Bio-inspired Robotic Fish with Multiple Fins

Abstract

In this chapter present the research leading to the design of a biologically inspired robotic boxfish using multiple fins. The design attempts to achieve the maneuverability of a small scale, multiple fin underwater system like that of the boxfish, while also incorporating a body with a self correcting mechanism. Experimental studies were conducted to characterize and optimize the flapping fin propulsion of the tail fin. Towards this a three DOF robotic flapper was designed to act as the flapping tail or side fin of the fish and a fixed beam based force sensor was designed to measure the instantaneous forces generated by the fin motion. Tail fin with optimal shape induced flexibility has been found. The hydrodynamic force generation of tail fin has been modeled using a combination of quasi steady lift generation and empirically found drag and added mass effects. Fluid flow simulations on 3D CAD models of boxfish like shapes were used to arrive at the outer shape of the MUV. A robotic prototype of the MUV was designed based on the above analysis. The propulsion and maneuvering of the MUV is achieved by tail fin and two 2DOF side fins. One of the immediate goals is to use the prototype to evaluate the efficiency of various gait patterns for a given set of flow conditions. Sensors and command architecture will also be used in future generations to give the robot greater autonomy. Currently, new mechanical sealing techniques and more processing power are being incorporated into the next generation of the prototype to facilitate longer trial runs and effective control of the robot. Studying fin-fin and body-fin interactions can help modify the design of body shape and/or fin kinematics for optimal thrust production or even better maneuverability. One such problem is that of the interaction between the side fin and tail fin. On a small robot like the present MUV the proximity of the side fin and the tail fin is more and can lead to strong interactions between them. Such mechanisms can be investigated using multiple flappers and/or body shape in the tow tank.