Reptile inspires rescuers
Machines able to navigate through the rubble of buildings in the aftermath of disasters such as earthquakes would be of great benefit to rescuers, saving vital time in the search for those trapped alive in the debris, but building effective machines is extremely challenging. Researchers at the Georgia Institute of Technology recently built a robot that can penetrate and 'swim' through granular material. They have now shown that varying the shape or adjusting the inclination of the robot's head affects the robot's movement in complex environments.
"We discovered that by changing the shape of the sand-swimming robot's head or by tilting its head up and down slightly, we could control the robot's vertical motion as it swam forward within a granular medium," explained Daniel Goldman, an assistant professor in the Georgia Tech School of Physics.
Desert reptile mechanics
"The biological inspiration for our sand-swimming robot is the sandfish lizard, which inhabits the Sahara desert in Africa and rapidly buries into and swims within sand," explained Goldman. "We were intrigued by the sandfish lizard's wedge-shaped head that forms an angle of 140 degrees with the horizontal plane, and we thought its head might be responsible for or be contributing to the animal's ability to maneuver in complex environments."
For their experiments, the researchers attached a wedge-shaped block of wood to the head of their robot, which was built with seven connected segments, powered by servo motors, packed in a latex sock and wrapped in a spandex swimsuit. The doorstop-shaped head – resembling that of the sandfish – had a fixed lower length of approximately 4 inches, height of 2 inches and a tapered snout. The researchers examined whether the robot's vertical motion could be controlled simply by varying the inclination of the robot's head. Before each experimental run in a test chamber filled with plastic spheres which had a 0.25 inch diameter, the researchers submerged the robot a couple of inches into the granular medium and leveled the surface. Then they tracked the robot's position until it reached the end of the container or swam to the surface.
Effect of adjustments
The researchers investigated the vertical movement of the robot when its head was placed at five different degrees of inclination. They found that when the sandfish-inspired head with a leading edge that formed an angle of 155 degrees with the horizontal plane was set flat, negative lift force was generated and the robot moved downward into the media. As the tip of the head was raised from zero to 7 degrees relative to the horizontal, the lift force increased until it became zero. At inclines above 7 degrees, the robot rose out of the medium. "The ability to control the vertical position of the robot by modulating its head inclination opens up avenues for further research into developing robots more capable of maneuvering in complex environments, like debris-filled areas produced by an earthquake or landslide," said Goldman. The robotics results matched the research team's findings from physics experiments and computational models designed to explore how head shape affects lift in granular media.
"While the lift forces of objects in air, such as airplanes, are well understood, our investigations into the lift forces of objects in granular media are some of the first ever," he added. Being able to precisely control the tilt of the head will allow the researchers to implement different strategies of head movement during burial and determine the best way to wiggle deep into sand. The researchers also plan to test the robot's ability to maneuver through material similar to the debris found after natural disasters and plan to examine whether the sandfish lizard adjusts its head inclination to ensure a straight motion as it dives into the sand.