Design of a controllable pitch underwater thruster system

Abstract

Control systems for underwater vehicles have reached the level of sophistication where they are limited by the dynamic performance of the thrust actuators. Standard fixed-pitch propellers have been shown to have very poor dynamic characteristics, particularly at low thrust levels The dynamic response of a fixed-pitch propeller is dependent upon highly non-linear transients encountered while the shaft speed approaches its steady-state value. This thesis proposes the use of a controllable pitch propeller system to address this problem. A controllable pitch propeller varies the amount of thrust produced by varying the pitch angle of the blades at a constant shaft speed. The bandwidth of this type of thrust actuator would be dependent primarily on the speed at which the pitch angle of the blades are changed. A variable pitch propeller system suitable for retrofit into an ROV is designed and built. The system is designed for maximal pitch angle bandwidth with low actuator power consumption.