From Space to Earth – Relative-CoM-to-Foot (RCF) control yields high contact robustness

This paper introduces the Simplest Articulated Free-Floating (SAFF) model, a low-dimensional model facilitating the examination of controllers, which are designed for free-floating robots that are subject to gravity. Two different state-of-the-art control approaches, namely absolute CoM control accompanied by an assumption about the foot acceleration, and a controller combining absolute CoM and foot control objectives, are shown to yield exponential stability in the nominal case, while becoming unstable if the foot contact is lost. As an improvement over the state of the art, the so-called Relative-CoM-to-Foot (RCF) controller is introduced, which again yields exponential stability nominally, while preserving a BIBO stable behavior even in case of a complete contact loss. The controller performance is validated in various simulations.