Bipedal Locomotion: A Continuous Tradeoff Between Robustness and Energy-Efficiency

Walking is a mechanical process involving all the limbs the body and subject to balance constraints. The structure of the body can allow the emergence of a stable walking using few to no energy, but this motion is sensitive to external perturbations and prone to fall easily. On the other hand, with strong actuation and anticipation, much more disturbances can be overcome, but at the cost of high energy consumption. The choice between these two modes of locomotion is more than a context-dependent binary selection. It is a continuous tradeoff, not only providing a span of different walking control policies but building the framework of a precise classification of these controllers. In this chapter, we discuss, for the humans and the robots, the two extreme walking paradigms and how to sort the solutions ranging between them. We analyze also the incentives behind the decision to change to a more robust or more efficient control policy. Finally, we show that the versatility of a walker depends deeply on the relationships lying between its controller dynamics and its mechanical design, both being ideally built together in a process of codesign.