The Mechanics of Quadrupedal Galloping and the Future of Legged Vehicles

Previous studies have noted that biological quadrupeds adjust their gaits when encountering drag in their locomotion. This paper investigates the hypothesis that these gait adjustments allow the legs to operate at an optimal working length when generating thrust. A 5-DoF dynamic model of a quadruped having a rigid trunk and massless legs is formulated. This model reflects the dimensions and inertial properties of a galloping machine the authors are designing. The constrained, steady-state motion equations governing the transverse and rotary gallops of the model are solved numerically for various levels of drag. The footfall phasing solutions for both forms of the gallop approach a partially in-phase gait, the half-bound, as drag increases. These gait transitions are the result of constraints requiring the legs to operate at their optimal working length when in contact with the terrain. Thus, the behavior of the model supports the original hypothesis. This paper also includes a discussion of future research directions in the field of artificial legged locomotion. KEY WORDS—galloping, quadruped, legged vehicles, impulse model