Aquatic Robot Propelled Without Motors or Power Supply

Artist rendering of the aquatic robot by Caltech and ETC Zurich.

Engineers at Caltech and ETH Zurich recently unveiled robots capable of self-propulsion without the use of any servos, motors, or power supplies. Instead, they move through water based on the way that the material of which they’re comprised is manipulated by changes in temperature. The deformation process is essentially their fuel source.

More specifically, the new propulsion system relies on strips of a flexible polymer that curls up when it gets cold and stretches out when warm. The polymer activates a switch inside the robot's body that is attached to a paddle that rows it forward like a rowboat.

The switch is fabricated from 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 release of energy paddles the robot forward. The polymer strips can also be tuned to generate specific responses at different times. For example, a thicker strip will take longer to warm up, stretch out, and ultimately activate its paddle than a thinner strip. This property translates into a form of speed control.  

In the past, chains of bistable elements were used to transmit signals and build computer-like logic gates. In the future, more functionalities and responsivities can be added. An example could include using polymers that respond to other environmental cues, like changes in pH or salinity. Applications could include containing chemical spills or even targeted medicine.


Image Credit: Tian Chen and Osama R. Bilal/

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