Measuring the Mechanical Coupling in Dynamic Locomotion to Inform Control

Dynamic locomotion is the result of coordination across distributed subsystems. For example, terrestrial animals maintain coordinated leg patterns to move. To maintain coordination, information is shared through coupling. As coupling magnitude increases, more information is shared globally throughout the subsystems compared to information shared locally, both of which can be measured. In a terrestrial robot, some coupling will be due to mechanical interactions between the legs mediated by the environment and body. As it may be difficult to model these physics, empirical measurements may be necessary to characterize a system to inform control strategies. Using our information measures, we characterize the mechanical coupling of a bounding quadrupedal robot as we alter its non-dimensional inertia, a known parameter of its body-mediated coupling. Global information minus local information is minimized for a particular moment of inertia where impulses from one leg pair have little effect on the other leg pair. Our empirical measurements match simplified analytic and computational models. Because of its applicability to many controlled dynamic systems, this information metric provides the start of a design framework for locomotor control of animals and robots.