The sight of a cockroach on the run may strike fear into your heart, but what if it were running to save you? That's what researchers at UC Berkeley had in mind when they designed CRAM, a robot prototype that looks just like a cockroach. CRAM ("compressible robot with articulated mechanisms") has a jointed exoskeleton and a soft shell that allow it to shape shift and move through small spaces. The researchers think CRAM, whose existence was partially funded by the US Army, could be the first step in creating an incredibly effective search-and-rescue robot.

The scientists behind CRAM, Kaushik Jayaram and Robert Full, thought the cockroach's unique way of moving and its general imperviousness to destruction made it the perfect inspiration for a rescue bot, which would need to be able to hunt through rubble and confined spaces. "[Cockroaches] are great at revealing nature’s secrets about design," Full said.

Cockroaches are basically indestructible

But before Jayaram and Full could take advantage of these secrets, they needed to first figure out what those secrets were. To do this, the researchers constructed a series of experiments to test how the American cockroach's body responded to various environments. They designed three custom apparatus, each meant to highlight a particular element of movement: "crevice traversal," "confined-space crawling," and the cockroaches' reactions to "dynamic compressive forces" while moving.

The "crevice traversal" apparatus tested the cockroach's movement in small horizontal spaces, while the "confined-space crawling" apparatus tested their movements in small vertical spaces. The cockroaches were able to continue moving rapidly in horizontal spaces as small as 3mm (the researchers compared the height to two stacked pennies), and in vertically confined spaces of 4mm. The scientists also tested the cockroach's exoskeleton by exerting force on its body as it was attempting to navigate a space. They found that cockroaches were able to withstand a force of 300 times their body weight even when moving through the narrowest crevices, and a force of 900 times their body weight without sustaining any injuries.

These tests alerted the researchers to a largely unexplored mode of movement, which they're calling "body-friction legged crawling." The cockroaches traveled most effectively when submitted to an "intermediate" level of friction, using a combination of "body drag" and "friction-dominated leg thrust." Too much ceiling friction could slow a cockroach down, as could too much floor friction. But the tests also revealed that too little floor friction didn't work either. In vertically confined spaces, the cockroaches were able to move very quickly even with their legs completely splayed out to the side.

Jayaram and Full captured these tests on film and slowed the video down to process what was happening to the cockroaches' bodies as they moved. Those results helped inform the design of the resulting prototype, which is about the size of a palm, and made of poster board and polyester. "We’re in an age of rapid customizable prototyping," Full said. "So we were able to think about the exoskeleton as kind of an origami piece."

"[Cockroaches] are great at revealing nature’s secrets about design."

The idea of a cockroach as a search-and-rescue animal isn't entirely new. In 2014, researchers at North Carolina State University figured out how to equip live cockroaches with tiny microphones and cameras so rescue teams could more easily search for people after a disaster. Engineers at Texas A&M University did the same thing. Last year, a separate team of researchers at UC Berkeley designed a robot similar to CRAM called the VelociRoACH, but Jayaram and Full's movement experiments add a new element to the cockroach robot field.

CRAM is still in the prototype stage and has only been tested in the lab so far. Full says the next step is to determine which construction materials would be most effective in a disaster situation. Eventually CRAM could be equipped with a wider range of movement, like the ability to turn, jump, and climb.