After the World Trade Towers collapsed in 2001, rescuers dispatched shoe box–size robots to explore the debris for trapped victims. Using two miniature bulldozer treads to muscle over the ruins and a video camera to beam back images, the robots managed to find a few remains. But what they really needed was a way to peer inside all the openings and crevices dammed up by curtains, paper, and loose materials.
Daniel Goldman, a biophysicist at Georgia Tech, is building just such a tool. His latest robot behaves less like an ATV and more like a sandfish lizard, relying on a chain of six motors encased in slick spandex to mimic that animal’s undulating motion. Last June a prototype version managed to crawl through a box of plastic beads, a significant first step toward more challenging environments such as rubble.
Goldman began the project by learning everything he could about reptile physics. To start, he placed a sandfish lizard in a vat of sand and snapped 1,000 X-ray images each second as it wiggled its way beneath the surface. He then broke down its motion frame by frame to characterize the movement of the lizard’s body in relation to the sand around it. He also calculated variations in the density and size of the sand particles affecting the lizard’s friction, drag, and thrust. When Goldman fed this torrent of data into a computer model, he discovered that the main mechanism underlying sand swimming was a wave that passed from head to tail, pushing off from the sand and generating enough thrust to propel the lizard forward. His robot now uses the same motion to move steadily at about three and a half inches per second.
This May, Goldman upgraded the design with a wedge that can be tilted up or down to allow the robot to burrow deeper or snake its way back to the surface. Robin Murphy, the Texas A&M computer scientist behind the 9/11 robots, calls Goldman’s work “very exciting,” but we hope the tool sees little use.