Snake-bot scales sandy slopes with sidewinder slither

Carnegie Mellon's modular robotic snake is able to traverse sandy environments, thanks to lessons learned from sidewinder snakes.

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Nico Zevallos and Chaohui Gong

They may not have legs, but snakes know how to get around: they can swim, climb, even glide through the air. If you could make a robot that could tap into snake locomotion, you'd have one versatile mechanical beast.

Modsnake -- a modular robotic snake that has been in development at Carnegie Mellon -- is working on that. Now, thanks to some assistance from researchers at Georgia Institute of Technology, Oregon State University and Zoo Atlanta, the robot will be able to learn to slither from the real-life sidewinding gait.

Although Modsnake's previous sidewinding gait was inspired by real snakes, it wasn't precisely like the gait of a real snake: it used one horizontal and one vertical sine wave, interacting to move the snake sideways.

If the Modsnake were to be placed on a sandy slope using this gait, parts of its body would dig into the sand -- which is not how a real snake sidewinds. Indeed, the Modsnake had real difficulty on sand and sandy slopes. Instead, the snake stretches its body out, staying low and increasing the amount its body in contact with the ground, using a series of wave motions to propel itself along by holding the parts of its body in contact with the ground still and only moving the parts it lifts off the ground.

"We realized that the sidewinder snakes use a template for climbing on sand, two orthogonal waves that they can control independently," said Hamid Marvi, a postdoctoral fellow at Carnegie Mellon who conducted the experiments while he was a graduate student at Georgia Tech. "We used the snake robot to systematically study the failure modes in sidewinding. We learned there are three different failure regimes, which we can avoid by carefully adjusting the aspect ratio of the two waves, thus controlling the area of the body in contact with the sand."

The Modsnake robot was programmed to move by passing both horizontal and vertical waves through its body in order to move through three-dimensional space.

"Think of the motion as an elliptical cylinder enveloped by a revolving tread, similar to that of a tank," said Carnegie Mellon professor of robotics Howie Choset. "As the tread circulates around the cylinder, it is constantly placing itself down in front of the direction of motion and picking itself up in the back. The snake lifts some body segments while others remain on the ground, and as the slope increases, the cross section of the cylinder flattens."

You can read more about Modsnake on its official website, and find the full paper online in the journal Science.