BlueGuppy: a miniature free-swimming robot for studying hydrodynamic interaction among schooling fish*

Schooling fish are known to take advantage of hydrodynamic interaction to save metabolic energy as they traverse the ocean. While fluid simulations and hydrofoil experiments have provided tremendous insights, it remains unclear how free-swimming fish-like swimmers interact with each other in formations. In this work, we designed a miniature fish-like robot, BlueGuppy, that can swim up to three body lengths per second. We characterize how a BlueGuppy's swimming speed increases with flapping frequency and how it turns with temporally asymmetric flapping. In addition, using PIV and force measurements, we reveal the flow field and the hydrodynamic consequences of a BlueGuppy following a leader at different relative locations. This project demonstrates the tremendous potential of free-swimming robots for revealing fluid-swarm interaction in biological collectives.