Mantis hybrid leg-wheel robot: Stability analysis and motion law synthesis for step climbing

Mantis is a hybrid leg-wheel small-size mobile robot, equipped with two front actuated wheels, a passive rear axle and two rotating legs, conceived for surveillance and inspection tasks in unstructured indoor and outdoor environment. While motion on flat and even ground is purely wheeled, in case of obstacles or terrain irregularities the front legs realize a mixed wheeled-legged locomotion to increase the robot climbing ability; in particular, step-climbing has been considered in the design phase. The paper discusses the influence of the main geometric parameters (wheelbase, leg length, leg joint position) and of the leg-wheel motion planning on the static stability during step-climbing, adopting a nondimensional model for sake of generality. Moreover, the results of multibody simulations are reported and compared to the analytical study. The work is the basis for the next step of the research, that is the development of an automatic guidance system capable of coordinating legs and wheels in step/stair climbing.