Cockroaches are able to trespass pretty much everywhere – on ceilings, up walls, and under doors at speeds of nearly 1.5 meters (4.9 feet) a second – thanks to shape-changing abilities made possible by their jointed external skeletons. According to new work published in Proceedings of the National of Sciences, roaches can squeeze through small cracks that are one-fourth their height by compressing their exoskeletons in half. And they can withstand forces nearly 900 times their body weight, too.
Because the stiffness of their exoskeletal tissue can differ dramatically, by as much as eight orders of magnitude, roaches with powerful appendages are able to retain the ability to conform to their environment much like soft-bodied animals. Yet their ability to traverse crevices and crawl in confined spaces has never been quantified. To study the limits of their remarkable abilities, UC Berkeley’s Kaushik Jayaram and Robert Full built an acrylic obstacle course for dozens of American cockroaches (Periplaneta Americana), which are known for their speed, maneuverability, robustness, and tenacity for entering and leaving spaces.
The duo discovered that cockroaches can traverse horizontal crevices that are smaller than a quarter of their body height in less than a second by compressing their compliant exoskeletons down to about 40 to 60 percent their original size. That means that 12-millimeter-high roaches can crawl through cracks as small as 3 millimeters, the height of just two stacked pennies. And after crawling into vertically confined spaces, roaches continue to move rapidly despite the compression and the changes to their posture. In fact, sprawled-out roaches can run at speeds of about 20 body lengths per second using a novel mode of locomotion known as “body-friction legged crawling.” Since they can't use their feet properly while squished, they use sensory leg spines to push against the floor in order to move.
The team also found that roaches can withstand crushing forces of nearly 900 times their body weight without suffering any injuries. And they can withstand compressive forces around 300 times their body weight while still slipping through the narrowest of cracks.
The researchers then developed a soft-bodied, palm-sized robot with six legs that mimics how a roach compresses its body in half to fit through extremely confined spaces. They call it “compressible robot with articulated mechanisms,” or CRAM (pictured right). A flexible back spine is paired with a deformable, low-friction shell made of overlapping plates that resemble the exoskeletal plates of a cockroach’s abdomen. The 46-gram (1.6-ounce), 75-millimeter (2.9-inch) robot can be compressed down to 35 millimeters (1.3 inches), and it can withstand compressive forces 20 times its body mass.
Roach-inspired robots like these might someday help with search-and-rescue missions by skittering through rubble and navigating through otherwise impassable cracks.
Image in the text: An American cockroach on top of a bio-inspired compressible robot. PolyPEDAL Lab/University of California at Berkeley