seeking slip(ring)age

I was told this might be a good place to ask.
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.
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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? --------------------------- "Hactar" wrote in message I was told this might be a good place to ask.
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.
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Josepi <After a 1 year Usenet restriction resulting from a criminal charge a troll, blaming me attempts to incite group harrassment abuse snipped-for-privacy@ocn.ad.jp Spends $100s monthly on accounts just to troll> wrote:

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.
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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?
-----------------
"Hactar" wrote in message 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.
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Josepi <After a 1 year Usenet restriction resulting from a criminal charge a troll, blaming me attempts to incite group harrassment abuse snipped-for-privacy@ocn.ad.jp Spends $100s monthly on accounts just to troll> wrote:

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.
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OK. I thought you posted a "commutator". This is a switching device. "Slipring" would be more appropriate.
The generation would have to be switched on when going downhill and the little bit of energy for a few LEDs would never be noticed by the human but.....
I have misread your request and it looks like you just want a way to get power to lights on the wheels from batteries on the mainframe. My guess is the brushes on the sliprings would cause more friction than a magnetic induction system to flash and flicker the LEDS, depending how many, of course...LOL
A few magnets on the chair, coils, diodes, capacitors and LEDs on the wheels and you would have it...wired for sound! Ohh yeah, you mentioned about them not lighting unless you move so I guess that is out.
--------------------
"Hactar" wrote in message 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.
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Josepi wrote:

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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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 http://cgi.ebay.com/220778507771 but I couldn't find a way to use it without the cord getting wrapped around the axle.
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Hactar wrote:

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.
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Good idea. That would make the commutator rather less complex. I would need a voltage converter and capacitor (to smooth out noisy conduction) on each wheel though. Hmm, I wonder if I'd need a contact on the inner end of the axle, or if using the chair frame is good enough. Multimeter to the rescue!

Yeah, but I have to consider the chance of it catching on other stuff when the wheel's removed (eg when it's put into some car trunks). That restricts me to things that are either springy (so they snap into the correct position) or really sturdy.
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Hactar wrote:
(...)

Bad idea. Current flow through wheel bearings = unreliable bearings.
Suggest that you mine 'inductive coupling' ideas from a worn-out Phillips Sonicare ultrasonic toothbrush.
Sorta like: <http://www.instructables.com/files/orig/FK9/HKLG/FAQDX9YM/FK9HKLGFAQDX9YM.pdf
--Winston
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Winston wrote:

Ignoring all the battery charge feedback stuff, that's essentially my rotary transformer suggestion.
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I think people did not understand your device mentioned. I have never heard of that.
More info?
-------------------
"Pete C." wrote in message
Ignoring all the battery charge feedback stuff, that's essentially my rotary transformer suggestion.
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Pete C. wrote:

Yes, both would be rotary transformers. I think the phrase was too 'scary', though we both know it is the right approach.
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On May 5, 9:57pm, snipped-for-privacy@verizon.net (Hactar) wrote:

Could you just put flashing lights on the frame in line with reflectors on the spokes?
jsw
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This is the look I'm going for:
http://royalty.mine.nu:81/decorations-2010.jpg
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Hactar wrote:

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.
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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.
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Hactar wrote:

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.
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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?
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