Development of a flipper propelled turtle-like underwater robot and its CPG-based control algorithm

This paper presents the construction and control of a turtle-like underwater robot with four mechanical flippers. Each flipper consists of two joints generating a rowing motion by combination of lead-lag and feathering motions. The control architecture is constructed based on central pattern generator (CPG). A model for a system of coupled nonlinear oscillators is established to construct CPG and has been successfully applied to the eight-joint turtle-like robot. The CPGs are modeled as nonlinear oscillators for joints and inter-joint coordination is achieved by altering the connection weights between joints. With cooperative movements of four flippers, the robot can propel and maneuver in any direction without rotation of its main body, and execute complicated 3-D movements including ascending, submerging, rolling, and hovering. The CPG-based method shows elegant and smooth transitions between swimming gaits, and enhanced ability to cope with transient perturbations due to nonlinear characteristic. The effectiveness of the proposed method is confirmed via simulations and experimental results.