I. Introduction
For humans, as for other living creatures, it is substantial to know the spatial orientation of our body with respect to the external world. Most of our sensory systems can contribute to this task. Interestingly, visual, auditory, tactile, proprioceptive, or olfactory sensory inputs can be easily put out of action, but the vestibular inputs are always available, even in the absence of gravity [1]. In artificial systems, robots in particular, inertial measurement units (imus) often play the role of a ‘robotic vestibular system’. These imus sense the movements of the robot and provide its control system with data that can be further processed to yield estimates of the robot location and displacement in space. The operating principle of biological motion sensors and of engineering inertial sensors is based on the same laws of mechanics. Thus, we believe that strategies observed in biological systems, such as head stabilization, can also benefit the design of robotic systems.