Watch a Snake Robot Go for a Swim


When sea snakes swim, they wind their way through the water by flicking their flattened tails, which is super graceful but requires a whole lot of coordination. So when roboticists at Carnegie Mellon University decided that it was time for their landlubbing robot snake to take to the water, they took a shortcut. They approximated the wildly complex biomechanics of a serpentand then loaded the machine with propellers.

The result is a sort of wiggling torpedo, sans warhead: the Hardened Underwater Modular Robot Snake. As you can see in the video below, it manages some impressive swimming by combining an aft thruster to produce forward movement with lateral thrusters along its body for stability control, plus it uses some bending joints (actuators, in the parlance) to position the lateral thrusters. It’s less biologically inspired right now, but still, it’s a pretty good robot, says CMU roboticist Howie Choset, who codeveloped the machine. We’re doing something in the middle. We’re trying to mimic the motion as best as we can, maybe at a macroscopic level, with conventional motors and actuation.

Courtesy of CMU

Thats the beauty of roboticsengineers dont have to follow the rules of natural selection. Choset and his colleagues want a robot that the US Navy can use to inspect ships and submarines, one that can slip into tight spaces, like ballast tanks. But its safe to say that the Navy doesnt need a snake robot that also, lets say, bites. When biology is evolving, it’s evolving a system, says Choset. It’s not evolving one unique capability. So a snake can slither on the ground in unique ways, but the snake also poops, it also eats, it also reproducesit has all these other things onboard that are there for the survival of the snake but certainly not to serve locomotive benefits in any way.

Think about how a bird compares to an airliner, which is biologically inspired in that it produces lift with wings, but those wings are fixed and paired with jet engines. And theyre missing a few of the add-ons that nature gave birds. Airplanes fly long distances, but their wings don’t flap, and they don’t have feathers, says Choset.

Chosets team can approach snake design in a way thats fundamentally different from evolution. The land-based version of their robot uses actuators that move in concert to propel the machine forward, which is similar to what a real snake does. But in the water, the robot doesnt have a hard surface to push off ofdrop the land version in a pool and itll sink like a very expensive stone. So instead of reproducing a sea snakes hypnotic winding movementsa complicated coordination between muscle and bonethe researchers opted for thrusters that push and steer the robot.

Courtesy of CMU

At the moment, the robots swimming isnt particularly sophisticated, though an operator can remote-control the machine through underwater hoops using a camera in the snakes face to find the way. But the teams idea is to refine the algorithms that control its movement by using machine learning: By building a digital version of the robot in simulation, an AI can try many, many random ways of swimming, eventually landing on the most efficient kind of locomotion through trial and error. Then Chosets team would port that knowledge into the real-world robot, giving it the maneuverability it would need to really squirm into tight spaces. Other roboticists are doing this with other machines that mimic animals locomotion, in fact, for instance teaching a doglike four-legged robot how to walk or adapt to different kinds of surfaces.



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