When the sandfish lizard wishes to escape predators, it can actually dive beneath the surface of the sand, and then swim through it. Inspired by the sandfish, researchers at the Georgia Institute of Technology have created an undulating robot that can likewise swim through a granular medium. While that medium has so far consisted of quarter-inch plastic balls in a lab setting, the team hopes that their robot – or one of its descendants – could someday be used to tunnel through debris to rescue earthquake victims.
The snake-like robot is composed of seven connected segments (each powered by a servo motor), encased in a latex sock which is then wrapped in a spandex swimsuit. At the front of the device is a wedge-shaped burrowing head, which closely resembles that of the lizard. Getting the angle of that head right took some research, however.
The sandfish itself has a doorstop-like head that forms a downward angle of 140 degrees with the horizontal plane. When the Georgia Tech team experimented with a robot head that sat at 155 degrees, the robot proceeded to swim down through the medium. When the tip of that head was then raised from 0 to 7 degrees, the robot's downward trajectory decreased until it became level. Once that tip was pointed above 7 degrees, the submerged robot proceeded to swim up out of the plastic balls.
Results of the tests with the robot matched those obtained by dragging blocks of wood, cut to different angles, through the medium. In the time since those tests were conducted, the robot has been equipped with an adjustable head, that can change its angle to move the robot up or down. The scientists are interested in seeing if the sandfish also changes the orientation of its head to steer itself through the sand.
They are now planning on testing their robot in material similar to that found at disaster sites.