Exploring metachronal swimming performance and maneuverability with bioinspired robotics.

Metachronal swimming with flexible appendages beating sequentially is common in many aquatic invertebrates. This widespread occurrence stems from the need to balance thrust, drag, and maneuverability to achieve higher efficiency and performance than a single propulsor. Biological and robotics research emphasized the fluid-structure mechanisms that enhance thrust during metachronal swimming but we still need an overview of the functional and physical mechanisms reducing drag and enabling mobility. Using marsh grass shrimp (P. vulgaris) as a model organism, we developed a metachronal robot with morphologically accurate flexible appendages (pleopods) and parameterized kinematics. Simultaneous flow and force measurements showed that leg asymmetrical bending reduces the pleopod drag coefficient by up to 76% relative to stiff legs during the recovery stroke. Combined with leg coalescence during the recovery stroke, net thrust increased by 30.2%. By adjusting the beat frequency, amplitude, inter-pleopod phase, and temporal asymmetry, we can generate rotational moments to evaluate maneuverability. Our approach addresses fundamental biological and physical principles of metachronal propulsion that will aid in developing a unifying theory and inspire novel bio-inspired underwater vehicles.