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Variable Speed Belt Drive

Old 11-18-09, 11:51 PM
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Variable Speed Belt Drive

I've been thinking a lot lately about how bicycle transmissions could be simplified. My bike has crappy components and the chain slips often during shifting and the like. I was thinking about using a belt driven mechanism. It seems like a belt drive would be much more reliable. Continuous speed transmissions are used in belt driven electronic power tools such as lathes. "A belt drive continuously-variable speed automatic transmission comprises two variable-pitch pulleys and a belt which is V-shaped or trapezoidal in cross-section, extended between the two variable pitch pulleys." I don't know how practical this could be on a bike because I don't know how widely variable the belt positions would be in the limited space the rear cassettes are generally located. I just thought this would be cool but I don't have the resources to design and build this myself.
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Old 11-18-09, 11:54 PM
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And you would have to get your frame modified in order to put the belt onto it and it would likely have to be a gearbox/internal shifting hub setup in order to have it work.
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Old 11-19-09, 12:17 PM
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Trek is starting to make urban bikes with a belt drive and an 8-speed hub.

https://www.trekbikes.com/us/en/bikes/urban/soho/soho/
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Old 11-19-09, 09:39 PM
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you may not have theresources or funding to do such a thing, but Georgia Tech did, and with me and 4 of my friends this was our senior design project.

having been there, and done that may i +1 on dannihilators suggestion of belt drive with an internal gearbox.

the prject was hugely complicated, and vastly over built. it weighed a ton, and was not practical in anyway.
That being said, we did build a prototype of the drivetrain, and it did work. so maybe it will work?

all i know i the frame that was to be our prototype is now my fixie, and it is a lot more useful!!!!
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Old 11-19-09, 09:44 PM
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Originally Posted by noonito
Trek is starting to make urban bikes with a belt drive and an 8-speed hub.

https://www.trekbikes.com/us/en/bikes/urban/soho/soho/
An 8 speed internal hub.
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Old 11-23-09, 10:03 AM
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If you read up on various cars with belt/chain drive CVTs, you'll notice that they all have reltively low torque ratings. It takes a lot of force on the belt to keep it from slipping. Not sure what the term is, but you couldn't have a belt with the groove/ridge thingy's that engage a cog with a CRT, which means it's even more likely to slip. This adds up to two things, one it'd have to be way overbuilt, and two, much of the gains you get from having a CRT would be cancelled out by higher friction.
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Old 11-23-09, 02:50 PM
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Cool Cool, I was just wondering if this type of thing has been tested/done before. Thanks. I'm going to do a little bit of research on this still.
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Old 11-23-09, 02:54 PM
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this is what I'm talking about. Regular derailleur lines could be used easily to adjust the width between the rear cog. This seems very feasible. If the frame was built well for high tension between these pulleys then I don't see how this would be a problem or how it could not work.
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Old 11-23-09, 03:22 PM
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I think you'll find the force needed to adjust the position of the pulleys will be too high to use derailleur shifters and cables, assuming the belt is tight enough not to slip. The cars that use this design have hydralics to move the pulleys.
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Old 11-23-09, 03:26 PM
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4evr, I was thinking that as well, but I also know that we cannot apply nearly the same amount of torque as a car engine, and hydraulic brake lines apply more force than cable ones do. I'm going to have to become friends with some mechanical engineers with CNC mills here at school.
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Old 11-23-09, 05:33 PM
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That design has been used on snowmobiles for decades. For a bike, such a system would probably end up too bulky. It's far easier to lern how to shif smoothly and go out riding.
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Old 12-05-09, 07:00 AM
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It's not like any of these things are "new fangled". They have all been tried. It turns out that the plain old derailleur open sprocket open chain bike is cheaper and more efficient.

Good luck with any other design.
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Old 12-05-09, 12:29 PM
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I blew my chain apart on a hill the other day, for some reason Shimano chains break on me all the time.
Time to go find a Sram...

anyway IDK I'f i'd trust a belt, it'd need to be tensioned highly, and would require some force to get it going.
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