Bio-inspired flow sensing using proprioception in a metachronal swimming robot

Underwater propulsors inspired by metachronal swimmers such as shrimp, krill, and copepods represent a potential paradigm shift in robotic ocean exploration by enabling higher maneuverability, lower power consumption, and thus greater spatial coverage compared with traditional propeller-based thrusters. In addition to using their appendages for propulsion, however, aquatic animals also extract information about their surrounding fluid environment by sensing hydrodynamic forces imposed on their appendages and body. This proprioceptive sensing modality could be well-suited for bio-inspired robots, potentially enabling obstacle avoidance and flow characterization without the need for dedicated flow sensors. In this work, we investigate proprioceptive flow sensing using a bespoke metachronal robot, which is propelled by two rows of five appendages each that mimic the morphology of marsh grass shrimp (P. vulgaris). Using electromagnetic actuators, each of the ten appendages is individually controllable, enabling real-time estimation of hydrodynamic forces and torques at the appendage level. We investigate the response of the appendages to different flow conditions during forward swimming, and compare the flow structures in the surrounding flow with the forces recorded by each appendage. Additionally, we test locomotion near a solid wall, which provides insights into object detection and avoidance. Our work sheds light on fluid-structure interactions during metachronal propulsion and explores the latent flow sensing capabilities of bio-inspired propulsors.