The jumping bot can take a flying leap and land on a narrow pipe ­­­— just like a squirrel soaring from branch to branch. It’s the first time scientists have been able to get a robot to land balanced on such a tiny target, says engineer Justin Yim, whose team reported the results March 19 in Science Robotics. 

“We’ve been inspired by squirrels,” says Yim, who worked on the project at the University of California, Berkeley and is now at the University of Illinois Urbana-Champaign. 

Squirrels are one of nature’s acrobats. They can scamper over telephone wires, vault between trees and even navigate Ninja Warrior-style obstacle courses. A secret to squirrels’ parkour prowess is exceptional balance. Even if a jump carries them a bit beyond or short of their target, squirrels can maneuver their bodies into staying upright. One way is by adjusting how hard their legs push against a branch as they land, Yim and his collaborators reported February 27 in the Journal of Experimental Biology. 

Think of playing hopscotch, he says. If you land on a square and feel like you’re going to fall forward, you might stand up tall, pushing hard against the ground to prevent yourself from toppling over. And if you land too far back, you might crouch down, so you don’t tip backward.

Yim’s team tried to mimic those strategies in Salto, a spindly little hopping bot that was developed in 2016, and named after “saltatorial,” or jumping, movement. In 2020, the researchers figured out how to make Salto stick the landing on flat surfaces. For the new work, the team made two big changes. They added a clawlike gripper to Salto’s foot so it could catch a pipe during landings. And they gave Salto the ability to stand or crouch to improve its balance. 

In test jumps in the lab, Salto successfully leapt from one PVC pipe to another 25 times out of 30, catching the tube and swinging over or under it most of the time. But in two trials, Salto leapt, landed and perched just perfectly, balancing upright on the pipe. 

“There’s lots of room for improvement,” Yim says. Salto may not be ready to join Cirque du Soleil yet, but he has ideas about how to improve the bot’s balance. One way would be enhancing its gripper, making it better for grasping the pipe upon landing, like a squirrel squeezing a branch with its toes. 

Yim envisions future bots that are even more agile than Salto and could one day help with construction, hopping onto pipes or girders while carrying cameras for inspection, for example, or working outside in a forest doing environmental monitoring. But Salto will need many more tweaks to catch up to its bushy-tailed brothers, Yim says. “The robot is definitely not able to do what a squirrel can do just yet.”