2021 Volume 19 Issue 5 Pages 639-646
Hopping mobility is effective for exploration robots present on small celestial bodies including asteroids and comets and their surfaces are covered in certain places with granular materials such as fine grain sand. However, existing studies do not address hopping mobility on the aforementioned types of granular materials in detail. Therefore, it is necessary to analyze hopping motion on sandy surface for future missions. This study presents a parametric analysis of the hopping motion on granular materials based on a discrete element method (DEM) simulation. In particular, the DEM allows for the numerical simulation of the dynamic behaviors of numerous fine particles. The DEM defines a sand particle as a simple sphere and computes mechanical interaction between each particle which follows some simple laws of dynamics. To analyze the hopping motion, we focus on two characteristics of the hopping motion: the initial hop velocity and hop angle of the robot. In DEM simulations, we change the friction and rolling friction coefficient of the sand particles, the acceleration of gravity and the angular velocity of the robot. We perform a simplified analysis and assume that the terrain surface in DEM simulation is smooth and flat and that the robot exhibits a cubic shape. Based on the research results, we qualitatively evaluate the exploration robot's motion on a sandy surface by DEM analysis when compared with its motion on a rigid surface.