Study on motion posture stability of undulatory fin robot multiple terrains based on bilateral fin phase optimization

To address the body pitch oscillation problem of undulatory fin robot during terrestrial locomotion, a bilateral fins anti-phase coordinated control method is proposed. First, the causes of body pitch oscillation during terrestrial locomotion are analyzed, and a body pitch dynamic model is established. Subsequently, a virtual prototype model of the robot is developed in SolidWorks and imported into ADAMS for simulation verification of the effectiveness of the proposed control method in suppressing body pitch oscillations. Finally, a prototype of the undulatory fin robot is developed, and comparative experiments are conducted on complex terrains, including meadow, brick, and snow-covered terrain. The experimental results demonstrate that the proposed dual-fin anti-phase coordinated control method reduces the amplitude of body pitch oscillation by 32.4%–42.7% and exhibits good oscillation suppression performance under different terrain conditions. Compared with the conventional bilateral fin symmetric in-phase control method, the proposed method significantly reduces body pitch oscillations of the robot in complex environments and improves locomotion continuity, providing a new analytical approach and theoretical basis for the cross-medium locomotion control of undulatory fin robots.