On finding the relevant dynamics for model-based controlling walking robots

Leg dynamics are often ignored in the real-time control of walking robots because of the high gearing used in leg transmissions. However, the use of a gear reduction high enough to discount Coriolis and centripetal components yields additional non-desired dynamics, which are friction, backlash and elasticity. In such cases, simplifying robot dynamics without considering the effect of gear dynamics leads to unavoidable errors. In order to make dynamic equations reflect the reality of the physical system, it is of paramount importance to model the most significant effects acting on the system. Robot dynamics could then be analyzed and related to trajectory parameters for motion-control purposes. In this paper, a method to derive the dynamics of a robot leg as a function of leg-trajectory parameters is proposed. The method experimentally finds the simplified equations of motion that reflect the reality of the physical system. The resulting model is an accurate and simple representation of the system dynamics, taking into account the most relevant dynamics affecting the system. The simplification of the model allows it to be used in a real-time dynamic-control system.