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Originally Posted by maxlobovsky
Team 1257 (Parallel Universe or something like that.... don't ask me, I just build the thing  ) is a rookie team this year without too much mentor support. We have started to settle on drive train idea but i have a few questions that no calculation or estimate could answer us well. We plan to use one Chiaphua per side (in a tank type steering system) in a four wheel drive with identical wheels front and back. We want to use a worm gear to gear it down about 15 times then a sprocket system for an additional 1.8 or so for a total of about 27. Assuming the the Chiaphua can give us 4000 rpm while driving the robot, that should give us a max speed of something like 8 ft/s.
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One other things to note about worm gears: they have horrible efficiencies. A typical spur gear drive or chain and sprocket drive probably has efficiency around 95% or better. A typical worm gear drive may have efficiencies in the 60% - 80% range, and some worm gear drives can be even worse. Sometimes this is an acceptable trade off for the other desirable properties of a worm gear (typically impossible to back drive, large reduction in a small space), but for FIRST I don't think it's worth it.
BTW, I am of course talking about typical values above. There are very good spur gears with efficiencies over 99%, and there are very good worm gears with efficiencies over 90%, but I doubt that many FIRST teams have the money, time, or expertise required to get that kind of performance. And, there are also worm gears which can be backdriven (e.g. this year's van door motor).