DuckyDog: An Erect Amphibious Robot with Variable-Stiffness Legs and Passive Fins

Cutting-edge applications require robots to be capable of navigating in different environments to improve the time and energy efficiency of travel and exploration. Amphibious robots address this need by operating in both aquatic and terrestrial settings, leveraging biomimetic designs and integrated mechanical propulsion systems. While these robots has traditionally drawn inspiration from reptiles, crustaceans, and amphibians, there has been comparatively less exploration of swimming-capable mammals and birds as biological models. In this work, DuckyDog, a quadruped amphibious robot using erect posture has been proposed and developed to take full advantage of the high mobility of mammals on land. By integrating a duck-like body and passive fins, it also has excellent swimming ability on the water surface. Whereas many robots rely on soft materials to construct compliant legs, DuckyDog is distinguished by its fused deposition modeling-printed legs made from polylactic acid (PLA) filament, featuring structurally induced variable stiffness and actuated through a tendon-driven mechanism. A series of experiments are conducted to evaluate DuckyDog's terrestrial and aquatic locomotion performance in both laboratory settings and complex natural environments, where it achieves maximum speeds of 0.40 body lengths per second on land and 0.30 in water.