New answers tagged gears
You can use a worm gear for a compact, high ratio gearbox. By putting a worm gear on the motor shaft and using it to drive a 24 tooth gear you can achieve a 24:1 reduction. For high torque applications you could use multiple parallel axles held together by gears or wheel hubs.
The XL motor runs at approximately 220 RPM. Therefore, the following gearbox from the ELEC 201 class LEGO Design module from Rice should be sufficient:
The Technic Riding Cycle theme features several bikes that may be of inspiration. One particular set Moto Cross Bike (42007) uses several 3711: Technic, Link Chain parts to make a chain. Based on Bricklink prices for the last six months, 39 chain pieces (the amount shown in the set above) would cost £4.29 (Aprox. $6.91 or €1.26). Pulleys and rubber ...
It looks like LEGO sells chain and sprockets, don't know if you'd have them lying around though. You could also try using pulleys instead. If you don't have any of the actual pulleys, take the tread off of two wheels and stretch a rubber band across, that should work too.
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