Strange ‘swimming robot’ was inspired by manta rays: video

The ever-swimming soft robot is inspired by manta rays.

A team of American researchers beat its own speed record by taking inspiration from the iconic sea creatures to improve their ability to control the robot’s movement in 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.

Corresponding author of the study, Professor Jie Yin, of North Carolina State University, said: “Two years ago, we demonstrated a soft aquatic robot that was able to reach an average speed of 3.74 body lengths per second.

“We’ve improved that design. Our new soft robot is more energy efficient and reaches a speed of 6.8 body lengths per second,” continued Yin.

“Besides, the previous model could only float on the surface of the water,” he said. “Our new robot is capable of swimming up and down 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 flex – similar to the downward stroke when a manta flaps its fins.

When the air is released from the room, the fins spontaneously return to their initial position.

The study’s first author Haitao Qing, Ph.D. student at North Carolina State University, said: “Pumping air into the room puts energy into the system.

“The feathers want to return to their steady state, so releasing the air also releases energy in the feather,” Qing explained.

“This means we only need one actuator for the robot and allows for faster activation.”

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 robot’s vertical motion.

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 to control whether the robot swims towards the surface, swims down or maintains its position in the water column.

“When manta rays swim, they produce two currents of water that propel them forward [and] change their trajectory by changing their swimming motion.

“We adopted a similar technique to control the vertical movement of this swimming robot,” Guo continued.

“We’re still working on techniques that will give us good control over lateral movements.”

The co-author of the study, 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 wings quickly, it will rise up.

“But if we slow down the actuation frequency, it allows the robot to sink slightly between flapping its fins — allowing it to either dive down or swim at the same depth.”

Qing added: “Another factor that comes into play is that we are powering this robot with compressed air.

“This is important because when the robot’s fins are at rest, the air chamber is empty, reducing the robot’s movement. And when the robot flaps its feathers slowly, the feathers rest more often,” Qing continued.

“In other words, the faster the robot flaps its wings, the more time the air chamber is full, making it more buoyant.”

The research team demonstrated the functionality of the soft robot in two different ways.

One iteration of the robot was able to navigate an obstacle course placed on the surface and floor of a water tank.

The team also showed that the untethered robot was able to tow a payload on the surface of the water, including its own air and power source.

“This is a highly engineered design, but the basic concepts are quite simple. And with just 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 actuation modes, which will significantly increase the capabilities of this system.

“Our goal is to do this with a design that maintains that elegant simplicity.”