Observing fish in the ocean depths is challenging. Water pressure, sparse light and more make exploring the ocean a tricky expedition. But researchers at MIT believe they have the answer: a soft robot fish called SoFi.
This small, fish-looking robot swims quietly through its environment, free from any tethers so it doesn't disrupt the ecosystem by knocking into things and breaking them. They've already taken SoFi out for a successful test swim and detailed their results in a paper published in Science Robotics.
"To our knowledge, this is the first robotic fish that can swim untethered in three dimensions for extended periods of time," Robert Katzschmann, lead author and Computer Science and Artificial Intelligence Laboratory (CSAIL) Ph.D. candidate, said in a statement.
"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."
Just keep swimming
SoFi (short for "soft fish" and pronounced "Sophie") has been in development for some time. In 2014, MNN highlighted early CSAIL work on a soft robot fish, back when the robot was just swimming in tanks. Now, as the video above shows, it's swimming around reefs in Fiji for 40 minutes at a time and handling changes in currents just like a real fish would.
This is a marked improvement over other autonomous underwater vehicles (AUVs), which are loud, large and have a limited range of motion as they're often tethered to boats. SoFi isn't any of those things thanks to its unique design and construction. For starters, the back side of the little robot fish is made of silicon rubber and flexible plastic, meaning it won't damage a reef if it bumps into it.
"Collision avoidance often leads to inefficient motion, since the robot has to settle for a collision-free trajectory," said CSAIL director and MIT professor of electrical engineering and computer science Daniela Rus. "In contrast, a soft robot is not just more likely to survive a collision, but could use it as information to inform a more efficient motion plan next time around."
That flexibility and softness also allows it to swim with greater ease.
A motor pumps water into balloon-like chambers in the robot's tail, and these chambers operate like pistons in an engine to propel the fish forward. As a chamber expands, it bends to one side. Then, actuators push water into the other chamber which bends to the other side. This back and forth creates a movement very similar to that of a real fish. If SoFi needs to swim at a different speed, then an operator changes the flow patterns of the water in the chambers which in turn enables different tail movements. Fins on its side help adjust the pitch if SoFi needs to dive up or down.
All of this means SoFi is quiet — no loud propellers — and blends into the environment a bit more than other AUVs thanks to its fish-like movements.
To control SoFi, the team turned to one of the best ways to control just about anything: a waterproofed and customized control pad for a Super Nintendo. The researchers also developed a custom acoustic communication system to send SoFi instructions. So long as they're within 70 feet (21 meters) of SoFi, pushing a right, left, up or down on the directional pad will send an ultrasonic command using wavelengths of 30 to 36 kilohertz. SoFi receives the command and follows suit. If SoFi doesn't receive a command, it'll just swim in the last commanded direction.
SoFi is powered by a lithium polymer battery, the kind found in smartphones, and it can film and take high-resolution photos thanks to a fisheye lens housed in its "nose."
SoFi still needs some work. It can reach depths of about 60 feet (18 meters) and that limitation poses a problem for deeper exploration.
Other improvements that Katzschmann and Rus are considering include a live-streaming video feed and a camera that would allow SoFi to automatically follow real fish. A whole school of SoFis may also be on the horizon as a way for biologists to study how fish respond to changes in their environment.
"We view SoFi as a first step toward developing almost an underwater observatory of sorts," Rus said. "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."