Video: MIT's robotic fish swims in the ocean. Source: MIT CSAIL/YouTube
Researchers at MIT have developed what they call a soft underwater robot that looks and moves like a fish, offering scientists a vehicle for observing marine life that's less conspicuous to other sea creatures than humans in diving gear.
The team at MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL) reckon SoFi could be the answer to the challenge of documenting marine life up close.
Unlike other underwater drones, SoFi doesn't need to be tethered to boats and doesn't have any noisy propellers, but rather relies on the same tail movements fish use to accelerate and pivot in water.
To achieve a fish tail motion, SoFi's lithium polymer battery powers a motor that pumps water into two diaphragms located inside its flexible silicone tail.
The expansion and contraction of each diaphragm causes the tail to bend left and right, just like a fish, and propels it at about "half a body length per second", according to MIT.
The key breakthrough is that the fish can be remotely controlled to move in every direction underwater for up to 40 minutes, offering ample time to capture footage of marine life.
"To our knowledge, this is the first robotic fish that can swim untethered in three dimensions for extended periods of time," said CSAIL PhD candidate Robert Katzschmann, lead author of a new Science Robotics journal article detailing SoFi.
See also: Our autonomous future: How driverless cars will be the first robots we learn to trust (PDF download)
Katzschmann and fellow CSAIL researchers took SoFi on 40-minute test dives in the Rainbow Reef in Fiji, where it swam at a depth of 50 feet and managed various currents.
SoFi is equipped with a camera just in front of its dorsal fin to take videos and photos of marine life. However, watching SoFi maneuver under water is more impressive than the wobbly video footage it captures due to its tail and head movements.
Nonetheless, as Cecilia Laschi, a professor of biorobotics at the Sant'Anna School of Advanced Studies in Pisa, Italy points out, the robotic fish does have a better chance of getting up close to other fish than humans.
"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," said Laschi.
To remotely control SoFi's speed and direction, the researchers customized a water-proof Super Nintendo controller which uses an ultrasound-based system to sends commands using 30kHz to 36kHz wavelengths.
The back of the fish is made of silicone rubber and flexible plastic, while the more rigid head, which houses the electronics, is 3D printed.
SoFi's design also offers advantages over other underwater drones in terms of getting close to subjects because its motor is quieter.
According to MIT, a major obstacle has been getting SoFi to swim at varying depths. The adjustable fins on its side help it swim up and dive down while a "buoyancy control unit" aids its vertical movement.
The researchers plan to optimize SoFi's tail design and pump to help it swim faster as well as add smarts to the camera so that it will automatically follow real fish.
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