Made
of silicone rubber, CSAIL’s “SoFi” could enable a closer study of aquatic life.
Adam Conner-Simons | CSAIL
This month scientists published rare footage of one of the Arctic’s most elusive sharks.
The findings demonstrate that, even with many technological advances in recent years, it remains a challenging task to document marine life up close.
This month scientists published rare footage of one of the Arctic’s most elusive sharks.
The findings demonstrate that, even with many technological advances in recent years, it remains a challenging task to document marine life up close.
But
MIT computer scientists believe they have a possible solution: using robots.
A
team from MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL)
unveiled “SoFi,” a soft robotic fish that can independently swim alongside real
fish in the ocean.
During
test dives in the Rainbow Reef in Fiji, SoFi swam at depths of more than 50
feet for up to 40 minutes at once, nimbly handling currents and taking
high-resolution photos and videos using (what else?) a fisheye lens.
Using its undulating tail and a unique ability to control its own buoyancy, SoFi can swim in a straight line, turn, or dive up or down. The team also used a waterproofed Super Nintendo controller and developed a custom acoustic communications system that enabled them to change SoFi’s speed and have it make specific moves and turns.
“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 the new journal article published today in Science Robotics.
“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 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.”
Katzschmann
worked on the project and wrote the paper with CSAIL director Daniela Rus,
graduate student Joseph DelPreto and former postdoc Robert MacCurdy, who is now
an assistant professor at the University of Colorado at Boulder.
How it works
Existing
autonomous underwater vehicles (AUVs) have traditionally been tethered to boats
or powered by bulky and expensive propellers.
In
contrast, SoFi has a much simpler and more lightweight setup, with a single
camera, a motor, and the same lithium polymer battery that’s found in consumer
smartphones.
To make the robot swim, the motor pumps water into two balloon-like chambers in the fish’s tail that operate like a set of pistons in an engine. 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.
To make the robot swim, the motor pumps water into two balloon-like chambers in the fish’s tail that operate like a set of pistons in an engine. 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.
These
alternating actions create a side-to-side motion that mimics the movement of a
real fish. By changing its flow patterns, the hydraulic system enables
different tail maneuvers that result in a range of swimming speeds, with an
average speed of about half a body length per second.
“The
authors show a number of technical achievements in fabrication, powering, and
water resistance that allow the robot to move underwater without a tether,”
says Cecilia Laschi, a 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.”
“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
entire back half of the fish is made of silicone rubber and flexible plastic,
and several components are 3-D-printed, including the head, which holds all of
the electronics.
To reduce the chance of water leaking into the machinery, the team filled the head with a small amount of baby oil, since it’s a fluid that will not compress from pressure changes during dives.
To reduce the chance of water leaking into the machinery, the team filled the head with a small amount of baby oil, since it’s a fluid that will not compress from pressure changes during dives.
Indeed,
one of the team’s biggest challenges was to get SoFi to swim at different
depths. The robot has two fins on its side that adjust the pitch of the fish
for up and down diving.
To adjust its position vertically, the robot has an adjustable weight compartment and a “buoyancy control unit” that can change its density by compressing and decompressing air.
To adjust its position vertically, the robot has an adjustable weight compartment and a “buoyancy control unit” that can change its density by compressing and decompressing air.
Katzschmann
says that the team developed SoFi with the goal of being as nondisruptive as
possible in its environment, from the minimal noise of the motor to the ultrasonic
emissions of the team’s communications system, which sends commands using
wavelengths of 30 to 36 kilohertz.
“The
robot is capable of close observations and interactions with marine life and
appears to not be disturbing to real fish,” says Rus.
The
project is part of a larger body of work at CSAIL focused on soft robots, which
have the potential to be safer, sturdier, and more nimble than their
hard-bodied counterparts.
Soft robots are in many ways easier to control than rigid robots, since researchers don’t have to worry quite as much about having to avoid collisions.
Soft robots are in many ways easier to control than rigid robots, since researchers don’t have to worry quite as much about having to avoid collisions.
“Collision
avoidance often leads to inefficient motion, since the robot has to settle for
a collision-free trajectory,” says Rus, the Andrew and Erna Viterbi Professor
of Electrical Engineering and Computer Science at MIT. “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.”
As
next steps the team will be working on several improvements on SoFi.
Katzschmann plans to increase the fish’s speed by improving the pump system and
tweaking the design of its body and tail.
He says that they also plan to soon use the on-board camera to enable SoFi to automatically follow real fish, and to build additional SoFis for biologists to study how fish respond to different changes in their environment.
“We
view SoFi as a first step toward developing almost an underwater observatory of
sorts,” says 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.”
This
project was supported by the National Science Foundation.