Borrowing from Mother Nature, MIT researchers have built a school of swimming robofish that slip through the water just as gracefully as the real thing, if not quite as fast. Mechanical-engineering colleagues Pablo Valdivia y Alvarado '99, SM '01, PhD '07 (above), and professor Kamal Youcef-Toumi, SM '81, ScD '85, designed the sleek and inexpensive robots to maneuver into areas where traditional underwater autonomous vehicles can't go. Fleets of them could be used to inspect submerged structures such as boats and oil and gas pipes; to patrol ports, lakes, and rivers; and to help detect environmental pollutants.

"Given the [robotic] fish's robustness, it would be ideal as a long-term sensing and exploration unit," says Valdivia y Alvarado. "Several of these could be deployed, and even if only a small percentage make it back, there wouldn't be a terrible capital loss."

Robotic fish are not new: in 1994, MIT ocean engineers demonstrated the four-foot-long Robotuna. Robotuna had 2,843 parts controlled by six motors, but the new robotic fish, which is less than a foot long, is powered by a single motor and is made of fewer than 10 individual components, protected by a flexible body. The motor, placed in the fish's midsection, initiates a wave that travels along the fish's body, propelling it forward. So far, the MIT prototype fish can swim as fast as one body length per second. That's much slower than real fish, which can cover up to 10 times their body length in a second.

As part of his doctoral thesis, Valdivia y Alvarado created a model that calculates how stiff each part of the robot's body should be to generate the desired speed and swimming motion. With this model, the researchers can use polymers to create a continuous fish body that is stiffer in some places and more flexible in others, instead of building each body section separately and then joining them together. "This philosophy can be used for more than just fish," says Youcef-Toumi. For example, it could help improve robotic prosthetic limbs.

This fall, the researchers plan to investigate more complex locomotion and test some new prototype robotic salamanders and manta rays, says Valdivia y Alvarado. This research should put their approach to a harder test.