This Robot Is Nuts!

The contestants on American Ninja Warrior and Floor Is Lava show off some seriously impressive acrobatic skills as they fly through the air from one obstacle to the next. But for a squirrel, that is nothing more than child’s play. These tiny masters of agility are known for the way that they race through trees like they are in the Indianapolis 500 watching the white flag wave in front of them. And when they need to make a quick getaway, they effortlessly leap to a distant — and very precarious — perch without batting an adorable little eyelash.

While us humans cannot match their skill (or furry cuteness), we can at least make a respectable showing of it (on the skill part, that is), but robots — not so much. Since robots are far behind even us in terms of agility, they have a long, long way to go. As such, it would be very difficult to design a robot that can jump like a squirrel. You might even say it would be a foolish undertaking. A waste of time. Madness, even.

However, a group of engineers and biologists at the University of California, Berkeley thought it sounded like a fine project to take on. And surprisingly, they pulled it off. It is certainly not like a squirrel in all ways, but it can jump long distances and balance on tiny perches with the best of them. That is something that robots have traditionally been unable to do, and it could open up new opportunities for robots to assist in areas like search and rescue, environmental research, and disaster relief.

The robot, called Salto (Saltatorial Agile Locomotion on Terrain Obstacles), was originally developed in 2016 as a single-legged machine designed to hop like a galago (a small, agile primate). But while Salto could land with precision on flat surfaces, jumping onto narrow, unstable perches was another challenge entirely.

To make this possible, the researchers took inspiration from the way squirrels land on branches. By closely studying high-speed videos of squirrels leaping, they discovered that squirrels use a combination of forelimb force absorption and body adjustments to stick even the trickiest of landings. Instead of simply grabbing a branch, they balance dynamically, absorbing impact with their shoulders and adjusting their inertia to prevent over- or under-shooting.

To mimic this, researchers modified Salto’s motor control system to actively adjust its leg force upon landing, just like squirrels do. The robot’s reaction wheel — a spinning disc that helps stabilize its body mid-air — was also reprogrammed to fine-tune its orientation upon landing. Unlike squirrels, Salto does not have grasping feet, so it relies purely on balance and force adjustments to stick its landings.

In a series of experiments the results proved to be impressive, but not perfect. Salto successfully managed to land upright on a narrow perch multiple times — something that no robot of its kind had done before. Although its success rate was still far from ideal (only two out of 30 trials resulted in a perfectly balanced landing), this work is still an important step toward building more agile robots.

The next steps for the researchers involve improving Salto’s landing consistency, exploring different types of foot designs, and integrating gripping capabilities for more stable perching. For now, though, Salto’s ability to leap and land like a squirrel — even if imperfectly — is an exciting breakthrough in robotic locomotion. With further development, robots may one day rival the agility of nature’s best acrobats.