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I need to get a motor from an electric motorbike to drive a single-speed BMX Bike chain, and I haven't worked with bikes/sprockets before so I don't know where to start (I was only supposed to be doing the throttle and electronics, not sure how I ended up with the chain drive).

I know I need a sprocket with as few teeth as possible (~10-14 or less) and can be mounted onto a 9.5mm shaft double flattened to 8.4mm, and 4.5mm long, and have the teeth fit a standard single-speed BMX bike chain.(measurements are from a set of calipers, motor doesn't have any specs :P) I have a sprocket from the motor, but it isn't the correct tooth size/spacing for a bike chain.

Is this something that exists or can be made on a part-by-part basis, or do I need to weld something up?

Picture of the motor shaft measurements, I guess twitter isn't a good way to host images

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  • $\begingroup$ Fantastic diagram! We encourage this kind of stuff a lot, and it is appreciated. Unfortunately you question is a recommendation question, which doesn't fit well with the site format. $\endgroup$
    – wwarriner
    Sep 29, 2016 at 22:35

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There are quite a few online websites you can find that specialize in the design and fabrication of gears/sprockets.

For example, a really nice website for generating custom sprockets and gears is Rush gears because they have a nice sprocket/gear online model generator. You can download the models of gears in CAD format and even order the gear to be made by them in a bunch of materials. Just click the Click to build CAD models and you can adjust a bunch of different specifications.

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That sort of shaft arrangement is often used for circular saws. Here the blade (or in your case the sprocket is clamped between two washers by a nut on the threaded part of the shaft. The inner washer has a slot matching the flats on the shaft instead of a round hole.

You may also need a spacer, slightly thinner than the sprocket to keep it concentric.

If you set the torque on the nut right this means that the sprocket should slip rather than rounding off the flats on the shaft if it is overloaded.

enter image description here

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