friction material

I'm thinking of friction drive for my next electrically assisted bicycle by means of a roller driving the tyre. It used to be common practice to make
such a roller of carberundum material, in fact they were probably small grinding wheels. Does anyone know of any better material? I wonder if any more modern material, plastics for example, would have a higher coefficient of friction against rubber bicycle tyres. Power transmitted is in the order of 500W. Jim Lugsden.
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James Lugsden wrote:

Did you ever drive a Solex mofa in the rain or -even worse- through mud?

The Solex used some porcellane (SP?).

A chain! You get them in bicycle-shops. :-)
Nick
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Nick Mueller wrote:

I'm not wishing to spoil anyone's fun here, but I think Nick is right. The chain is used because it's the best all round solution.
Best wishes,
Chris
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bicycle by

to make

small
wonder if

transmitted is

Jim,
How about turning the profile you want out of steel, epoxy coating it, and dusting with the abrasive powder of your choice. This has the advantage that the shape is more under your control, and when wear develops you can strip the epoxy with a bit of heat, and start over again.
Have you considered increasing your surface contact area by driving an abrasive belt on two rollers ?
AWEM
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On Tue, 16 Jan 2007 14:39:52 -0000, "Andrew Mawson"

Just another idea, you could make it of steel and get it 'metal sprayed' with a powder containing tungsten carbide. I have such a powder, I've never tried it though the particles must be pretty small to go through the gun and so might be too fine. I would think that if it worked, it would last a very long time.
Cheers Tim Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service
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On Tue, 16 Jan 2007 14:39:52 -0000, "Andrew Mawson"

Of course, if you were able to machine a roller so that it perfectly mated with the tread pattern there wouldn't be any slippage...
Regards, Tony
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That was quick Chaps! All ideas worth a try. I like using the tire as a rubber gear but I don't think I could make it work with the small roller giving the correct gear ratio. Epoxy and abrasive powder has been done and works but with a limited life. I think the tungsten carbide is worth a try. I'd like to increase the area with a belt but the main reason I'm considering friction drive is to use a multi diameter roller to give me a simple gear change mechanism . Thanks Everyone, Jim
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On Tue, 16 Jan 2007 14:56:48 +0000, Tony Jeffree wrote:

The problem that was found in the late 40's was tyre wear. My father had an attachment that contained a 20+ cc 2stroke engine that drove a ribbed roller bearing onto the rear tyre and was rubbish.
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Neil
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I was going to suggest something like a very coarse knurled steel roller. The load will need to be high enough not to get "wheel-spin", if you see what I mean. There will still be some wear because the tyre will be stretched different amounts at different points on the contact, so there will be some relative slip between the tyre and the roller. For "novel" applications where you can't compare with something very similar, the uncertainty in any wear estimate is going to be large. My first guess would be that it could reduce tyre life by a factor ~ 10 on the grounds that perhaps 10x as much power will be dissipated at the roller contact than between the tyre and the road.
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I like that idea : how about using a toothed belt to engage the motor and running a long length of the untoothed side against the tyre ? Not necessarily abrasive : just a rubber surface, perhaps roughened with rubber compound. The lower abrasion amd longer contact area would help avoid the tyre wear another poster warned about. I don't think the teeth would last long if you used them as a friction surface.
Changing gear is more tricky than with a stepped roller, but you could do two gears (might be enough, for electric drive) by using a tumbler action to offer a choice of pinions to the belt (the swapping mechanism could also provide belt tension).
On a completely different tack, how about a wood burr with the sharp edges dulled ? A cone-shaped one might even allow continous gear ratios, like a Daf transmission.
-adrian
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On Tue, 16 Jan 2007 14:04:31 -0000, "James Lugsden"

Doesn't sound like the battery will last very long between charges...
Regards, Tony
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wrote:

charges...
Have you never seen a tethered electric bicycle going in circles round an electric lamp post <G>
I would imagine Jim is talking peak power, Tony
AWEM
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Andrew Mawson wrote:

Isn't that ever decreasing circles !!!
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On Tue, 16 Jan 2007 17:48:41 -0000, "Andrew Mawson"

Yep..I would hope so too ;-)
Clearly the answer is overhead power - try out my newly patented invention - the Trolley Bicycle.
Alternatively, attach a large array of solar cells - with the size of array you would need to drive that motor it would probably double as a usable sail, so you could carry panniers full of baked beans for that all-important turbo boost. How's that for a truly Green mode of transport? <G>
Regards, Tony
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wrote: (snip)>

.......yes, but think of the incalculable damage to the ozone layer !! --
Chris Edwards (in deepest Dorset) "....there *must* be an easier way!"
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James Lugsden wrote:

My personal preference is to improve the bicycle rather than add (heavy) electrical assistance.
BugBear
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I reckon an abrasive wheel will wear your tyre out too quickly. What about just using a steel roller but with plenty of pressure against the tyre? Or a roller with its own solid rubber tyre?
Scrim
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Scrim wrote:

... or a conical roller to give a continuously variable drive ratio, a la Daf??
Dave
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    The weakness of this whole concept is the problem of any source of applied friction drive operating against the (relatively) soft rubber tyre...could you not contrive something using the wheel rim, or a geared hub?
--
Chris Edwards (in deepest Dorset) "....there *must* be an easier way!"
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Chris Edwards, who mends Mustard writes.........

When bicycle-assisted motors were all the rage after WW2 one of the common forms of drive was a very simple lantern wheel. From memory about one and a half inches diameter, with about ten pins. This was pressed straight onto the tyre, a believe with a tension spring and was effective. 'Mini-motor' perhaps?
Mike
--
Mike Whittome - Frequently wrong; seldom without opinion!

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