Imma Perfetto
Cosmos science journalist
Researchers in the US have taken inspiration from manta rays’ graceful bird-like motion to design a fast robot that can deftly manoeuvre in water.
They say their design for a soft, swimming robot, is suited for complex and unstructured environments, such as deep-sea exploration and environmental monitoring on the surface and underwater.
The new soft robot reaches a speed of 6.8 body lengths per second.
“The previous model could only swim on the surface of the water,” says Jie Yin, an associate professor of mechanical and aerospace engineering at North Carolina State University and corresponding author of a paper describing the work in Science Advances.
“Our new robot is capable of swimming up and down throughout the water column.”
Its fins, shaped like those of a manta ray, are attached to a flexible, silicone body which contains a chamber that can be pumped full of air.
Inflating the chamber forces the fins to bend in a similar way to the downstroke of a manta flapping its fins. When the air is let out of the chamber, the fins spontaneously snap back into their initial position.
A power supply and air pump floats on the water’s surface connected to the robot by a small air tube.
Co-author of the paper Jiacheng Guo, a PhD student at the University of Virginia, says: “We observed the swimming motion of manta rays and were able to mimic that behaviour to control whether the robot swims toward the surface, swims downward, or maintains its position in the water column.
“When manta rays swim, they produce 2 jets of water that move them forward. Mantas alter their trajectory by altering their swimming motion,” Guo says.
“We adopted a similar technique for controlling the vertical movement of this swimming robot.”
According to co-author Yuanhang Zhu, an assistant professor of mechanical engineering at the University of California, Riverside, the downward jet of water produced by the robot is more powerful that its upward jet.
“If the robot flaps its fins quickly, it will rise upward,” says Zhu.
“But if we slow down the actuation frequency, this allows the robot to sink slightly in between flapping its fins – allowing it to either dive downward or swim at the same depth.”
The air chamber is also full for longer when the robot is flapping its wings more rapidly, making it more buoyant.
The researchers showed that their manta-inspired robot could navigate obstacles on the surface and floor of a water tank. It could also haul a payload on the surface of the water, including its own air and power source.
“This is a highly engineered design, but the fundamental concepts are fairly simple,” says Yin.
“With only a single actuation input, our robot can navigate a complex vertical environment.
“We are now working on improving lateral movement, and exploring other modes of actuation, which will significantly enhance this system’s capabilities. Our goal is to do this with a design that retains that elegant simplicity.”
