Running a motor in a vacuum

Not for more than a few moments. There are special motors designed for running in a vacuum. They are usually used on satellites. They ARE expensive. The last one I encountered cost $80,000.00

Bearings are a problem, and heat is removed by conduction.

A permanant magnet DC brushless motor should survive if you can conduct enough heat away through the case and it's mounting.

You might have problems with the oil in the bearings though. Might boils off and become thick.

Cooling is a big problem, you need some hefty heatsinks. NASA have used some largely unmodified Maxon precious metal brushed motors on Mars (Spirit, Opportunity and Sojourner). It's not a vacuum, but it is very low pressure (~10 millibars). There are a few mentions in some NASA papers and on the Maxon site, dig around a bit. You might want to find out what motors NASA used on its space probes (particularly the "cheap" Discovery missions).

Tim

Air is not great as a thermal conductor. A motor can be run in a vacuum by providing a thermal circuit. Copper is an excellent choice as are other metals and liquids.

Would the motor idle in a vacuum? Yes.

Would you have to derate the hp of the motor? Yes.

Would you have to be concerned about lubricants outgassing away? Yes.

If the motor was DC with brushes and commutator, I think you need to use special brushes. I seem to remember the military having problems with generators wearing out the brushes at high altitudes.

The motor in a turbomolecular vacuum pump runs continuously in a vacuum.

As long as the motor can be properly cooled in a vacuum, there is no reason that it should have a problem. I would guess that a large type of heatsink would be the way to go. Normally the air surrounding the motor, and also having some air turbulence generated by the armature all contribute to cooling it down in some way.

The other problem is that if lubricants are required, in a high vacuum many of them would boil down and become thickened, unless they are of a special type for operation in a vacuum environment. Thickened lubricant would cause greater resistance for movement.

I know that the motors used in the aerospace industry are extremely expensive. But, these are made to also be very reliable under very stressful conditions.