New friction drive concept...

[loquin]

There would be complexities when you want to change the gearing, though.

If you make the drive cog bigger, then

• the idler pulley would have to be smaller, so that the same number of teeth would be engaged by the belt, or
• the belt size would have to change, or,
• the idle pulley position would have to shift towards the drive cog.

Having a large adjustment on the idle pulley probably makes the most sense.

 

[augidog]

interesting concept, lou...i see possible trouble with maintaining constant equal pressure in the gap between rollers, i think it may turn out that the only working friction will be the two tangents of the rollers...however...imo that's not a bad thing: two rollers working in conjunction, tied by a belt. simple tensioning-adjustment allows for gear changes.

sketch this one out, a bit complicated but still simple: lay a vertical shaft engine on a triangular plate over the back wheel. two rollers (geared for opposing rotation, or one could simply be an idler for proper pressure) on each side of the tire. they wouldn't have to be knurled metal or treated surfaces, rc/car or small kart tires would work, i don't think there'd be any wet slippage problems with that. gear changes would easily happen at the clutch output.

anyways, that's just a crazy idea that's been in me brain for a while now...

 

[moondog]

We got a kit from Boygofast that had an 1 1/2 steel roller. It has grooves across but not knurled like the others.

It does real well in the rain. I think larger rollers work better but you need a big enough motor to turn it.

Gearing it down with sprockets would be a way to use a smaller motor with a larger roller. Deacon uses a scooter tire for his roller but it is geared down with sprockets.

Your two rollers could be just a few inches apart and both apply pressure to the tire and the belt would push against the tire.

Seems like this would be max friction drive traction.

I went to sleep thinking about this and woke up thinking about it !

 

[liscos439]

I've got a Sinclair Zeta that works like that.
It's a bit naff but I think it's because of the weedy motor rather than the belt.
Oh, and the side of the belt that touches the tyre is smooth.
I can't say how good the grip is in the wet because there's not a lot protecting the motor from the elements.

 

[augidog]

http://www.gotwind.org/diy/solar_electric_bicycle_project.htm

 

[motorbikemike45]

Rats, we will have to get permission from Sir Clive Sinclair to use his patented belt drive.

 

[loquin]

If it were patented in the U.S., you would if you were building them for sale. Now, if the patent has expired, anyone could make them. Sinclair's Zetas were manufactured beginning 12-13 years ago, and it probably took several years from issuance of patent until manufacturing began. In the U.S., there's a 17 year life on patents, so, in all probability, either the patent has expired, or, it is due to expire shortly.

I had no idea that anyone else had come up with something similar, though. Hats off to Sir Clive.

 

[moondog]

Yes, thanks for showing that ! I am learning about friction drive.

Like it a lot.

A friction drive section would be nice. Is there one anywhere else ?

I am looking for a small lathe to make parts for friction drive tests.

great thread here. http://motoredbikes.com/showthread.php?t=15845

 

[Tinker1980]

interesting concept, lou...i see possible trouble with maintaining constant equal pressure in the gap between rollers, i think it may turn out that the only working friction will be the two tangents of the rollers...however...imo that's not a bad thing: two rollers working in conjunction, tied by a belt. simple tensioning-adjustment allows for gear changes.

sketch this one out, a bit complicated but still simple: lay a vertical shaft engine on a triangular plate over the back wheel. two rollers (geared for opposing rotation, or one could simply be an idler for proper pressure) on each side of the tire. they wouldn't have to be knurled metal or treated surfaces, rc/car or small kart tires would work, i don't think there'd be any wet slippage problems with that. gear changes would easily happen at the clutch output.

anyways, that's just a crazy idea that's been in me brain for a while now...

Not too crazy an idea. It's been done. Have a look. I'm nearly done building such a creation myself, I'll post pictures when it's done IF I can avoid getting flak about a couple of amatuer-ish welds

-Mark

 

[loquin]

The problem with the vertical drive roller is this: The roller makes contact with a chunk of the tire rubber, vertically. The distance from the axle to the top of the contact area (call this diameter d1) is greater than the distance from the axle to the bottom of the contact area (call this diameter d2).

So, as the wheel rotates, the distance 'traveled' by d1 with every tire rotation is greater than that 'traveled' by d2. Let's suppose that this drive roller is 1 inch high, and, with a 26 inch wheel, d1 could be 12.5 inches, and d2 could be 11.5 inches. This means that d1 is 8.7 percent larger than d2, and the tire sidewalls will be generating friction and heat at the sidewalls at the top and bottom of the drive roller, and the captive roller.

Sidewalls are thinner than the face of the tire, so, it won't take as long for the friction (and scuffing) to cause problems. (sidewall blowouts, anyone?)