Watch This Quadrupedal Robot Tackle the Balance Beam, Thanks to a Smart Reaction Wheel System

Jan 24, 2024

Researchers from Carnegie Mellon University's Robotics Institute and Department of Mechanical Engineering have figured out a way to help quadrupedal robots like Spot tackle tricky balance beam terrain — by strapping an active reaction wheel to their back.

"This experiment was huge," claims Zachary Manchester, senior author of the work and head of the Robotic Exploration Lab at Carnegie Mellon. "I don't think anyone has ever successfully done balance beam walking with a robot before."

Walking along a balance beam is a tricky task for a human, but for robots it's considerably more challenging. There's little margin for error, and nowhere to stumble — and when you're working with four legs, rather than two, things get even more difficult. "With current control methods, a quadruped robot's body and legs are decoupled and don't speak to one another to coordinate their movements," Manchester explains. "So how can we improve their balance?"

The solution is a two-parter, spanning software and hardware: a pair of reaction wheel actuators (RWAs) strapped to the robot's back, and a novel control technique which can use the wheels to control the robot's angular momentum independently of its legs.

"You basically have a big flywheel with a motor attached," says Manchester of the RWA approach, which is used to provide remote control of satellites in space. "If you spin the heavy flywheel one way, it makes the satellite spin the other way. Now take that and put it on the body of a quadruped robot."

Testing the concept out on a commercial Unitree A1 quadrupedal robot, the team found that two RWAs were enough to orient the body and increase the robot's agility — and could be treated in the control software as a simple gyrostat, easily added to a model-predictive control algorithm.

Simulations proved the system theoretically capable of allowing the robot to always land on its feet, like a cat, regardless of dropped orientation, while physical testing had the modified robot tackling the balance beam with aplomb.

"Quadrupeds are the next big thing in robots," Manchester predicts. "I think you're going to see a lot more of them in the wild in the next few years."

The team's work has been accepted to the 2023 International Conference on Robotics and Automation (ICRA '23), and is available as an open-access PDF download.