Simulation-Based Evaluation of a Shape-Transformable Autonomous Surface Robot Switching between Traveling and Station-Keeping Modes

This paper presents a simulation-based evaluation of Intelligent WAter Knowledge Observer-8 (BIWAKO-8), a compact autonomous surface robot equipped with a trans- formable locomotion mechanism that switches between the Station-keeping mode and the Straight-travel mode. A Webots- based simulation environment replicating field conditions was used to compare the two modes under four settings: ideal, disturbance-only, localization-error-only, and a realistic combi- nation. Across all settings, the Straight-travel mode completed missions faster, whereas the Station-keeping mode consistently consumed less energy, revealing a clear speed–energy trade– off. Disturbances had negligible impact on the energy efficiency of the Straight-travel mode, while localization error increased energy use in both modes by inducing more frequent heading corrections. These findings support hybrid operation—using the Straight-travel mode for transit and the Station-keeping mode for precise positioning—as an effective strategy for long- duration autonomous surface missions.