[Olpc-open] Foot power revisited...

[Mike Dawson]

Hi All,

Thanks for the quick replies back - we do indeed have to consider how
much force a child can comfortably generate over a sustained period of
time.

I guess the question is more to do with the strength of the muscles
than the weight - and that comes back to health.

The other thing I am wondering is what might be the difference between
something that is more pedal based such as the designs shown and
something that is more foot pump based such as the Weza...  I am sure
that kids around here when they are cycling to school are generating
considerbly more than 20W to move the bike around here, not to mention
the 200W they must have to use for their brain to work around the
traffic in Kabul.

What if got some kids around and measure how much force they can
comfortably generate?  Maybe that would be a sensible experiment
direction?   Maybe we can work out a training program for the kids ;)
??  Good bye childhood obesity issues...

Then I would also be very interested in another calculation - how much
is that food going to cost?  These days 1 kg of rice I have not heard
of in the city for less than $1 USD...  This one might be tricky...
Yet the problem with solar under a tent, class room etc. and the price
of copper speaks for itself.

I guess we could do something like this - if we get a traditional
style scale and put a weight of however many kg on it - we can then
see how well the children can move the weight by placing their foot on
the other side of the scale...  That could give us some proper
parameters, what do you guys think?

Thanks/Regards,

-Mike



2009/1/14 Benjamin M. Schwartz <bmschwar at fas.harvard.edu>:
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> Mike Dawson wrote:
>> So the force required to generate 9W (e.g. for charging a little and
>> running the laptop):
>>
>> 9 = 0.15F / 2
>> F = 120N = 12.23kg (given gravity = 9.81N per kg)
>>
>> Which does not seem to be an unreasonable amount...
>
> I applaud your effort, and I look forward to seeing the results.  Your
> calculation is a bit iffy, but the correct biomechanics are messy, and
> probably not terribly informative.
>
> The thing to remember is: the average 7-year-old American girl only weighs
> 24 kg, so 12 kgf is a lot.  It's probably about like climbing stairs,
> which, if you've ever climbed a lot of stairs, you know is very tiring.
> What really killed OLPC's human-power initiative was this realization:
> that a bunch of healthy well-fed young adult first-world men do not have a
> good sense for how much power a Rwandan child can comfortably generate.
> (At age 13, or 16, the story is very different.)
>
> Nonetheless, I think this project is tremendously important.  I recommend
> that you consider designs like
> http://www.mattshaver.com/bikegen/index.htm, especially if bicycles are
> readily available in your area.   This approach uses the rear wheel of the
> bicycle as a friction gear to spin the driveshaft at the very high RPM
> typically required by generators.
>
> Software improvements have been steadily decreasing the effective power
> draw of the XO, and I expect that these improvements will continue, making
> alternative power sources more and more effective.
>
> - --Ben
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