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Re: wind-up wearables

Tim Gray wrote:
----- SNIP -----
> I would love to cut my battery pack in 1/2 if I can find an 
> alternativecharging system... (Solar panel hats are not socially 
> acceptable yet  :-) and winding up the power system might get 
> strange looks in the resturant...
----- SNIP -----
>>From: Christopher Allen <>
>>Yes. From CMU's Metronaut page:
>>"Metronaut could alternatively be powered by a mechanical flywheel
>>converting kinetic energy to electrical energy."
----- SNIP -----
>>On Thu, 28 May 1998  wrote:
>>http://www.cs.cmu.edu/afs/cs.cmu.edu/project/vuman/www/metronaut.html
>>On Thu, 28 May 1998  wrote:
>>> The Metronaut, presented by CMU at ISWC'97, was a wind-up wearable
>>> computer!

I saw an entrepreneur documentary a year ago on a company who is making
a Wind-up radio for sale in Africa.  The company is now selling lots of
the product because radio is the only way of getting information,
particularly political reports, in rural areas.  

When they were prototyping the unit they went to Africa and asked the
target market what the most important features were and the answer was
loud sound (the units are mostly used outside) and long playing time
between windings.  This proved to be very hard to do in a product that
would still be reasonably priced.  

The final product is about 14 inces wide, 10 inces high and six inches
deep.  From the pictures I saw of people carying the radio it looked
heavy too (about 3-4 pounds). The electronics for tuing and amplifying
in the radio are probably only a few ounces.  I have an old "getto
blaster" portable radio that is plenty loud and weighs a lot less,
especially without the batteries. It had to be cranked for about 2
minutes to produce 20 to 30 minutes of sound.

I am not an electronics engineer, but I guess a radio that is generating
100watt sound would need about an amps (P=I2R with a 16 Ohm speaker =
2.5 amps but the radio would be using less because 100watts is the peak
output). I doubt the unit was that loud. A wearable computer seems to
draw about 3 amps.

My point (finally) is that the wind up generator needed to provide power
to a wearable computer would be a lot larger than the batteries it
replaces and would require a lot of cranking. Even if the charging unit
did not have to be attached to the wearable all the time the user would
have to carry it around all the time because of the frequent need for a
recharge.

Also, I think the radio stored the power in a capacitor bank instead of
a rechargable battery. This might demand a substantial re-engineer of a
wearable power supply to compensate for the more linear fall in
available power. 

As an aside, if a capacitor bank could safely be used instead of a
battery they could be charged very quickly with a small circuit and a
110V wall outlet. (I would be scared of powering my caps to 10,000V and
getting rained on)

Oak Davis

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