We be crankin'
Here are two observations:
If you've ever used the OLPC crank charger, you'll know that while it works as advertised, it takes a lot of cranking. The charger would work better if it could be attached to a wheel. Then, you could rotate it by fitting it on to a bicycle, a sewing machine, etc. To that end, I took apart the handle and saw that one could easily fit a small wheel on to the shaft.
- On one of our usual visits to UCSF, I was walking by their clock, when it struck me (no pun intended) that the clock is a large wind-up mechanism that stores potential energy by pulling up large weights to a significant height, and then trickles it into the clock mechanism to power it. You may have seen something like this in a cuckoo clock. Alex and June Kleider have a similar mechanism at their place to roast a pig (community summit bbq party goers must have seen it).
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:
The mechanism is a planetary gear (1:6 ratio) hub that has a outer gear wheel which takes a length of string. The string goes over a pulley and has a weight on the other end (a 1 gallon water jug). The mechanism itself can be attached on to the charger easily.