The fastest-ever swimming soft robot has been inspired by manta rays.
A team of American researchers beat its own speed record by drawing inspiration from the iconic sea creatures to improve their ability to control the robot’s movement in the water.
The record-breaking robot has fins shaped like those of a manta ray and is made of a material that is stable when the fins are spread wide.
Study corresponding author Professor Jie Yin, of North Carolina State University, said: “Two years ago, we demonstrated an aquatic soft robot that was able to reach average speeds of 3.74 body lengths per second.
“We have improved on that design. Our new soft robot is more energy efficient and reaches a speed of 6.8 body lengths per second,” Yin continued.
“In addition, the previous model could only swim on the surface of the water,” he said. “Our new robot is capable of swimming up and down throughout the water column.”
He explained that the robot’s fins are attached to a flexible, silicone body that contains a chamber that can be pumped full of air.
Inflating the air chamber forces the fins to bend – similar to the down stroke when a manta flaps its fins.
When the air is let out of the chamber, the fins spontaneously snap back into their initial position.
Study first author Haitao Qing, a Ph.D. student at North Carolina State University, said: “Pumping air into the chamber introduces energy into the system.
“The fins want to return to their stable state, so releasing the air also releases the energy in the fins,” Qing explained.
“That means we only need one actuator for the robot and allows for more rapid actuation.”
The research team, whose achievement was described in the journal Science Advances, said that studying the fluid dynamics of manta rays also played a key role in controlling the vertical movement of the robot.
Study co-author Jiacheng Guo, a Ph.D. student at the University of Virginia, said: “We observed the swimming motion of manta rays and were able to mimic that behavior in order 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 two jets of water that move them forward [and] alter their trajectory by altering their swimming motion.
“We adopted a similar technique for controlling the vertical movement of this swimming robot,” Guo continued.
“We’re still working on techniques that will give us fine control over lateral movements.”
Study co-author Dr. Yuanhang Zhu, an Assistant Professor of mechanical engineering at the University of California, Riverside, said: “Specifically, simulations and experiments showed us that the downward jet produced by our robot is more powerful than its upward jet.
“If the robot flaps its fins quickly, it will rise upward.
“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.”
Qing added: “Another factor that comes into play is that we are powering this robot with compressed air.
“That’s relevant because when the robot’s fins are at rest, the air chamber is empty, reducing the robot’s buoyancy. And when the robot is flapping its fins slowly, the fins are at rest more often,” Qing continued.
“In other words, the faster the robot flaps its fins, the more time the air chamber is full, making it more buoyant.”
The research team demonstrated the soft robot’s functionality in two different ways.
One iteration of the robot was able to navigate a course of obstacles arrayed on the surface and floor of a water tank.
The team also showed that the untethered robot was capable of hauling 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. And with only a single actuation input, our robot can navigate a complex vertical environment,” said Jie Yin, an associate professor of mechanical and aerospace engineering.
“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.”
