I am thinking about doing something similar to the idea shown in the video below. It is basically a light bulb powered by a rat on a wheel. I want to make it a lot more efficient. There are several ways to make it more efficient mechanically. I am just not sure what the best form of power generation would be. I have read that stepper motors can be used to generate power with low rps so I am thinking about going that route. I am looking to draw from your knowledge to find the most efficient way of channeling power from the shaft of a rats exercise wheel. I know its a quirky idea but I think it will be a cool project once it is complete.
Thanks
http://www.youtube.com/watch?v=X5LEcmPoVgs

 

I like it. You won't get much power, but it could power up a red or a white LED with a little effort, better than the light bulb (it is a matter of efficiencies).

I liked how the kid did it in the video. Most of the schemes I envision involve rare earth magnets, which are fairly toxic if chewed, and rats like to nibble on everything.

Whatever scheme you end up with it will add drag on the wheel, making it harder to turn. Not a showstopper by any means, but something to be aware of.

I'd do this by using a bunch of rare earth magnets on a wheel, going through a bunch of coils each with a schottky diode to turn it into DC and isolate the coil from the others.

 

With power generation RPM is King, so a basic gearing system to increase the RPMs before the motor would be good, a ball bearing well greased transmission will cause minimal losses from friction and dramatically increase efficiency.

The chances of a rat trying to chew on a rare earth magnet aren't that high I wouldn't think, most of them have chrome/nickle plating over the top that's so hard no rat would touch it, they can't chew on them cause it'd break teeth not wear them, they'll only chew on something they can actually wear down.

Steppers have a pretty heavy 'cogging' effect that I think would be quiet wasteful. I'd lean more toward using a small DC brushless motor, remove the controller and tap the coils directly to a polyphase rectifier using Schottky diodes. You'll find it hard to get more efficient than a ball bearing supported brushless motor with schottky diodes. Even with gearing you might gain more efficiency on the low end using a step up transformer before rectification but the transformer would have to be pretty well thought out or it'll just add to losses.