Nitinol is a kind of wire that has a memory. If you heat it, it tries to return to the shape it remembers. [Latheman666] recently posted a video (see below) of a Nitinol engine that uses a temperature differential to generate motion.
[Dr. Alfred Johnson] holds a patent on this kind of motor. The concept sounds simple enough. A Nitnol spring shrinks in hot water and expands in cold. The spring is looped over two pulleys. One pulley is geared so it has mechanical advantage over the other one so that there’s a net torque which moves the hot part of the spring towards the cold side, and feeds more cold spring into the hot water. The cold spring then contracts and the entire process starts again.
We haven’t entirely gotten our heads around the gearing, but it seems plausible. On the other hand, this video was posted on April 1. What say you, Hackaday Commenteers?
If you are expecting a slow, low-energy motion, watch the video and you may be surprised at the activity. We’ve talked about wire-based motion before, but it was a little more leisurely. Then there are always jumping robots.
Thanks for the tip [Keith O].