When search and rescue workers respond to a structure that has collapsed, one of the greatest threats they face is another cave-in while seeking out survivors. Over the years, there have been several attempts to address this, from mobile cameras to audio sensors to drones and more, but they all face severe limitations when it comes to navigating unstable wreckage.
Researchers at the University of California Berkeley’s Biomimetic Millisystems Lab are currently working on a possible solution to this problem: a small, maneuverable robot inspired by a species known as Galago senegalensis - more commonly referred to as a “bushbaby.”
The bushbaby is a small nocturnal primate, typically no more than 30 cm long. Their powerful legs can propel them over two meters high, due in part to the elastic energy storage found in the tendons of their lower legs. A bushbaby’s legs act in a similar way to the way in which the gears in a compound bow make it possible to release an arrow with more power than arm strength alone. Their motion in flight also allows them to remain compact and then extend their feet at the last possible second, which enables them to chain huge jumps together, one after another, off multiple surfaces.
The jumping abilities of bushbabies have been extensively recorded and documented by a host of researchers. That made the small creature ideal for the Biomimetic Millisystems team, as they considered new ways to harness features of animal movements and control strategies to improve the capabilities and performance of small robots. This led to the creation of their new project, Saltatorial Locomotion on Terrain Obstacles, or Salto for short.
Developed by roboticist Duncan Haldane, electrical engineering and computer sciences professor Ron Fearing, electrical engineering PhD student and postdoctoral scholar Justin Yim, and postdoctoral scholar Dr. Mark Plecnik, the group began work in 2015. The result is Salto, a pint-sized robot roughly the size of a smartphone, which is capable of jumping huge distances and navigating obstacles. Although still very much a prototype, it can spring up, bounce off walls, and – in theory – move through small and unstable places quickly, with relative ease.
To help develop Salto, the researchers turned to Vicon. The motion capture lab at Berkeley now consists of two Vicon MX Giganet boxes and 12 MX T40 cameras, operating alongside Nexus version 1.8.5 software, all aimed at providing highly accurate pose tracking, which is necessary for controlling Salto.
The Vicon system offers pose tracking at 100Hz over an area of roughly two meters wide by four meters long. Recorded data is then sent to a laptop running the Robot Operating System (ROS), which estimates Salto’s velocity based on the pose data. It then calculates control signals and sends necessary data back to the robot over an XBee radio connection. The Vicon system replaced a set of high-speed cameras, which lacked Vicon’s detail and required a separate system to process the data.
“Vicon is a very convenient way to take high-quality measurements of robot performance, and is sufficiently fast for good real-time control of our highly dynamic terrestrial robots,” said Yim. “The ease and consistency of setup made it smoother to run day-to-day robot experiments.”
The current version of the robot, known as Salto-1P, features a durable, but lightweight carbon fiber shell. It has a takeoff velocity of over four meters per second, and spends around 70m/s on the ground during each stance. The team controls the battery-powered robot by setting its orientation in the air, based on its location, how fast it’s going, and where it will touch a solid surface. Once it lands, the optical system detects contact. The controllers then transmit a burst of energy to send it airborne again, and repeat.
Ultimately, it will be up to the end users to decide how best to use Salto, including the type of controls and cameras or observation tools with which they want to equip the robot. There is still a lot of work to be done before the little robot can be used in a real-life rescue situation. For now, the team will continue to work on precision controls, followed in the near future by onboard sensors, in the hope that one day, their little robotic bushbaby will help save lives.