Design of a low cost Thruster for an Autonomous Underwater Vehicle Srujana Eega, Student Member, Matthew A. Joordens, Member IEEE, Mo Jamshidi, Fellow, IEEE Member, Autonomous Control Engineering (ACE) Center and ECE Department The University of Texas San Antonio, TX, USA Email:e.srujana@gmail.com Abstract- Brushless Dc Motor (BLDC) is widely used in industries for various applications. The advantages of BLDC motor over the other types of motors made it a best choice for the design of low cost thruster. Presently the remotely operated underwater vehicle uses bilge pump motors to drive the vehicle under the water. Improvements are being done to make the vehicle autonomous and more efficient to run deeper under the water. To satisfy such improvements a more efficient thruster is essential and this paper explores the design of efficient, low cost and less weight thruster. The propeller is surrounded by the motor fitted in plastic or carbon fiber. Rotor holds the propeller and all electronics are embedded in plastic or carbon fiber. The mathematical model, design, controlling techniques of the motor and the future work are reported. Keywords: Thruster, Brushless Dc Motor I. INTRODUCTION Underwater vehicles are always driven by the thrusters and they being very expensive units raise the overall cost of the vehicle. Currently a huge research is going on in the area of underwater vehicles (robots) all around the world. System of Systems incorporating underwater vehicles along with air and land vehicles to working together has the potential to increase effectiveness over individual robots or swarms in any of the three environments. Swarms of low-cost vehicles in each environment can be used to cover more area with less cost and lower risk and higher fault tolerance than individual vehicles, since loss of a few vehicles in a large swarm does not lead to the failure of the entire mission as it would for a single expensive vehicle. If each robot is costly and if the application needs around 10 to 15 vehicles then the overall cost of the project is more. So there is undoubtedly need for low cost underwater vehicles. The costly part of the robot is thruster. An efficient, less weight, very small in size thruster is not less $3000. An autonomous underwater vehicle with six thrusters will have to spend around $15000 exclusively for thrusters. A thruster that costs less than $1200 would definitely be a good commercial product. To design a more efficient, small in size, less weight and low cost thruster is a challenging task. II. INITIAL PROTOTYPE It is a remotely operated underwater vehicle (robot). Bilge pump motors are used to drive the thruster. They are modified in way that computer fan is attached in the place of impeller and a computer fan grill is used as a finger guard over the fan blades. Thrusters are controlled using Pulse Width Modulation technique. The robot has three vertical thrusters, two forward thrusters and one aft and two horizontal thrusters .The body of the robot is built with the DWV PVC pipe [1]. (Fig.1) The robot works under the shallow water, at a depth of 9 feet. Fig. 1. Initial Prototype with all thrusters [1] III. NEW DESIGN The aim is to build a low cost autonomous underwater vehicle that is targeted at a depth more than 1 meter. The electronics of the robot are pretty much the same as the initial design except the changes like making it autonomous instead controlling it remotely, need for more efficient thrusters and the chassis is built using the PVC pipes as they are strong enough to withstand the pressure under the water. So the most interesting and the challenging task is the design of the thruster. The thrusters used initially are good for shallow water. So a better thruster is needed. The features of the new design are it should have more efficiency, should be really small in size and less in weight, simple water proofing system and have large staring torque. Thrusters are very expensive units. As each unit being very expensive, the underwater vehicle with 6 thrusters would raise up the cost of the overall vehicle. The best design with the required features will be achieved with the right choice of the motor to drive the thruster and very effective way of controlling the motor. With many advantages over the other types of the motor, Brushless Dc motor best fits to serve the purpose. The Characteristics of