Soft robotic fish offers close-up view of underwater life

Technology News | March 22, 2018

By Rich Pell

Electromechanical Data Acquisition Automotive Software & Embedded tools Digital Signal Processing Optoelectronics Analog Materials & processes Power Management Batteries / Power Supplies Wireless Communications Sensing / Conditioning Flexible Electronics

Made of silicone rubber, the remote-controlled robot – called “SoFi” – is able to independently swim alongside real fish in the ocean. Featuring a built-in high-resolution camera, the robot, say the researchers, has the potential to be a new type of tool for ocean exploration and could open up new possibilities for studying marine life.

Current robotic prototypes, say the researchers, don’t provide adequate platforms for studying marine life in their natural habitats. SoFi, however, with its undulating tail and an ability to control its own buoyancy, can swim in a straight line, turn, or dive up or down to continuously record the aquatic life it is following.

“To our knowledge, this is the first robotic fish that can swim untethered in three dimensions for extended periods of time,” says CSAIL PhD candidate Robert Katzschmann, lead author of an article on the project. “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.”

SoFi is built around a single camera, a motor, and a common lithium polymer battery. The entire back half of the “fish” is made of silicone rubber and flexible plastic, with several components 3-D-printed, including the head, which holds all of the electronics.

To swim, the robot’s motor pumps water into two balloon-like chambers in the “fish’s” 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.

The alternating actions create a side-to-side motion mimicking the movement of a real fish. The hydraulic system can enable different tail maneuvers by changing its flow patterns, resulting in a range of swimming speeds, with an average speed of about half a body length per second, say the researchers.

In order to enable SoFi to swim at different depths, the researchers equipped it with two fins on its side that adjust the pitch of the robot for up and down diving. To change its vertical position, SoFi has an adjustable weight compartment and a “buoyancy control unit” that can change its density by compressing and decompressing air.

In addition to its basic functionality, the researchers also considered the robot’s effect on its environment, with a goal of being as non-disruptive as possible. This involved minimizing the noise of SoFi’s motor and of the communications system, which uses ultrasonic emissions at 30 to 36 kHz to receive commands from a diver piloting the device.

In test dives in the Rainbow Reef in Fiji, SoFi swam at depths of more than 50 feet for up to 40 minutes at once. It handled currents well and took high-resolution photos and videos using a fisheye lens, while appearing not to disturb real fish, say the researchers.

“We view SoFi as a first step toward developing almost an underwater observatory of sorts,” says Daniela Rus, the Andrew and Erna Viterbi Professor of Electrical Engineering and Computer Science at MIT and co-author of the paper. “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 researchers next plan to increase the robot’s speed by improving the pump system and tweaking the design of its body and tail. In addition, they are looking to soon use its on-board camera to enable it to automatically follow real fish. They also plan to build additional SoFis for biologists to study how fish respond to different changes in their environment.

For more, see “Exploration of underwater life with an acoustically controlled soft robotic fish.”