Realistic tuna robot created to improve next-gen underwater vehicles

Underwater robots are useful in a range of applications, such as defence, marine resources exploration, infrastructure inspection and recreation.

Designed by engineers at the University of Virginia (UV) in collaboration with Harvard University biologists, the fish is positioned as the first step to achieving greater understanding of how fish and other creatures move through water to improve future propulsion systems.

“Our goal wasn’t just to build a robot. We really wanted to understand the science of biological swimming,” said UV professor Hilary Bart-Smith. “Our aim was to build something that we could test hypotheses on in terms of what makes biological swimmers so fast and efficient.”

The 'Tunabot' they constructed not only moved like a fish underwater but also beat its tail fast enough to reach nearly equivalent speeds when compared with live specimens.

“What is so fantastic with the results we are presenting in the paper are the similarities between biology and the robotic platform, not just in terms of the swimming kinematics, but also in terms of the relationship between speed and tail-beat frequency and energy performance,” Bart-Smith said. “These comparisons give us confidence in our platform and its ability to help us understand more about the physics of biological swimming.”

The eyeless, finless replica fish is roughly 25cm long, while the biological equivalent can grow up to seven feet long. A fishing line tether keeps the robot steady, while a green laser light cuts across the midline of the plastic fish.

The laser measures the fluid motion shed by the robot with each sweep of its fabricated tail. As the current of water in the flow tank speeds up, the Tunabot’s tail and whole body move in a rapid bending pattern, similar to the way a live yellowfin tuna swims.

The relationship between biology and robotics is circular, said Harvard biology professor George V. Lauder.

“One reason I think we have a successful research program in this area is because of the great interaction between biologists and roboticists,” he said.

Each discovery in one branch informs the other, a type of educational feedback loop that is constantly advancing both the science and the engineering.

“We don’t assume that biology has evolved to the best solution,” Bart-Smith said. “These fishes have had a long time to evolve to a solution that enables them to survive, specifically, to eat, reproduce and not be eaten. Unconstrained by these requirements, we can focus solely on mechanisms and features that promote higher performance, higher speed, higher efficiency.

"Our ultimate goal is to surpass biology. How can we build something that looks like biology but swims faster than anything you see out there in the ocean?”