Integrable Whole-body Orientation Coordinates for Legged Robots

Abstract-- Complex multibody legged robots can have complex rotational control challenges. In this paper, we propose a concise way to understand and formulate a whole-body orientation that (i) depends on system configuration only and not a history of motion, (ii) can be representative of the orientation of the entire system while not being attached to any specific link, and (iii) has a rate of change that approximates total system angular momentum. We relate this orientation coordinate to past work, and discuss and demonstrate, including on hardware, several different uses for it. Many legged robots are best represented by nontrivial multibody dynamic models. The total system center of mass (CoM) is likely the most well-known of these model-based coordinates.