Design and Hydrodynamic Performance of an Amphibious Quadruped Robot with Multi-Modal Propulsion Gaits

To extend quadruped robots’ aquatic locomotion capabilities and accommodate different water-surface locomotion requirements, an amphibious quadruped robot with active flippers was developed. The same multi-joint leg mechanism enables terrestrial walking, dog paddling, and frog-inspired swimming without a separate aquatic propulsion system. Hip-joint rotation reconfigures the limb-motion plane, while coordinated joint trajectories, interlimb phases, and flipper orientations enable both swimming gaits. Performance was characterized through single-leg and whole-robot force measurements in quiescent water, free water-surface locomotion, and terrestrial walking experiments. Under the gait trajectory parameter configurations used in this study, the mean surface speeds were 0.151 m/s (0.514 BL/s) for dog paddling and 0.143 m/s (0.486 BL/s) for frog-inspired swimming; the mean walking speeds were 0.123 m/s (0.418 BL/s) on rough ground and 0.142 m/s (0.483 BL/s) on smooth ground. Dog paddling provided more continuous propulsion and turning but greater vertical-force disturbances. Frog-inspired swimming provided more concentrated propulsion and turning with smaller vertical-force disturbances. These results demonstrate the feasibility of dual-mode surface propulsion through leg-mechanism reuse and gait reconfiguration while retaining terrestrial walking capability, supporting the selection of propulsion modes with complementary characteristics on the same platform.