A Methodology to Investigate the Design Requirements of Plant Root-Inspired Robots for Soil Exploration

This letter proposes a methodology to investigate soil penetration requirements to extract specifications for designing robotic soil excavators and explorers. To this purpose, a three-dimensional (3-D) numerical model based on the Discrete Element Method (DEM) is proposed to simulate an intruder penetration and its interaction with the environment. In this study, the penetration process was analyzed as a function of the intruder diameter to median particle size ratio (Droot/D50), highlighting important differences for small and big ratios conditions (i.e., Droot/D50<<1 and Droot/D50>>1). In particular, the soil resistance force that autonomous penetration systems must overcome when moving into cohesionless granular soil was estimated based on the intruder size (diameter) and the median granularity (D50). This study estimates how the penetration requirements vary according to different penetration strategies. Specifically, a plant root-inspired axial movement emulating the growth from the tip adopted by plants is compared with a penetration obtained by pushing a system from the top. Our findings provide important guidelines about the design requirements (system size, penetration strategy, and actuation power) for artificial penetrating systems, like autonomous explorative robots, to improve their performances during underground exploration.