Scientists from MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL) have engineered a robotic fish capable of swimming naturally alongside fish in open water and record them in their natural habitat. The fish was aptly named SoFi by CSAIL PhD candidate and lead author Robert Katzschmann.
“I chose SoFi, pronounced like Sophie, as a name because it not only abbreviates the word Soft Fish, but it also reminded me of a girl I liked a lot and had a crush on in high school,” said Katzschmann.
“The name is mellifluous just like the way the robot glides and undulates in water,” said CSAIL Director Daniela Rus.
SoFi is a pale, fish-shaped robot with one eye (with a fisheye lens) and a tail that moves side-to-side. The outside is comprised of a combination of silicone rubber, flexible plastic, and 3D-printed pieces.
“With an instrument that does not impact the marine life, that is not scary or foreign to marine life, who knows what kind of magical and miraculous moments we can capture?” said Rus, adding that SoFi and its observations “will give us a better understanding of underwater phenomena.”
SoFi had humble beginnings as a 9-inch tail, wiggling with the aid 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 Katzschmann. “But we wanted to show this wasn’t just working on a test bench or table top.”
After a massive redesign of SoFi, which included tweaking its weight distributions, waterproofing, buoyancy control, and other extensive changes, the robotic fish was ready for sea life. Testing included swims in Fiji’s Rainbow Reef, where SoFi swam for up to 40 minutes in 50 feet of water with a diver directing its movements from 32 feet away using a waterproof Super Nintendo controller.
Communication with the robot is achieved through a custom, sound-based system developed by the team. “Radio frequency communication underwater just works for a few centimeters,” said Katzschmann. “Acoustic signals in water can travel for much longer and with much less energy consumption.” This method would allow divers to control the fish from a distance of nearly 70 feet.
A composite depicting SoFi’s path along a reef. Credit: Robert Katzschmann
SoFi is also completely untethered and is powered by a lithium polymer battery, similar to that found in smartphones. The realistic movement of the tail is achieved by pushing water into two balloon-like chambers, causing the fish to bend and flex. One chamber expands, bending and flexing to one side. Then the actuators push water to the other channel, causing it to bend and flex in the opposite direction.
“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, 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.”
The quiet, motor-powered tail mimic the movements of real fish, while its sensors aid in avoiding marine environments such as coral reefs. Research has thus far shown little to no disturbance in the movements of other fish or in their habitat.
The team’s findings were documented in the journal Science Robotics. “To our knowledge, this is the first robotic fish that can swim untethered in three dimensions of water for extended periods of time,” said Katzschmann. “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,” said 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.”
“The robot can be used as a marine biology instrument and also to measure pollution in coastal waters, to create maps, to do inspection, to monitor and track,” she added.
“This hopefully serves as inspiration for many more soft robotic creatures to come, both on land and in water,” said Katzschmann.
The primary goal of the project was to create something usable by biologists and to create robots capable of observing sea life and determining the extent of climate change’s impact. However, the team is aware that there are certain risks involved in releasing SoFi into the deep blue sea. For instance, a shark or other large fish may mistake the robot for an actual fish and make SoFi its next meal. “If a shark would have come and ate our fish, that would have been the most amazing footage,” said Katzschmann.
Going forward, the team is working to improve SoFi so that it can make decisions without human interference and travel within coordinated schools of robot fish. They will also be making slight modifications to SoFi’s body and tail.
SoFi swimming in the ocean; Credit: MIT’s CSAIL via YouTube