Exoskeleton Makes Robotic Roach Flexibly Squishy

Photo: UC Berkeley

Last July, we wrote about a pair of papers from UC Berkeley that explored what happens when you put rigid shells on top of the skittery little legged robots that they’ve been working on over there for like a decade now. As it turned out, the shells offered some environmental protection, while also enabling the robots to autonomously negotiate obstacles that they’d have gotten stuck on otherwise. But real insects use their exoskeletons for much more, and by taking inspiration from that most noble of beasts, the mighty cockroach, UC Berkeley has developed a legged robot that can flatten itself out to slide through the narrowest of gaps. 

In a paper published in PNAS, Kaushik Jayaram (from Robert Full’s lab at UC Berkeley) discusses how cockroaches are the ideal mix of firm outsides and soft, chewy insides. Their exoskeletons are flexible and segmented, allowing them to squish down to squeeze through narrow gaps, which explains why you probably have a whole bunch of them (or similar structured insects) living in your house RIGHT NOW despite your best efforts to keep them out. Even under some rather intense compressive forces (up to 300 times their body weight), the insects had no trouble running around while being squished, which is pretty remarkable. A comfortably standing cockroach is about half an inch tall, but when “highly motivated” (whatever that means to a cockroach), they were able to squeeze through gaps just a tenth of an inch high.

The really cool thing is not just that the cockroaches can squeeze, but they can move while squeezed. A nearly flattened cockroach can’t use its feet very well because they’re splayed out to the side, so it uses its legs (tibias) instead in a sort of swimming motion. This slows it down a lot, but not necessarily as much as you might expect: 15 cm/s while squeezing through a 4 mm gap as opposed to just under 60 cm/s when running flat out without any compression. The researchers refer to this method of locomotion as “body-friction legged crawling,” where the predominant factors are body drag against the ceiling and floor along with friction between legs and floor that leads to thrust.


This seems like a really great idea if you want to have robots that can crawl through narrow gaps and cracks and stuff, so Jayaram applied a flexible segmented exoskeleton to the basic design of UC Berkeley’s roachbots to make it even more roach-y, and ended up with this:


CRAM is a “compressible robot with articulated mechanisms” that can cram itself into places that other robots can’t. It’s 18 cm long, 75 mm high when uncrammed, and weighs 46 g. It can cram itself down to just 35 mm in height, a vertical compression of over 50 percent. It can also withstand loads of about a kilogram, or 20 times its body mass. Besides that big deformable plastic shell, CRAM is also hinged in the middle, along where its spine would be if it had a spine, which it doesn’t. Rather than just a shell stuck on top of a roachbot, CRAM’s exoskeleton is (as with insects) an integral part of its structure, and as such, only represents an increase in mass of about 25 percent. This picture explains the compressible sprawlyness pretty well, if you stare at it for a minute or two:


As CRAM gets compressed downwards, the two halves of its are pushed downwards and outwards, causing the robot’s roach-inspired spiny legs to rotate 90 degrees. Just as with the real roaches, this doesn’t seem to bother CRAM all that much: 

Uncrammed, CRAM can run at 27 cm/s (1.5 body lengths per second). Fully crammed, CRAM can do its body-friction legged crawling thing at 14 cm/s, which is impressively quick for the uncomfortable-looking state it’s in. This gives the robot an unprecedented amount of versatility, especially in the (potential) contexts of disaster relief and stuff like that. Based on a printable structure and inexpensive components, you could toss a squirming handful of these guys into (say) the rubble of a collapsed building, and they could do a better job of quickly searching through all the nooks and crannies than just about anything else.

Of course, to do all this stuff, CRAM is going to need some sensors, and that’s the next step, Jayaram says. They also plan to make the robots smaller, faster, and even more compressible. There’s one more curious idea for future applications for CRAM, according to the paper:

“A promising future direction for soft-arthropod–inspired legged robots is to combine the advantages of soft-bodied robots with appendages shown to be effective in tubular environments such as gastrointestinal tracts.”

This sounded weird enough that we asked Jayaram to elaborate, and this is what he said:

“In addition to search and rescue, we hope that robots like CRAM could one day be used to for more diverse applications involving confined environments. Chimney and pipe traversal is one potential application. If sufficiently miniaturized, such robot might offer surgical benefits and assist doctors.”

Whoa. You heard it here first, folks: robot cockroaches in your intestines.

[ PNAS ] via [ UC Berkeley ]

Thanks Kaushik!



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