Re: more weird DC motor

--- In CAD_CAM_EDM_DRO@y..., "Dale Smith" <mediasmith@m...> wrote:

>
> There are two sets of brushes. Earlier, I stated they appeared

offset by

> about 45 degrees. A second look shows only the wire exits are

offset. The

> brush holders are in axial alignment.
>
> The motor will run equally well with power on either set of

brushes/pair of

> wires.

If it runs ==equally== well on either set, then they must both be
intended for powering the motor, not a set each for motor and tach.
Brush offset is not needed as the commutator bars could also be
offset.

> Hook a voltmeter across either pair and it is easy to get 12 to 30

VDC

> turning the shaft by hand.

This indicates that there is a permanent magnet field that does not
require external power.

> I didn't try a parallel hookup but there was an obvious speed

increase when

> wired in series (properly).
> There was absolutely some serious bucking going on when the series

winding

> was reversed.

The bucking would be natural for reversed polarity of one pair in
either
parallel or series modes. The speed increase baffles me. A permanent
magnet field is similar to a shunt field and speed should vary as
VOLTAGE/(armature coil turns). Armatures in series would be more
turns
and less speed for the same voltage. Armatures in parallel should run
with the same speed as a single armature, just with more current,
torque,
and possibly smoother due to overlapping commutator switching.

> I took a look at the Gecko 340 and 320 drives last night. The price

is not

> all that bad (from an experimental point of view) but money is

tight right

> now and really don't feel qualified to experiment with these things

and I

> would hate to let the magic smoke out without learning/gaining

anything.

For use as a spindle drive, the Gecko style servo drive is not needed,
a plain variable speed DC drive would do. For testing you can still
use the light bulb in series method to protect the motor and drive or
power supply. The biggest problem is comming up with a high voltage
DC power source if you do not have a drive. Keep in mind that 230 VDC
is dangerous stuff.

If you want to try to use these motors as servos I would recommend
seeking
assistance from Jon Elson as he has experience with investigating
motor
properties related to speed/voltage constants and inertia as related
to
servo operation.

Regards,
Steve Stallings