This paper is devoted to the active turn control of a free-swimming multilink dolphin-like robot, with emphasis on yaw and pitch controls. With full consideration of both mechanical configuration and propulsive principle of the robot consisting of a yaw joint and multiple pitch joints, a viable approach to perform yaw maneuvers via laterally directed biases is formed, providing an advantage in qualitative and quantitative assessment. Meanwhile, based on the feedback of the pitch angle measured by an onboard gyroscope, a closed-loop control strategy in dorsoventral motions is proposed to achieve agile and swift pitch maneuvers. More remarkably, two hybrid acrobatic stunts, i.e., frontflip and backflip, are first implemented on the physical robot. The latest results obtained demonstrate the effectiveness of the proposed methods. It is also confirmed that the dolphin robot achieves better performance for pitch maneuvers than it does for yaw maneuvers, agreeing well with the biological observations.

In this paper, we present the formulation of a dynamic model of a free-swimming multi-joint robotic fish with a pair of wing-like pectoral fins, in which the whole robot is regarded as a moving multilink rigid body in fluids. Considering that the thrust of fish mainly results from the force of trailing vortex, added lateral pressure, and leading-edge suction force, the dynamic equations of the swimming fish have been derived by summing up the longitudinal force, lateral force, and yaw moment on each propulsive component in the framework of Lagrangian mechanics. Furthermore, using the bio-inspired Central Pattern Generators (CPGs) as the swimming data generator, the overall dynamic propulsive characteristics of the swimming robot are estimated in a mathematical environment (i.e., Mathematica). As a case study, the created dynamic model offers a good guide to seeking pragmatic backward swimming patterns for a carangiform robotic fish, which exemplifies the validity of the CPG-coupled dynamic model.

This paper deals with a novel closed-loop maneuvering control method to enhance the turning precision and turning response speed of a robotic fish propelled via the body and/or caudal fin (BCF) mode. Although the BCF propulsion is favorable for the cases requiring greater thrust and accelerations, its maneuverability can be compensated by effective turning control. In our method, the turning maneuver is divided into three phases: the bending, holding, and unbending phases. After much consideration on turning details, the functions of each phase and the basic control laws are further identified. Results of experiments on in-situ direction tracking and direction maintaining verify the effectiveness of the proposed turning control.