The researchers from the University of California San Diego detail their work in Bioinspiration and Biomimetics.
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"Essentially, we recreated all the key features that squids use for high-speed swimming," said Michael T. Tolley, one of the paper's senior authors and a professor in the Department of Mechanical and Aerospace Engineering at UC San Diego. "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."
This squid robot is composed mainly of soft materials such as acrylic polymer, plus a few rigid, 3D printed and laser cut parts. Soft robots in underwater exploration can protect fish and coral but they tend to move slowly and have difficulty manoeuvring. This prompted the research team to look at cephalopods to solve some of these issues. In particular, squid can reach the fastest speeds of any aquatic invertebrates due to a jet propulsion mechanism.
According to UC San Diego, the team’s robot takes a volume of water into its body while storing elastic energy in its skin and flexible ribs. It then releases this energy by compressing its body and generates a jet of water to propel itself.
At rest, the squid robot is shaped roughly like a paper lantern, and has flexible ribs, which act like springs, along its sides. The ribs are connected to two circular plates at each end of the robot. One of them is connected to a nozzle that both takes in water and ejects it when the robot's body contracts. The other plate can carry a water-proof camera or a different type of sensor.
Engineers first tested the squid robot in a water testbed in the lab of Professor Geno Pawlak, in the UC San Diego Department of Mechanical and Aerospace Engineering. It was then tested in a tank at the UC San Diego Birch Aquarium at the Scripps Institution of Oceanography.
They demonstrated that the robot could steer by adjusting the direction of the nozzle and recorded its speed at about 18 to 32cm per second, which is faster than most other soft robots.
"After we were able to optimise 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," said Caleb Christianson, who led the study as part of his Ph.D. work in Tolley's research group.
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