AMHERST, Mass. – A robotic fish designed and built at a research lab at the University of Massachusetts Amherst can accelerate up to 20g, an acceleration comparable to the fastest live fish that has been measured so far. No other robotic fish has achieved such acceleration. The research was recently published in Bioinspiration & Biomimetics.
“The very large acceleration that some species of fishes can achieve during their escape maneuver has long fascinated the researchers,” said Yahya Modarres-Sadeghi, professor of mechanical engineering. “We asked ourselves, could we make a robot that is as fast as the fastest live fishes?”
The bio-inspired robotic fish designed and built by Modarres-Sadeghi and his Ph.D. student Todd Currier is made mostly of 3D-printed plastic components using a Northern pike as a model. The plastic components reduced weight and improved acceleration performance. The robotic fish is designed to use the snap-through buckling of its spine to generate and mimic the fast-start response of a startled live fish. Many fishes use such a maneuver to avoid predators or to capture prey.
The robotic fish is actuated using a piston and cable assembly. The cable links the tail to the piston that is placed in the head, forcing the net displacement of the tail to the stroke of the piston. A series of ribs are constrained to the spine, and guide the cable and support the skin along the length of the body. To make the fast maneuver, the robotic fish bends its spine to a “C-shape,” similar to a live fish that goes through a fast-start maneuver. Then it changes the direction of rotation of its head, bringing its spine to an unstable “S-shape,” from where the robotic fish goes through a snap-through buckling, which imposes a traveling wave along the length of the fish, creating a body form very similar to what has been observed in live fishes undergoing the fast-start.
To test how the robotic fish can co-exist with its live counterparts, the researchers took it to a shallow, swift river to test it. In the river, the fish, though not designed to swim straight, was able to swim against a swift current by performing repeated fast-start maneuvers. It was also able to approach live fish and stay close to them until it performed a fast-start, which, as expected, scared the live fish.
The members of this research team believe that the design of the robotic fish could eventually help researchers explore the fauna of unexplored areas of the ocean. Current exploration tools typically generate light and noise that can startle live fish and animals and influence their behavior. Additionally, many of the regions of unexplored ocean are inhospitable to humans and require the use of autonomous underwater vehicles (AUVs), which are unmanned. AUVs are inorganic and do not integrate into the marine environment. The intrusive vehicles often startle marine life making observation difficult. Robots that emulate the motion of the fishes are more likely to co-exist with their live counterparts.
YouTube video of the Robotic Fish in action.