_DRO] Interesting Observation

Joe Vicars wrote:

> I was playing with a bunch of motors on the bench last night,
> seeing
> which ones would run off my 20V .5A power supply.
> I observed an interesting difference between my servos and the
> regular DC motor. If you grab the shaft of a vanilla DC motor and
> stop
> it you can feel the shaft pushing against your grip, trying to go.
> If you do the same thing with the servo, you feel a definate
> cogging
> when the shaft speed gets to zero. It's like the torque "switched
> off". If you let go of the shaft, the servo starts spinning again. I
>
> am guessing that this has something to do with the servo's ability to
> "hold" postion.
> Anyone want to enlighten me as to why? I still don't understand
> the
> difference.

A good servo motor will not exhibit torque ripple of velocity ripple
that you can
feel. Both ripples will be in the 1.5% or better neighborhood (which is
WAY
better than an ordinary motor). There are details in the winding
pattern of the
armature to make the smooth transition from one winding to the next, and
where
the magnetic flux of the field magnet switches from one armature pole to
the next.

I don't quite know what you mean by "the torque switched off". Perhaps
your
power supply went into overload shutdown, due to the low armature
resistance
of the servo motor. The MOTOR, itself, didn't stop working at zero
speed.
But, at zero speed, it looks like a dead short to the power supply.

Jon