While biology often inspires robotics, our attempts at such imitation normally mean trying to mirror an animal or human’s external behaviors. The fish in the video below, however, as described in the research paper Electrolytic vascular systems for energy-dense robots by researchers at Cornell and the University of Pennsylvania, has a different take on things.
The soft robotic fish uses a liquid flowing through its body to both move about hydraulically, as well as supply electrical power to two pumps and a control system, implemented with an Arduino Uno and Bluetooth module. The trick is that this liquid — “blood,” you might say — is a liquid triiodide cathode. As it circulates, it forms half of a redox flow battery, with zinc submerged in an electrolyte providing the other half as an anode. This gives the robo-fish an energy density of 322 watt-hours per liter, and allows the 0.2 liters of “cathode-blood” contained within to theoretically power it for 36 hours.
For hydraulic actuation, a pump cycles liquid through a flexible tail, and moves the device forward at a leisurely 1.5 body lengths per minute. Another pump provides power for pectoral fins, though these appear to be more for waving at other at other robo-fish than locomotion, in a similar manner to its lionfish bio-inspiration.