ORIGINAL ARTICLE Development of a dual-shaft propeller thruster equipped with rotational speed sensor for UVMS control Radzi Bin Ambar • Shinichi Sagara • Takuya Yamaguchi Received: 7 May 2013 / Accepted: 6 October 2013 / Published online: 20 October 2013 Ó ISAROB 2013 Abstract Majority of underwater robots utilize single propeller thrusters for navigation. A disadvantage of using a single-shaft propeller thruster is that the thrust force generated from a single propeller for reverse and forward thrust is asymmetric due to the disturbed flow caused by the thruster’s body which may reduce thruster efficiency. Moreover, measurement procedures to precisely calculate propeller’s rotation speed were also not available. To address these problems, this paper proposes a dual-shaft magnetic coupling-driven propeller thruster for underwater robot, equipped with sensors for measuring propeller’s rotational speed. Numerical studies and experimental results on the position and orientation control of the pro- posed thruster are presented. Detail comparison of the rotational speed, thrust force and duty ratio between numerical calculation and actual experimental measure- ment results show the effectiveness of the proposed thruster. This paper also demonstrated that by using the proposed thruster, the control performance of an under- water robot can be improved significantly compared to commercially available thruster. The ability to determine propeller rotation directions is also a major advantage of this work. Keywords Dual-shaft  Thruster  Rotational speed  UVMS  Control 1 Introduction As underwater operations explore into extreme depths and dangerous environments which is beyond the reach of human divers, underwater robots grow further in impor- tance and utilization. For this reason, various development activities have been carried out by researchers for the advancement of underwater robots technology [1–4]. However, one of the issues faced in the development of underwater robots is the nonlinear behavior of the under- water thrusters which affects the robot motion control. Generally, single-shaft propeller thrusters were used in underwater robots researchers compared to dual-shaft propeller thrusters [2–4]. Moreover, we have been designing an underwater vehicle-manipulator system (UVMS), which is also utilizing six single-shaft propeller thrusters [5–7]. Usually, a single-shaft propeller thruster typically comprises an electric motor, propeller blade and a magnetic coupling mechanism. While a dual-shaft propel- ler thruster consists of two magnetic couplings, two pro- peller blades and an electric motor. Magnetic coupling is use to transmit torque through an air gap between motor driven shaft and load shaft (propeller). This mechanism provides several advantages such as cushioned start, low power usage and low maintenance cost. Through several experiments, we observed that the design of single-shaft propeller thruster gave a significant effect on the overall control performance of the UVMS. For instance, the thrust force generated from a single propeller for reverse and forward thrust is asymmetric due to the disturbed flow caused by the thruster’s body which may reduce thruster efficiency. This causes difficulty when controlling UVMS for motions such as hovering and manipulating an object by using robotic arm. We assumed that a dual-shaft pro- peller thruster is capable of producing a symmetric thrust This work was presented in part at the 18th International Symposium on Artificial Life and Robotics, Daejeon, Korea, January 30–February 1, 2013. R. Bin Ambar  S. Sagara (&)  T. Yamaguchi Department of Mechanical and Control Engineering, Kyushu Institute of Technology, Tobata, Kitakyushu 804-8550, Japan e-mail: sagara@cntl.kyutech.ac.jp 123 Artif Life Robotics (2013) 18:241–247 DOI 10.1007/s10015-013-0124-y