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  #1  
Old 09-26-2016, 10:06 AM
TheNecromancer13 TheNecromancer13 is offline
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Default Theoretical way to make a cheap 79cc friction drive.

So I haven't actually tried this, but the idea popped into my head and it's too simple to not throw out there. You could take a 79cc predator, or any similar or larger 4 stroke, and a centrifugal clutch like a max torque, and use the outside of the centrifugal clutch as the roller to drive the wheel. You might have to grind some grooves in the outside of the clutch to help it grip the wheel. I would think that since the clutch is like 3 or 4 inches in diameter, the gear ratio would be pretty much perfect for a 79cc if you used something larger than a 26" tire. 26" would probably be pushing it though. You could probably build this friction drive easily for under $200 (not including a bike). Thoughts?
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Old 09-26-2016, 12:37 PM
Slogger Slogger is offline
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Default Re: Theoretical way to make a cheap 79cc friction drive.

A 3 1/2" clutch housing would get you about 42 mph at 4000 rpm if the bearings can take the stress and you can get traction on the tire. You'd probably want something bigger than the 79cc to go fast.
A small clutch that could handle 3 to 5 hp and it might be doable.
It definitely obeys the KISS principle, keeping it simple.
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Last edited by Slogger; 09-26-2016 at 12:43 PM.
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Old 09-29-2016, 02:52 AM
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Springfieldscooter Springfieldscooter is offline
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Default Re: Theoretical way to make a cheap 79cc friction drive.

Ive never thought about it but it seems feasible!
And like Slogger said....Simple enough!
But then again, with the addition of a chain and sprocket, you would eliminate all the drawbacks of a friction drive.
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Old 09-29-2016, 09:45 AM
TheNecromancer13 TheNecromancer13 is offline
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Default Re: Theoretical way to make a cheap 79cc friction drive.

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Originally Posted by Springfieldscooter View Post
Ive never thought about it but it seems feasible!
And like Slogger said....Simple enough!
But then again, with the addition of a chain and sprocket, you would eliminate all the drawbacks of a friction drive.
Yes, but you'd also add a few hundred dollars to the cost.
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Old 09-30-2016, 05:48 PM
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racie35 racie35 is offline
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Default Re: Theoretical way to make a cheap 79cc friction drive.

I think the bushing or bearing in the clutch...without support from the outside..might say bye bye. Then again, it might work!
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Old 10-01-2016, 06:41 AM
curtisfox curtisfox is online now
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Default Re: Theoretical way to make a cheap 79cc friction drive.

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Originally Posted by racie35 View Post
I think the bushing or bearing in the clutch...without support from the outside..might say bye bye. Then again, it might work!
I think you are right ,as I have a old KS bike machine motor from the 50's. It has a clutch, but has a shaft hooked to the end with bearings on both ends off the shaft..............Curt
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Old 10-01-2016, 04:26 PM
Slogger Slogger is offline
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Default Re: Theoretical way to make a cheap 79cc friction drive.

The stress on the output shaft and the clutch bearings would be increased, that's why I mentioned it up above there. The bearing is designed for the torque load from the chain, then you add the force to get good traction on the tire and you have a load on it from two directions.
If that traction could be gained with a minimum of force on the tire, it might hold up ok, who knows? Some sort of gnurled surface or a rubber sheath with knobby bumps maybe.

What about a toothed belt turned inside out and glued on to the clutch bell...
(you'd need some darned good glue.)
If it works even temporarily some clutch company would make a good one sooner or later.
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Last edited by Slogger; 10-01-2016 at 04:30 PM.
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Old 11-08-2016, 01:14 PM
DRATS DRATS is offline
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Default Re: Theoretical way to make a cheap 79cc friction drive.

I will let you know if it works out. I had the same idea. Right now i am using a v-belt pulley filled with jb-weld. The pulley is a 3 inch diameter. It is about 10 inches when measured around the perimeter.

With the 3 inch wheel it cruises at 31.3 mph. It doesn't go any faster than that.
I have been using the brakes to stop and I feel comfortable coming to a stop.
it goes up hills ok.

When i track down a large enough clutch I will throw it on and report.
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  #9  
Old 11-26-2016, 05:19 PM
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a_dam a_dam is offline
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Default Re: Theoretical way to make a cheap 79cc friction drive.

Sorry for bringing up old thread. Haven't been around much - just noticed it.

Slogger is right on his math. 4000 rpm with 3.5 in roller would give about 42mph. Sounds doable if the motor has the torque.

I just wanted to throw in these couple of pennies. Wheel size doesn't matter when dealing with friction drive. Your "gear ratio" is determined by roller diameter.

I wouldn't build a friction drive without a bearing on both sides of the shaft. But I've found that you really don't need a lot of pressure on the tire, even with my skinny 10-speed tires and little weed-wacker motors. A bigger motor/roller like you're suggesting would take even less pressure because of the bigger contact area.

Since TheNecromancer13 is talking about a Predator and centrifical clutch, this will be a homemade build. You won't be wasting chain-drive parts from a china girl kit.
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