Re: [CAD_CAM_EDM_DRO] PM DC Motors

Doug Harrison wrote:

> I have acquired several PMDC motors that were take-outs from upgraded
> equipment. These are 90V NEMA 56C frame and are rated at 1/2, 3/4 and 1HP.
> The rear shaft has a fan and could be adapted for an encoder. Other than
> high rotor inertia and a lot of bulk, is there any reason these could not be
> used for servo motors?

Maybe. If the motors have much cogging due to fluctuations in the amount
of iron in the field flux (design of field pole and rotor laminations control this)
or fluctuations in the number of armature turns in the field flux (design of
the winding pattern affects this) then they won't run as smooth as a motor
designed for low-speed servo applications. They will still work, though.

> My concern is the limit of overcurrent the motors will tolerate without
> going poof or sucking the life out of the magnets. The high inertia can be
> partially overcome with 1:1 drive but can a motor designed for more-or-less
> continuous loads withstand the continuous load reversals of a servo system?

Those are BIG motors for machine tool positioning. The larger ones might
be used for spindle drives. I'm using motors rated at 1/8 Hp continuous
on my Bridgeport, and I get (by calculation) 1000 Lbs of linear force at
the max current. That comes out to about 1/2 Hp PEAK on those motors.
But, if you have them, they should work.

Jon