[ncmncm]

You can make very tiny motors with nitinol, but it is a real waste of the capability of the material.

Those work by using electrical resistance to heat a sample, which moves, and then cools off and can be moved back again, such as by a spring. Turning high-grade electrical energy to low-grade heat, thence to motion, wastes most of it (probably ~70%) vs. a magnetic motor that wastes normally less than 10%.

But nitinol can extract high-grade mechanical energy (kinetic energy of motion, or potential spring tension) from existing low-grade heat by conducting the heat from a higher temperature source to a lower temperature sink. I don't know why the other commenter claimed they wear out; the reported experience from labs was that after 20M cycles they were (a little) stronger than they began.

[thecount122195]

Yea thats how it tied in with the over all microcombusters talk, they were using tiny swiss roll burners to power the nitinol motors. Due to liquid fuels having higher energy densities than batteries apparently they could go for much longer than their electrical counterparts even though they weren't as efficient.

[kybernetikos]

What sort of orders of magnitude are we talking about here? Could you wind a watch with body heat?

[pjc50]

You have to find a way of applying and removing the heat in order to make that happen - for watches I would have thought the normal "self winding" kinetic mechanism was best.

[ncmncm]

They usually say you need 40 degrees of difference. So, probably not.