Research on the parasitic evolution of the leg mechanisms and the spatial stiffness of a tracked–legged robot

For high-payload applications in complex terrains, tracked–legged robots must maintain adequate mechanical stiffness while preserving terrain adaptability. Their legs, however, often employ complex spatial multi-link mechanisms, making stiffness modeling a challenge in balancing accuracy and computational efficiency. To address this issue, this study proposed a novel hybrid tracked-legged robot (TL) based on the host-parasite (HP) mechanism principle, incorporating a parallel decoupled spatial multi-link mechanism for its leg structure. To comprehensively evaluate the mechanical stiffness characteristics of the robot, this study thoroughly analyzed the stiffness distribution of six mechanisms ( M 2 –M 7 ) during the parasitic evolution process. First, a high-precision non-fitted stiffness distribution (Non-FSD) model with numerous computational elements was established using the finite element method (FEM). Subsequently, taking the M 7 mechanism as the research object, a fitted stiffness distribution (FSD) model with significantly fewer computational elements was developed based on spatial multi-link mechanism analysis algorithms. Finally, experimental validation was conducted to verify its accuracy. The results demonstrated that, compared to the Non-FSD model, the multi-pose FSD model achieved an average error of only 5.64%, significantly improving stiffness accuracy while reducing computational time by 99.19%. Further analysis reveals that during parasitic evolution, the mechanism’s stiffness distribution improves in the x-direction and significantly strengthens in the y -direction (primary load-bearing direction), with mechanism M 7 showing a 1563.86% increase in average stiffness( y -direction) compared to M 5 . This study provides an efficient and accurate method for robot stiffness modeling and optimization.