Robofish Takes To Water

Aug. 28, 2009 -- A school of small, robotic fish has been developed by MIT scientists. Made with a only handful of parts and a blend of polymers, the fish wiggle their way through water like trout and tuna.

These new robofish could be equipped with sensors to monitor oil spills or other environmental contaminants.


"The interesting aspect of this research is that we are the first group to tailor different polymers in different parts of the body with different dampening and stiffness properties," said Kamal Youcef-Toumi, a scientist at MIT who, along with Pablo Vildivia Y Alvarado, is developing the robofish.

"We are also looking at using the natural motion and behavior of the fish and replicating those motions," said Youcef-Toumi.

The 18 new robofish have advanced significantly since the original Robotuna was created at MIT in 1994. Robotuna had more than 2,000 parts, including six motors, encased in its four-foot body.

These new models have less than 10 parts, including one motor, and are between five and eight inches long.

Youcef-Youmi and Vildivia Y Alvarado began developing the five-inch robofish four years ago, modeling their movements on freshwater fish like trout and bass. These small fish swim mostly by moving the tail, while the rest of the body remains motionless.

The most recent robofish are eight inches long and modeled to swim like salt water tuna. Instead of wiggling just the tail, tuna swim by moving their body as well, undulating back and forth to swim faster than trout or bass.

Whatever the length or swimming method, all the robofish are encased in a special blend of molded polymers. The body of the fish is one single piece of material, but each section of the body has a different stiffness, allowing the motion of one actuator to move through the robofish's entire body, propelling it forward.

One actuator allows for limited movement, basically forward and side to side. To move up and down and more complex movements will require two additional actuators be installed.

The unibody construction also protects the electrical and mechanical parts inside the robot; some robofish have been swimming for more than four years.

The robofish might mimic real fish, but they can't compete in terms of speed. The maximum speed of the robofish is less than one body length per second. Some fish can swim up to 10 body lengths per second.

Movement requires energy, and the robofish currently get their power from an attached power cable. Batteries could be installed to power robofish remotely in streams and bays, where they could be equipped with sensors to detect pollution or cameras to study animals that would be disturbed by the noise caused by propellers.

Fish aren't the only underwater creatures the MIT robotics team is studying. During the next few weeks, MIT scientists plan to test robotic salamanders and robotic manta rays.

Whatever type of robot is being created, "the underwater environment is the most difficult environment for robotics," said Huosheng Hu, a professor of computer science and electronic engineering at the University of Essex. Hu has built his own realistic robotic fish which was on display at the London Aquarium.

Hu likes the new unibody robofish, but doesn't think that the new robofish have any particular new advantage in terms of three dimensional swimming, or at least won't until the additional actuators are installed.

Despite the current limitations of robofish, human engineers will continue to chase natural fish in terms of speed, maneuverability and endurance.

"We still have a long way to go to achieving the same performance as real fish," said Hu.