Manta ray fins inspire new swimming soft robot

The new swimming robot was engineered by researchers at NC State University and is detailed in Science Advances.

“Two years ago, we demonstrated an aquatic soft robot that was able to reach average speeds of 3.74 body lengths per second,” said Jie Yin, corresponding author of a paper on the work and an associate professor of mechanical and aerospace engineering at NC State. “We have improved on that design.”

According to Yin the new soft robot can reach an average speed of 6.8 body lengths per second and is more energy efficient. The new robot is also capable of swimming underwater.

“The previous model could only swim on the surface of the water. Our new robot is capable of swimming up and down throughout the water column,” Yin said in a statement.

The swimming robot’s fins are similar to those of a manta ray. Attached to a flexible body made of silicone, the fins can flap but remain stable when fully spread out. The robot’s body has an air chamber that, when inflated, forces the fins to bend, which is like a manta ray’s downward stroke. When the air is released, the fins move back into their initial position.

“Pumping air into the chamber introduces energy into the system,” said Haitao Qing, first author of the paper and a PhD student at NC State. “The fins want to return to their stable state, so releasing the air also releases the energy in the fins. That means we only need one actuator for the robot and allows for more rapid actuation.”

Qing said their compressed-air power system also helps it swim up and down. Qing added that when the robot’s wings are at rest the air chamber is empty, which decreases buoyancy; and the faster it flaps its fins, the fuller the air chamber becomes, thereby increasing buoyancy. 

The researchers showed their soft robot could navigate an underwater obstacle course and was also strong enough to tow a payload along the surface.

“This is a highly engineered design, but the fundamental concepts are fairly simple,” said Yin. “And with only a single actuation input, our robot can navigate a complex vertical environment.”