Walking machine leg design: The effect of leg geometry on knee torque

Abstract

The authors have been studying the fundamental mechanics of legged vehicles with the aim of establishing generic principles for their mechanical design. The approach to date has been to consider overall machine design and leg mechanism design separately. In leg design there is inevitably a trade-off between workspace (reach) and leg weight for given loading conditions. To understand this trade-off, the effects of leg geometry on both kinematic workspace and leg weight must be investigated. Leg weight is largely a function of the hip and knee design torques; the former is determined by the overall machine design which has been discussed elsewhere. This paper considers the effect of leg geometry on the total design torque that the knee must support through both its structure and the knee actuator. The actuator design torque is also considered. The leg geometry varied includes link lengths and knee twist angles. The necessary mathematical analyses are developed and data presented showing the relationship between knee or actuator torque and leg geometry.