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In a vacuum chamber how would one transfer mechanical power (either rotation or linear) from inside to the external environment?

I'm working on an idea for a new/different type of motor that would require an evacuated internal atmosphere and am wondering how to transfer the generated motion outside the case.

I have thought about using rotating magnetic coupling on either side of a thinned wall section but don't think it would scale well for larger versions of the motor (perhaps powering a bike or car). I expect with a high enough budget (which I don't have) that an extremely high-tolerance mechanical seal could be machined but am wondering if there are any solutions that could sidestep the high tolerances by thinking laterally.

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    $\begingroup$ You might have a look at how modern ships and submarines seal the prop shafts. $\endgroup$
    – dmckee --- ex-moderator kitten
    Commented Jun 8, 2014 at 16:35
  • $\begingroup$ thanks @dmckee - that's the type of lateral thinking I was hoping for! $\endgroup$
    – user263399
    Commented Jun 8, 2014 at 16:37
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    $\begingroup$ all information on prop shafts I found sofar points to high tolerances, lots of grease, and a pump for the water that gets through [according to wikipedia Australian Collins-class submarine design allows for 10 litres per hour through the seal on a good day - although during test dives at one point there was 1000 litres per minute!] $\endgroup$
    – user263399
    Commented Jun 8, 2014 at 17:02
  • $\begingroup$ Yes, and that basic system has been in use for about 150 years. There is a tradeoff between spinning resistance and leak rate. The total leak rate also depends on both the raw size of the system and the pressure difference. Submarines have to deal with much higher pressure differences than you care about. $\endgroup$
    – dmckee --- ex-moderator kitten
    Commented Jun 8, 2014 at 17:19
  • $\begingroup$ Wondering if NASA ever had any mechanical coupling between inside and outside on any of there craft. Maybe a parascope on one of there old looner modules :) $\endgroup$
    – user263399
    Commented Jun 8, 2014 at 19:38

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Second answer, what about the phenomenon of “Quantum Locking”? Right now it is being used to levitate superconductors over magnets, but I am sure you could exploit the phenomenon to transmit torque. Plus, you can put the superconductor on the vacuum side of the seal to keep it cold.

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  • $\begingroup$ Not sure how much torque it would be able to transfer but +1 just because that's the first time I had heard of quantum locking and all the youtube footage is kinda jaw dropping. $\endgroup$
    – user263399
    Commented Jul 17, 2014 at 21:17
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One standard way is a rotary fitting using a ferrofluidic seal. These are fairly standard parts in your favorite vacuum components catalog. Often used in semiconductor processing equipment.

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Might be overly complicated, but...

Put electrical generator inside vacuum chamber and drive it with the internal mechanical power; pass electric current through conducting patches in chamber wall; use current directly to drive motors in wheels of bike/car...

Cooling the generator could be a problem...

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  • $\begingroup$ I'm allready drawing in energy to create the motion inside the chamber so conversion losses would then kill any benefit of my motors design unfortunately - working on this design for power efficiency $\endgroup$
    – user263399
    Commented Jun 8, 2014 at 19:32
  • $\begingroup$ As the cooling is a problem he could use iron-only rotor reluctance machines. The largest part of the heating happens on the outside in that case. Only eddy current losses in the rotor would heat the interior. The problem with such an approach is that you need special alloys for use in vacuum. You will probalbly need to use a non-sheeted rotor. Yeah it is complicated and expensive, but worth thinking about. $\endgroup$
    – WalyKu
    Commented Jun 9, 2014 at 14:24
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If you attach the motor so that it rotates the casing, then you can simply mechanically attach the casing to whatever it is that needs to be driven. Not sure how you would implement this, but it is a rather lateral solution, if I do say so myself.

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  • $\begingroup$ Except that now you either can't hold the thing in the center in place or you still need to build a pass-through bearing of some kind to do it. And any cables and tubes have to be taken care of---that's a solvable problem but an unnecessary complication. $\endgroup$
    – dmckee --- ex-moderator kitten
    Commented Jun 9, 2014 at 2:26
  • $\begingroup$ Right...I never said it was easy (or even possible), I just wanted to throw a lateral answer out there. $\endgroup$
    – Dave Coffman
    Commented Jun 9, 2014 at 20:08
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Take a look at the torque converters of cars with automatic transmissions. They are rotational couplings where the working fluid is completely sealed from both the source and sink environments, so one of those could be vacuum. One shell of the device rotates inside the other, to the outer one could be stationary and form an integral (welded) part of the wall of the vessel which contains your power-producing device. The rotating seal has to keep the converter fluid at bay against ambient pressure, not total vacuum.

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  • $\begingroup$ Of course, there could be leakage around the shaft, so that may not work after all... $\endgroup$
    – Bryson S.
    Commented Jul 16, 2014 at 17:42

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