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Mechanics and Simulation of Six-Legged Walking Robots

Legged locomotion is used by biological systems since millions of years, but wheeled locomotion vehicles are so familiar in our modern life, that people have developed a sort of dependence on this form of locomotion and transportation. However, wheeled vehicles require paved surfaces, which are obtained through a suitable modification of the natural environment. Thus, walking machines are more suitable to move on irregular terrains, than wheeled vehicles, but their development started in long delay because of the difficulties to perform an active leg coordination. In fact, as reported in (Song and Waldron, 1989), several research groups started to study and develop walking machines since 1950, but compactness and powerful of the existent computers were not yet suitable to run control algorithms for the leg coordination. Thus, ASV (Adaptive-Suspension-Vehicle) can be considered as the first comprehensive example of six-legged walking machine, which was built by taking into account main aspects, as control, gait analysis and mechanical design in terms of legs, actuation and vehicle structure. Moreover, ASV belongs to the class of “statically stable” walking machines because a static equilibrium is ensured at all times during the operation, while a second class is represented by the “dynamically stable” walking machines, as extensively presented in (Raibert, 1986). Later, several prototypes of six-legged walking robots have been designed and built in the world by using mainly a “technical design” in the development of the mechanical design and control. In fact, a rudimentary locomotion of a six-legged walking robot can be achieved by simply switching the support of the robot between a set of legs that form a tripod. Moreover, in order to ensure a static walking, the coordination of the six legs can be carried out by imposing a suitable stability margin between the ground projection of the center of gravity of the robot and the polygon among the supporting feet. A different approach in the design of six-legged walking robots can be obtained by referring to biological systems and, thus, developing a biologically inspired design of the robot. In fact, according to the “technical design”, the biological inspiration can be only the trivial observation that some insects use six legs, which are useful to obtain a stable support during the walking, while a “biological design” means to emulate, in every detail, the locomotion of a particular specie of insect. In general, insects walk at several speeds of locomotion with a