No obstacle too high for climbing snakebots

Bryn Nelson Columnist

Snake-like robots that can climb scaffolding to inspect high-rise construction sites, bend at will to defuse roadside bombs or roll down your esophagus to peer at your digestive tract may soon be lending construction workers, soldiers and doctors a flexible hand.

Among the growing menagerie of crawling, scuttling, swimming and slithering robots, researchers have developed a collection of articulated snakebots that reach beyond the usual repertoire of biological motion by literally rolling up or down obstacles.

Dennis Hong, director of the Robotics & Mechanisms Laboratory (RoMeLa) at Virginia Tech in Blacksburg, Va., said most snake-inspired robots have been engineered for sidewinding or other ground-based locomotion. Likewise, his lab’s HyDRAS-Ascent prototype (or Hyper-redundant Discrete Robotic Articulated Serpentine) can unfold and move around on the ground.

But the big idea behind the 3-foot-long snakebot, which came to Hong in a middle-of-the-night inspiration, was to use flexible universal joints to let the mechanical snake roll up poles, scaffolds and other structures.

“The quick big picture application is reducing human injuries — and ultimately death— at construction sites,” said Gabriel Goldman, a graduate student in Hong’s lab who has worked extensively on the award-winning project.

Goldman cited recent U.S. Bureau of Labor Statistics reports, which suggest that falls remain a major source of workplace fatalities. They accounted for 355 of the 877 reported deaths among construction workers in the bureau’s preliminary report for 2007, for example.

For the past decade, falls have been second only to highway incidents in the number of reported work-related deaths.

Snakebots equipped with built-in cameras and sensors could take the place of workers in performing dangerous tasks like visual inspections of high-rises or bridge piers.

“The pole doesn’t have to be circular,” Goldman said. “Imagine you have a rectangular or square support — as long as there’s sufficient area to contact, it could be used on other workplace structures.”

But how does the snake hold on?

Courtesy of Dennis Hong/Virginia Tech Like its simpler counterpart, this coiled HyDRAS-Ascent II snakebot uses flexible universal joints between its segments to create a wobbling motion. The overall effect: an up or down rolling motion without the need for actual wheels.

“Imagine you’re holding a Coke can,” he said. “Similarly, the snake would be holding that pole using its grasping force.” The HyDRAS-Ascent and its more powerful successor, the HyDRAS-Ascent II, can wrap around a pole in either a helical or doughnut-like shape.

The climbing movement, he said, is akin to that of rotational joints in the human body. Your fingers, for example, have single rotational joints that allow each digit to bend forward. The snake robots have a universal joint structure, in which two rotational joints intersect like a plus sign. The result is a capacity for much broader movement, like the rotation of your wrists.

Within each HyDRAS robot, small electric motors generate an oscillating motion at the universal joints between each module, leading to a sort of wobble along the entire length.

“The cool thing is that you can coordinate that in a particular way,” Hong said, “and the entire snake actually generates a rolling motion, twisting about its own axis, so that it actually rolls up the pole — but it’s not on wheels.”

The unusual motion offers other advantages.

“Let’s say you’re rolling up a pole and you come to a T-junction or an X-junction,” Hong said. The robot could unwrap its head and use a camera to look around, letting the controller choose where to direct it next. “Even if the pole diameter changes, or if it changes from circular to rectangular, you can get the snake to move over obstacles or take a branch if it’s a tree-like structure,” he said.

A related robot called CIRCA (or Climbing Inspection Robot with Compressed Air), relies on artificial muscles that could tap a construction site’s compressed air stores to contract and expand. “When you put pressure into them, they contract like your arm does. It’s like you’re taking your arm and putting your bicep up,” Goldman said. That contraction generates the wobbling motion that collectively creates the roll.

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