Snakes Not on a Plain
The amazing ability of sidewinder snakes to quickly climb sandy slopes was once something that puzzled biologists and that roboticists only dreamed of replicating. But, by studying the snakes in a unique bed of inclined sand and using a snake-like robot to test ideas spawned by observing the real animals, both biologists and roboticists have now gained long-sought insights.
In a study published in the journal Science, researchers from Georgia Tech, Carnegie Mellon University, Oregon State University, and Zoo Atlanta report that sidewinders improve their ability to traverse sandy slopes by simply increasing the amount of their body area in contact with the granular surfaces they’re climbing.
As part of the study, the researchers used a modular snake robot to test principles used by the sidewinders. Before the study, the snake robot was unable to climb the inclined sand trackway the real snakes could gracefully ascend. However, when the robot was programmed with the unique wave motion discovered in the sidewinders, it was able to climb slopes it would have been unable to otherwise.
“Our initial idea was to use the robot as a physical model to learn what the snakes experienced,” said Daniel Goldman, an associate professor in Georgia Tech’s School of Physics. “By studying the animal and the physical model simultaneously, we learned important general principles that allowed us to not only understand the animal, but to also improve the robot.”
“We realized that the sidewinder snakes use a template for climbing on sand, two orthogonal waves that they can control independently.” — Hamid Marvi
The detailed study showed that both horizontal and vertical motion had to be understood and then replicated on the snake-like robot for it to be useful on sloping sand.
“During sidewinding, the snake lifts a section of its body and moves it forward, places it down on the sand, then repeats the motion,” explained Henry Astley, a postdoctoral fellow in Goldman’s lab. “This allows the snake to move with a stepping motion, even though the animal doesn’t have legs, and the belly never slides against the substrate. As the slope increases, the snake places more body in contact with the sand.”
Using high-speed video cameras, the researchers observed several sidewinders at Zoo Atlanta as they moved in a large enclosure containing sand from the Arizona desert.
“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 in the laboratory of Associate Professor David Hu in Georgia Tech’s School of Mechanical Engineering. “We used the snake robot to systematically study the failure modes in sidewinding.”
The modular snake robot used in this study was specifically designed to pass horizontal and vertical waves through its body to move in three-dimensional spaces. The Carnegie Mellon robot is 2 inches in diameter and 37 inches long; its body consists of 16 joints that allow it to move using a variety of gaits – some similar to those of a biological snake.
“In this study, we got biology and robotics, mediated by physics, to work together in a way not previously seen.” — Howie Choset
“This type of robot often is described as biologically inspired, but too often the inspiration doesn’t extend beyond a casual observation of the biological system,” said Howie Choset, a Carnegie Mellon professor of robotics. “In this study, we got biology and robotics, mediated by physics, to work together in a way not previously seen.”
The robot could be used in search and rescue operations, for archaeological explorations, and for inspecting piping in facilities such as nuclear power plants. Many people dislike snakes, but in this study, the venomous animals were easy study subjects that provided knowledge that may one day benefit humans, noted Joe Mendelson, director of research at Zoo Atlanta.
“If a robot gets stuck in the sand, that’s a problem, especially if that sand happens to be on another planet,” he said. “Sidewinders never get stuck in the sand, so they are helping us create robots that can avoid getting stuck. These venomous snakes are offering something to humanity.”
For Goldman’s team, the work builds on earlier research on how turtle hatchlings, crabs, sandfish lizards, and other animals move on complex surfaces such as sand. In its research, the team tested what it learned from the animals on robots, often gaining additional insights into how the animals move.
Co-authors of the Science article included Chaohui Gong and Matthew Travers from Carnegie Mellon University, and Nick Gravish from Georgia Tech. The research was funded by the National Science Foundation, the Army Research Office, and the Army Research Laboratory.
The opinions expressed are those of the authors and do not necessarily represent the official views of the sponsoring agencies.