Researchers at MIT CSAIL have created a soft robotic fish that can independently swim beside real fish without spooking them, giving scientists a better opportunity to observe marine life.

The Soft Robotic Fish, SoFi for short, is 18.5 inches long from snout to tail and weighs about 3.5 pounds. It can dive 60 feet underwater and is powered by enough juice for about 40 minutes of exploration. It doesn’t just look like a fish; it also moves like one, undulating its tail to propel itself through the water.

See it in action in recent test dives around Fiji:

The problem, both with human scuba divers and earlier generations of robotic fish is that they tend to scare away the marine life they are attempting to study. SoFi appears to be accepted and can film fish without frightening them. For now, the robot records only video, but its creators envision adding other sensors, such as thermometers, expanding its ability to gather information for marine biologists.

The latest SoFi is part of ongoing work by Professor Daniela Rus at MIT's Computer Science and Artificial Intelligence Lab (CSAIL) and her students, including Robert Katzschmann and Joseph DelPreto. Since 2014 they have built various prototypes of robotic fish but earlier versions couldn't be controlled remotely, nor could they withstand dives more than three feet underwater.

The new version, which is detailed in a recent paper that has been published in the journal Science Robotics. brings together a number of different innovations.

The housing is made from molded and 3D printed plastics making it cheap and fast to fabricate. It has a built-in buoyancy tank full of compressed air that means it can adjust its depth and linger at specific points in the water column (good for stakeouts). It can swim semi-autonomously, and will keep going in a specific direction without oversight, but a handler can steer it left or right, up and down, using a modified gamepad controller. It’ also has a custom control system, which uses coded audio bursts to transmit instructions from a human operator. SoFi’s propulsion system is a powerful hydraulic actuator that pumps water in and out of a pair of internal chambers, moving its tail fin back and forth. Not only is this quieter than using propellors like a submarine, but it’s also less dangerous, as there are no sharp moving parts, and better camouflage. According to Joseph DelPreto:

 “When we were designing the robot, we tried to make sure that it's moving to conserve the life we're trying to observe." 

Future versions of SoFi will improve its swimming and vision capabilities to further enhance the information it can provide about aquatic life. The researchers are also planning for SoFi “swarms” - schools of artificial fish set loose to monitor ocean health, perhaps recharged by solar-cell platforms floating on the water's surface.

More Information 

Soft robotic fish swims alongside real ones in coral reefs (MIT News)

Exploration of underwater life with an acoustically controlled soft robotic fish by Robert K. Katzschmann, Joseph DelPreto, Robert MacCurdy, Daniela Rus in Science Robotics  21 Mar 2018: Vol. 3, Issue 16.

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