I'm new to this area of electronics, but I feel I have a decent idea of what I'm doing. I'm basically just throwing this out there for any help from some seasoned veterans in this area. I should probably start by stating my skill level. I am 17 years old, a high school senior, attend Electronics Technology at Mercer County Career Center (Mercer PA, USA) for my 2nd year, have received high praise from those already in the field, and have already been accepted to Pittsburgh Technical Institute for Electronics Engineering.
I don't care too much about the legalities for this project. I'm doing it more so when I ride around my small town I can be lazy and I don't want to be pedaling at all. I plan on using the existing lower 7 gears, attaching the motor to the crank through a chain. I would disconnect the pedals (3-peice crank) and attach the pedals further up the frame for foot rests. And for the sake of range, I wanted to attach a car alternator to the front tire (a modified back tire with a single gear freewheel) to charge while riding. I'll probably need some sort of regulator here, but I'll work that out more once it's at least road ready.
I originally wanted to use a AC motor I pulled out of a washing machine. 1/2 hp, 120vac, about 10A max draw, and 1750 RPMs. I realized that with the batteries I wanted to use (2 12vdc sealed lead acid at about 12Ah), a inverter for this would be useless. With the motor pulling over a 1000W, this would drain the battery in a few minutes from the sheer amps it would pull.
Then after talking to some friends, I got the idea to use a wheelchair motor. I found one, but couldn't find any specs from it. I would guess that it would pull quite a bit of weight, but not sure of the speed and battery specs of it. Any help here would be very nice.
Then I started to think of a treadmill motor. They reach speeds of 10MPH with their current gearing and are designed to pull along plenty of weight already, so I thought that this would work well for me if it could be geared for some more RPMs. I found one on ebay for about 30 bucks and it has already been re-listed once, so I say it's a good bet I can get it for that price. Specs are 1.75 hp, 4800 rpm, 15 A, 90vdc. For the additional voltage, I think I would just run it through a simple DC-DC converter to step it up. A problem here that I can see is that while increasing the voltage, I may decrease the total amp I produce. But I'm not 100% sure on this.
For throttle control, I will use a 555 ic based PWM (Pulse Width Modulation) device to cut the voltage using a high voltage and amp NPN transistor. I figured this would work better than my original idea which was just a push button and then speed control through shifting. Not only will I save battery life at slower speeds (since it wont run full speed all the time), but I reduce the chance of popping the chain.
As you can tell, I have done my homework on this. I'm not just some kid asking obvious questions that I'm too lazy to answer myself. I would just like some advice from people who have had far more experience than I had before I invest money and time into something that might not work. I've been playing with this idea for a few weeks now, and have come across this site googling some info. I would really appreciate some help on this. And it might help my case if I say I hope to use this for my high school senior project (needed to graduate from my school).
And if any of my ideas (or those given in responses) are any good I would say feel free to use them. Knowledge is power, so power is limitless.