Enhancing Quadruped Robot Balance with Reaction Wheel Actuator System
Researchers from Carnegie Mellon University’s Robotics Institute (RI) have achieved a groundbreaking feat in robotics by designing a system that enables an off-the-shelf quadruped robot to walk on a narrow balance beam. This accomplishment is believed to be the first of its kind and marks a significant advancement in the field of robotics.
Zachary Manchester, an assistant professor in the RI and the head of the Robotic Exploration Lab, expressed the significance of this experiment, stating, “I don’t think anyone has ever successfully done balance beam walking with a robot before.”
To overcome the existing limitations of the quadruped robot’s design and improve its balancing capabilities, the team leveraged hardware commonly used to control satellites in space.
The Challenge of Balance in Quadruped Robots
Most modern quadruped robots consist of a torso and four legs, similar to a four-legged animal. However, unlike real animals that possess instinctive agility and balance, these robots lack the ability to make agile turns or correct themselves when off-balance. As long as at least three of the robot’s feet are in contact with the ground, it can maintain balance. However, when only one or two feet are touching the ground, the robot struggles to correct for disturbances and has an increased risk of falling. This lack of balance poses challenges when navigating rough terrain.
In order to address this issue, the team sought to improve the robot’s balance by developing a control system that allows the body and legs to coordinate their movements.
Introducing the Reaction Wheel Actuator (RWA) System
The team’s solution involves the use of a reaction wheel actuator (RWA) system, commonly utilized in the aerospace industry for spacecraft attitude control. The RWA system consists of a large flywheel attached to a motor. By spinning the flywheel in one direction, the robot can counteract any imbalance and stabilize its orientation.
For their experiment, the team mounted two RWAs on a commercial Unitree A1 robot, allowing independent control over the robot’s angular momentum on the pitch and roll axes. This means that the robot remains balanced, regardless of whether its legs are in contact with the ground or not.
One advantage of this approach is that it can be easily integrated into existing control frameworks without requiring significant modifications. The RWA system does not alter the robot’s mass distribution or have the joint limitations of a tail or spine, allowing for seamless integration with a standard model-predictive control algorithm.
Successful Results and Future Implications
The team conducted a series of successful experiments to test their system’s capabilities. They demonstrated the robot’s ability to recover from sudden impacts in simulations, simulating the falling-cat problem. In hardware tests, the robot showcased its recovery and balancing capabilities by walking along a narrow 6-centimeter-wide balance beam.
Looking ahead, the researchers anticipate a future where quadruped robots transition from being primarily research platforms to widely available commercial products, similar to the development of drones in recent years. By further enhancing the stabilizing capabilities of quadruped robots, they can potentially be utilized in high-stakes scenarios such as search-and-rescue missions.
“Quadrupeds are the next big thing in robots,” said Manchester. “I believe we’ll see a significant increase in their presence in various domains in the coming years.”
Watch the video demonstration here.