At the University of California San Diego (UC San Diego), engineers have developed a squid-like robot that can swim without being tethered and propel itself by producing jets of water.
The robot includes its own power source within its body. It can also carry a camera, for underwater exploration. The scientists have elaborated their work in a recent issue of Bioinspiration and Biomimetics.
Essentially, we recreated all the key features that squids use for high-speed swimming. This is the first untethered robot that can generate jet pulses for rapid locomotion like the squid and can achieve these jet pulses by changing its body shape, which improves swimming efficiency.
Michael T. Tolley, Study Senior Author and Professor, Department of Mechanical and Aerospace Engineering, University of California San Diego
Mainly, this squid robot has been made from soft materials such as an acrylic polymer, with some stiff, 3D-printed, and laser-cut parts. It is vital to use soft robots in underwater exploration to safeguard coral and fish, which could be affected by stiff robots. However, soft robots tend to move gradually and have trouble maneuvering.
The research group, including roboticists and experts in experimental fluid dynamics and computer simulations, resorted to using cephalopods as a fine model to overcome some of these problems. Squid, for instance, can reach the highest speeds of any aquatic invertebrates through the jet propulsion mechanism.
The robot developed by the researchers absorbs a volume of water into its body while accumulating elastic energy in its flexible ribs and skin. Then, it discharges this energy by squeezing its body and produces a jet of water to propel itself.
When the squid robot is resting, it is shaped approximately such as a paper lantern and has flexible ribs that serve as springs, along its sides. The ribs are linked to two circular plates at each end of the robot.
One of the ribs is linked to a nozzle that both absorbs water and releases it when the robot’s body is compressed. The other plate could carry a different type of sensor or a water-proof camera.
Initially, the engineers tested the robot in a water testbed in the laboratory of Professor Geno Pawlak, in the UC San Diego Department of Mechanical and Aerospace Engineering. Then, they took the robot out for a swim in one of the tanks at the UC San Diego Birch Aquarium at the Scripps Institution of Oceanography.
The engineers then showed that the robot could maneuver by adjusting the nozzle’s direction. Quite similar to any other underwater robot, waterproofing was the main concern for electrical components like the camera and battery. The speed of the robot was clocked at around 18 to 32 cm/second (approximately half a mile per hour), which is faster compared to a majority of the other soft robots.
After we were able to optimize the design of the robot so that it would swim in a tank in the lab, it was especially exciting to see that the robot was able to successfully swim in a large aquarium among coral and fish, demonstrating its feasibility for real-world applications.
Caleb Christianson, Study Lead, University of California San Diego
Christianson headed the study as part of his PhD work in Tolley’s research team and is currently a senior medical devices engineer at San Diego-based Dexcom.
The team carried out many experiments to determine the ideal size and shape for the nozzle that would drive the robot. This, in turn, enabled them to enhance the efficiency of the robot and its potential to maneuver and travel faster.
This was executed mostly by mimicking this type of jet propulsion, work that was performed under the guidance of Professor Qiang Zhu and his group in the Department of Structural Engineering at UC San Diego.
Furthermore, the team learned more about how to store energy in the elastic component of the skin and body of the robot, which is discharged later to produce a jet.
Engineers at the University of California San Diego have built a squid-like robot that can swim untethered, propelling itself by generating jets of water. The robot carries its own power source inside its body. It can also carry a sensor, such as a camera, for underwater exploration. Video Credit: University of California San Diego.
Christianson, C. M., et al. (2020) Cephalopod-inspired robot capable of cyclic jet propulsion through shape change. Bioinspiration and Biomimetics. doi.org/10.1088/1748-3190/abbc72.