Engineers have designed robots that crawl, swim, fly and even slither like a snake, however no robotic can maintain a candle to a squirrel, which may parkour via a thicket of branches, leap throughout perilous gaps and execute pinpoint landings on the flimsiest of branches.
College of California, Berkeley, biologists and engineers try to treatment that scenario. Based mostly on research of the biomechanics of squirrel leaps and landings, they’ve designed a hopping robotic that may stick a touchdown on a slim perch.
The feat, to be reported within the March 19 difficulty of the journal Science Robotics, is a giant step within the design of extra agile robots, ones that may leap among the many trusses and girders of buildings below building or robots that may monitor the setting in tangled forests or tree canopies.
“The robots we’ve now are OK, however how do you’re taking it to the following stage? How do you get robots to navigate a difficult setting in a catastrophe the place you’ve gotten pipes and beams and wires? Squirrels may try this, no drawback. Robots cannot try this,” mentioned Robert Full, one in every of paper’s senior authors and a professor of integrative biology at UC Berkeley.
“Squirrels are nature’s greatest athletes,” Full added. “The best way that they will maneuver and escape is unbelievable. The thought is to attempt to outline the management methods that give the animals a variety of behavioral choices to carry out extraordinary feats and use that info to construct extra agile robots.”
Justin Yim, a former UC Berkeley graduate pupil and co-first writer of the paper, translated what Full and his biology college students found in squirrels to Salto, a one-legged robotic developed at UC Berkeley in 2016 that would already hop and parkour and stick a touchdown, however solely on flat floor. The problem was to stay the touchdown whereas hitting a particular level — a slim rod.
“If you consider attempting to leap to some extent — possibly you are doing one thing like enjoying hopscotch and also you need to land your ft in a sure spot — you need to stick that touchdown and never take a step,” defined Yim, now an assistant professor of mechanical science and engineering on the College of Illinois, Urbana Champaign (UIUC). “Should you really feel like you are going to fall over ahead, then you definitely may pinwheel your arms, however you may additionally most likely arise straight with a view to preserve your self from falling over. If it feels such as you’re falling backward and also you may need to sit down down since you’re not going to have the ability to fairly make it, you may pinwheel your arms backward, however you are seemingly additionally to crouch down as you do that. That’s the identical conduct that we programmed into the robotic. If it’ll be swinging below, it ought to crouch. If it’ll swing over, it ought to lengthen out and stand tall.”
Utilizing these methods, Yim is embarking on a NASA-funded challenge to design a small, one-legged robotic that would discover Enceladus, a moon of Saturn, the place the gravity is one-eightieth that of Earth, and a single hop may carry the robotic the size of a soccer subject.
The brand new robotic design relies on a biomechanical evaluation of squirrel landings detailed in a paper accepted for publication within the Journal of Experimental Biology and posted on-line Feb. 27. Full is senior writer and former graduate pupil Sebastian Lee is first writer of that paper.
Mixing biology and robotics
Salto, quick for Saltatorial Agile Locomotion on Terrain Obstacles, originated a decade in the past within the lab of Ronald Fearing, now a Professor within the Graduate Faculty in UC Berkeley’s Division of Electrical Engineering and Laptop Sciences (EECS). A lot of its hopping, parkouring and touchdown potential is a results of a long-standing interdisciplinary collaboration between biology college students in Full’s Polypedal Lab and engineering college students in Fearing’s Biomimetic Millisystems Lab.
Through the 5 years Yim was a UC Berkeley graduate pupil — he obtained his Ph.D. in EECS in 2020, with Fearing as his adviser — he met with Full’s group each different week to study from their biology experiments. Yim was attempting to leverage Salto’s potential to land upright on a flat spot, even open air, to get it to hit a particular goal, like a department. Salto already had a motorized flywheel, or response wheel, to assist it stability, a lot the way in which people wheel their arms to revive stability. However that wasn’t enough for it to stay a direct touchdown on a precarious perch. He determined to attempt reversing the motors that launch Salto and use them to brake when touchdown.
Suspecting that squirrels did the identical with their legs when touchdown, the biology and robotics groups labored in parallel to substantiate this and present that it might assist Salto stick a touchdown. Full’s staff instrumented a department with sensors that measured the drive perpendicular to the department when a squirrel landed and the torque or turning drive with respect to the department that the squirrel utilized with its ft.
The analysis staff discovered, primarily based on high-speed video and sensor measurements, that when squirrels land after a heroic leap, they principally do a handstand on the department, directing the drive of touchdown via their shoulder joint in order to emphasize the joint as little as doable. Utilizing pads on their ft, they then grasp the department and twist to beat no matter extra torque threatens to ship them over or below the department.
“Nearly the entire vitality — 86% of the kinetic vitality — was absorbed by the entrance legs,” he mentioned. “They’re actually doing entrance handstands onto the department, after which the remainder of it follows. Then their ft generate a pull-up torque, if they are going below; if they’ll go excessive — they’re overshooting, probably — they generate a braking torque.”
Maybe extra vital to balancing, nevertheless, they discovered that squirrels additionally modify the braking drive utilized to the department when touchdown to compensate for over- or undershooting.
“If you are going to undershoot, what you are able to do is generate much less leg-breaking drive; your leg will collapse some, after which your inertia goes to be much less, and that can swing you again as much as right,” Full mentioned. “Whereas in case you are overshooting, you need to do the other — you need to have your legs generate extra breaking drive so that you’ve got an even bigger inertia and it slows you down with the intention to have a balanced touchdown.”
Yim and UC Berkeley undergraduate Eric Wang redesigned Salto to include adjustable leg forces, supplementing the torque of the response wheel. With these modifications, Salto was capable of bounce onto a department and stability a handful of occasions, even though it had no potential to grip with its ft, Yim mentioned.
“We determined to take probably the most tough path and provides the robotic no potential to use any torque on the department with its ft. We particularly designed a passive gripper that even had very low friction to reduce that torque,” Yim mentioned. “In future work, I believe it might be fascinating to discover different extra succesful grippers that would drastically broaden the robotic’s potential to regulate the torque it applies to the department and broaden its potential to land. Perhaps not simply on branches, however on complicated flat floor, too.”
In parallel, Full is now investigating the significance of the torque utilized by the squirrel’s foot upon touchdown. In contrast to monkeys, squirrels should not have a usable thumb that permits a prehensile grasp, so they have to palm a department, he mentioned. However that could be a bonus.
“Should you’re a squirrel being chased by a predator, like a hawk or one other squirrel, you need to have a sufficiently steady grasp, the place you possibly can parkour off a department rapidly, however not too agency a grasp,” he mentioned. “They do not have to fret about letting go, they only bounce off.”
One-legged robots might sound impractical, given the potential for falling over when standing nonetheless. However Yim says that for leaping actually excessive, one leg is the way in which to go.
“One leg is the most effective quantity for leaping; you possibly can put probably the most energy into that one leg should you do not distribute that energy amongst a number of completely different units. And the drawbacks you get from having just one leg reduce as you bounce increased,” Yim mentioned. “Whenever you bounce many, many occasions the peak of your legs, there’s just one gait, and that’s the gait through which each leg touches the bottom on the identical time and each leg leaves the bottom at roughly the identical time. So at that time, having a number of legs is sort of like having one leg. You may as effectively simply use the one.”
Different co-authors of the Science Robotics paper are Fearing and former UC Berkeley undergraduate Eric Wang, now a graduate pupil at MIT, and former graduate pupil Nathaniel Hunt, now an affiliate professor on the College of Nebraska in Omaha. Co-authors of the J. Exp. Bio. paper are Wang, Hunt, Fearing, UC Berkeley Affiliate Professor of Mechanical Engineering Hannah Stuart and former UC Berkeley undergraduates Stanley Wang and Duyi Kuang. The analysis was funded by the U.S. Military Analysis Workplace (W911NF-18-1-0038, W911NF-1810327) and the Nationwide Institutes of Well being (P20GM109090).
