The aftermath of an earthquake or warehouse fire creates environments too dangerous and too sensitive for humans to clomp through. Survivors trapped by fallen debris could be killed by rubble moved by rescuers. Meanwhile, rescuers could be killed, too. While drones are already being used in search and rescue operations, a surface-level bot might also be crucial. What’s needed is a lightweight, high-jumping robot that can bounce atop debris without disturbing it. Enter Salto.
The prototype for Salto — short for Saltatorial Locomotion Terrain Obstacles — a robot developed by a team from University of California, Berkeley, has one leg and uses a spring motion modeled after the galago: a nocturnal African primate adorably nicknamed the “bush baby.”
“We next wanted to figure out how to build a better jumping robot, and we looked to biology for inspiration, because it’s fair to say that animals can outclass any robot when it comes to jumping,” Duncan Haldane, one of four authors of a research article on the project, told reporters on Monday. He said the galago’s legs and jumping style are most similar to that of a bullfrog.
And by their measure, while Salto’s not as good as the galago at jumping, it is the best jumping bot in the world. They scored it based on a metric called “vertical jumping agility,” which is “the ratio of the maximum jump height to the time it takes to complete one jump.” Other robots can jump higher but they take longer.
“To have a higher vertical jumping ability, you have to be able to jump high and do it quickly,” Haldane says. “If you can jump to two meters in the air, but you have to wind up for three minutes on the ground, you’re just not going to do very well.”
Meanwhile, Salto has “56 percent more vertical jumping agility than any other untethered robot.”
Here’s how it works: The single-legged robot uses a “series elastic actuator, which means it has a motor and then a spring and then the leg,” Haldane said. The leg itself is engineered with hinges and eight bars that move when the motor applies torque to one of them, which pushes down on the ground. The leg then springs up with great energy similar to how a lever or crowbar works.
Mark Plecnik, a postdoc at Berkeley who studies kinematic design of linkages in its Biomimetic Millisystems Lab, explains: “A crowbar provides you with a lever arm to generate a large prying force by exerting a small force at the end of a lever. It is a force multiplier, and that multiplication factor is called mechanical advantage. Similarly, salto’s leg multiplies motor torque to create a new force at the foot.”
The work was published in research article Tuesday in the first-ever edition of the journal Science Robotics, a new peer-reviewed journal that aims to provide “a much-needed forum for the latest technological advances and for the critical social, ethical and policy issues surrounding robotics.”
Salto also uses vertical surfaces — long the enemy of robots — to its advantage, as it can jump onto one and pivot off, sort like a very advanced parkour jumper.
And about that one-leg: The researchers want to push what their monopedal-bot to its limit in the lab first and then add more legs.
“We also think that there are some interesting things that can happen when you start adding extra legs,” Haldane says.
As for energy usage, the researchers said they used a fully charged battery for each experiment but said a larger battery could be used while noting there would be a trade-off between frequent smaller jumps or fewer bigger jumps.