This is a modular assembly to sandwich together a number of small hobby motors (MM10 size). These motors can be scavenged from all sorts of throwaway products and toys. I took a couple of these from some vibrating toothbrushes. Here is a video which shows the gear motion (https://youtu.be/mjIyzF06KFg) there is another on my channel which shows one motor being driven by a 9V battery.

This assembly was designed to couple with my CD Tesla Turbine (http://www.thingiverse.com/thing:595380) and I have included a video from testing here (https://youtu.be/PvrO0FS4luE). With the faucet on nearly full, I got only 0.5V from a single motor (last in train of 4)--since these run at 12000RPM driven at 3V, I guess that would put the motor RPM somewhere around 2000 or so. I have not yet tried to wire these all up appropriately and link to a battery for charging, but plan to do so if I can get the total voltage up to ~5V. I may also make a hand crank coupling to mate with with something like http://www.thingiverse.com/thing:135718. As you can see from the second image (and perhaps the video as well), there is some serious splashing, so I may need to make a cover to protect the motors for this particular application---and I need to optimize the exit flow path of my turbine to avoid so much water coming out the shaft and getting flung everywhere on the driver gear...

I hope someone else finds this interesting and useful.