Motor with 2 independent co-axial shafts?

[rivershack]

I'm find myself in need of a motor with 2 independent co-axial shafts.

The "outside" or "surrounding" shaft/cylinder must run at 500 RPM and the "inside" must be capable of turning at 225 RPM faster or slower than the "outside" shaft. The majority of the time this inside shaft will run at the same speed as the outer, but at the beginning and end of it's duty cycle it must be able to deliver the differential motion described. The torque here is negligible.

I would be grateful if someone could tell me if such an animal exists, as I'm a ways out of my field here.

 

[jraef]

By the time someone designed and built a custom motor with custom windings to operate as you describe, I'd imagine it would cost you more than you would be willing to spend.

Better to just use 2 motors, one with a hollow shaft like a pump motor and one with a solid shaft small enough to fit inside. Mount the solid shaft motor behind the hollow shaft and run it through. Control speed on the solid shaft motor with a VFD.

I think the hollow shaft motor will still be a special, but only for the shaft, not the windings. That would make it much more attractive for a motor shop. Shaft support, legnth, torsional problems etc. would all need to be overcome, but they are simple mechanical issues. The electrical problems in having 2 independent windings within the same frame and the interrelated effects on each other would be a serious problem to overcome. Subvert the dominant paradigm... Think first, then act!

 

[BJC]

Try looking up Holec on google or Hytec power protection.
@

http://www.hitecups.com/ups/

May not answer your question but may be interesting. Holec is an old Dutch designed system that uses a generator with concentric windings, a magnetic clutch and a BIG diesel generator. I cna't explain them here but one of the websites will give you something to study.
Basically one of the windings ( field winding ) turns at twice syschronus speed and if outside power is interrupted it connects the generator up to the rotating stator, As the rotating stator slows down to generator speed the generator speed. see I told you I couldn't explain it. They do work however up to 1600 KW - very noisy and very expensive. You ahve to be the goverment or Intel or someone like that to afford one( or two or three).

 

[jbartos]

Suggestion: It appears that such electrical motor drive will have to be custom built. Perhaps, one could have the shaft of one motor accommodating inside a shaft of the other motor, both being aligned as a tandem motor set.