DYNAMIC EFFECTS IN STATICALLY STABLE WALKING MACHINES

Discontinuous gaits for walking machines present some advantages over wave gaits such as better stability margins and greater speed for smal l duty factors, for instance. The:problem is that a machine using disc ontinuous gaits starts and stops its body motion several times I,er lo comotion cycle. This means that high accelerations appear, therefore t he theoretical static stability margin can be inadequate for measuring stability. This paper addresses how dynamic effects modify the measur ement of the static stability of a discontinuous gait and determines t he acceleration under which the criterion of using the static stabilit y margin for measuring the stability is valid. For this study, a dynam ic planar model of a four-legged walking machine was derived. Then, bo th the longitudinal and dynamic stability margins were computed and co mpared. Final results show that the static stability margin is an adeq uate measurement for studying stability in massless leg mai:hines with the constraint that the acceleration of the body be smaller than the inversion acceleration. When the mass of the legs is significant, stab ility is determined by the dynamics of the legs and the distribution o f the mass of the legs as well.