Swimming robots made of deformable materials tend to be slow. Tiefeng Li, Zhilong Huang and their colleagues at Zhejiang University in Hangzhou, China, built a robotic fish with a soft body, fins and a tail, using elastic polymers, a conductive hydrogel and silicone. A ‘muscle’ in the body makes it bend and straighten, causing the fins to flap like those of a manta ray to move the robot through the water (see video). When a voltage was applied to the robot, it swam at a speed of 6.4 centimetres per second, or 0.69 body lengths per second — double the speed of previous soft robot swimmers.
The robot carried its own onboard system for power and remote control, and was able to swim for three hours on a single battery charge.