Control of contact forces in wheeled and legged off-road vehicles

Abstract

The use of variable configuration vehicles creates the possibility of direct control of the contact forces between the foot or wheel of a vehicle and the ground. That control is an important element of the coordination of practical walking machines. Control of the contact forces at each wheel is also attractive for wheeled vehicles. For example, the power consumed in driving such a vehicle is quite sensitive to wheel-ground conditions. In conditions of strict power budgets, as in planetary roving vehicles, it becomes attractive to attempt to minimize power consumption by optimizing the wheel-ground contact forces. Unfortunately, control of contact forces in a wheeled vehicle is very complex because of the non-holonomic nature of the system.

In this paper we will review the allocation of contact forces in legged systems and examine the attempts that have been made to apply similar principles to the guidance and propulsion of wheeled systems on uneven terrain. The Adaptive Suspension Vehicle (ASV) and Wheeled Actively Articulated Vehicle (WAAV) from the authors’ laboratory will be used as examples, and as sources of experimental validation of theoretical and numerical results. The former is a six-legged walking machine with each leg having three actively controlled degrees of freedom relative to the vehicle body. The latter is a six-wheeled variable configuration vehicle with three-axis, actively controlled, spherical articulations between successive axles.