Make:

Posted by: Chris W on October 7, 2009 at 3:50 AM

Would a motorcycle or car alternator be too big? They have heavy duty brushes for the field, and mounting surfaces.

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How about using ballraces? - one for each conductor. This is what the electric 'Round the pole' flyers use.

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Might want to check out this old Make article:
http://blog.makezine.com/archive/2006/06/how_to_make_a_slip_ring_p.html

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Posted by: anachrocomputer on October 7, 2009 at 5:56 AM

To give a good answer to this question, we really need to know more about the application. First of all, how many volts will be across the joint? 12V DC and 240V AC solutions would be quite different. How much current must the joint carry? How fast must it rotate? And how much friction is tolerable?

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Something I have have done is to use the bearing(s) and a slipring for power, then LEDs and photodiodes for signal. A low cost AVR or PIC can decode / encode the data signals over the optical links (one in each direction).

To insure smooth power for the electronics in the rotating section, I used an electrolytic capacitor across the power feed.

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For supplying 12V power to my R2-D2 droid domes that rotate(make issue #2) I used a 1/4" stereo headphone jack and plug. I mounted the jack in the top center of the body, and the plug is on a rigid coax that is mounted to do a gentle arc from inside the dome to the plug. The beauty is that because of the curve of the rigid coax, the two did not need to be mounted dead center, or even near center. The trick is to use the tip and mid section of the plug/jack, NOT the shield as that gives intermittant contact when rotating. Also, switch off power when plugging/unplugging it or for a split second the tip will short out the tip and midsection spring contacts. I ran up to 5 amps for 10 minutes through mine once I 'broke it in' as a test and it never even got warm.

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Posted by: Aud1073cH on October 7, 2009 at 8:45 AM

A common use of rotary transformers is VCR head drums.
Old VCRs are cheap at second hand stores, or free if you find one being thrown away.

http://en.wikipedia.org/wiki/Rotary_transformer

The motors are usually 2 or 3 phase brushless, and the controllers sometimes on the motor PCB, or nearby. You may also be able to attach a microcontroller to do the job.

Don't forget to save the other parts, like tape drive motor, rollers, optical sensors, etc.

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Someday I want to have a project with the $'s behind it to use something from these guys:
http://www.meridianlab.com/index.html

nanoamperes through 1000's of amps and Any Voltage
(Depending on the model)

Ah....someday.....

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If you just needed power and you had access to both ends of the shaft you could use a second DC motor as a generator. Spin the body with the first motor and lock the shaft on the other end.

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When I say I 'broke-in' the large 1/4" stereo headphone jack/plug, I sat watching TV for awhile holding the spring loaded tension parts tight against the inserted plug and twisted the plug back and forth. This made the actual contact points conform to a larger surface rather than a pin-point. I ran a 100W razor scooter motor through the plug as a test. Occasionally I bogged down on the wheel to put a load on it. Now I was certain it was good for dome lighting & electronics. I put a thin dab of dialectric grease on it, and after many outings at conventions and museum tech nights, it looks the same as day one. Not wearing out one bit. My dome motor spins the dome uber fast too. People think it's going to spin right off the droid it's so fast.

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Carl Pisaturo has a nice tutorial on how he makes slip rings for high-speed applications. He uses epoxy and turns the whole assembly in a lathe.
http://www.carlpisaturo.com/_ElNo_SLIP.html

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