A gravity mechanism such as a cuckoo clock, and a sustained rpm crank charger - putting the two together seemed ideal. So, I discussed this with Joachim Pedersen, our OLPC SF repair guy, who also runs a course at SF State on desigining objects, gears, tricopters, and other such serious research (something to do with materials, evidently). We spoke with a student (Bret Cooke) who was interested, and after a few tries, and design changes, we got a 1:6 ratio gravity charger design going. This prototype was on display at the recent SF State University Science and Engineering showcase. His description of the project is:
More details to come soon.