Re: [CAD_CAM_EDM_DRO] Digest Number 1779

OK Guys, I hoped this wouldn't get too long but that really must not be my
style. I would be happy to go off-list if it is not close enough to the
regular exchange.

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.

Hook a voltmeter across either pair and it is easy to get 12 to 30 VDC
turning the shaft by hand.

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.

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. UPS
to an expert would be cheaper. the local motor control place could only
marvel at the square mounting flange and mumble about never seen nothing
like that.

Concept is even a problem with me. I've read a fair amount on how steppers
work but haven't found anything on servos so have no idea what to expect out
of these things if used as servos within the op limits of a Gecko 340.
Should they drive a 12 inch lathe leadscrew, a large mill table feed or only
a Sherline crossfeed? Am I better served by using them as plain DC motors or
as servos?

I have a serious educational deficit her and we haven't even touched on the
other 4 large servos I have on the shelf.

Thanks again,

Dale Smith







Date: Wed, 14 Nov 2001 03:00:16 +0000

>
> Best bet would be to have a good look at the real motors
> and run some measurements or experiments.
>
> Steve Stallings
>
> From: Jon Elson <elson@...>
> Subject: Re: Re: weird DC motor
>
> stevesng@... wrote:
> >
> > Pictures of the motors were posted by Dale at:
> >
> > http://home.mmcable.com/mediasmith/DCmotor.jpg
> >
> > The detail is hard to see, but on the rear the brush holders
> > are flush.
>
> Yes, I see the brush caps in the photo marked rear of motor 2.
> I don't see any brush caps on the front end of the motor.
> If it has external caps at the rear, I can't imagine it would have
> concealed caps on the front.
>
> > I cannot tell if there are brush holders at the
> > front, but the end bells look the same. Paralleling armature
> > windings that were not designed to be paralled could be a
> > problem, however armature windings in single commutator
> > motors run in parallel all the time because the brushes
> > make contact with multiple segments of the commutator at
> > once.
> >
> > If it is a wound field motor it should not run with
> > power on only one set of wires unless there are internal
> > connections putting the field across the armature. This
> > seems unlikely as field control would not be possible and
> > because the pictures of the open rear end bell do not seem
> > to show such connections.
>
> Ahhh, wait a minute! Dale said the motors would 'jump around'
> when he had it wired in one particular way. this could be a clue
> that that wiring is essentially differential compound. Anyway,
> these motors are most likely not meant for series field use.
>
> As I said before, there were motors made to use a PM field, but
> that the field could be reduced with a field winding for high speed
> operation.
>
> Jon
>
>