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 by 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 slender perch.
The feat, to be reported within the March 19 challenge of the journal Science Robotics, is an enormous step within the design of extra agile robots, ones that may leap among the many trusses and girders of buildings underneath development or robots that may monitor the atmosphere in tangled forests or tree canopies.
“The robots we’ve now are OK, however how do you’re taking it to the subsequent stage? How do you get robots to navigate a difficult atmosphere in a catastrophe the place you’ve pipes and beams and wires? Squirrels might try this, no downside. Robots cannot try this,” mentioned Robert Full, one among paper’s senior authors and a professor of integrative biology at UC Berkeley.
“Squirrels are nature’s finest athletes,” Full added. “The way in which 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 scholar 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 selected level — a slender rod.
“If you consider making an attempt to leap to some extent — perhaps you are doing one thing like enjoying hopscotch and also you wish to land your ft in a sure spot — you wish 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). “When you really feel like you are going to fall over ahead, then you definately may pinwheel your arms, however you will additionally in all probability get up straight with the intention to hold your self from falling over. If it feels such as you’re falling backward and also you might 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 probably additionally to crouch down as you do that. That’s the similar habits that we programmed into the robotic. If it may be swinging underneath, it ought to crouch. If it may swing over, it ought to prolong out and stand tall.”
Utilizing these methods, Yim is embarking on a NASA-funded mission 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 might carry the robotic the size of a soccer discipline.
The brand new robotic design is predicated 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 scholar Sebastian Lee is first writer of that paper.
Mixing biology and robotics
Salto, brief 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 College in UC Berkeley’s Division of Electrical Engineering and Pc 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.
In the course of the 5 years Yim was a UC Berkeley graduate scholar — he received 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 making an attempt to leverage Salto’s potential to land upright on a flat spot, even open air, to get it to hit a selected goal, like a department. Salto already had a motorized flywheel, or response wheel, to assist it steadiness, a lot the best way people wheel their arms to revive steadiness. However that wasn’t adequate 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 could assist Salto stick a touchdown. Full’s workforce instrumented a department with sensors that measured the pressure perpendicular to the department when a squirrel landed and the torque or turning pressure with respect to the department that the squirrel utilized with its ft.
The analysis workforce discovered, primarily based on high-speed video and sensor measurements, that when squirrels land after a heroic leap, they mainly do a handstand on the department, directing the pressure of touchdown by their shoulder joint in order to emphasize the joint as little as potential. Utilizing pads on their ft, they then grasp the department and twist to beat no matter extra torque threatens to ship them over or underneath the department.
“Virtually all the 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 underneath; if they’re going to go excessive — they’re overshooting, doubtlessly — they generate a braking torque.”
Maybe extra essential to balancing, nevertheless, they discovered that squirrels additionally regulate the braking pressure 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 pressure; your leg will collapse some, after which your inertia goes to be much less, and that may swing you again as much as appropriate,” Full mentioned. “Whereas if you’re overshooting, you wish to do the alternative — you wish to have your legs generate extra breaking pressure so that you’ve got a much bigger inertia and it slows you down so 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 soar onto a department and steadiness a handful of instances, even supposing it had no potential to grip with its ft, Yim mentioned.
“We determined to take probably the most troublesome 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 could be attention-grabbing 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 advanced flat floor, too.”
In parallel, Full is now investigating the significance of the torque utilized by the squirrel’s foot upon touchdown. Not like monkeys, squirrels wouldn’t have a usable thumb that permits a prehensile grasp, so they have to palm a department, he mentioned. However which may be a bonus.
“When you’re a squirrel being chased by a predator, like a hawk or one other squirrel, you wish to have a sufficiently secure grasp, the place you may parkour off a department rapidly, however not too agency a grasp,” he mentioned. “They do not have to fret about letting go, they simply bounce off.”
One-legged robots could sound impractical, given the potential for falling over when standing nonetheless. However Yim says that for leaping actually excessive, one leg is the best way to go.
“One leg is the perfect quantity for leaping; you may put probably the most energy into that one leg should you do not distribute that energy amongst a number of totally different gadgets. And the drawbacks you get from having just one leg reduce as you soar greater,” Yim mentioned. “Once you soar many, many instances the peak of your legs, there’s just one gait, and that’s the gait wherein each leg touches the bottom on the similar 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 properly simply use the one.”
Different co-authors of the Science Robotics paper are Fearing and former UC Berkeley undergraduate Eric Wang, now a graduate scholar at MIT, and former graduate scholar 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).
