Influence of moving direction on normal force acting on a single lug during translational motion in sandy soil

To access loose sandy terrains, lugs (i.e., grousers) are attached on the surface of wheels/tracks to enhance the traveling performance of mobile robots. To clearly understand lug-soil interaction mechanism, an empirical model of normal force acting on lug during horizontal shearing motion has been established in our previous research. Moreover, it has been found that before this model can be extended to an arbitrary planar shearing motion of a lug, the effects of vertical motion on reaction forces should be studied as well. Inspirited by these founding, in this paper, experimental results from the vertical shearing motion of the lug were mathematically fitted to facilitate quantitative analyses on relationship between lug vertical motion and reaction force. It has been found that the reaction force demonstrates different characteristics in the two shearing motions. Then, by comparing the results measured from various moving directions with the empirical equations concluded from the two shearing motions, we confirmed how the two shearing motions contribute to the normal force acting on the lug that is translating at different moving direction angles.