Picture of whats under the hood of my bike. The electric assist only drives the left side, and that is a big freewheel it is connected to an the left axle. The pedals drive both sides, there is a small BMX freewheel on both axles that the jack shaft is chained to. So when you are going straight, both wheels pull evenly. When you go into a turn, the outer wheel freewheels faster than the inner one which is driving. So that makes this a positrac rear end. If one wheel slips, the other will grab. Works great. I thought it up myself, but as usual, found later it wasnt a new idea. Theres actually a guy in Oklahoma who makes what he calls a differential for bikes like this. It isnt a real differential, but 2 little freewheels fastened together with one sprocket driving both. So the really simple setup for this kind of bike would be one of his differentials with axles into both sides, and an internal geared hub like a Shimano Nexus as a mid drive. I found with the electric assist, I dont need all those gears for the pedals. Basically only used 2 gears, one in the middle, and high. High is pretty slow on this bike because it is geared like a mountain bike, but with 20 inch wheels. The electric assist gets me going, up to speed and across intersections very quick. So if I were planning this again, it would be much simpler. One of the little differentials, and maybe an old Sturmey Archer 3 speed. They are cheap, everywhere, and bulletproof. I dont need all those low gears unless the battery goes dead. This is a 36 volt, 600 watt system. In Iowa it is classified as a bicycle as long as it can be completely powered by pedals, has 3 wheels or less, and electric assist of no more than 750 watts. So I dont have to license or insure it. If that was a gasoline engine, it would be a moped, and need to be licensed. 600 watts seems to be very capable. The batteries are 22 ampere hour, so are small enough not to add too much weight, (50 pounds, ouch!) but big enough for me to get myself and 3 HDs out to FedEx and back and still have half a charge. There is a fabulous calculator online that calculates the battery size for you for whatever your normal trip will be. You mark your trip on the map it provides, enter all the parameters of your bike and yourself, and enter battery sizes until you find the happy medium. If anybody really gets serious about having one of these, or another kind of electric assist bike, I now know a lot about it, and can help. It is very fun! I now believe electric assist bikes can revolutionize our in town errand running or commuting. Every home should have one!
Posted on: Sat, 30 Aug 2014 12:26:32 +0000
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