PDR AUV-NIOT

8/2/2019 PDR AUV-NIOT

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TORTUGAREGISTRATION ID SAV1100020

PRELIMINARY DESIGN REPORT OF TORTUGA (AUV)

GUIDE

Prof. U S RAMESH

[email protected]

Team

1.Dasari Pavan Srikar2.Roy Thomas

3.S Vijay Narayanan

4.Sujyot S Gaonkar

5.Mukesh K


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Concept:

The mechanical model is designed to be hydro dynamically stable. The vehicle features a seamless,

smooth contoured ellipsoidal body. The shape of the vehicle has been decided after calculations, keeping

various hydrodynamic parameters in mind to improve the overall performance of the robot. The

mechanical body is designed to be propelled by 4 thrusters and has net positive buoyancy. The

fabrication material is chosen to be acrylic sheets because it is light and strong while being easily

workable. The compressive strength of the material allows a working depth of approximately 25meters for

the design thickness of 6mm throughout.

The models hull is of made by joining two circular shells which is built around a unique propulsion

system comprised of four reversible, propeller based thrusters. Three of these are mounted around the

perimeter of a circular chassis (centre supporting frame), each facing 120 degrees apart from the other

two. By firing these thrusters at the correct ratio, it can move in any direction. The fourth thruster ismounted vertically at the middle of the vehicle to control the vertical motion.

The power of the system is provided by two lithium polymer batteries of 14.8 volts and 8000mAh.

Movement and direction control is done by the onboard microcontroller and the image processing

is also done by using mini pc running with LINUX. Sensors include pressure sensor, velocity sensor,

temperature sensor, internal measurement unit and echo sounders. An underwater camera meant for

underwater photography and hull leak monitor (meant for hull breaches) are also to be equipped with the

AUV.

The device uses WIFI for the communication with the dock after it surfaces.

A generic double pole single throw switch is mounted on the vehicle which is fully submersible in water

and placed outside the main body of the hull. The switch is used to activate and deactivate the power

circuitry of the vehicle.

The thrusters can be utilized to control three degrees of freedom, i.e.

(i) Translation along x-axis

(ii) Translation along z-axis

(iii) Rotation about z-axis

The other three degrees of freedom (roll, pitch, sway) are stabilized without any external thrust

application, by virtue of the mechanical design. The profile of the vehicle makes it easily

maneuverable. The vehicle is even capable of rotating about central axis of the body.


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Cad model:

Literature review:

The AUV is slender which enables it to maneuver easily and possess good directional stability.

The equipments are arranged in such a way that the center of gravity is below the centre of buoyancy to

maintain the stability. The 3 thrusters are strategically placed at 120 degrees maintaining stability as well

as propelling the AUV efficiently. The concept is based on positive buoyancy which enables the AUV to

pop out of the water in case of thruster failure, thereby eliminating the need for a emergency retrieval

system. The total displacement of the AUV is less compared to other models which reduce the powerrequirements for propulsion and vertical movement thereby enabling the AUV to move at high velocities

than contemporary AUVs.


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Design methodology:

It is a highly symmetrical design about all the three axes x, y, and z. For instance, to ensure symmetry the

horizontal motors are positioned with equal angles between them, which make their resultant centre to be

at the midpoint of the body. The vertical motor is placed at the mid of the body itself. This design thus

makes stability and modeling less problematic. The symmetry also consequently aligns centre of drag

with centre of thrust.

The design makes use of four thrusters. One horizontal, two vertical and one for turning the vessel. The

vertical thruster account for the vertical motion of the vessel (i.e. heave control in both downward and

upward directions).The vertical thruster is placed at the middle of the body. The two horizontal thrusters

are present at 120 degrees apart on the circumference they account for the surge control in both forward

and backward directions. One thruster is proved 120 degrees to both horizontal thrusters which is used

for turning. Thus the design has 4 DOF that can be easily controlled that is, surge and heave as well aspitch and yaw.

The electrical systems design of the vessel serves the purposes of motion control, sonar and vision

processing, measuring vehicles depth, its attitude, surge velocity, pressure, detecting hull breaches and

supply efficient power for ample testing periods.

Mechanical Design:

Hull:

The hull consists of two shells resembling circular halves joined together. They are made up of acrylic

polymer of 6mm thick. The central disk (chassis) within the acrylic shells provides a stable platform to

mount the many components of the AUV. Ultra High Molecular Weight (UHMW) plastic is chosen due to it

neutral buoyancy and it can retain its shape under high pressure.


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MODEL IN CATIAWaterproofing of the hull:

The hull is sealed and a special clamping system is used for waterproof it. It provides the compressive

force to compress and hold the two halves of the hull together. The clamps are easy to handle and are

used for opening and closing of the hull.

Thrusters:

Four thrusters are used to maneuver the vehicle. Two thrusters facilitate the horizontal motion (surge),

while one facilitate the vertical motion (heave) and the remaining one for the rotation motion along z-axis

(yaw). The placement of the thrusters is such that it aligns with the centre

of drag and the required thrust is produced.


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Underwater Connectors and cables :

The peripherals include professionally built underwater circular connectors conforming to IP68 rating,

provided by Samtec. The connectors and cables provide effective leak proof electrical connections from

systems outside to the main circuitry present inside the hull and are easy to install and dismantle.

Weight buoyancy relationship:

The main concept is that the body is to maintain minimum buoyancy and weight difference.

The body is maintained in positive buoyancy so that the addition buoyancy force is provided by the

thruster at the centre of the vessel.

Weight=Buoyancy + Thrust.

Buoyancy = density * g * v.

Where g is acceleration due to gravity and v is the volume.

Mass volume relationship:

The main concept of the vessel is that it should be maintained in positive buoyant condition.

This means that the total weight should be greater than buoyancy force.


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Mass of the system expected:

Components Weights in kg.

Hull 0.940 kg

Thrusters 3.6kg

Chassis 1.1 kg

Electronic equipment 1 kg

Batteries 1.4 kg

Total 8.04 kg

Buoyancy of the system expected:

Components Buoyancy kg

Hull 7.07 kg

Thrusters .8 kg

Chassis 1.1kg

Total 8.87

Weight =8.04 kg.

Buoyancy = 8.87 kg.

Additional buoyancy = 0.77 kg

With a thruster of 5 kg thrust the AUV can be pulled down at a rate of 3.75m/sec2.

MOTION CONTROL:

ADAM 4024 & ADAM 4520 are connected to the thrusters as the thruster control boards.

PRESSURE SENSOR:

An analog pressure sensor from Honeywell has been used to gauge the pressure and hence, the depth of

the AUV below the water surface.


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INERTIAL MEASUREMENT UNIT:

We are using MTi 28A manufactured by XSens. The MTi is a miniature, gyro enhanced attitude and

heading reference system. It provides us with calibrated 3D linear acceleration, rate of turn, orientation

data as well as earth magnetic field data.

CAMERA:

Two Logitech USB HD webcams are used for image processing. One points straight ahead, another

points straight down.

IMAGE PROCESSING:

Two webcams are used to capture images. They are processed by the on-board single board computer.

COMMUNICATION SYSTEM:

Communication between docking station and AUV is achieved by using WLAN when it is above watersurface. Once submerged, the link can be set up through acoustic underwater communication link.

MARKER DROPPER:

A pull type 30V pulse solenoid is used to accomplish this task. The solenoid is housed in a waterproof

chamber with two aluminium end caps. Two stainless steel balls are housed in the bottom end cap, with

the magnetic shaft of the solenoid holding the balls in place. When the solenoid is activated, the shaft

retracts, breaking the magnetic bond that holds the balls in the end cap. The balls fall from the end cap

and travel downwards to the targets.

Methodology of operation:

Once the vessel is launched, the vertical thruster take control of yaw, heave and the horizontal ones start

controlling the roll and surge(as such the vessel has 4 DOF).The different sensors sense information like

pressure, velocity, temperature, orientation and the eye bot processes those information. Eye bot also

controls the speed and direction of motors. The underwater camera captures images and mini PC

processes the captured images. Communication between docking station and AUV (immediately after

launch) is set up via WLAN, once submerged can be done through standard acoustic underwater

communication link.


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(AUV System Objectives)

(3-D Views)

PDR AUV-NIOT

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