Not to hijack the thread but,I've been researching this myself, wondering if anyone knows of anything like this.
What I want is a a motor that runs entirely off of a generator and a capacitor, instead of a battery. I've tried to look into a generator (not sure what the correct name is) that bike lights run off of. And plug that into the motor. My goal is to have the pedaling generate enough electricity and power the motor. I don't care if it won't run motor if I'm not pedaling, I don't need it to. This way I'm hoping to cut down on battery weight.
The problem I've found is that on average from a few different motor types, they require about 200-600 watts (not sure if I'm talking correct electrical unit, I don't understand difference between joules, amps, watts, volts, etc). The only generators that come close to that amount are wind turbines that seem they might be small enough to fit onto a bike. I've thought about removing the wind mills and somehow modifying it to let my pedals turn it instead of wind mill pedals. Somehow fitting it into the pedals. I know this isn't feasible, cost/size/etc, but is there a product that does this already that I haven't come across? Since a wind mill cost $100-1000+, I haven't taken to trying it.
I have however bought a few $5-15 toy wind mills, and connected them to toy motors just to see it work. Problem is the parts don't scale well and if scaled to real bike size, I'd be better off riding an e-bike with a battery.