I. Introduction
The precise estimation of both the center of mass (CoM) position and the angular momentum derivative is an important issue for legged robots control [1], [2]. It also has various applications in humans for motion analysis in biomechanics or for disorders diagnosis in medicine. The main challenge of this estimation problem lies in the fact that these two quantities are not directly measurable, and depend at the same time on fixed parameters (e.g. mass distribution of the system, dimensions of the limbs, etc.) as well as on varying quantities (e.g. joints configurations).