  Marine exploration is essential to understanding ocean processes and
organisms. While the use of current unmanned underwater vehicles has enabled
many discoveries, there are still plenty of limitations toward exploring
complex environments. Bio-inspired robots are a promising solution for highly
maneuverable underwater swimming at moderate speeds. Krill, especially, are
efficient swimmers in the intermediate Reynolds number regime and can inform
engineering solutions for ocean exploration. In this paper, we present the
design, manufacture, and validation of a new krill-inspired, metachronal,
drag-based robotic system. By combining active and passive actuation of the
joints with 3D printed parts, our unique design recreates the swimming
kinematics of Euphausia superba in a compact and reproducible robotic platform.
The motion of the anterior and posterior appendage segments is achieved using
servo motors and a multi-link mechanism, while the out-of-plane motion of the
biramous distal segments is attained via fluid-structure interactions. Going
forward, our platform will be leveraged to study metachronal, drag-based
swimmers across taxa to identify unifying success mechanisms at different
scales, facilitating the development of a new generation of underwater robots.
