For those unfortunate enough to be trapped in a caved-in mine or under the rubble of a collapsed building, the chance of being rescued largely depends upon trained humans and dogs. The equipment they may be outfitted with—thermal imaging sensors, carbon dioxide detectors and flexible video cameras—may also provide some limited help.
But those buried too deeply for searchers to detect them must put all hope of rescue upon the slim possibility that first responders uncover them by chance. For this reason, researchers are trying to develop search and rescue robots that could vastly improve the odds for victims trapped underground.
“The dream and goal in this field is to turn a robot into a multifunctional device capable of moving everywhere,” says Daniel Goldman, a physicist at the Georgia Institute of Technology. “We’re seeking inspiration for how teams of little robots could self-organize to create structures that allow them to efficiently and effectively move around in nasty environments.”
Goldman and colleagues from the physics and biology departments turned to fire ants for clues about how organisms manage to navigate in confined underground environments. Until recently, not much was known about subterranean ant locomotion, including whether the insects get caught in traffic jams or lose their footing in the tunnels.
Getting a glimpse of the invisible
The team collected thousands of fire ants from around the university’s campus and placed them in containers filled with soil-mimicking materials of various particle diameters and moisture levels. They constantly monitored the animals with high-speed-video tracking equipment and peered in on the 3-dimensional tunnels with X-ray computed tomography. Depending upon soil type and moisture levels, the ants’ underground excavations varied in length and direction, the team found, but the tunnel diameter always remained the same—just slightly larger than the length of an ant. The researchers think the creatures engineer their tunnels this way to optimize movement and reduce the need for complex neural processing—akin to the way stairs in buildings optimize human movement by adhering to a certain height and width.
In a second experiment, the researchers placed ants in glass tubes of different diameters, and then occasionally fired an air piston that jolted the tubes and caused the ants to lose their grip. Surprisingly, the team discovered, the ants quickly arrested their fall and even used their antennae to grip the sides of the tubes and stabilize themselves. The larger the diameter, however, the more difficult it was for them to stop their fall. “This experiment wasn’t simulating any sort of perturbation ants may experience in their natural environment,” says physicist Nick Gravish, the lead author of a paper describing the study in Proceedings of the National Academy of Sciences. “We needed to experimentally make them slip to tease out their behaviors.”
“When you see the behaviors these ants do when they’re flung from the walls, it’s just hilarious and totally unexpected,” Goldman adds.
Antennae to the rescue
Thanks to the high-speed camera, the team noticed that ants do trip in their subterranean tunnels and use their antennae and limbs to brace themselves, though those falls are miniscule compared to the ones artificially induced by the researchers. The tunnel’s purposeful diameter allows the ants to quickly recover from slips. “This is just a subtle slip, but it’s very important because it shows their capabilities to use their antennae and limbs,” Gravish says. “The ants can arrest themselves rapidly, whereas in a slightly larger tunnel they wouldn’t be able to do that.”
The team thinks these initial findings may someday lead to biologically inspired robots that apply the same principles and behaviors to search and rescue missions. “Organisms have solved lots of interesting problems of how to move around in the natural environment,” Goldman says. If all goes well, he says, in future disaster zones we could have multitudes of mechanical ants or “little robots that look like cockroaches that will swarm all over the place.”
Top Image: Frame from a high-speed camera that recorded how a fire ant arrested its fall in a synthetic tunnel. Courtesy Daniel Goldman/ Georgia Institute of Technology.