Venomous sidewinder rattlesnakes traverse sandy slopes in the American Southwest quickly and smoothly. By understanding how these snakes are able to accomplish these difficult feats, researchers have developed a robot that can navigate landscapes that rolling robots can’t. This serpentine template is described in Science this week.
From search-and-rescue operations and inspecting nuclear power plants to crawling through pipes and hunting for lost treasures in unstable caves, robots must traverse lots of different terrains covered in various substrates. One that can scramble over concrete rubble or a collapsed mine might be inoperable on a slippery, sandy hill. For an all-terrain limbless robot, researchers have turned to sidewinding snakes. To minimize slip, these rattlers lift certain body segments up while keeping others in contact with the ground. Previously, Howie Choset of Carnegie Mellon and colleagues built a sidewinding robot that moves fine across level ground, but couldn’t climb up an inclined sand trackway the way real snakes rapidly do. Because sidewinding hasn’t been studied much on loose, flowing material, we still don’t completely understand how it works and can’t fully replicate those moves.
So the researchers, together with a team led by Daniel Goldman from Georgia Institute of Technology, monitored six sidewinder rattlesnakes (Crotalus cerastes) at Zoo Atlanta as they climbed a sandy enclosed track at varying inclines. By recording their motions with high-speed video cameras, the team studied how deeply the snakes sank in the sand, the points of contact between snake and substrate, and how things changed with the angle of incline.
They found that sidewinders don’t slip on granular surfaces as the slope increases -- unlike other pit vipers who just tumble down the hill -- because as the incline steepens, the snakes increase the length of their bodies that’s in contact with the sand. “Think of the motion as an elliptical cylinder enveloped by a revolving tread, similar to that of a tank,” Choset explains in a news release. “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.”
At any moment, 25 percent of their body is in contact with the ground, Science explains, but they tune their motion to the terrain accordingly: On 10-degree slope, contact increases to 40 percent, and on a 30-degree slope, contact ups to 45 percent. Once this change was implemented in the robotic snake, it behaved a lot more like the real thing. The resulting robot passes horizontal and vertical waves through its body to move in 3D spaces. It’s about five centimeters in diameter and almost a meter long -- with 16 joints, each arranged perpendicular to the previous one.
What’s more, the team even got the robot to do things that snakes can’t (or won’t) do, such as turn on a dime. Here’s a very cool video where you can watch real sidewinders and robot sidewinders maneuvering on sand dunes:
Images: Nico Zevallos and Chaohui Gong (top), Adam Thompson (middle)