3-Speed motorized bike experiment

Yeah, I have the same clearance issues from using the centrifugal clutch on the right side. You take the crank, put it in a vice, and bend the holy h*ll out of it. Now it's wider. :)
 
here is the drivetrain on my current build
I used a jackshaft to get around the fat tire
I put two sprockets on the hub, and someday I hope to create a shifter/tesioner to shift on the fly
this is a similar idea to the one originally posted except that I have never seen a derailer made to go on the left side
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I've seen pics of bikes with jack shafts that move the power to the right side of the bike and use the original sprocket [of the pedal chain]. I've always wondered about them but have never seen them in action. Keep us updated; I'm curious how it will all work out.

Also, streetstrip80, I was looking closely at your third pic of your rear fat-tired chopper in the "Pictures" forum and wondering how you ran the left side, but now I see. Nice job!
 
Very cool drive train. Thank you for the close up. I'm looking forward to hear more about your testing stages...Kelly
 
Lots of new pics of the 3-speed build

OK, here are some photos of the bike so far.

This isn't the motor I will be using, it's just there for a fit-test. The actual motor will be the same size, though.

The jackshaft looks like it's going to work great. It's made out of the center hub of a front bicycle wheel with sprockets riveted to it, installed into a cutom fabricated jackshaft brace which will be welded to the frame.

The handlebars and gooseneck were flipped upside-down to lower the riding stance.

The 3-speed-motor/1-speed-pedal hub modification is exactly how I planned it. The BMX freewheel sprocket needed a lot of modification to fit the hub, but it works. Now, when the motor is turning the hub via one of the 3 changeable gears, it won't turn the pedals which are on the BMX sprocket. In the photos, the pedal chain is attached and working, but the motor chain is not on yet. The final version will have the pedal chain going straight from pedals to wheel, with the derailler only used for the motor chain.

We are hoping for 50mph, maybe 60mph with nitrous if necessary (or probably even if it isn't necessary.

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Whoa!!!! that blew way over my little brain! I'll let this one sink in some and reread what you just posted. Way cool I think I like what you did. Seems like a niffty Idea.
 
very nice work!
Keep us posted as this progresses; I'm very interested to see the end result (as well as the build-up process) of this experiment.
 
It runs!

I finally rode it last night. The derailleur is off right now, and I am just running it in 1st gear only. IT IS FAST! I still have a few details to work out, but the major engineering obstacles have been resolved. I'm sure adding the derailleur will be the final challenge, but I need a pull starter before I can do that.

Gearing on these bikes is universally measured (by us) by teeth on the rear sprocket, so here it is: 1st gear is 32t, but the jackshaft has a 1.17 (21/18) ratio, so the effective 1st gear is actually equal to 37.44t. 2nd gear is 24.75t (21t actual), and 3rd gear is 21.06t (18t actual).

I don't know if 3rd gear will be useful, but it has a good spread from one gear to the next, and I can always lower the whole thing by adjusting the jackshaft. If I change the jackshaft to 21/15, I would get 1st=44.8t, 2nd=29.4t, 3rd= 25.2t.

I will post photos soon. JFleck took a few really good photos last night after the test run.
 
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