New material eliminates need for motors or actuators in future robots(kurzweilai.net)
kurzweilai.net
New material eliminates need for motors or actuators in future robots
http://www.kurzweilai.net/new-material-eliminates-need-for-motors-or-actuators-in-future-robots-other-devices
Roughly, the effect is that moisture causes a nickel hydroxide material to expand. You can drive the moisture out with light or heat and it contracts. In a humid environment, you can cycle it. The fastest cycle time they show graphs for is 0.1 Hz (a cycle every 10 seconds.) They use a thin film of about 1 micrometer -- presumably a thicker film would take a lot longer to change the moisture level.
They don't try to measure the efficiency, but usually anything that involves temperature change is pretty inefficient.