[Olpc-open] Foot power revisited...

[Benjamin M. Schwartz]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

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
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2.0.9 (GNU/Linux)

iEYEARECAAYFAkluH1sACgkQUJT6e6HFtqTK9wCfcbgPKi4jFHr+PVKBs12h8+Ug
aqUAoIVMh/1c93KDXsB63U8+01s7jXfV
=TUS6
-----END PGP SIGNATURE-----