Ostraciiform Underwater Robot With Segmented Caudal Fin

Ostraciiform body/caudal fish locomotion requires high-frequency oscillation of the caudal fin, yielding negligible body oscillations. It is the most ideal form of biomimetic locomotion for underwater robots where body-stabilization is required for photography or manipulation applications. This letter presents a two-segment caudal fin design with substantial improvements over existing single-segment fins. The proposed fin helped reducing drag, increasing resonant frequency, and achieving a wide controllable range of thrust forces. The design, modeling, fabrication, and validation of an Ostraciiform robot with the proposed caudal fin are presented in detail. Over 1200 test trials on six fin designs were compared, showing nearly three-times higher resonant frequency and 12% thrust force increase over single-segment homogeneous fin. It is also demonstrated that the peak frequency could be selected via mechanical fin designs, enabling customized caudal fin design according to applications.