Modeling and Analysis of Surface Motion Characteristics for a Dual-Propulsion Amphibious Spherical Robot

This paper presents the design and water-surface motion analysis of an amphibious spherical robot equipped with a dual-propulsion system (ASR-DPS). Owing to its unique spherical geometry, the robot exhibits significantly different hydrodynamic behavior from conventional vessels. A comparative analysis of the frontal wetted area is conducted, followed by computational fluid dynamics (CFD) simulations to evaluate its water-surface motion characteristics. Results reveal that the hemispherical front increases hydrodynamic resistance and induces large-scale vortex structures due to intensified flow separation. Despite the higher resistance relative to traditional hulls, the robot’s deeper draft and dual propulsion configuration offer enhanced stability and improved maneuverability during surface operations. To validate its performance in real-world conditions, standard maneuvering experiments, including the circle test and zig-zag test, are conducted to assess the effectiveness of the propeller propulsion system. In addition, experiments are conducted to evaluate the water-surface motion performance of the pendulum propulsion system. A four-degree-of-freedom kinematic and dynamic model is developed to describe the robot’s water-surface motion. To handle model uncertainties and external disturbances, two control strategies are proposed: one based on model simplification and the other on adaptive control. Both strategies aim to regulate surge velocity and yaw angle. Simulation results are presented to compare the control performance of the proposed methods.