LEARNING FROM GYMNOTIFORM SWIMMERS — DESIGN AND IMPLEMENTATION OF ROBOTIC KNIFEFISH NKF-II

Abstract

Gymnotiform swimmer uses single undulating anal fin below the rigid body as the propulsor. This special morphological structure is generally thought to have advantages in reducing the friction drag in undulatory movements. The finned body form and the undulatory swimming gait give the inspiration to the design of underwater robot. We have developed a robotic fish (Nanyang KnifeFish, NKF-I), which learns from a Gymnotiform swimmer: Black Ghost Knifefish. A new version of biomimetic robotic fish (NKF-II) is presented in this paper. To mimic the actual flexible fin of real fish, an optimized fin-like propulsion mechanism is modelled with a series of connecting linkages for enhancing its propulsive performance. Workspace of the proposed mechanism is studied and optimized. Swimming motion function is also established for the planning of the undulatory gait movement. The manoeuvrability and buoyancy control has also been achieved by the integration of mechatronics design of a buoyancy module with the undulating fin. The design philosophy of modularity has also been incorporated into the design of the fish. Hence, the modularity of the prototypes not only provides versatility for the robot system and also facilitates in the maintenance and future development of fish with undulating fins/body, as new modules can be added to replace the existing modules easily. By reconfiguring the components of NKF-II, other version of robotic fish with undulating fins/body is derived. This evolution of the undulating fins is also discussed.