The University of Massachusetts Amherst
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Robotic Fish Mimics Fastest Fish Alive with “Snap-through Bucking of Its Spine”

Robot fish

robotic fish

A robotic fish, designed and built in the Fluid-Structure Interactions Lab of Mechanical Engineering Professor Yahya Modarres-Sadeghi and modeled after the Northern Pike, mimics the fast-start response of the fastest live fish measured so far, accelerating at values of up to 20g. No other robotic fish has achieved such acceleration. The research was recently published in Bioinspiration & Biomimetics. See Robotic Fish Built by UMass Researcher Mimics Fast Acceleration of Live Fish (posted by UMass News Office) and this YouTube video of the Robotic Fish in action.

As Modarres-Sadeghi said in Bioinspiration & Biomimetics, “Inspired by the fastest observed live fishes, we have designed, built, and tested a robotic fish that emulates the fast-start maneuver of these fishes and generates acceleration and velocity magnitudes comparable to those of the live fishes within the same time scale. We have designed the robotic fish such that it uses the snap-through bucking of its spine to generate the fast-start response.”

The Bioinspiration & Biomimetics paper was authored by Todd M Currier, Samuel Lheron, and Modarres-Sadeghi.

Modarres-Sadeghi and his team engineered the snap of the robot’s spine to mimic the fast-start response of a startled live fish. Many fishes use such a maneuver to avoid predators or to capture prey.

According to Modarres-Sadeghi, the robotic fish, made of 3D-printed plastic components, 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.

“In its transient fast-start maneuver, our robotic fish produces mode shapes very similar to those observed in live fishes,” as Modarres-Sadeghi said, “by going through a snap-through bifurcation.”

According to the News Office story, the robotic fish makes this fast maneuver by bending its spine into a “C-shape,” similar to a live fish that goes through a fast-start maneuver. Then it changes the directional rotation of its head, bringing its spine to an unstable “S-shape,” from which it then goes through a snap-through buckling. This sudden snap imposes a traveling wave along the length of the fish, creating a body form very similar to what has been observed in live fishes.

“The very large acceleration that some species of fishes can achieve during their escape maneuver has long fascinated the researchers,” said Modarres-Sadeghi. “We asked ourselves, ‘could we make a robot that is as fast as the fastest live fishes?’”

The UMass News Office said the members of Modarres-Sadeghi’s 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,” said the News Office article. “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.”

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. (March 2021)