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Robotuna Project To Model Real Fish

By Damian Isla

Second in a series profiling research projects at MIT.

Robotuna, a project of the Department of Ocean Engineering, will develop a new and better means of propulsion for underwater vehicles, in particular Autonomous Underwater Vehicles, by producing a robot that swims like a fish.

Modeled after the blue-fin tuna - the sea's fastest fish - the team hopes the Robotuna will both open up new areas of scientific exploration and shatter the current paradigm of how quick and strong underwater propulsion can be.

The robot, affectionately known as "Charlie" around the MIT testing tank, has a skeleton of aluminum lined with 40 polystyrene ribs. This set-up is wrapped in a skin of reticulated foam and lycra, a coating which helps to smooth out wrinkles as well as reduce extraneous turbulence.

The fish's contractions are produced by six servo-motors, each rated at two horse-power. The servo-motors route that power through the body through a complex system of stainless-steel cables and pulleys, which act as muscles and tendons. Several force sensors mounted on the side of the ribs provide continuous feed-back to the robot so that it can adjust its motions in real-time. It is tested several times weekly in MIT's tow-tank.

In its current incarnation, the Robotuna is towed by a large metal strut which holds the assembly upright. Wires and cables pipe data back through Robotuna's midsection to a computer, where data and swimming efficiency are analyzed.

Charlie' modeled after real fish

The Robotuna departs from conventional underwater propulsion in one major way - instead of a screw or propeller, it uses a fin.

"Current technology aims to minimize the vortices formed by moving through water, since these cause an enormous amount of drag which slows the vehicles down," said Professor of Ocean Engineering Michael S. Triantafyllou ScD '77, the lead researcher on the project.

"Fish, however, purposely create these vortices and exploit them for their own befit. This what we're doing with the Robotuna. We want to create the vortices but we want to control them."

In addition, other standard technology, such as sonar and video, is easily transferable to the Robotuna, said David S. Barrett G, a student working on the project.

"The Robotuna will be able to go much deeper than current AUVs, since the ones in operation now require a pressurized chamber of some sort," Barrett said.

So far the tests of the Robotuna have been "flawless", although the robotic fish is in a state of "continuous evolution," said Triantafyllou.

"Right now the fish can swim straight and start from rest. What we're working on right now is to get it to turn corners," he said.

Soon, the group is also hoping to develop a version of the three-year-old tuna that can swim on its own without any help from the metal strut.

Robotuna to revolutionize design

In the longer run, the Robotuna promises to revolutionize the design of AUV. As an illustration of the power of this new approach to AUV design, Triantafyllou cited the example of thermal vents. "When exploring thermal vents at the sea floor, the water temperature can vary by 100 degrees celsius within just a few feet.

"Because of this, you need a system which is flexible, and which can react extremely quickly to unforeseen occurrences. Current AUVs do not have the kind of speed and agility that such dangerous situations require, and so many are lost to unforeseeable circumstances.

"The Robotuna, on the other hand, would have the speed and agility necessary, to get out of a bad situation," Triantafyllou said. "With that, the Robotuna will minimize risk in exploring areas which are being covered now by the clumsy traditional propeller-driven AUVs, as well as open up new areas which have until now been considered too dangerous. This allows for new applications and closer observation," Triantafyllou said.

The project is funded by a number of organizations, including the Advanced Research Projects Agency, the Office of Naval Research, the Woods Hole Oceanographic Institution, and MIT's Undergraduate Research Opportunities Program.

It is also in large part funded by the MIT Sea Grant Program, one of 29 National Sea Grant Programs, which is administered by the National Oceanic Atmospheric Administration, which in turn is administered by the U.S. Department of Commerce.