UC Berkeley

Legged robots have excellent potential for all-terrain mobility, and are capable of many behaviors wheeled and tracked robots are unable to perform. However, legged robots have difficulty turning rapidly, or turning while running forward. For maximum maneuverability, terrestrial robots need to be able to turn precisely, quickly, and with a small radius. Previous efforts at turning in legged robots primarily have used leg force or velocity modulation. This work presents two novel methods of legged robot turning.

The first of these methods is inertial tail turning, or using a rapidly actuated, weighted tail to cause a sudden change in angular momentum, turning the body of the robot. The tailed robot presented here is able to make rapid, precise turns. By rapidly rotating the tail as the robot runs forward, the robot was able to make sudden 90 degree turns at 360 degrees per second, making it the fastest turning legged robot known to the author at the time of this publication. Unlike other turning methods, this turn is performed with almost no change in forward running speed. The dynamics of this maneuver have also been modeled, to examine how features, such as tail length and mass, affect the robot's turning ability. This approach has produced turns with a radius of 0.4 body lengths at 3.2 body lengths per second running speed. Using a nonlinear feedback controller, turns with an accuracy of 5 degrees for a 60 degree turn have been achieved.

The second method of turning presented here allows a legged robot to turn continuously while running at high speeds. This remains a difficult task for legged robots, but is crucial for maneuvering quickly in a real-world environment. SailRoACH is the first running robot that uses aerodynamic forces to turn. A flat plate serves as an aerodynamic surface, and depending on its position, can be used to impart positive or negative aerodynamic yaw torques on the robot as it runs forward, causing turns of up to 70 degrees per second at a radius of 1.2 meters and a running speed of 1.8 meters per second. A scale analysis of aerodynamic steering is also presented, showing this method is most effective for small robots. Comparisons to other steering methods are made, showing that inertial and aerodynamic steering are superior for high speed turns at high forward velocity, compared to existing methods.