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A team from MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL) unveiled the untethered SoFi robot fish that can swim alongside fish in the ocean. MIT hopes to use the SoFi robot fish to observe fish in their natural habitats to get a better understanding of their behavior.

The soft robotic fish, was recently tested in the Rainbow Reef in Fiji. The SoFi robot fish swam at depths of more than 50 feet for up to 40 minutes. The work was published today in Science Robotics.

How the SoFi Robot Fish Works

Perhaps the first thing you’ll notice about the SoFi robot fish is its tetherless, smooth motion. MIT said SoFI only has a “few on-board sensors for perception, a servo motor and the same lithium polymer battery that’s found in consumer smartphones.”

To swim, the SoFi robot fish features a motor that pumps water into two balloon-like chambers in its tail.
As one chamber expands, it bends and flexes to one side. When the actuators push water to the other channel, that one bends and flexes in the other direction. MIT said these alternating actions help the SoFi robot fish mimic how real fish swim.

The SoFi robot fish captures high-resolution photos and videos using, you guessed it, a fisheye lens.

“The authors show a number of technical achievements in fabrication, powering and water resistance that allow the robot to move underwater without a tether,” said Cecilia Laschi, a professor of biorobotics at the Sant’Anna School of Advanced Studies in Pisa, Italy. “A robot like this can help explore the reef more closely than current robots, both because it can get closer more safely for the reef and because it can be better accepted by the marine species.”

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MIT’s Love of Soft Robot Fish

MIT has been developing soft robot fish for years. Here’s a look back at a different soft robot fish MIT developed in 2014 that was powered by carbon dioxide. The robot fish consisted of a hard control module that stores the electronics and a carbon dioxide canister in its head and abdomen. Two inflatable tubes traveled down each side of the fish to its tail containing carbon dioxide to make the fish move.

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The entire back half of the SoFi robot fish is made of silicone rubber and flexible plastic. Several components are 3D-printed, including the head. MIT filled the head with baby oil to reduce the chance of water leaking.

Soft robots are in many ways easier to control than rigid robots, since researchers don’t have to worry quite as much about having to avoid collisions.

“Collision avoidance often leads to inefficient motion, since the robot has to settle for a collision-free trajectory,” says Daniela Rus, director of MIT CSAIL. “In contrast, a soft robot is not just more likely to survive a collision, but could use it as information to inform a more efficient motion plan next time around.”

SoFi Robot Fish Swims at Different Depths?

MIT said one of its biggest challenges was designing the SoFi robot fish to be able to swim at different depths. The robot has two fins on its side called “dive planes” that adjust the pitch of the fish for up and down diving. To adjust its position vertically, the robot has an adjustable weight compartment and a so-called “buoyancy control unit” that can change its density by compressing and decompressing air.

Katzschmann said that the team developed SoFi with the goal of being as non-disruptive as possible, from the minimal noise of the motor to the low-frequency emissions of the team’s communications system, which sends commands using wavelengths of 30 to 36 kilohertz.

“The robot is capable of close observations and interactions with marine life and appears to not be disturbing to real fish,” says Rus.

What’s Next for the SoFi Robot Fish?

Going forward, the researcher want to boost speed of the SoFi robot fish, use it to study marine life over long periods of time, see if it can be used to influence the behavior of marine life and create robot swarms.

“To our knowledge, this is the first robotic fish that can swim untethered in three dimensions for extended periods of time,” CSAIL PhD candidate Robert Katzschmann, a researcher on the project, said. “We are excited about the possibility of being able to use a system like this to get closer to marine life than humans can get on their own.”

“We view SoFi as a first step toward developing almost an underwater observatory of sorts,” says Rus. “It has the potential to be a new type of tool for ocean exploration and to open up new avenues for uncovering the mysteries of marine life.”