No Motor, No Battery, No Problem

Harnessing bistability for directional propulsion of soft, untethered robots

An artist's rendering of the new design for a robot that uses material deformation to propel itself through water. (credit: Tian Chen and Osama R. Bilal)

October 22, 2018 | Source: California Institute of Technology,, 15 May 2018, Robert Perkins

New robot concept uses responsive materials to swim through water.

Engineers at Caltech and ETH Zurich have developed robots capable of self-propulsion without using any motors, servos, or power supply. Instead, these first-of-their-kind devices paddle through water as the material they are constructed from deforms with temperature changes.

The work blurs the boundary between materials and robots. In the self-propelled devices, the material itself makes the machine function. "Our examples show that we can use structured materials that deform in response to environmental cues, to control and propel robots," says Daraio, professor of mechanical engineering and applied physics in Caltech's Division of Engineering and Applied Science, and corresponding author of a paper unveiling the robots that appears in the Proceedings of the National Academy of Sciences on May 15.

The new propulsion system relies on strips of a flexible polymer that is curled when cold and stretches out when warm. The polymer is positioned to activate a switch inside the robot's body, that is in turn attached to a paddle that rows it forward like a rowboat.