Spherical Amphibian Robot: Aquatic Performance Analysis

This study presents the design and experimental evaluation of a novel spherical amphibian robot engineered for enhanced aquatic mobility and versatile operation across diverse environments. Inspired by the protective rolling mechanism of pangolins, this spherical robot offers inherent advantages in concealment, adaptability, and stability for both terrestrial and aquatic applications, including harbor patrolling and exploration of challenging terrains. Our research addresses the critical role of the center of mass (CoM) in ensuring robotic stability, proposing a unique driving principle for effective operation in aquatic settings. The robot's innovative design incorporates a yoke acting as a CoM manipulator and features two propellers with adjustable thrust direction (0 to 90 degrees) based on the equilibrium body concept. Experimental results demonstrate that the proposed system enables controlled thrust orientation via roll (x) and pitch (y) rotations to subsequently facilitate translation along the surge (x) and heave (z) axes. However, our findings also reveal that increasing both the ballast mass and yoke angle correlates with an increase in positional error. This inaccuracy is primarily attributed to an imbalance in the liquid volume and velocity within the internal ballast system, highlighting key considerations for future advancements in amphibious robot stability and control.