# A Review of Foot-Terrain Interaction Mechanics for Heavy-Duty Legged Robots
## 5 Conclusions  
(1) The factors influencing the terrain adaptability of the heavy-duty legged robots are explored. Various foot shapes, including cylindrical, semi-cylindrical, spherical, hemispherical, square, and special configurations, are examined, each presenting distinct advantages and disadvantages. When designing the mechanical structure of a robot, the selection of foot configurations and the design of appropriate foot patterns, tailored to specific needs, prove beneficial in enhancing the robot's adaptability to unstructured environments and improving its overall mobility. However, challenges persist as heavy-duty legged robots' feet encounter difficulties adapting to certain unstructured surfaces. Common terrains such as deserts, uneven lunar surfaces, and areas containing stones pose particular challenges for heavy-duty legged robots. Addressing these challenges will be crucial in further refining the design of heavy-duty legged robots for diverse terrains. (2) The ultimate goal is to design feet for heavy-duty legged robots with enhanced anti-sinkage capabilities, increased traction, and a lightweight structure. To augment the terrain adaptability of heavy-duty legged robots, insights from the characteristics of large legged animals' feet have been distilled. Furthermore, the proposed design elements for biomimetic feet aim to emulate nature's solutions. The incorporation of biomimetic foot plantar patterns onto the sole of the foot proves particularly impactful, substantially amplifying the robot's adhesion capabilities. (3) The mechanics of foot-terrain interactions encompass both normal and tangential forces occurring between the foot and the contact terrain. An accurate model detailing the mechanics of foot-terrain interaction plays a crucial role in investigating the terrain adaptability of robots. While research on wheel-terrain interaction models is relatively advanced, there is a noticeable gap in the exploration of mechanical models for foot-terrain  
Figure 41: Process of choosing appropriate mechanical model to use multimodal information fusion. interactions. A comprehensive and fully established system for the mechanical model of heavy-duty legged robots' foot-terrain interactions is yet to be realized. The challenges in terrain mechanics for heavy-duty legged robots necessitate support from a systematic theoretical framework. (4) To enhance the model's precision, an area evaluation parameter is introduced. Subsequently, a mathematical model incorporating the interaction between feet and terrain is proposed to calculate the tangential force. The resultant force equation on the robot's foot is predicted. The mechanical properties of the soil in contact with the foot-terrain interaction significantly influence performance. Investigating various soil parameters for the classification of unstructured terrain holds paramount importance in understanding the mechanics of foot-terrain interactions. Furthermore, exploring the soil on other planets is crucial for the future success of heavy-duty legged robots in interstellar exploration missions. This study includes mechanical performance parameters for real lunar soil, simulated lunar soil, and Martian soil. In future research, the integration of multimodal information fusion and foot-terrain interaction mechanics will be leveraged for cross-application purposes. Conceptualization, H.Z. ; methodology, H.Z. and J.W. ; formal analysis, N.W., W.L., N.L. and L.D. ; data curation, H.Z. and J.W. ; writing--original draft preparation, H.Z. and J.W. ; writing--review and editing, H.Z. ; visualization, J.W., N.W. and B.L. ; supervision, H.Z. ; funding acquisition, H.Z., W.L. and N.W. All authors have read and agreed to the published version of the manuscript. This research was supported by the National Natural Science Foundation of China (Grant No. 51505335 and Grant No. 52175007), the Industry University Cooperation Collaborative Education Project of the Department of Higher Education of the Chinese Ministry of Education (Grant No.