Robo-Cthulhu: a robotic squid takes the plunge to see what lurks in the eldritch dark

Cthulhu might keep dreaming down in the murk of R’lyeh, but does he see any robots that look remotely like him swimming around in those blasphemous dreams?

Using bioinspiration from how a squid propels itself through the water, a team of scientists developed a robotic cephalopod that could pass for a distant relative of the Great Cthulhu. This alien-looking machine carries its own power source and camera while propelling itself through the water. The thing about soft robots is that they can make observations of undersea life — and even search for the bodies of accident victims and sunken evidence—without hard outer shells that risk damage to fish and coral and whatever else may lurk in the deep.

“The initial hurdle was developing a mechanism that could cyclically store elastic energy while intaking a volume of fluid and then rapidly release both the energy and jet of water,” Caleb Christianson, who led a study recently published in Bioinspiration and Biomimetics, told SYFY WIRE.

The squid bot was so successful because the same team of scientists, in collaboration with a team from UC Berkeley, had already been creating robotic sea creatures and previously developed another soft robot eerily reminiscent of a glowing eel. They weren’t the only ones. In 2017, researchers in China came up with a manta ray bot that glides through the water with flexible wings.

"The key with bioinspired design (as opposed to biomimicry) is to determine the essential components of a biological design that we need to reproduce to capture the beneficial properties of the biological system," Christianson's colleague and co-author Michael Tolley also told SYFY WIRE.

With so many advantages for surrounding flora and fauna, the only thing holding back many previous soft robots was their slowness. Getting them to swim fast when facing the resistance of water was the biggest challenge Christianson and his team had to overcome. Cephalopods like squid use jet propulsion to their advantage, rocketing in any direction by taking water into their mantle cavities and then ejecting it from their siphons. Changing speed and direction involves pointing the siphon elsewhere and adjusting the force used to suck in water and pump it out. This is why squid can reach some of the fastest speeds of any aquatic invertebrates.

"We narrowed down on an approach using a slip-gear that comprised a rack and pinion where the pinion (or gear) was fixed to a motor and had missing teeth. As the motor spun, the slip-gear pulled the ends of the robots together, sucking in water. When the gear slipped, the body of the robot elongated, ejecting a jet of water," Christianson said.

As the mechanical version of a squid, this robo-Cthulhu is made from an acrylic polymer and has flexible ribs along its sides, which are attached to a circular plate at each end. Connected to one of the plates is a waterproof camera or sensor. The other has an adjustable nozzle that functions like an actual squid’s siphon. Tentacles that can light up float at its sides. It moves just like a cephalopod when it takes water into its body then releases it. At about half a mile an hour, it is also faster than most soft robots. Swimming in a tank of actual sea creatures, it proved to be the first untethered robot that can get around using jet propulsion.

“Previous work has indicated that a key parameter for jet propulsion is the ratio of the amount of water ejected to the jet diameter (called the stroke ratio). There is an ideal ratio where all of the water ejected gets wrapped up in a single jet, which turns out to be the most efficient situation for propulsion," Tolley said. 

More robotic cephalopods could spawn from this in the future. The torpedo-like morphology of a squid, which can streamline itself even more to catch prey or escape predators even faster, is an asset to movement. Replicating this is almost as difficult as summoning the Old Ones (though not nearly as dangerous). Just figuring out the ideal size and shape for the nozzle, which is so critical to jet propulsion, took several experiments, but watching this creation swim is unreal. It pulses like some unknown species of cephalopod that looks right at home among fish that pass by and barely notice a strange contraption from the human world is among them.

"A soft robot like this one may be able to swim gently through coral reefs and among fish without the risk of propellers or hard, rigid parts that may damage the environment or sea life," said Christianson.

The bot also takes incredible HD underwater photos without scaring anything away like the presence of divers often does. If there was a R’lyeh, it would fit right in.