Build of 3 Speed Friction Drive

[Lee_K]

Winter is just about here and its too cold for me to do much riding so I think I will fill my time by building another bike. I started planning this project a few months ago and was working on rack mount with chain drive. A few guys have had positive things to say about friction drives and they are making me want to give that a try.

I can't resist adding extra complication so I will be building the drive roller around a 3 speed sturmey archer hub. I bought the bike at walmart about 5 years ago, its a 3 speed with coaster brake. Here's photos of the SA roller and the bike. More photos will be coming as I make parts.

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[BigBlue]

Interesting! Look forward to more pictures and updates.

Chris
AKA: BigBlue

 

[Lee_K]

A few more comments on the drive roller. It's made from a urethane scooter wheel which is epoxied to the SA hub. It was then machined in a lathe to 3.7 inch diameter.

I see two advantages of friction drive--simplicity and reliability. And three disadvantages--only one gear, slip, tire problems. The SA hub gives me 3 gears, the large dia urethane roller will give good traction to the tire without deforming it and reducing the flex that causes tire issues. But I have to give up simplicity to get the 3 gears and large roller, I do not intend to give up reliability.

The CAD image shows how I expect it to work, two belt drives and a jackshaft.

I am currently working on the engine pulley and bell housing.

 

[Richard H.]

Hi Lee, I remember your other project so no doubt you possess the skills and resourcefulness to achieve desired results. I wonder though after going to all the work you'll still end up with the less than optimum engagement that is inherent in the nature of all friction drives, IE: they slip and profusely so when lubricity is added in the equation. Not sure of your riding habits but obviously much of this is climate related. Also, you don't mention the engine choice but it seems like you would expect some not insignificant power loss with double reduction to the rear wheel.

Don't get me wrong, not meaning to come off as negative. For all the pluses that direct friction drive can offer like simplicity and ease of install, yours is a quite complex solution with 4 pulleys, 2 belts and a jackshaft. Just curious because of mention in the opening post your initial thought of using chain. Wouldn't the system you're devising be better suited to use chain or belt? For that matter, I can see it would probably be a fairly straight forward conversion to chain or belt at a latter point if you don't care for the results with FD.

 

[Lee_K]

Richard--those are all real good observations. I have gotten all the kinks worked out of my first MAB and have ridden it over 1000 miles. This project is a bit of an experiment.

I’m using another robin-subaru 35cc engine, the same as my other bike so I will have a good use for the engine if this project fizzles out.

I like belt drives because they are quite, I believe they are better than chains for these short center distances (5.75“ and 6.50“), and I can build them without idlers. It’s my guess that the power loss at the roller is much greater than a good belt drive, I’m prepared to accept these inefficiencies.

I actually like the complexity because it makes it more challenging to build. Stay tuned because there will be even more weird stuff coming. And you’re right, I can always convert to chain drive to the wheel if I don’t like the end results.

I hope this explains my thinking.

 

[darwin]

Interesting and complicated.......good luck. Any pics of your 1st build? Remember its a bicycle, honda 50cc metro in good condition/low milage will run you just $1000. Keep us informed with pics.

 

[Lee_K]

I think I might just be getting addicted to building bikes. I don't really need another one, but if I can come up with what I have in mind, then I will use it. My first bike is in the recumbent section.

http://www.motoredbikes.com/showthread.php?37613-Build-of-Recumbent-with-RS-35cc

 

[Lee_K]

I won't be using the centrifugal clutch, I have two socket cap screws and rubber grommets that will go where the clutch used to be mounted. I just finished the engine pulley, it rides on two skate bearings and will be mounted to a bell housing. The back side of the pulley has two slots which will be driven by the rubber grommets. When I get the bell housing done and a photo this will make more sense.

 

[Lee_K]

Here's a photo of the bell housing. Now it's on to the frame and jackshaft which will take at least a week. I will post again when those parts are done. Thanks for following along.

 

[Lee_K]

Just finished the jackshaft, the pulleys, and enough of the frame to fit them together. The pulley ratios, sturmey-archer ratios, and roller size calculate to equivalent engine mounted rollers of 0.77, 1.03, and 1.38 diameters for the three gears. Next, I will be working on a starter mechanism.