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Phil writes in with an interesting question:

When I found out about this neat Ubuntu tablet that is powered by AA batteries, I started wondering if it’s possible to recharge those batteries using the musclepower of kids.

Sure, it’s easy enough for adult muscle power to generate some electricity, but could there be some ways for kids’ musclepower to be harnessed (gently) to recharge AA batteries?

What kind of not-very-tiring machines could be devised that could store mechanical energy in such a way that the energy could later be released more quickly to recharge AA batteries via a cordless power drill running in reverse?

Of all the possible machines that could be set up (pulley systems, water pumps, hydraulic lifts), which would be the simplest, least costly and least dangerous to set up? Are there any kinds of contraptions that could be created so that even a five year old could be involved in creating electricity to recharge AA batteries?

While this would be a potentially fun tool for families to use here in the United States, this could be a vital energy production/computing/education tool for families where there is no existing electrical infrastructure.

The idea of storing up a bunch of mechanical energy in order to power a high-torque generator is a good start, but I don’t think it is the right way to go. Instead, it would probably be better to skip the cordless drill, and use something designed to be a crank generator. Most rechargeable batteries can be trickle charged, or charged slowly, so it is probably better to design a hand crank that is easy to turn, and just puts out lower current. Of course, the the trade-off is that it will take longer to charge the batteries. I would start with this design for an ipod charger.

Another alternative might be to make a kid-sized pedal-powered generator, and use that to charge the batteries. David Butcher made one that looks really nice, and sells plans from his website.

Anyone have other ideas about how to harness kid power to charge batteries? How about a giant hamster wheel?