need advice on a friction-drive project



Sometime within the next few weeks (fingers crossed) I'm going to finally begin cutting metal for my setup. I was donated the engine and clutch (thanks, Pat) and I'm almost done with the tooling I know I'm going to need. So, the first part:

I'm going to need chain and sprockets as part of this friction drive setup (large *pair* of rollers needing to be coupled together, plus about a 2.25 to 1 reduction to get the desired cruising speed range of 10-13 mph (breakin period) to 12-15 mph afterward. The question is this:

Does anyone have experience with the 'heavy' #25 chain?

Thanks in advance.


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I used #25 chain on my electric and gas scooters but I gotta tell ya, It's not that heavy!
I don't quite understand the set-up you are using. Since it is going to be " friction drive ", why do you need chain, sprockets, etc.???
explanation as to the need of chain

1) firstly, there are two rollers on a pivoting arm underneath the mounting plate - the rollers being coupled fore-and-aft. Neither roller is directly attached to the clutch.
1A) Why two rollers? First, the contact area for friction is doubled. Secondly, the first roller should - in theory - deal with the bulk of the dampness on the tire, should it be present.
2) Secondly, the rollers are a bit large for 'direct drive' at the mentioned speeds. Were I to attempt that, they would need to be perhaps five eighths of an inch in diameter - which means the rollers tend to abrade the tire a great deal. Within reason, you want the largest possible roller to be in contact with the tire, as then the friction area is larger (and the roller is less likely to slip)
3) With direct-off-the-clutch drive, the engine is offset markedly. I want a centered engine (easier to put under cover, easier to balance, looks neater(!)), which means I need a compact and efficient means of coupling the clutch output shaft to first the central sprocket on the 'down arm', then the two rollers together.
The whole appears to be 'overly complex', 'heavy', and generally troublesome, but I have decent answers to all three of those issues.
The answer I do not have is 'how strong is the 'heavy' #25 chain? I've investigated #35, which is close to the strength of #415 with usefully smaller dimensions, but #25 really has its attractions, chiefly with the smaller diameter on the sprockets.

Thanks in advance.
I've also thought that you could come up with a "two speed" friction drive, with 2 differently sized rollers mounted on a "rocker arm" arrangement. Rock the arm forward for one size and back for the other, with neutral in the center...

What roller material are you using?
OK, I see, now. I like to keep things as simple as possible. So, direct drive friction roller with a clutch, is what I have always used. Also, I believe too much power is lost with the extra " pivots" of jackshafts, etc. BUT, I do like the idea of the motor centered over the rear wheel !!


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Each too his own but it sounds like you're making this very complicated. First, a good roller won't slip on dry pavement, but it will slip on even a damp tire. I don't believe your first roller will dry the tire enough to stop slippage on the second. Two rollers should give more traction than one but with all this, why not go chain all the way? You can get a 3 to 1 gear box with a clutch pretty cheap and with the jack shaft, the rest of the reduction would be simple.
further explanation

1) based on what information I could find, there are two grades of #25 chain. The regular stuff - no dice. The #25H chain, however, is significantly stronger. (thicker side-plates, mostly.)
1B) I anticipate regular chain replacement (same as on motorcycles and what I'm currently riding... Speaking of which, it's about due for a Preventative Chain Replacement.
2) I recall reading somewhere that all design is a tradeoff, and that in response to certain needs. I need something that A) is easy to maintain; B) is readily removed and replaced, while being hard to *steal*; C) does not attract undue attention from
neighbors and police. D) is *reliable*. E) Does not add much weight to the bike.

Why the above? Firstly, I need to keep the bike in an apartment - a second story appartment, one where I need to lug the thing up a longish flight of stairs. I do not have anywhere safe on the ground floor - such as a garage - where I could lock things up. Secondly, I want the option of riding the bike without the power-pack's presence (and I want to keep it on the balcony when it's not attached so I don't have to worry about complaints and possible fires.) Thirdly, that part about
'reliable' is based on a *lot* of hard experience. For me, 'simple' has too often meant 'a marginally-functional jury-rigged mess that gives little satisfaction and a vast number of regrets and headaches'. I suspect more than a little that it has to do with the way my mind works, e.g. I've had decent luck with carburetor overhaul, while a number of people I've known won't touch them.

I'm getting so I can no longer endure the crowding and noise of the bus.

In regard to the roller material: that will most likely be a 'hard' grade of aluminum with slots, as per the drawing supplied.


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prism, the only caution I might have is with the concave surface of the roller you show in the sketch. I think it will cause excessive wear toward the sides of the tires.

Since the linear velocity of a rotating wheel is directly proportional to diameter, and the outer parts of this roller are a larger diameter than the center, the outside will therefore has a higher linear velocity than the center of the roller.

Plus, if it DOES make contact on most of its surface, it will be trying to move the bike faster on the outside part of the tire, which, being a smaller diameter than the center, would normally be moving at a little slower linear velocity, which will worsen the effect slightly...

Even without the effect of the smaller tire diameter at the outside, at 5000 RPM, the center of the wheel will pushing the bike along at 23.04 MPH, while the edge, if in contact with the tire, will be TRYING to push the bike at 26.02 MPH. That 3 MPH speed difference will increase heat and wear on the tire...

Sorry to shoot down what looked like a promising idea.
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curved roller vs flat...

I could just as easily 'delete' the curved portion and make the roller
flat (which is what I had orignally intended to do.) However, someone mentioned the idea of a 'form-fitting' roller, and while I had thought of the matter (including the part you mentioned about unequal speeds tending to abrade the tire) I was - and am - willing to try it.

A flat roller's easier to machine, though, and would only need tooling I more or less already have.

Thanks for the suggestion.