Amphibious robotic dog: design, paddling gait planning, and experimental characterization

Mammal-inspired quadruped robots excel in traversing diverse terrestrial terrains but often lack aquatic mobility, limiting their effectiveness in amphibious environments. To address this challenge, an amphibious robotic dog (ARD) was developed, integrating efficient paddling gait in water with trotting capabilities on land. A canine-inspired paddling trajectory was first developed for a two-segment leg, and validated through theoretical modeling and experimental measurements of hydrodynamic forces. A waterproof ARD was then fabricated, with careful consideration of center-of-gravity and center-of-buoyancy relationships to ensure stable aquatic movement. Three distinct paddling gaits were developed and tested to evaluate the ARD's swimming speed and stability: two lateral sequence paddling gaits (LSPG) featuring 25% and 33% power phases (PP), and one trot-like paddling gait (TLPG) featuring a 50% PP. Theoretical modeling and numerical calculations were conducted to analyze the stability of different paddling gaits. Static water experiments measured gait-specific hydrodynamic forces, followed by dynamic swimming tests demonstrating that LSPG delivers superior propulsion and speed, while TLPG offers enhanced stability. The ARD achieved a maximum water speed of 0.16 m s^-1(0.54 BL s^-1) and a land speed of 0.35 m s^-1(1.2 BL s^-1). These findings provide theoretical and practical guidance for the development of mammal-inspired amphibious quadruped robots, particularly in structural design and paddling gait planning.