project specification

SURIII

A propulsion system for the third-generation Spherical Underwater Robot (SURIII) designed and analyzed to verify its increased stability compared to the second-generation Spherical Underwater Robot (SURII) Te inspiration for the design of the SUR propulsion system comes from the propulsive mechanism of a jellyfish which are the most energy efficient underwater swimmers. Jellyfish, through the alternate contraction and relaxation of their bodies, produce a jet of water whose propulsive force propels them through the water. The design of the SURIII, as described subsequently, is aimed at mimicking the efficient motion of the jellyfish and attaining symmetry, stability and performance.

Specifications

Diameter48 cm
Propulsionulti-vectored water-jet thrusters
6 DOF
Weight6.3 - 6.9 kg
SensorGyroscope

Overview

Te inspiration for the design of the SUR propulsion system comes from the propulsive mechanism of a jellyfish which are the most energy efficient underwater swimmers. Jellyfish, through the alternate contraction and relaxation of their bodies, produce a jet of water whose propulsive force propels them through the water. The design of the SURIII, as described subsequently, is aimed at mimicking the efficient motion of the jellyfish and attaining symmetry, stability and performance.

The system is symmetric on the X axis but also on the Y axis, which increases the flexibility of its movement and reduces the space constraints of servomotors and vectored water-jet thrusters. 

Mechanical design

The system has a ring like structure which can provide support for four thrusters. The maximum distance between the two opposite thrusters is 48 cm, the inside diameter of the annular support is 19 cm and its thickness is 0.5 cm. The structure is fixed to the robot with by jackscrews. 

The basic movements of the robot include three motions: up, down and forward motion. 

Each set of vectored water-jet thrusters is made of four parts, which includes a water-jet thruster, a waterproof box for protecting DC motor, two servo motors and a support for them. The propulsive force of the system comes from vectored water-jet thrusters and the orientation of propulsive force can be controlled by the rotation angle of two servo motors. Two servo motors are rotated in two planes which are vertically intersecting, so they provide two rotational DoFs for the thruster. 

Structure Design

All control circuits are assembled in the waterproof bin. Four screws are used to hold up the waterproof bin in the hull. The spherical hull, has four symmetrical openings to accomodate the four vectored water-jet thrusters. The the hull can block the external damage to protect the internal structure, and the spherical hull can realize a zero turning radius smoothly.

Motions of SURIII

The degrees of freedom (DoF) for the robot include surge, sway, heave, roll, pitch and yaw. There are four water-jet thrusters in the robot and the inclined angle between two thrusters is 90 degrees, so it can be switched between the surge and sway directly by changing the working thrusters. Three DoFs which are surge, heave and yaw will be researched as the main target. In surge motion, three thrusters can work simultaneously to achieve a high-speed mode and the remaining thruster can be used to brake or veer. Two opposite thrusters work together to achieve a low-speed mode, the other two thrusters can be used to brake and veer. In yaw motion, a gyroscope will be leveraged to measure the rotation angle. If all thrusters work at the same time, the robot can be realized a high-speed rotating mode.

References

Describes the mechanical design and analysis, the propulsion system, structure design, and hydrodynamic analysis. Goes into the Computational Fluid Dynamics simulation, and the experiments and results.

Shuoxin Gu and Shuxiang Guo. 2017

Describes the hardware of the electrical system of the spherical underwater robot. The software design includes software structure and communication law are introduced in detail. Experiments are carried out and the conclusion and future work are listed.

Chunfeng Yue, Shuxiang Guo, Maoxun Li, et al. 2013 (Paywall)

Provides background for the research and escribes the second‐generation Spherical Underwater Robot (SUR‐II), which has an improved water‐jet propulsion system. Provides the motion states of the robot to each degree of freedom. Presents the main hydrodynamic parameters of the SUR‐II and analyses it.

Chunfeng Yue, Shuxiang Guo, Maoxun Li, et al. 2013

Wevolver 2022