Self-Propelled Robot Challenges Nature Laws

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A new robot project blurs the boundary between materials and robots. 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 robots can turn and move at different speeds.

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.

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, according to caltech.edu.

The switch is made from a bistable element, which is a component that can be stable in two distinct geometries. In this case, it is built from strips of an elastic material that, when pushed on by the polymer, snaps from one position to another.

When the cold robot is placed in warm water, the polymer stretches out, activates the switch, and the resulting sudden release of energy paddles the robot forward. The polymer strips can also be “tuned” to give specific responses at different times: that is, a thicker strip will take longer to warm up, stretch out, and ultimately activate its paddle than a thinner strip.