Most underwater robots use one of two ways of getting around. Way one is with propellers, and way two is with fins. But animals have shown us that there are many more kinds of underwater locomotion, potentially offering unique benefits to robots. We’ll take a look at two papers from ICRA this year that showed bioinspired underwater robots moving in creative new ways: A jet-powered squid robot that can leap out of the water, plus a robotic scallop that moves just like the real thing.
Prototype of the squid robot in (a) open and (b) folded states. The soft fins and arms are controlled by pneumatic actuators. Image: Beihang University
This “squid-like aquatic-aerial vehicle” from Beihang University in China is modeled after flying squids. Real squids, in addition to being tasty, propel themselves using water jets, and these jets are powerful enough that some squids can not only jump out of the water, but actually achieve controlled flight for a brief period by continuing to jet while in the air. The flight phase is extended through the use of fins as arms and wings to generate a little bit of lift. Real squids use this multimodal propulsion to escape predators, and it’s also much faster—a squid can double its normal swimming speed while in the air, flying at up to 50 body lengths per second.
The squid robot is powered primarily by compressed air, which it stores in a cylinder in its nose (do squids have noses?). The fins and arms are controlled by pneumatic actuators. When the robot wants to move through the water, it opens a value to release a modest amount of compressed air; releasing the air all at once generates enough thrust to fire the robot squid completely out of the water.
The jumping that you see at the end of the video is preliminary work; we’re told that the robot squid can travel between 10 and 20 meters by jumping, whereas using its jet underwater will take it just 10 meters. At the moment, the squid can only fire its jet once, but the researchers plan to replace the compressed air with something a bit denser, like liquid CO2, which will allow for extended operation and multiple jumps. There’s also plenty of work to do with using the fins for dynamic control, which the researchers say will “reveal the superiority of the natural flying squid movement.”
“Design and Experiments of a Squid-like Aquatic-aerial Vehicle With Soft Morphing Fins and Arms,” by Taogang Hou, Xingbang Yang, Haohong Su, Buhui Jiang, Lingkun Chen, Tianmiao Wang, and Jianhong Liang from Beihang University in China, was presented at ICRA 2019 in Montreal.
The EPFL researchers studied the morphology and function of a real scallop (a) to design their robot scallop (b), which consists of two shells connected at a hinge and enclosed by a flexible elastic membrane. The robot and animal both swim by rapidly, cyclicly opening and closing their shells to generate water jets for propulsion. When the robot shells open, water is drawn into the body through rear openings near the hinge. When the shells close rapidly, the water is forced out, propelling the robot forward (c). Image: EPFL
RoboScallop, a “bivalve inspired swimming robot,” comes from EPFL’s Reconfigurable Robotics Laboratory, headed by Jamie Paik. Real scallops, in addition to being tasty, propel themselves by opening and closing their shells to generate jets of water out of their backsides. By repetitively opening their shells slowly and then closing quickly, scallops can generate forward thrust in a way that’s completely internal to their bodies. Relative to things like fins or spinning propellers, a scallop is simple and robust, especially as you scale down or start looking at large swarms of robots. The EPFL researchers describe their robotic scallop as representing “a unique combination of robust to hazards or sustained use, safe in delicate environments, and simple by design.”
And here’s how the real thing looks:
As you can see from the video, RoboScallop is safe to handle even while it’s operating, although a gentle nibbling is possible if you get too handsy with it. Since the robot sucks water in and then jets it out immediately, the design is resistant to fouling, which can be a significant problem in marine environments. The RoboScallop prototype weighs 65 grams, and tops out at a brisk 16 centimeters per second, while clapping (that’s the actual technical) at just over 2.5 Hz. While RoboScallop doesn’t yet steer, real scallops can change direction by jetting out more water on one side than the other, and RoboScallop should be able to do this as well. The researchers also suggest that RoboScallop itself could even double as a gripper, which as far as I know, is not something that real scallops can do.