Oh fish! That's a robot

Joanna Klein reports on a robotic fish that can keep an eye on ocean health 

  • Published 11.06.18

You're a fish in the ocean. It's 2023 and humans have begun deploying swarms of sentinel robot fish along the reef where you live that will monitor your environment, track pollution and collect intelligence on your behaviour. Welcome to the future, my finned fishy friends.

OK, so you're not a fish. And this sci-fi fishland doesn't exist. But it could - not long from now.

Allow me to introduce SoFi - like "Sophie," but short for "Soft Robotic Fish," revealed in Science Robotics, by scientists at the Massachusetts Institute of Technology (MIT) Computer Science and Artificial Intelligence Lab. Robotic fish like her could be essential to understanding and protecting marine life in danger of disappearing.

This foot-and-a-half long robot mimics a real fish. She can swim in the ocean at speeds up to half-its-body-length a second and at depths up to 60 feet. SoFi has a battery that will last 45 minutes.

She's not quite fish flesh, but she's not a typical marine robot either. Although critical for studying the ocean, remote operated vehicles and submersibles can be expensive to build and operate. They also can startle the sea creatures they're supposed to study. But without a line giving her away by connecting her to a boat, a noisy propeller or the big, rigid, awkward or angular body of a metallic land-alien, she doesn't seem to bother or scare off real fish. Some even swim along with her. Sleek, untethered, relatively inexpensive and well-tolerated, SoFi may provide biologists a fish's-eye view of animal interactions in changing marine ecosystems.

For this group of MIT roboticists, SoFi was a dream, combining their love of diving with their work on soft robots. She was also an engineering challenge.

SoFi started as a 9-inch silicon tail that wiggled with the assistance of a hydraulic pump.

"I was amazed at how well it was working, how well I was able to get this tail to beat back and forth or swim left and right, like a shark or some other fish," said Robert Katzschmann, a graduate student at MIT who led the team. "But we wanted to show this wasn't just working on a test bench."

SoFi had to swim in the ocean - at multiple depths. This meant waterproofing, buoyancy control, tweaking weight distributions and figuring out an unobtrusive way to share information underwater. It also meant compact equipment.

"We wanted to build a fish," Katzschmann said. "And the fish can't be as big as a submarine - unless we wanted to build a whale."

A couple years later SoFi had a finned body and head equipped with a camera, two-way hydrophone, battery, environmental sensors, operating system and communication system that allowed a diver to issue commands using a souped-up Super Nintendo controller.

The communication system was the biggest challenge because normally it requires a cable. Common remote signals used for piloting aerial drones don't travel below water.

But sound waves do.

They built their own language, sending coded messages on high-pitched sound waves between SoFi and the diver. Different bits of information were assigned their own tones, kind of like how numbers are represented by dial tones when you make a phone call. A processing system decoded and relayed the messages to tell the diver things like "SoFi is currently swimming forward" or command her to "turn left, 20 degrees." The high-pitched signals only travel about 65 feet and are inaudible to fish, although it's possible some whales or dolphins could hear them, which may require future research.

"Our primary goal was to make something for biologists," said Katzschmann, who envisions a future network of sensor-clad SoFis for studying schooling dynamics or monitoring pollution over time.