Slip-resistant mechanism of bio-inspired foot end based on particle morphology and friction on ice and frozen ground

Abstract The attachment characteristics of the mechanical foot end are crucial for enhancing the traversability and locomotion of robots on extreme terrains. In this study targeting the reindeer touchdown unit, four bio-inspired foot ends and one conventional multi-baffle foot end were designed. Dynamic friction data of the bio-inspired foot ends were collected under various ground conditions, and the macro- and micro-structures of these surfaces were analyzed. The impacts of multiple factors on the attachment performances of the bio-inspired foot ends were explored, including the moisture content and compactness of frozen soil, and the ridges and convex crowns of foot ends. Additionally, a sliding/rolling friction conversion model was proposed to describe the interaction between the foot ends and frozen soil. When the ends interacted with the frozen ground and simulant for water-ice lunar soil, the attachment of the bio-inspired ribbed foot end and convex-crown was the best, and its dynamic coefficient of friction (DCOF) increased by 24.19%-44.68% and 35.14%-51.47% than the multi-baffle foot end. Upon interacting with the ice surface, the bio-inspired ribless foot end and non-convex crown demonstrated the best attachment performance. The DCOFs of these designs increased by about 24% compared to the multi-baffle foot end. The attachment performances of foot ends were more affected by moisture content compared with the compacted state of frozen ground. Compared to the ribless and non-convex-crown structures, the structures of ribs and convex-crown increased DCOF by 1%-15% and 18%-42%, respectively. Therefore, the effect of convex-crowns was greater than that of ribs. This study can improve the adaptability and traversability of robots on extreme terrains, which is of great significance for their applications in exploring polar regions, the moon, and other harsh environments.