Stable Formations and Energetics of a Schooling Bio-Robots

The energy savings of fish schools have inspired previous studies to examine of the energetics of bio-robots tethered together or to a rig in a fixed formation. However, these bio-robots were not independently free-swimming like fish in a school. We present new experiments on a pair of independently free-swimming tuna-like bio-robots. The tuna-like robots are attached to independent air bearing platforms making them free-swimming in the streamwise direction. We examine the bio-robots swimming speed, potential for stable formations, and their energetics at a range of phase synchronies, lateral separation distances, and amplitudes. It is determined that the bio-robots have a stable side-by-side formation like interacting hydrofoils, yet contrary to hydrofoils the formation is stable for both in-phase and out-of-phase synchronizations. It is revealed that this stable formation is driven by a body-to-body interaction rather a fin-fin interaction. In addition, mismatched amplitudes are examined as a means for the robots to save energy while maintaining a stable formation.