**Development of a Vectored Water-Jet-Based Spherical Underwater Vehicle**

Shuxiang Guo and Xichuan Lin *Kagawa University Japan*

## **1. Introduction**

The applications of underwater vehicles have shown a dramatic increase in recent years, such as, mines clearing operation, feature tracking, cable or pipeline tracking and deep ocean exploration. According to different applications, the mechanical and electrical configuration and shape of an underwater vehicle are different. For instance, manipulators are necessary when doing mines clearing operation or some other tasks which need to deal with environment. If an underwater vehicle is used for underwater environment detection or observation, it is better to make this vehicle smaller and flexible in motion that it can go to smaller space easily. If the vehicle needs high speed moving in the water then a streamline body is required.

Different structures with different size of underwater vehicles are developed. Most of these underwater vehicles are torpedo-like with streamline bodies, like (Sangekar et al., 2009). And there are some small size AUVs like (Allen et al., 2002) and (Madhan et al., 2006). And also there are some other AUVs adopt different body shape, such as (Antonelli & Chiaverini, 2002). Meanwhile, the propulsion system is one of the critical facts for the performance of underwater vehicles, because it is the basis of control layers of the whole system. Propulsion devices have variable forms, for instance, paddle wheel, poles, magneto hydrodynamic drive, sails and oars.

Paddle wheel thrusters are the most common and traditional propulsion methods for underwater vehicles. Usually, there are at least two thrusters installed on one underwater vehicle, one for horizontal motion and the other for vertical motion. The disadvantages of paddle wheel thrusters are obvious, for example, it is easy to disturb the water around the underwater vehicles. Meanwhile, the more the paddle wheel thrusters are used, the weight, noise and energy consumption increases.

The steering strategies of traditional underwater vehicles are changing the angular of rudders or using differential propulsive forces of two or more than two thrusters. Of course, there are vectored propellers being used on underwater vehicles. Reference (Cavallo et al., 2004) and (Le Page & Holappa, 2002a) present underwater vehicles with vectored thrusters. Reference (Duchemin et al., 2007) proposes multi-channel hall-effect thrusters which involves vector propel and vector composition. Reference (Le Page & Holappa, 2002b) proposes an autonomous underwater vehicle equipped with a vectored thruster. At the same time, the design of vectoring thrusters used on aircrafts is also an example of vectored propulsion system (Kowal, 2002), (Beal, 2004) and (Lazic & Ristanovic, 2007).

(a) Top View (b) Front View

Development of a Vectored Water-Jet-Based Spherical Underwater Vehicle 5

(c) Side View (d) Computer Rendering

(a) Design (b) Prototype

(a) Design (b) Prototype

Fig.4 is the structure of one single water-jet propeller. It is composed of one water-jet thruster and two servo motors (above and side). The water-jet thruster is sealed inside a plastic box for waterproof. And we use waterproof glue on servo motors for waterproof. The thruster can be

Fig. 1. Mechanical System Schematics of the Spherical Underwater Vehicle

Fig. 2. Spherical Hull

Fig. 3. Design of Waterproof Box

**2.1.3 Mechanism of the water-jet propulsion system**

The purpose of this research is to develop such a kind of underwater vehicle which can adjust its attitude freely by changing the direction of propulsive forces. Meanwhile, we would like to make the vehicle flexible when moving in the water. Inspired by jet aircraft, we adopt vectored water-jet propellers as the propulsion system. According to the design purpose, a symmetrical structure would be better for our underwater vehicle (Guo et al., 2009).

This spherical underwater vehicle has many implementation fields. Because of its flexibility, our vehicle can be used for underwater creatures observation. For example, we can install underwater cameras on the vehicle. It can track and take photos of fishes. Another example is that, due to its small size, we can use it to detect the inside situation of underwater oil pipes.

### **2. Mechanical and electrical design**

#### **2.1 Mechanical system design**

Before the practical manufacture, we try to give a conceptual design of the whole structure for this spherical underwater vehicle. At this stage, we need to consider about the dimension, weight distribution, material, components installation, and so on. And we also need to consider about the configuration of the propulsion system, for example, how many water-jet propellers should we use for the purpose of optimizing power consumption without decreasing propulsion ability. Therefore, by all of that mentioned above, we give the conceptual designed structure of our spherical underwater vehicle as shown in Fig.1.

It adopts a spherical shape, all the components are installed inside the body. Its radius is 20*cm* which is smaller than that in (Antonelli et al., 2002). Its overall weight is about 6.5*kg*. Its working depth is designed to 0 10*m*, with a max speed of about 1.5*m*/*s*.

Inside the vehicle, there will be three water-jet propellers used as propulsion system, which is enough for surge, yaw and heave. One waterproof box is used for all the electronic components such as sensors, batteries and the control boards. And all of these are mounted on a triangle support which is fixed on the spherical hull. The whole structure is symmetrical in z-axis. Therefore, it can rotate along z-axis, and by doing this, the vehicle can change its orientation easily.

#### **2.1.1 The spherical hull**

As shown in Fig.2, the spherical hull of this underwater vehicle is made of acrylic which is light and easy to be cut. It is about 3*mm* thick and the diameter is 40*cm*. Actually, we can see that this spherical hull is composed of two transparent hemisphere shells. There are three holes which can provide enough space for water-jet propellers to rotate for different motions. We will discuss the details about the principles of the water-jet propulsion system in the next section.

#### **2.1.2 The waterproof box**

Waterproof is essential for underwater vehicles. Fig.3 shows the design of the waterproof box. The whole size of this box is about 22*cm*(hight) × 14*cm*(inner diameter). An O-ring is used for seal, which has the ability to provide waterproof in our case. Inside the waterproof box, there will be two control boards, one or two lithium batteries, depending on tasks. Meanwhile, at the top part inside the box, there will be an digital rate gyro sensor for orientation feedback. The body of waterproof box is also transparent, therefore, we can easily observe the inside working status .

Fig. 1. Mechanical System Schematics of the Spherical Underwater Vehicle

(c) Side View (d) Computer Rendering

(a) Design (b) Prototype

2 Will-be-set-by-IN-TECH

The purpose of this research is to develop such a kind of underwater vehicle which can adjust its attitude freely by changing the direction of propulsive forces. Meanwhile, we would like to make the vehicle flexible when moving in the water. Inspired by jet aircraft, we adopt vectored water-jet propellers as the propulsion system. According to the design purpose, a

This spherical underwater vehicle has many implementation fields. Because of its flexibility, our vehicle can be used for underwater creatures observation. For example, we can install underwater cameras on the vehicle. It can track and take photos of fishes. Another example is that, due to its small size, we can use it to detect the inside situation of underwater oil pipes.

Before the practical manufacture, we try to give a conceptual design of the whole structure for this spherical underwater vehicle. At this stage, we need to consider about the dimension, weight distribution, material, components installation, and so on. And we also need to consider about the configuration of the propulsion system, for example, how many water-jet propellers should we use for the purpose of optimizing power consumption without decreasing propulsion ability. Therefore, by all of that mentioned above, we give the

It adopts a spherical shape, all the components are installed inside the body. Its radius is 20*cm* which is smaller than that in (Antonelli et al., 2002). Its overall weight is about 6.5*kg*. Its

Inside the vehicle, there will be three water-jet propellers used as propulsion system, which is enough for surge, yaw and heave. One waterproof box is used for all the electronic components such as sensors, batteries and the control boards. And all of these are mounted on a triangle support which is fixed on the spherical hull. The whole structure is symmetrical in z-axis. Therefore, it can rotate along z-axis, and by doing this, the vehicle can change its

As shown in Fig.2, the spherical hull of this underwater vehicle is made of acrylic which is light and easy to be cut. It is about 3*mm* thick and the diameter is 40*cm*. Actually, we can see that this spherical hull is composed of two transparent hemisphere shells. There are three holes which can provide enough space for water-jet propellers to rotate for different motions. We will discuss the details about the principles of the water-jet propulsion system in the next

Waterproof is essential for underwater vehicles. Fig.3 shows the design of the waterproof box. The whole size of this box is about 22*cm*(hight) × 14*cm*(inner diameter). An O-ring is used for seal, which has the ability to provide waterproof in our case. Inside the waterproof box, there will be two control boards, one or two lithium batteries, depending on tasks. Meanwhile, at the top part inside the box, there will be an digital rate gyro sensor for orientation feedback. The body of waterproof box is also transparent, therefore, we can easily observe the inside

conceptual designed structure of our spherical underwater vehicle as shown in Fig.1.

working depth is designed to 0 10*m*, with a max speed of about 1.5*m*/*s*.

symmetrical structure would be better for our underwater vehicle (Guo et al., 2009).

**2. Mechanical and electrical design**

**2.1 Mechanical system design**

orientation easily.

section.

**2.1.1 The spherical hull**

**2.1.2 The waterproof box**

working status .

(a) Design (b) Prototype

Fig. 3. Design of Waterproof Box
