Traction performance test using variable-area anti-subsidence walking wheel

Traveling wheels have been limited to severe subsidence, continuous slippage, and insufficient traction performance, particularly when working on muddy, loose, and waterlogged paddy field soil. Technical defects have seriously reduced the running stability and efficiency of agricultural machinery in the field, leading to serious power loss and unnecessary energy consumption. It is often required for the high flexibility and environmental adaptability of farming equipment in complex wet and soft tillage environments. In this study, a variable-area anti-subsidence bionic walking wheel was proposed for paddy field farming, according to mature engineering bionic theories and advanced bionic techniques. The bionic prototype was taken from mallard webbed feet living in wetland environments, due to its physical structure, flexible deformation, and adaptive dynamic movement. A walking wheel was newly developed to dynamically adjust its contact area with soil in real time during rotating operation, suitable for the complex and variable mechanical properties of different soil layers in paddy fields. Wheel-soil kinematics and mechanical test platform were conducted for the standardized and controlled performance experiments. Two types of widely distributed soil were selected as test media in farmland areas, namely sandy soil with three continuous gradient moisture contents and ordinary farmland soil with four moisture levels. Diverse field working conditions were fully simulated to verify the wheel’s universal adaptability. Three typical bionic structures of walking wheels were evaluated, including the variable-area adaptive, fully expanded, and fully closed webbed type. Performance parameters were also measured, such as driving torque, soil subsidence depth, and effective forward displacement. Finally, a systematic investigation was made to clarify the influence of soil moisture content and wheel structural state on the traction of walking wheels. Experimental results indicate that soil moisture content and wheel structure shared a strong interaction on the overall performance, anti-subsidence, and traction stability of the walking wheel. The variable-area bionic walking wheel performed the best for environmental adaptability under all test conditions. Compared with the two conventional webbed wheels, the maximum drawbar-pull and traction efficiency were improved by 50.0% and 27.7%, respectively. The influence of soil moisture exhibited the medium-dependent trends: moisture content effectively enhanced the traction performance in loose sandy soil, while the traction capacity and running stability were outstandingly weakened in cohesive farmland soil. Furthermore, the wheel-soil interaction revealed that the superior anti-subsidence and high-traction performance was attributed to the adaptive motion of the expanding contact area, while touching the soil and closing the structure while lifting off. A mathematical correlation model between traction efficiency and slip ratio was established after a discrete element simulation. The optimal slip ratio was quantitatively quantified as suitable for the soil environments. This study provides a solid theoretical and valuable technical reference that can provide for the bionic optimization of walking devices in paddy fields. The findings can effectively improve working efficiency and complex terrain adaptability under various wet soft soil environments in modern agricultural machinery.