As a snake owner, I can personally attest to the fact that lack of limbs is no impediment to mobility. In fact, snakes are masters of moving over all kinds of terrain where wheeled or legged robots usually fail. They’re also excellent swimmers, and they can even jump and glide. Part of what makes snakes so adaptable is how they can choose from a variety of gaits depending on what they’re trying to do or where they’re trying to go. Robot snakes can do this too, and in some ways, they can do it even better, because they can execute behaviors that real snakes don’t know how to do, like rolling longitudinally to climb up poles (or legs).
We don’t mean to say that robot snakes would have real snakes trounced. Far from it: we have a lot to learn about how, and why, snakes move the way they do. In the latest issue of Science, researchers from Georgia Tech, roboticists from Carnegie Mellon, and herpetologists from Zoo Atlanta describe how sidewinders climb up steep sandy slopes, and show how snake robots can learn from their technique.
When a sidewinder moves, the parts of its body that are in contact with the ground remain still. This helps to minimize slip, especially on loose surfaces like sand or dirt. The value of this technique increases as slope increases, since slipping becomes more likely. However, the researchers wanted to figure out exactly how the snakes would change their gaits to better adapt to steeper slopes.
High speed footage of six adult sidewinders from Zoo Atlanta revealed that the snakes would progressively increase the length of their bodies in contact with the sand as the slopes got steeper (up to 20 degrees of incline), keeping themselves stable. Other kinds of pit vipers who didn’t use this sidewinding motion would tumble down the hill instead, which must have been frustrating for the poor snakes.
Once the researchers figured they had a reasonable idea of how this sidewinding gait worked, they taught it to one of CMU’ssnakebots, with excellent results, according to the paper: “despite the many differences between the biological and robot sidewinding, comparable performance was achieved through use of a similar strategy of increasing contact length with increases in [slope angle].”
Here’s how the researchers describe their findings:
“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 David Hu, an associate professor in Georgia Tech’s School of Mechanical Engineering. “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.”
“Think of the motion as an elliptical cylinder enveloped by a revolving tread, similar to that of a tank,” said Howie Choset, a Carnegie Mellon professor of robotics. “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.”
What’s the point of all this? Well, beyond being very cool that it’s possible to identify useful gait components in an animal, replicate them on a robot, and then use what the robot is doing to teach you more about what the animal is doing in the first place, snake robots are potentially useful when you know you’re going to need mobility, but you have no idea what kind of situations you might find yourself in.
Snake robots are versatile and durable, and teaching them to climb steep slopes covered in loose, granular material seems like it would come in especially handy somewhere like, oh, how about Mars? Or anywhere else in the solar system? We’re talking about snake robots in space, and I for one can’t imagine anything more awesome than that.