Mike Dawson wrote: > Hi All, > > Such a device would need adaptation for the OLPC to be possible for > kids (particularly those in the developing world) to use. We found by > experimentation with weights that kids 8-12 average max sustained > power applied against gravity was around 11W. They would need at
This seems a bit pessimistic. Say 25Kg, 11W will raise 25Kg about 4cm in one second. Or about one step of a normal stair per 2 seconds. When was the last time you saw a kid go up stairs that slow? I have a scribble-blueprint of my ideal phone charger, but it's complex. Imagine a box ~100*25*80mm about 300g or so. This then unfolds into a device like a car footpump - an A frame. http://www.argos.co.uk/static/Product/partNumber/7402436.htm You step on this, and it generates a pulse of 100W or so. This is stored in a couple of LiFePO4 cells, which can take about 30W of charge each. It charges enough to recharge a phone in perhaps 100-200 steps. The gearbox and frame is challenging - it requires a light robust gearbox capable of perhaps withstanding impacts of 200Kg, and normal cyclic use of 120Kg or so. The electrical design is similarly complex, you need a peak power tracker to efficiently charge the battery from the variable speed, as well as smarts to optimise the speed profile for ergonomics. Then you need to use it as a motor to pop the pedal back up. (this is lighter than a spring.) This can be made a lot easier to make if you allow the weight to grow to a kilo or two, and drop the required efficiency. This also makes it a whole lot less usable. _______________________________________________ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel