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Top. A sidewinder. Bottom A robot model. |
The amazing ability of sidewinder snakes to quickly climb
sandy slopes was once something biologists only vaguely understood and
roboticists only dreamed of replicating. 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 October 10 issue of the journal Science, researchers from the
Georgia Institute of Technology, 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 principles used by the sidewinders to gracefully climb
sand dunes were tested using a modular snake robot developed at Carnegie
Mellon. Before the study, the snake robot could use one component of
sidewinding motion to move across level ground, but was unable to climb the
inclined sand trackway the real snakes could readily ascend. In a real-world
application – an archaeological mission in Red Sea caves – sandy inclines were
especially challenging to the robot.
However,
when the robot was programmed with the unique wave motion discovered in the
sidewinders, it was able to climb slopes that had previously been unattainable.
The research was funded by the National Science Foundation, the Army Research
Office, and the Army Research Laboratory.
“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 also to improve the robot.”
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.
“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.”
At
Zoo Atlanta, the researchers observed several sidewinders as they moved in a
large enclosure containing sand from the Arizona desert where the snakes live.
The enclosure could be raised to create different angles in the sand, and air
could be blown into the chamber from below, smoothing the sand after each snake
was studied. Motion of the snakes was recorded using high-speed video cameras
which helped the researchers understand how the animals were moving their
bodies.
“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.”
Limbless
animals like snakes can readily move through a broad range of surfaces, making
them attractive to robot designers.
"The
snake is one of the most versatile of all land animals, and we want to capture
what they can do," said Ross Hatton, an assistant professor of mechanical
engineering at Oregon State University who has studied the mathematical
complexities of snake motion, and how they might be applied to robots.
"The desert sidewinder is really extraordinary, with perhaps the fastest
and most efficient natural motion we've ever observed for a snake."
Many
people dislike snakes, but in this study, the venomous animals were easy study
subjects who 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 in the
sand. These venomous snakes are offering something to humanity.”
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 robot is two inches in diameter and 37 inches long; its body
consists of 16 joints, each joint arranged perpendicular to the previous
one. That allows it to assume a number of configurations and to move
using a variety of gaits – some similar to those of a biological snake.
“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,” Choset said. “In this study, we got biology and robotics, mediated by
physics, to work together in a way not previously seen.”
Choset’s
robots appear well suited for urban search-and-rescue operations in which
robots need to make their way through the rubble of collapsed structures, as
well as archaeological explorations. Able to readily move through pipes, the
robots also have been tested to evaluate their potential for inspecting nuclear
power plants from the inside out.
For
Goldman’s team, the work builds on earlier research studying how turtle
hatchlings, crabs, sandfish lizards, and other animals move about on complex
surfaces such as sand, leaves, and loose material. The team tests what it
learns from the animals on robots, often gaining additional insights into how
the animals move.
“We
are interested in how animals move on different types of granular and complex
surfaces,” Goldman said. “The idea of moving on flowing materials like sand can
be useful in a broad sense. This is one of the nicest examples of collaboration
between biology and robotics.”
Note you can see video of the snakes and robots inaction on several websites. Try this one.
Citation:
Hamidreza Marvi, Chaohui Gong, Nick Gravish, Henry Astley, Matthew Travers, Ross L. Hatton,Joseph R. Mendelson III, Howie Choset, David L. Hu, and Daniel I. Goldman. 2014. Sidewinding with minimal slip: Snake and robot ascent of sandy slopes. Science 2014: 346 (6206), 224-229. [DOI:10.1126/science.1255718]