Researchers at ETH Zurich developed a new propulsion concept for swimming robots. As a proof-of-concept study, they made a 3D printed mini submarine, made with shape memory polymer strips.
The little submarine of only 7.5 centimetres (3 inches) is equipped with paddles, but no engine of other power supply. The paddles are actuated by two shape memory polymer strips that act like muscles. In warm water, the polymer expands, triggering a paddle stroke. The directional motion, force and timing of the paddle strokes are precisely defined by the robot’s geometry and material.
The mini-submarine can paddle forward with one stroke, release cargo (in this case, a coin), and navigate back to the starting point with a second paddle stroke in the opposite direction. Varying the geometry of the polymer muscles allowed the scientists to define the sequence at which the paddle stroke is triggered: thin polymer strips heat up faster in warm water and therefore respond faster than thicker ones.
Currently, each actuating element can execute a single paddle stroke and then has to be reprogrammed manually. However, it is possible to fabricate complex swimming robots with multiple actuators.
A potential development would be using polymers that do not react to temperature, but other environmental factors, such as the acidity or salinity of the water. This method could possible be developed further to create a low-power vessel for exploring ocean depths.
Image: ETH Zurig / Tim Chen