Free Gait — An architecture for the versatile control of legged robots

This paper introduces Free Gait, a software framework for the control of robust, versatile, and task-oriented control of legged robots. In contrast to common hardware abstraction layers, this work focusses on the description and execution of generic whole-body motions (whole-body abstraction layer). The motion generation and motion execution algorithms are connected through the Free Gait API. This facilitates the development and execution of higher level behaviors and motion planning algorithms. The API is structured to accommodate a variety of task-space control commands. With these, the framework is applicable to intuitive tele-operation of the robot, scripting of user defined behaviors, and fully autonomous operation with motion planners. The defined motion plans are tracked with a feedback whole-body controller to ensure accurate and robust motion execution. We use Free Gait with our quadrupedal robot ANYmal and present results for rough terrain climbing, whole-body stair scaling, and special motions such as push-ups and squad jumps. Free Gait is available open-source and compatible with any type of legged robot, independent of the number of legs and joints.