It’s possible that if you were trapped under a pancaked skyscraper after an earthquake, or in a mine that had just collapsed, you’d be totally fine with getting rescued by a giant robot cockroach. What are you going to do? Say, “No, thanks, I’m good, send something cute"?
Even if you did request something more charismatic, odds are it couldn’t reach you. The American cockroach, says a paper out today, is perfectly adapted for getting into tiny spaces a human-shaped rescuer might not, thanks to a collapsible exoskeleton and really creepy mode of locomotion. The cockroach, it turns out, is a good model for a rescue robot. The researchers even built a prototype. It skitters.
Yes, it had to be cockroaches. “We are not entomologists. We also think they’re disgusting,” says Robert Full, who works on biomechanics and animal locomotion at UC Berkeley and is lead author on the article, published in the Proceedings of the National Academy of Sciences. “But they can teach us bigger principles.” As is typical for insects, cockroaches have an exoskeleton---overlapping plates of a tough material called chitin held together with a flexible membrane. In the wild, that flexibility lets American cockroaches run about 5 feet per second, more than 3 mph. So, terrible.
It gets worse. Full and his colleague, Kaushik Jayaram, sent the cockroaches through lower and lower spaces, as if making them go under a limbo stick. They found that the bugs could fit into a space less than a quarter of their height by collapsing their exoskeletons nearly in half, spreading out to the sides. It takes less than a second and it barely slows them down, thanks to a form of locomotion the researchers named “body-friction legged crawling.” It looks like a cross between the way sand-swimming lizards move through sand and how sea turtle hatchlings use their flippers to move across it. “Except drag on your belly and on your back is different than what you see in swimming or moving through sand, where the medium is all over your body,” Full says. “High ceiling friction, you slow down. If the friction’s too high on the ground, you slow down. But if it’s too low, you slow down, because your legs slip.”
Find the Goldilocks level of friction, though, and those cockroaches can really move---even with up to 300 times their body weight pressing on their backs in the smallest crevice. Oh, and they can take up to 900 times their own weight without getting hurt. “We actually measured it,” Full says, which is horrible.
Don’t blame the cockroaches for their extraordinary adaptability to that space between your floorboard and your wall. That's not what their skill set evolved for. It actually keeps them safe. “Cockroaches like to be against walls, against surfaces, and the more surfaces they can contact, the more comfortable they are,” says Coby Schal, an entomologist at North Carolina State University. It’s called “thigmotaxis,” and the roaches feel most OK when they perceive a slow, light brushing against bristles that grow from their bodies, mechanoreceptors that can also tell when the air around them is moving so fast it must mean a foot’s descending. “If that bristle is accelerated fast, the cockroach takes off and escapes,” Schal says.
That collapsible exoskeleton is yet another physiological marvel. Not only does it flex and expand---allowing for developing insects to grow and molt, and bloodsucking insects like bedbugs to accommodate the meal they have made out of your precious life essence---it also shunts their mass around. “In a cockroach the blood flows in an open cavity called a hemocoel,” Schal says, “so it can deform its body by moving blood from one part to another.” It’s like a disgusting, insectile, armored balloon.
“Once you have a system like that, the adaptation to being in cracks and crevices is to depress your body,” Schal says. “Some insects are almost pencil-like, and you want to squeeze that pencil to a flat, sheetlike morphology. The cockroach fits that.”
Gross, sure, but it also makes a great model for robot mobility. Full visited a prototyping lab and laid out an origami-like arrangement of plates, laminated them like the cockroach’s exoskeletal membrane, and wrapped it all around a robot. His team named it CRAM, for Compressible Robot with Articulated Mechanisms. It stands 75 millimeters tall, or about three inches, but can crawl under a ceiling less than half that height. “It’s a robot to an engineer, but to us it looks like a physical model,” Full says. “We can build things quickly, like in a day, and test hypotheses in our mathematical design.”
Full’s robo-roach isn’t ready for deployment yet, but it already has a mission---in situations like the apartment building that collapsed in Saturday's earthquake in Taiwan. “People have been using ground robots where the voids are about 20 inches or less in cross section,” says Robin Murphy, director of the Center for Robot-Assisted Search and Rescue at Texas A&M University. “What would be really great, when you get into these pancake collapses where you have survivable voids but they’re really deep, would be if you could go less than that, a couple of inches.” Murphy, who consulted with Full on his work, says rescuers can’t really help anyone buried under more than 20 feet of rubble. Get a device that can burrow, that can handle tiny spaces---like, oh, let’s say, a cockroach---and you might be able to go 40 feet or deeper.
That’s why you might not mind if a robot bug comes to rescue you. A Terminator wouldn’t be able to get there at all. “It’s not like the Darpa robotics challenges where you go down a hall, down stairs, skip over some rubble. No, no, no,” Murphy says. “You’re going into spaces too small for a human or a dog to get into. Or maybe they’re on fire.”
Full’s work, says Murphy, is a good first step. Mobility for a robot in those kind of situations is a high priority. Next: Controlling their movements and figuring out how to make them transmit real-time data to rescuers evaluating a scene. But locomotion has to come first. “Not only is it solid work, but Bob actually asks questions. What are you seeing? What are the characteristic dimensions?” Murphy says. “It’s great to have someone like Bob, who’s doing fundamental research but is respectful of the domain.”
If you still can’t handle the idea of someday being carried to safety by a swarm of chittering, exoskeleton-wearing robot bugs, Full has you covered. He’s also working on a giant crab.
