The role of tensegrity in the diversity of avian postural stability

Like humans, all birds adopt a strictly bipedal posture. However, unlike humans, birds have such good balance that they can sleep while standing up, which must require minimal energy. This makes them an interesting model for studying bipedalism in robotics. In this study, we examine balance and postural stability via a tensegrity system (assembly in parallel of rigid bodies and cables). To test this hypothesis, we created mathematical models based on anatomical observations of the legs of various birds (zebra finch, little egret, mallard and military macaw) to investigate different configurations. Building on a previous model, we demonstrate that tensegrity systems can achieve passive stability under simplified loading. Here, we aim to establish whether this model can be generalized, to determine stability, and to identify the impact of certain kinematic, dynamic and material parameters. Our results enabled us to identify the parameters that allow the model to be generalized. We determined that adding two cables corresponding to tendinous and muscular sets generalizes the model to a varied range of configurations and exploits the rear part of the foot when present. These findings offer new insights into avian bipedalism and could inspire the design of bipedal robots with passive stability for greater autonomy.