Linked by David Adams on Tue 20th Jul 2010 18:09 UTC
Hardware, Embedded Systems Japanese printer company Brother has invented a battery that can be recharged by shaking it. It's intended for devices like remote controls that use very little power and would normally require infrequent battery charges, so unfortunately you couldn't use it to power a car that could drive forever on a bumpy road.
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RE[3]: more energy
by xiaokj on Sat 24th Jul 2010 13:41 UTC in reply to "RE[2]: more energy"
xiaokj
Member since:
2005-06-30

"Not really. A huge part of the energy is recycled through elasticity in our tendons and joints. That's why a human can walk using only 50 W of power, while most human-sized walking robots need something in the order of 700 W.


The human body is efficient in it's workings. That isn't the same as recycling energy. Anyhow, the energy expelled from the body in the form of kinetic energy can be harvested by piezoelectric mechanisms to create electricity.
"

Emphasis for typo.

That is not true. The human body is really inefficient for walking. I do not have the data with me right now, but it is definitely quite a bit less than 50% efficient. That, of course, is compared to wheels, which are much more efficient.

What happens is that the robots are much more inefficient than humans, not that humans are efficient at walking. That is quite a big difference, and is also the reason why we can harness energy out of walking by having these machines in there.

Furthermore, I can tell you that efficiency is not what is evolutionarily selected for, so there is not much point in this discussion. I think a compromise between maximising power output (so that you can push harder than you need), efficiency, generality (not stuck to just flat land like wheels are) and minimising materials (to save on muscles and whatnot) is what is wanted, so the inefficient design is actually wanted to be so.

Given less constraints than nature, we ought to do a lot better, but alas the maths is not there yet.

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