Squirrel-inspired leaping robot can stick a landing on a branch

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 beneath 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 subsequent stage? How do you get robots to navigate a difficult setting in a catastrophe the place you’ve got pipes and beams and wires? Squirrels might do this, no drawback. Robots cannot do this,” stated Robert Full, considered one of 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’ll maneuver and escape is unbelievable. The concept 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 data to construct extra agile robots.”

Justin Yim, a former UC Berkeley graduate pupil and co-first creator 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 might 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 concentrate on making an attempt to leap to a degree — perhaps you are doing one thing like taking part in hopscotch and also you wish to land your toes 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). “Should you really feel like you are going to fall over ahead, you then would possibly pinwheel your arms, however you may additionally most likely get up straight with a view to hold 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 would possibly pinwheel your arms backward, however you are seemingly additionally to crouch down as you do that. That’s the identical habits that we programmed into the robotic. If it’ll be swinging beneath, it ought to crouch. If it’ll swing over, it ought to prolong out and stand tall.”

Utilizing these methods, Yim is embarking on a NASA-funded challenge to design a small, one-legged robotic that might 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 area.

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 creator and former graduate pupil Sebastian Lee is first creator 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 College in UC Berkeley’s Division of Electrical Engineering and Laptop Sciences (EECS). A lot of its hopping, parkouring and touchdown capacity 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.

Throughout the 5 years Yim was a UC Berkeley graduate pupil — he received his Ph.D. in EECS in 2020, with Fearing as his adviser — he met with Full’s group each different week to be taught from their biology experiments. Yim was making an attempt to leverage Salto’s capacity 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 best way 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 strive 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 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 toes.

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 pressure of touchdown by way of their shoulder joint in order to emphasize the joint as little as potential. Utilizing pads on their toes, they then grasp the department and twist to beat no matter extra torque threatens to ship them over or beneath the department.

“Nearly the entire power — 86% of the kinetic power — was absorbed by the entrance legs,” he stated. “They’re actually doing entrance handstands onto the department, after which the remainder of it follows. Then their toes generate a pull-up torque, if they are going beneath; if they’ll go excessive — they’re overshooting, probably — they generate a braking torque.”

Maybe extra vital to balancing, nonetheless, they discovered that squirrels additionally alter 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 can swing you again as much as appropriate,” Full stated. “Whereas in case you are overshooting, you wish to do the alternative — you wish to have your legs generate extra breaking pressure so that you’ve an even bigger inertia and it slows you down in an effort 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 instances, even if it had no capacity to grip with its toes, Yim stated.

“We determined to take essentially the most tough path and provides the robotic no capacity to use any torque on the department with its toes. We particularly designed a passive gripper that even had very low friction to reduce that torque,” Yim stated. “In future work, I feel it might be fascinating to discover different extra succesful grippers that might drastically increase the robotic’s capacity to manage the torque it applies to the department and increase its capacity to land. Possibly 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 enables a prehensile grasp, so they need to palm a department, he stated. However which may be a bonus.

“Should you’re a squirrel being chased by a predator, like a hawk or one other squirrel, you wish to have a sufficiently steady grasp, the place you possibly can parkour off a department rapidly, however not too agency a grasp,” he stated. “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 best way to go.

“One leg is the very best quantity for leaping; you possibly can put essentially the most energy into that one leg for those who 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 bounce increased,” Yim stated. “If you bounce 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 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 would possibly as nicely 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).