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Soft robotic fish swims “like real thing”

March 13, 2014
Courtesy of MIT News Office
and World Science staff

Soft ro­bot­s—with soft ex­te­ri­ors, pow­ered by flu­ids mov­ing through flex­i­ble tubes—have be­come a pop­u­lar enough re­search top­ic that they now have their own re­search jour­nal, Soft Robotics

In its first is­sue, out this month, en­gin­eers re­port the first “self-contained, au­ton­o­mous soft ro­bot” ca­pa­ble of rap­id body mo­tion. It’s a “fish” that can ex­e­cute an es­cape ma­neu­ver, con­vuls­ing its body to change di­rec­tion in a frac­tion of a sec­ond, al­most as quickly as a real fish.

Credit: Melanie Gonick, MIT News


“We’re ex­cit­ed about soft ro­bots for a va­ri­e­ty of rea­sons,” said Dan­iela Rus, one of the de­sign­ers, who di­rects the Com­put­er Sci­ence and Ar­ti­fi­cial In­tel­li­gence Lab­o­r­a­to­ry at the Mas­sa­chu­setts In­sti­tute of Tech­nol­o­gy. 

“As ro­bots pen­e­trate the phys­i­cal world and start in­ter­act­ing with peo­ple more and more, it’s much eas­i­er to make ro­bots safe” if they’re soft.

An­oth­er rea­son to study soft ro­bots, Rus said, is that “with soft machines, the whole ro­botic plan­ning prob­lem changes.” In most ro­botic mo­tion-plan­ning sys­tems, avoid­ing col­li­sions is the top pri­or­ity. That of­ten leads to in­ef­fi­cient mo­tion, as the ro­bot has to set­tle for col­li­sion-free tra­jec­to­ries.

With soft ro­bots, col­li­sion poses less dan­ger. “In some cases, it is ac­tu­ally ad­van­ta­geous for these ro­bots to bump in­to the en­vi­ron­ment, be­cause they can use these points of con­tact as means of get­ting to the des­tina­t­ion faster,” Rus said. Soft ro­bots can al­so change di­rec­tion more flexibly and quick­ly, she added.

The “fish” was built by An­drew Mar­che­se, an MIT grad­u­ate stu­dent and lead au­thor of the new pa­per, where he’s joined by Rus and post­doc­tor­al re­searcher Cagdas D. Onal. Each side of the fish’s tail is bored through with a long, tightly un­du­lat­ing chan­nel. Car­bon di­ox­ide re­leased from a can­is­ter in the fish’s ab­do­men makes the chan­nel in­flate, bend­ing the tail in the op­po­site di­rec­tion.

Each half of the fish tail has just two con­trol param­e­ters: the width of the noz­zle that re­leases gas and the amount of time it’s left open. Mar­che­se found that the lat­ter de­ter­mines the an­gle at which the fish changes di­rec­tion—which can be as much as 100 de­grees—while the noz­zle width de­ter­mines the ro­bot’s speed. That separa­t­ion or “de­cou­pling” of the two param­e­ters, he said, is some­thing seen in real fish.

“To be hon­est, that’s not some­thing I de­signed for,” Mar­che­se said. “I de­signed for it to look like a fish, but we got the same in­her­ent pa­ram­e­ter de­cou­pling that real fish have.”


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Soft robots—with soft exteriors, powered by fluids moving through flexible tubes—have become a popular enough research topic that they now have their own research journal, Soft Robotics. In the first issue of that journal, out this month, researchers report the first “self-contained, autonomous soft robot” capable of rapid body motion. It’s a “fish” that can execute an escape maneuver, convulsing its body to change direction in a fraction of a second, almost as quickly as a real fish. “We’re excited about soft robots for a variety of reasons,” said Daniela Rus, one of the designers, who directs of the Computer Science and Artificial Intelligence Laboratory at the Massachusetts Institute of Technology. “As robots penetrate the physical world and start interacting with people more and more, it’s much easier to make robots safe” if they’re soft. Another reason to study soft robots, Rus said, is that “with soft machines, the whole robotic planning problem changes.” In most robotic motion-planning systems, avoiding collisions is the top priority. That often leads to inefficient motion, as the robot has to settle for collision-free trajectories. With soft robots, collision poses less danger. “In some cases, it is actually advantageous for these robots to bump into the environment, because they can use these points of contact as means of getting to the destination faster,” Rus said. Soft robots can also change direction more flexibly and quickly, she added. The “fish” was built by Andrew Marchese, an MIT graduate student and lead author of the new paper, where he’s joined by Rus and postdoctoral researcher Cagdas D. Onal. Each side of the fish’s tail is bored through with a long, tightly undulating channel. Carbon dioxide released from a canister in the fish’s abdomen makes the channel inflate, bending the tail in the opposite direction. Each half of the fish tail has just two control parameters: the width of the nozzle that releases gas and the amount of time it’s left open. Marchese found that the latter determines the angle at which the fish changes direction—which can be as much as 100 degrees—while the nozzle width determines the robot’s speed. That separation or “decoupling” of the two parameters, he said, is something seen in real fish. “To be honest, that’s not something I designed for,” Marchese said. “I designed for it to look like a fish, but we got the same inherent parameter decoupling that real fish have.”