seeking slip(ring)age

Is this a repair or a new creation you are experimenting with?

IOW: Is this an exact part that needs replacing?

To understand this better: are we to understand that the wheels on a wheelchair contain the bearings and the axle does not turn?

Could a ring of PM magnets be installed installed inside the wheels and a series of pickup be mounted on the chair to avoid moving contacts, like commutators?

I'm looking for a slipring or commutator to go around the axle to my wheelchair wheels. The catches are, it needs a 1" center hole (to go around the axle nut), nothing can break if the wheel's removed (that's easy, just push a button) and the body's put in a car trunk, and it only has about 10mm clearance axially. On the plus side, it only needs to carry a hundred mA, its radial clearance is something close to two feet, and my maximum speed is around 75 RPM. Four conductors would be nice, but I can live with two. Does such a thing exist for a reasonable amount of money, perhaps in the model-making or robotics communities?

I have an idea about making one (per side) out of a CD-R, some alternator brushes, and some sheet metal, if a pre-made one can't be found. I figure I'll put the CD part on the wheel, to keep its angular momentum down.

New. See, I have lights on my wheels, two strings each. That's four miniature slide switches and four battery packs, one of each for each string. It's a real pain to turn them all on, and AAs last a long time when they're only driving LEDs but not indefinitely. One master 6V battery and one master switch would be much more convenient. I figure a flashlight carcass will fit the bill.

There's not really a bearing, just a greased axle maybe 4" long protruding from the center of each wheel that locks into a hole on the frame. Push the release button in the wheel hub, and a ball on the side of the axle retracts, allowing the wheel to be removed. The axle-holes are angled a few degrees, so the track is wider than the top of the wheels.

PM? That sounds like a moving-magnet generator to me, which might have problems if I stop, which I might do for an hour or two.

PM = permanent magnet.

I guess your motives are unclear then. I understand you want to generate electrical energy form a mechanism installed on your whel chair wheels. A generator would be the only way to do this whatever the mechanism.

Is my logic too far off?

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I'm afraid you won't find much for off the shelf slip ring assemblies, and what there are will be $$$$. Give the small amount of power you need to transmit, I'd consider using a rotary transformer coupling to transmit the power as AC instead of DC.

Indeed, sorry if I was unclear. A generator would make it too hard to push (OK, harder than it is now), and wouldn't work at all without constant energy input. Right now each string is independently powered and switched, by a wheel-mounted battery pack. I aim to have one centralized battery (+ voltage conversion if necessary) and one switch. That's where the slipring comes in.

Yes , he wants to supply power two strings of LEDs that he has mounted on his wheels . Though I don't understand why he wants two separate power feeds, unless he has them strobing or flashing independently of each other . Hactar , you're on the right track with the CD/plastic disc idea . I suggest the static component could be something similar to the power pickup brushes used on slot cars . Simple and robust , with mimimal protrusion that can be damaged when the wheels are off the chair .

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What's a rotary transformer? I really need to minimize the "on wheel" weight; it's especially important not to cause a torque in the wheel.

On 5/5/2011 11:30 AM, Hactar wrote: The catches are, it needs a 1" center hole (to go

The most common slipring assembly is the slipring on the steering column of an auto for the horn. Perhaps two different size diameters can be found.

Kevin Gallimore

I don't. I'll remove each string's separate battery pack, and connect it to the system power.

That's a biggie, since for some people the only way to fit my chair in the trunk is to take off the wheels, and there can be no poky-out bits that'll get snagged on something. I'll have to think carefully to come up with something that'll work, is fairly flush when the wheels are removed, and there's nothing extra to do when taking off the wheels since I won't be the one doing it.

I was thinking about using a phone cord anti-twist thingy like

They use clocksprings these days, not continuous rotation compatible.

Basically just two coils of magnet wire, concentric with the rotary axis, one mounted on the rotating part (wheel) and one on the fixed part (chair/axle), AC voltage applied to one is coupled to the other with the rotation of the moving part having essentially no effect on the coupling. Also has the advantage of being non-contact and non-wear.

They were used in VCRs to transfer the RF between the rotating heads and the electronics.

Seems to me everybody is making this way more difficult than it needs to be . A plastic disc with two rings of thin brass glued to it , holes thru to solder a wire to the back side of the rings . Mount 'em on the wheel , use a pair of slot car type brushes mounted to the frame of the chair to feed the power to the rings . Done deal , and if he wants 4 rings instead of two , that just ain't that much harder. Fer cryin' out loud , I could whip this up outta scraps I have layin' around in an afternoon !!

That sounds like it would work, if it were thin enough. I'd need a rectifier/capacitor and voltage converter on each wheel, and an inverter on the body. Where do I find one, or is it something I make?

You could use the axle for one conductor, and only need a single slip ring. Even better would be a flat disk for the other conductor, and a small carbon brush like those in electric power tools or a cordless drill for the other contact. They are spring loaded, so you could put a thin insulator on the inside of the wheel, then a copper or brass disk. That way the brush would face straight out and in parallel with the axle. This will make it easy to keep it aligned.

Printed circuit board material might be a better approach to the plastic and metal - it's already well-glued.

Something like bullet catches (spring-loaded metallic, robust) might make a less fiddly connection than the slot car type springs (are we all revealing our age by even knowing what those are, or are they still around these days?) Probably want a capacitor on (in) each wheel to make up for momentary glitches owing to lack of perfection. Also want something to cut the contacts off from power before it's taken apart and loaded in a car trunk. Carbon brushes would work better when assembled, but are not very rugged apart.

Hactar expressed precisely :

Many childrens scooters come with flashing lights in the small wheels.

Some of those things (in wheels, shoes, bouncy balls) use a light spring where vibration or centrifugal force causes it to contact a terminal wire etc etc.

You'd have to build it. Also, you wouldn't be running 120V 60Hz AC to it, you'd be using something like 12V AC and probably a few KHz frequency. This is similar to the setup used for waterproof non contact charging stations as seen on some electric shavers.