GEARING 8/1/11

   The original gearing involved too many jack shafts. The rear hubs we used were low quality. We had the cheapest shifters and derailleurs. We also did not really know what the gearing should be. The Parlor car was very slow and hard to pedal for some reason. The axles were fighting each most likely.
   Here's my new idea: No hub gears. The cassettes are linked together and go straight to the main jack shaft. When we need ultra low gears for Kinetic Sculpture race sand hills, we can switch out the outer sprocket for a smaller one. This will be easy since it's on the outside. We can take out a couple of chain links to make it right. The chain tensioner will take up the remaining slack and there's no jack shaft brake so no chain adjustments are necessary.
   So chain rings are 28, 32, 48. and Cassettes are 11 -34 sprockets. We would like 10 mph top speed at 1 pedal per second. Low speed will be whatever it is.
   High gear: 48/11 = 4.36 hub turns per pedal. We will need 144/4.36 = 33 tooth sprocket on jack shaft. I believe we have a 30 tooth. This will give us 9 mph or so. This is close enough. I think.
   Low gear: 28/34 /4.8 = 1.71 wheel turns per pedal = about 1 1/2 mph = 29 inches per pedal, which is probably fine for the road. Who knows?
   Ultra Low gear: 9/29 * 30 tooth = 9.3 tooth. The smallest sprocket for 1" jack shaft is 13. This would give us .074 wheel turns per pedal = 12.6 inches per pedal. We want 9". We could have a smaller secondary gear on the cassette hub and a larger second gear on the jack shaft. The ratio there needs to be 3/4. So whatever the sprocket is on the bike hub, the jack shaft needs to be 1.34 times bigger. We can do that. This reduces the top speed. So the high speed outer sprocket needs to be 33 * 1.3 = 42.

So the jack shaft would normally have a 42 tooth sprocket on it and for low gears it would have a 13 tooth sprocket.

Compare this to using Hub Gears