2.4 HP Friction Drive

Discussion in 'Photos & Bicycle Builds' started by CoconutFriction, Aug 17, 2008.

  1. CoconutFriction

    CoconutFriction New Member

    Here's a shot of my 2.4hp / 81cc friction drive. It did about 45mph with bad low end tourque until I changed a sprocket. Now it jumps out of the gate at a red light and top speed is 30mph (I'm 190 lbs)

    Attached Files:

  2. levsmith

    levsmith Member

    looks good

    looks nice. do you have any pictures of the friction part?
  3. SirJakesus

    SirJakesus Guest

    That thing looks darn cool! Are you sure you're only pulling 2.4hp with an 81cc? I get 2.2 from my 43cc. Just sounds low is all. Nice ride.
  4. s_beaudry

    s_beaudry Member

    Very nice ride....

    That has to be the biggest friction drive engine I have seen on this site!
  5. That friction wheel looks like a rim with the tire taken out.
    That's awesome for you have more rolling surface that should equal less tire wear.
    What's up with all that down there?
    We need more pics dude!
    What's this sprocket?
    And man if that doesn't look like a B&S 3.5 hp engine.
    And you plated it!
    Last edited by a moderator: Aug 17, 2008
  6. Happy Valley

    Happy Valley Active Member

  7. CoconutFriction

    CoconutFriction New Member

    I'll post some more pictures soon, dealing with the whole hurricane/tropical storm fay thing today, that'll keep the ride in the garage for a few days. I have a centrifugal clutch chain driving a sprocket I welded on to a trailer tire rim. There's so much stuff down there, because I tried several different ways to make this work. I first tried a chain driven system, but had so much problems with the chain hopping off and mounting the sprocket to the spokes, etc, I got rid of that. So there was a lot of welding and cutting going on until I found a system that works, and this set up works awesome. The engine does look big, but the specs list it as a 2.4/81cc
  8. Mountainman

    Mountainman Active Member

    Nice looking MB - yes - I am still new - that engine looks big !! My little Subaru 35cc seems to be a lot smaller - would like some of that power you are talking about - but for now - staying under the Ca 2.0 hp law - legal issue.. Happy Riding from - Mountainman
  9. CoconutFriction

    CoconutFriction New Member

    More Pics, New Rack System, Check it out!

    I've been working on a rack system that fits any bike and is adjustable in all directions. The same rack with the friction drive system will be for an electric drive, 49cc or 81cc 4 cycle. The 81cc is mounted on it and works awesome. A couple hundred flawless miles so far. Any yes, it's a 2.4 hp 81cc engine on the bike.

    Attached Files:

  10. loquin

    loquin Active Member

    The only thing I would be concerned about is the concave roller. Yes, it gives you more surface contact with the tire. But, since the diameter of the rim is greater than the diameter of the center of the face, the linear speed (the speed which the roller is trying to push the bike) of the rim is correspondingly higher than the linear speed of the center of the face.

    In one revolution of the roller, the rim, with its larger diameter, moves farther than the center of the roller. But, the rubber of the tire cannot move farther on it's edge than at the center of the tire face. So, you have relative motion, and increased friction, resulting in more tire wear than if you use a flat faced roller.

    With a flat faced roller, the tire, being flexible, can conform to this shape, so you will not experience the surface wear you will get with a concave roller.

    Ref the attached diagram.

    Lets assume that you have a 5 inch larger diameter (D1), and a 4 inch smaller diameter (D2), with 1500 RPM rotational velocity. The rim speeds of the two circles would be:

    D1 = 1500 * 5 * 3.14 * 60 / (12 * 5280) = 22.3 MPH

    D2 = 1500 * 4 * 3.14 * 60 / (12 * 5280) = 17.8 MPH

    So, the crown of the tire is being pushed almost 5 miles per hour faster than the 'corner' of the tire. That is a situation which will lead to poor tire wear, and increased opportunity for tire blowouts on long runs

    There's a reason why all the friction drive makers run with 'flat' rollers, and it's not because it's easier to make. (although, coincidently, that IS a plus...)

    Attached Files:

    Last edited: Aug 19, 2008
  11. So could he correct that by welding on a bit of sheet metal in the rim to make it true and maybe even some grip tape to help in wet weather?
    I like the idea that that wheel is gripping more tire.. I think.
  12. CoconutFriction

    CoconutFriction New Member

    The roller is concave because I use a trailer rim (made for high speed). It only contacts the crown of the tire. I first fabricated a standard steel roller with high speed bearings, but this set up seems to work better (it self centers), is super quiet and is inexpensive compared to the the other set up. Looks cool too
  13. CoconutFriction

    CoconutFriction New Member

    tire wear

    It only contacts the crown of the tire, so no additional wear. I've fabricated it both ways, this seems to work great with this engine and set up.
  14. s_beaudry

    s_beaudry Member

    Hey Coconut,

    Have you come to a final prototype of that rack mount yet?

    That seems to be very strong and well built!

    I know I would be interested in buying one...