New Robotic Fish Mimics Speed and Movements of Live Specimen

Steering a collaboration with Harvard University biologists, mechanical engineers from the University of Virginia School of Engineering (UVA Engineering) have developed the world’s first robotic fish that imitates the movements and speed of live yellowfin tuna.

The team’s peer-reviewed paper titled “Tuna robotics: a high-frequency experimental platform exploring the performance space of swimming fishes,” was published on September 18^th, 2019, in Science Robotics—an offshoot of Science magazine dedicated to technological developments in robotic science and engineering.

The robotic tuna project, headed by Hilary Bart-Smith, a professor in UVA Engineering’s Department of Mechanical and Aerospace Engineering, was the outcome of a five-year, $7.2 million Multi-disciplinary University Research Initiative. Bart-Smith received the fund from the U.S. Office of Naval Research to study the fast and efficient swimming behaviors of different fishes.

The objective of Bart-Smith’s project is to gain a deeper understanding of the physics of fish propulsion. Such research can ultimately lead to the development of sophisticated underwater vehicles, fueled by fish-like systems that are better than propellers. Moreover, underwater robots are handy in a wide range of applications, like marine resources exploration, defense, recreation, and infrastructure inspection.

However, much before bio-inspired propulsion systems turn out to be viable for the public as well as commercial applications in unmanned and manned vehicles, scientists should consistently figure out how various creatures, including fish, are able to move through water.

Our goal wasn’t just to build a robot. We really wanted to understand the science of biological swimming. Our aim was to build something that we could test hypotheses on in terms of what makes biological swimmers so fast and efficient.

Hilary Bart-Smith, Professor, Department of Mechanical and Aerospace Engineering, UVA Engineering

First, the researchers had to examine the biological mechanics of high-performance swimmers. Along with his research team, Harvard biology professor George V. Lauder accurately determined the swimming dynamics of mackerel and yellowfin tuna.

With the help of that data, Bart-Smith and her group, which included research scientist Jianzhong “Joe” Zhu and PhD student Carl White, built a robot that moves just like a fish underwater and also beats its tail sufficiently fast to reach the similar speeds of live specimens. The researchers subsequently compared the robot, which they dubbed “Tunabot,” with the live fish.

There are lot of papers on fish robots, but most of them don’t have much biological data in them. So I think this paper is unique in the quality of both the robotic work and the biological data married together into one paper.

George V. Lauder, Biology Professor, Harvard University

“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 added. “These comparisons give us confidence in our platform and its ability to help us understand more about the physics of biological swimming.”

UVA Engineering’s strengths in autonomous systems formed the basis for the researchers’ work. The Department of Mechanical and Aerospace Engineering is a member of UVA Engineering’s Link Lab for cyber-physical systems. The laboratory focuses on smart health, smart cities, and autonomous systems, such as autonomous vehicles.

The new Tunabot project is an extension of Bart-Smith’s second, highly competitive Multi-disciplinary University Research Initiative from the Office of Naval Research; Bart-Smith obtained a $6.5 million award in 2008 to create an underwater robot based on a manta ray.

The Tunabot tests are carried out in a huge laboratory at UVA Engineering’s Mechanical Engineering building, in a flow tank that occupies roughly a quarter of the room, and in a similar facility at Harvard University.

The finless and eyeless replica fish measures about 10″ in length, while the biological counterpart can grow 7 feet in length. When a green laser light cuts through the midline of the plastic fish, a fishing line tether makes sure that the robot remains steady.

The robot sheds fluid motion with every sweep of its fabricated tail, and this motion is measured by the laser. As the water current in the flow tank builds up, the tail and whole body of the Tunabot move in a quick bending pattern, mimicking the swimming movements of a live yellowfin tuna.

We see in the fish robotics literature so far that there are really great systems others have made, but the data is often inconsistent in terms of measurement selection and presentation. It’s just the current state of the robotics field at the moment. Our paper about the Tunabot is significant because our comprehensive performance data sets the bar very high.

Carl White, PhD Student, University of Virginia

The association between robotics and biology is circular, Lauder added. “One reason I think we have a successful research program in this area is because of the great interaction between biologists and roboticists.”

Every discovery in one branch tells the other, a kind of educational feedback loop that is continuously developing the engineering as well as scientific fields.

“We don’t assume that biology has evolved to the best solution,” Bart-Smith added. “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?” concluded Bart-Smith.

(Video credit: University of Virginia School of Engineering and Applied Science)