Berkeley’s High-Flying Robot Leaps over Obstacles Effortlessly

Barely less than a foot, Salto the robot resembles a miniature version of the Star Wars imperial walker. But let its size not fool anyone — this tiny robot has a massive spring in its step. Salto can vault over three times its height in a single leap.

Robotics graduate student Justin Yim led the effort to program Salto with sophisticated control software that lets the robot master complex maneuvers. (UC Berkeley photo by Stephen McNally)

Salto’s high-flying capabilities were first revealed by scientists at the University of California, Berkeley in 2016. Currently, they have fitted the robot with a bunch of new skills, rendering it with the ability to bounce in place like a pogo stick and jump through obstacle courses like an agility dog. Salto can even perform short jaunts around campus, motorized by a radio controller.

The scientists expect Salto will drive the development of small, agile robots that could leap through rubble to aid in search-and-rescue tasks. They have described the robot’s new skills at the 2019 International Conference on Robotics and Automation held on May 21st in Montreal.

Small robots are really great for a lot of things, like running around in places where larger robots or humans can’t fit. For example, in a disaster scenario, where people might be trapped under rubble, robots might be really useful at finding the people in a way that is not dangerous to rescuers and might even be faster than rescuers could have done unaided. We wanted Salto to not only be small, but also able to jump really high and really quickly so that it could navigate these difficult places.

Justin Yim, Robotics Graduate Student, UC Berkeley

Yim collaborates with Ronald Fearing, an electrical engineering and computer sciences professor at UC Berkeley, whose Biomimetic Millisystems Lab investigates how the mechanics of animal movement can be applied to develop more nimble robots.

Fearing’s lab is famous for constructing insect-inspired robots that can safely crawl across complicated surfaces that are too smooth or too rough for a wheeled robot to traverse. In making Salto, which stands for “saltatorial locomotion on terrain obstacles,” Fearing instead was keen to create a robot that traveled from one place to the next by hopping.

The inspiration for Salto’s single, robust leg came from the galago, or Senegalese bush baby. The small, tree-dwelling primate’s muscles and tendons store energy in such a way that bestows the spry animal the ability to string together many jumps in a few seconds. By connecting a string of quick jumps, Salto also can steer complex terrain — similar to a pile of debris — that might be difficult to cross without flying or jumping.

“Unlike a grasshopper or cricket that winds up and gives one jump, we’re looking at a mechanism where it can jump, jump, jump, jump,” Fearing said. “This allows our robot to jump from location to location, which then gives it the ability to temporarily land on surfaces that we might not be able to perch on.”

Three years ago, Salto’s design team showed how the robot could perform a leap and then instantly spring higher by ricocheting off a wall, making it the most vertically agile robot in the world. Since then, Yim has been leading the effort to develop hi-tech control systems that allow Salto to master progressively complex tasks, such as bouncing in place, following a moving target or navigating an obstacle course.

Yim has also fitted Salto with new technology that enables it to “feel” its own body, informing it what angle it is pointing and the bend of its leg. Without these capabilities, Salto has been limited to a room in one of Berkeley’s engineering buildings, where motion capture cameras monitor its precise angle and position and convey that data back to a computer, which quickly consolidates the data to tell Salto how to angle itself for its following leap.

Now that Salto possesses a sense of itself and its own motion, the robot can perform these calculations by itself, enabling Yim to take the robot outside and use a joystick and radio controller to instruct it where to go.

Motion capture is great for getting the robot to jump around in a controlled environment really precisely, and it gives us tons of really great data. The problem is, we can’t take this out and use it anywhere else, because it takes a long time to set up all of these cameras. We really wanted to be able to take the robot out and go jump around. And to do that, we needed the robot to be able to compute where it is and what it is doing — just with the computer on top of its own body.

Justin Yim, Robotics Graduate Student, UC Berkeley

Salto can, at present, take walks around the Berkeley campus, where it has effectively maneuvered over brickwork, sidewalks, and grass. The mathematical models that render this possible for Salto also could be generalized to regulate the motion of other types of robots, Yim said.

“By understanding the way that these dynamics work for Salto, with its mass and size, then we can extend the same type of understanding to other systems, and we could build other robots that are bigger or smaller or differently shaped or weighted,” Yim said.

Going forward, Fearing wants to pursue exploring the possibilities for hopping robots.

Salto is our first step toward robots that bounce around. We could extend Salto to add the ability to, for example, grab onto branches to land and launch from those things. So, Salto starts out with a very simple mechanism. It’s just one leg. It provides a basis for more complicated robots that also could be very highly dynamic and doing a lot of bouncing.

Ronald Fearing, Professor, Electrical Engineering and Computer Sciences, UC Berkeley

This study received support from the Army Research Office Grant No. W911NF-18-1-0038. UC Berkeley undergraduate Eric Wang also authored the conference paper.

Since first unveiling Salto in 2016, UC Berkeley researchers have upgraded the robot with a host of new abilities. Now, it can navigate an obstacle course with ease and go on walks through Berkeley’s campus. (Video by Roxanne Makasdjian and Stephen McNally)

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