A team of robotics researchers at Disney Research Pittsburgh made news last month when they revealed their untethered hopping robot at the International Symposium on Experimental Robotics in Tokyo. Billed as a “Tigger” robot in the popular technology press, the bouncy bot captured the hearts of tech journalists and denizens of the 100-Acre Wood alike. Autonomous bouncing tiger technology is only a small part of the story, however.
History and Success of Hopping Robots
Bouncing is not only the reason Tiggers famously have so much fun, it’s also an extremely useful skill for a robotic leg, enabling the limb to handle uneven terrain without getting tripped up. This type of locomotion has been under development since the early 1980s when Boston Dynamics founder, Marc Raibert and others, first at Carnegie Mellon and then at M.I.T. built the early hopping bots that bounced around the lab attached to tethers. The cables fed power and instructions to the robotic mechanism while relaying information from sensors back to the computer that controlled the machine’s balance and trajectory.
What the Disney researchers sought to accomplish was to remove the tether, creating a self-contained hopping “leg” that could carry its own power, in the form of lithium polymer (LiPo) batteries, as well as the computer that would translate sensor data into balance control to keep the bot erect. So far, the Disney team, composed of Zachary Batts, Joohyung Kim and Katsu Yamane have managed to keep the robot bouncing, untethered, for up to 19 hops or roughly seven seconds. This is the first time to the researchers’ knowledge that this has been achieved.
How The Hopping Bot Works
The basic structure of the robot and the aptly named Linear Elastic Actuator in Parallel or LEAP mechanism it employs to hop around is outlined in the video below. The Disney engineers kept their robot as similar as possible to Raibert’s original design in order to be able to use his algorithm to control the bouncing bot’s balance. This eliminated the need to write brand new code for purposes of this experiment. The body of the robot sits on an actuated gimbal mechanism that employs two servomotors to handle movement in four directions. The body houses power, computing and sensing components, including the batteries, inertial sensors and a microcomputer. The leg mechanism pairs two compression springs with a voice-coil actuator like those used in audio speakers. These types of actuators are frequently used in applications that require generating thrust. The two springs support most of the robot’s weight while the voice coil provides thrust for upward motion – this forms a Linear Elastic Actuator in Parallel or LEAP mechanism which enables the robot to hop.
The research team has identified several opportunities to modify their design in order to achieve longer run times and you can read about these findings and find more detail about the mechanism at https://www.disneyresearch.com/publication/hoppingbot/ (Download the PDF to read the whole paper.)
See video of Raibert’s one legged robot and other legged robots from MIT’s leg lab here