Design and optimization of a one-degree-of-freedom eight-bar leg mechanism for a walking machine

Abstract

It has been established that legged, off-road vehicles exhibit better mobility, obtain higher energy efficiency and provide more comfortable movement than those of tracked or wheeled vehicles while moving on rough terrain. Previous studies on legged mechanism design were performed by selecting the length of each link by trial and error or by certain optimization techniques where only a static force analysis was performed due to the complexity of the mechanisms. We found that these techniques can be inefficient and inaccurate. In this paper, we present the design and the optimization of a single degree-of-freedom 8-bar legged walking mechanism. We design the leg using the mechanism design theory because it offers a greater control on the output motion. Furthermore, a dynamic force analysis is performed to determine the torque applied on the input link. The optimization is set up to achieve two objectives: i) to minimize the energy needed by the system and ii) to maximize the stride length. The kinematics and dynamics of the optimized leg mechanism are compared to the one by trial-and-error. It shows that large improvements to the performance of the leg mechanism can be achieved. A prototype of the walking mechanism with 6 legs is built to demonstrate the performance.