Role of Spine Compliance and Actuation in the Bounding Performance of Quadruped Robots

There is so far no quadruped robot that exhibits locomotion performance matching to that shown by animals every day. Both differences in general design concepts, in available materials and actuation mechanisms as well as a lack of understanding on the control of the robots’ actuators contribute to the current performance gap between robotic platforms and their biological counterparts. While for example many legged animals actively take advantage of compliant spines for energy storage, maneuverability and achieving energy efficient locomotion with high velocities, most of the existing successful quadruped robots solely exploit the dynamics of their leg mechanics and actuators. From biomechanics studies we know that spine can play important roles in quadrupedal locomotion such as kinematic increase in leg length, providing auxiliary power to the legs and storing and transferring energy [1]. The problem of exploiting these properties in the robotic quadruped locomotion however has not been yet addressed in systematic ways. Complexities arise due to the nonlinear and coupled dynamics of legged systems with compliant and active spines as well as from the trade-off between different performance criteria such as speed, energy efficiency and stability. Studies to gain better understanding can be performed on robots and in simulation. A verification by building and testing robots can provide us with good insights but is time-consuming when many robot morphologies and environmental conditions need to be evaluated. We thus prefer performing extensive studies on the details and parameters of robot and spine morphologies and control in simulation. However, for this simulation studies we need sufficiently detailed mathematical models that can both correctly describe the basic physical properties and capture the dynamics featured by a robot. In this contribution we introduce novel dynamics model based on existing dynamics modeling approaches [2] that allow detailed studies on the role of a compliant spine in quadruped locomotion. We use this model to address our key questions on locomotion control and the effect of robot morphologies by performing extensive sets of experiments.