UAV report vFINAL

2014-2015
Cardiff University
School of Engineering
Autonomous ROV
EN4105 UAV Project
Chris Corkill, Chris Powell, David Iddles, Faizan Masood, Ismail Al-Jeffery, Marcus Yap,
Peter Jackson & Stuart Sheath
SUPERVISORS:
Steve Watts (WattsS@cf.ac.uk)
Alastair Clarke (ClarkeA7@cf.ac.uk)
Carlton Byrne (Byrne@cf.ac.uk)

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Acknowledgements
We would like to thank Steve Watts, Alastair Clarke and Carlton Byrne for their support, guidance
and invaluable feedback throughout the course of the project. Furthermore, technical support from
David Billings, Andrew Rankmore, Richard Rogers and Steve Mead has been very beneficial during
this project. Our appreciation towards these three for taking time away from their responsibilities
to assist us.

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Abstract
The aim of the project was to develop an existing submersible Remotely Operated Vehicle (ROV)
for deployment within Cardiff Bay. During deployment, the ROV was required to collect soil
samples from the sea floor and deploy microsensors to measure oxygen concentration and pH
levels. The final design consists of a 3-legged, submersible ROV, equipped with one sediment
sampling mechanism and one microsensor deployment mechanism. A floating buoy facilitates
wireless communication between the ROV and its operator. Control signals are sent from the
operator to the buoy via a Wi-Fi connection then passed to the ROV’s controller via an Ethernet
cable. The same channel is used to send sensor data from the ROV to the operator. The buoy also
supplies power to the ROV’s thrusters via a power cable. The entire system has been found to
operate correctly when tested in a 3.8 m depth, indoor diving pool.

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Table of Contents
1. INTRODUCTION...........................................................................................................1
2. 2013/14 UNRESOLVED ROV ISSUES..............................................................................7
3. FULL SYSTEM TEST OF 2013/14 ROV DESIGN..............................................................11
4. 2014/15 CHASSIS MODIFICATIONS ............................................................................12
5. SENSOR DEPLOYMENT SYSTEM .................................................................................17
6. SEDIMENT SAMPLING MECHANISM...........................................................................21
7. DEVELOPMENT OF THE ROV’S CONTROL SYSTEM.......................................................27
8. BUOY ........................................................................................................................38
9. FULL SYSTEM VALIDATION.........................................................................................46
10. FUTURE RECOMMENDATIONS...................................................................................51
11. FINAL SUMMARY ......................................................................................................52
12. REFERENCES..............................................................................................................53
APPENDIX A: BILL OF MATERIALS.....................................................................................55
APPENDIX B: ROV CHASSIS ..............................................................................................56
APPENDIX C: ROV HULLS..................................................................................................58
APPENDIX D: ROV BUOYANCY CALCULATIONS.................................................................60
APPENDIX E: ENLARGED HULL DESIGN .............................................................................61
APPENDIX F: MICROSENSOR DEPLOYMENT MECHANISM DESIGN ....................................63
APPENDIX G: SEDIMENT SAMPLING MECHANISM DESIGN ...............................................82
APPENDIX H: BUOY DESIGN.............................................................................................89
APPENDIX I: TETHER MANAGEMENT SYSTEM DESIGN......................................................93
APPENDIX J ELECTRICAL SCHEMATICS..............................................................................97
APPENDIX K: DETAILED SOFTWARE INFORMATION........................................................ 100
APPENDIX L: THRUSTER BATTERY SPECIFICATION .......................................................... 121
APPENDIX M: LIST OF USER COMMANDS....................................................................... 124

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1. Introduction
1.1. Project Brief
The ROV is to be used by Cardiff University’s Earth and Ocean Sciences Department (EOSD) for
exploration and data collection in Cardiff Bay. After discussions with the EOSD at the beginning of
the 2014/15 academic year, the following ROV specifications were agreed upon:
 A manageable size and weight for the ROV
 A mission duration of 15-45 minutes
 A mission radius of 50-200 metres
 An operating depth of up to 20 metres and temperature 4-25 degrees Celsius
 Ability to acquire a sediment sample from the seabed.
 Ability to deploy a Unisense Microsensor (Unisense, 2015) into the seabed.
1.2. Budget
A budget of £2000 was provided for further development and completion of the existing design.
Of this amount, £1793.72 was spent. The full bill of materials for the ROV, including each
component referenced within this report, can be found in Appendix A: Bill of Materials.
1.3. Previously Completed Work and its Limitations
The UAV ROV project was started in the 2013/14 academic year and is now in its second year of
development. As such, a ROV had already been designed and constructed prior to the beginning
of the 2014/15 academic year, details of which are provided by Bentley et al (2014). It was decided
to further develop this existing ROV to achieve the aforementioned specification.
Because of time restrictions encountered in the previous academic year a number of issues
associated with the ROV had remained unresolved. The most critical of these issues was the

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waterproofness of the hulls that housed the electronic components. It had been discovered that
the cable glands originally installed did not prevent water from entering the hulls. Additional
inspections performed at the beginning of this academic year highlighted the poor condition of
the O-rings used to create a seal between the hull body and its end-caps. It was found that pinching
of the O-rings would occur when inserting the end-caps. This was due to over-sized O-rings being
used as well as incorrect dimensions of the glands they sat in.
Another outstanding issue was the state of the ROV’s control system. Because of the leaking cable
glands, the control system designed during the previous year had not been validated.
Furthermore, the main hardware components had been disconnected and there was no
information available to indicate how they were wired originally. It was also discovered that three
thruster controllers and the batteries used as the main power supply had been broken, and as
such were no longer usable. In addition, the battery used to power the National Instruments
myRIO was missing.
Finally, the LabVIEW program written to accompany the hardware was undocumented and had
vital sections of code missing. Without this code or the documentation necessary to replicate it,
controlling the ROV as it was originally intended was not possible.
All of these issues needed to be resolved before development of the ROV could commence.
1.4. Group Management
Eight individuals were involved in the project. Because of the need to resolve the outstanding
issues outlined in Section 1.3, this group was initially divided into two smaller groups of four. The

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first group focused on resolving the outstanding issues whilst the second group investigated ways
in which the ROV could be modified to achieve the specification.
Table 1 summarises the actions completed by the first group to resolve the outstanding issues. In
depth detail of each action can be found in the report section indicated.
Table 1: Actions taken to resolve the outstanding issues outlined in Section 1.3.
Action
Report
Section
Replacement cable glands ordered and fitted. 2.1
Inside edges of both hulls chamfered. 2.1
114 mm ID O-rings ordered and fitted to end-caps to replace the original 118 mm ID
O-rings.
2.1
Silicon grease ordered and applied liberally to both end-cap and cable gland seals. 2.1
Control system hardware understood and rewired. 2.2
Broken thruster controllers replaced with new controllers. 2.3
New myRIO battery purchased. 2.4
New control program written using LabVIEW allowing the ROV’s motion to be
controlled in the horizontal plane.
2.5
Test performed in Maindy swimming pool to validate ROV waterproofness and
control system.
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The outcome of the second group’s investigation was the identification of a number of necessary
ROV modifications. These are listed in Table 2.

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Table 2: Modifications performed on the ROV during the 2014/15 academic year.
Category Modification
Report
Section
ROV Hardware
& Chassis
Revalidation of hulls to account for increased operating
depth.
4.2
Modification of end-caps to enable the addition of a larger
number of cable glands as well as an easily accessible battery
charging point.
4.3
Re-design and manufacture of hardware fastenings within
each hull.
4.4
Distribution of additional weight to prevent unwanted pitch
or roll.
4.4
Addition of legs and feet to chassis. 4.5
Sensor &
Sampling
System
Hardware
Design and construction of a micro-sensor deployment
mechanism.
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Design and construction of a sediment sampling mechanism. 6
Control Systems
&
Communication
Expansion of the control system to incorporate the electrical
hardware associated with the microsensor deployment
mechanism.
7.2.1
Expansion of the control system to incorporate the electrical
hardware associated with the sediment sampling mechanism.
7.2.2
Implementation of wireless communication between the user
PC and ROV.
7.2.3
Expansion of the control system to incorporate a spot light to
increase camera visibility.
7.2.6
Further expansion of the control program to facilitate the
deployment of micro-sensors and sediment sampler.
7.5.1
Rewrite of the control program to allow all ROV actions to be
easily controlled from a remote PC, as well as to acquire data
from the ROV’s sensors.
7.5.1
Design and implementation of an intuitive user interface. 7.5.2
Buoy Hardware
& Chassis
Design and construction of a waterproof compartment. 8.1
Design and construction of a buoy chassis. 8.1
Design and implementation of a tether management system. 8.4

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It can be seen how these modifications were split into four categories. Once the actions listed in
Table 2 had been completed four new groups were formed. Each group was then tasked with
implementing all the modifications in one of the four categories. Figure 1 shows how tasks were
divided within the group.
Figure 1: Division of work within the group.
It must be noted that each group did not operate independently as the decisions of one would
almost certainly affect the decisions of the other three. As such, continuous collaboration between
each group was key to the project’s success. Weekly meetings were held to discuss direction and
progress, with targets set to manage time and effort. Meeting minutes were recorded regularly
which served as written record and were archived for reference.
1.5. System Overview
The entire system design, illustrated by Figure 2 and Figure 3, consists of a submersible ROV with
one sediment sampling mechanism and one microsensor deployment mechanism. A buoy is used
to facilitate wireless communication between the operator and the ROV, as well as to provide
power to the ROV’s thrusters.
UAV ROV
Control Systems &
Communication
Buoy Hardware
& Chassis
Sensors & Sampling
System Hardware
ROV Hardware &
Chassis

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Figure 2: System overview.
Figure 3: Models of the sediment sampling mechanism (1), microsensor deployment mechanism (2) and buoy (3).

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2. 2013/14 Unresolved ROV Issues
There were a number of issues with the existing ROV design, identified during the 2013/14
academic year, which had prevented a full system test of the ROV. Further issues were also
discovered when an inspection of the ROV was performed at the beginning of this academic year.
It was decided that performing a full system test would be the first objective of this academic year,
hence it was necessary to resolve all of these issues, summarised in Table 3.
Table 3: Summary of all the issues that required resolution.
Issue No. Description
1 Water ingress into hulls used to house electronic components.
2 All electronic hardware disconnected.
3
Batteries used to power thrusters damaged.
Three of five thruster controllers damaged.
4 Battery used to power myRIO missing.
5 Existing control program incomplete.
2.1. Water Ingress into Hulls
It had been shown that the cable glands fitted to each end cap did not prevent water ingress into
the hull. Alternative cable gland options were therefore researched. Legrand Cable Glands (PG9,
4-8mm), were found to be the most suitable replacement.

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It was also noticed that the O-rings used to create a
seal between the end-cap and the main body of the
hull had been damaged. It was concluded that the
inner diameter of the O-rings was too large which
regularly caused the O-rings to be pinched between
the end-cap and hull body when inserting the end-cap,
as shown in Figure 4.
It was also found that the glands in which each O-ring
sat were not wide enough to allow for compression of
the O-rings. This further increased the occurrence of pinching. It was necessary to prevent this
pinching as continued damage to the O-rings would result in their eventual failure.
Replacement O-rings were sourced with a smaller inner diameter of 114 mm. These smaller O-
rings effectively eliminated the occurrence of pinching. As an extra precaution, the inner edges of
the hull bodies were chamfered to limit any damaged caused if pinching were to occur. The O-ring
glands were also redesigned in accordance with BS ISO 3601-2:2008 (2008), however it was
advised that the modifications would be difficult to implement. Since the pinching problem had
been effectively resolved with the smaller O-rings it was decided not to implement the gland
changes. As a reference for any future end-cap design, drawings of the planned O-ring gland
modifications can be found on the accompanying CD.
Silicon grease was also applied liberally to all sealing surfaces to further increase the
waterproofness of the hulls.
Figure 4: Example of pinching that occurred as a
result of oversized O-rings.

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2.2. Disconnected Electronic Hardware
All electrical connections between the main components of the control system had been removed
prior to the beginning of this academic year. Reconnection was clearly necessary if the ROV’s
control system was to be tested. Whilst the task of reconnecting the hardware was not a complex
task, the lack of informative documentation resulted in a large amount of time being spent
ensuring each connection was correct. Further time and budget was spent sourcing the wiring and
fastenings required to implement the connections.
2.3. Damaged Thruster Batteries and Controllers
All four batteries used to power the ROV’s thrusters had been damaged at the end of the 2013/14
academic year and were no longer usable. A replacement power supply was therefore required to
perform the test. Because of the planned ROV developments it was not yet known whether the
original battery capacity would need to be increased. As such, it was decided not to order
replacement batteries at this stage in case these also needed replacing further into the project.
A desktop power supply was sourced from the electrical technicians’ workshop at the University.
This was able to produce the required voltage of 22.2 V with a maximum current of 10 A. The
power supply would be remote from the ROV, with a length of cable transferring power between
the two. Because each thruster was expected to draw about 4 A continually at maximum power,
it was only possible to have two thrusters active at any one time. Since the ROV design required
two thrusters to be active when moving horizontally, the first full system test in Maindy pool did
not include the fifth vertical thruster.

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Three of the five thruster controllers had also been damaged and were no longer responding to
commands. Spare components from the previous academic year included one controller,
therefore two more controllers were purchased.
2.4. Missing myRIO Battery
The whereabouts of the battery used to power the myRIO was unknown at the beginning of this
academic year. A replacement Turnigy, 11.1 V, 2200 mAh, LiPo battery was therefore purchased.
The specification of the battery was based upon the calculations shown in Appendix L.
2.5. Incomplete Control Program
Files containing the control program written in the 2013/14 academic year were provided,
however a number of critical files were incomplete or missing. It was decided that completely
rewriting the program for the test was the best course of action for two reasons. Firstly, it was
agreed that the method the original program used to control the ROV’s motion could be improved
upon. Secondly, it was anticipated that the majority of the program would need to be rewritten at
some point in order to meet this year’s specification.
Once rewritten, the program used for the test enabled the user to move the ROV in the horizontal
plane, either forwards, backwards, sideways, clockwise or anticlockwise, using the PC keyboard.
The program also displayed the ROV’s bearing and streamed real-time video images to the user
PC. These images could then be saved as video files or photos on the PC's hard drive.

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3. Full System Test of 2013/14 ROV Design
Because of the issues described in Section 2, a full system test of the ROV’s systems was not
performed in the 2013/14 academic year. A full system test was therefore the first objective of
this academic year.
3.1. Objectives of Test
The objectives of the test were as follows:
 Correction of any observed roll or pitch imbalances.
 Assessment of the ROV’s manoeuvrability.
 Comparison of the ROV’s horizontal and rotational velocities with the velocities predicted
by the CFD analysis performed in the 2013/14 academic year.
 Assessment of the camera’s visibility under water.
 Identification of any other unforeseen problems in a practical setting.
3.2. Test Results
With an equal mass in each hull the ROV sat level in the water without any significant pitch or roll.
The same was also true when the ROV was in motion.
When moving in a straight line the ROV had a tendency to drift left or right. This appeared to be
caused by a drag force from the power and Ethernet cable.
The ROV had an average maximum velocity of approximately 0.45 m/s when moving either
forwards, backwards or sideways. This was just over half of the 0.8 m/s predicted by the CFD
analysis. It had a maximum angular velocity of approximately 1.6 rad/s when rotating clockwise or
anti-clockwise but predictions for this had not been provided by CFD analysis.

12
In clean pool water the camera had a range of visibility of approximately 15 m.
A significant delay was observed between the motion commands input at the PC and the
subsequent activation of the ROV’s thrusters. This also meant that the two thrusters in operation
did not activate at the same time, causing the ROV to rotate about its vertical axis. It was suggested
that this was due to the large amounts of data being transferred between the ROV and the PC, a
result of the high resolution and frame-rate image stream. It was decided to reduce this delay in
future tests by reducing the image quality as well as utilising more efficient data transfer protocols.
4. Chassis Developments
4.1. Shape of ROV
The existing ROV design did not leave much room for the addition of any sampling equipment. The
sensors being used could only be deployed vertically which was extremely difficult with the current
design. These specific requirements meant that the design needed to shift to a Benthic Lander
shape form for the ROV. Such a design has been displayed below in Figure 5, to give an idea of
how sensors are deployed vertically from a stable position.
1) Benthic Lander (Unisense 2015) 2) 2013/14 Design 3) 2014/15 Final design
Figure 5: ROV chassis modification based upon a Benthic Lander design.

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Legs were added to the ROV, in a tripod arrangement to maximise stability at the slight expense
of overall manoeuvrability. Polycarbonate feet were added to allow for a larger surface area over
which to spread the weight of the ROV, to avoid sinking into the soft mud found on the seabed of
Cardiff Bay. The feet were made of clear polycarbonate sheets because it was lightweight and in
line with the aesthetics of the overall design.
Sampling equipment was to be attached to each leg to allow vertical deployment as required.
Figure 5 shows how the chassis base was made wider, with the quarter round sections of the
chassis (red) being replaced by regular square sections (green) to facilitate the attachment of the
legs.
ROV buoyancy calculations are provided in Appendix D: ROV Buoyancy calculations.
4.2. Hull Pressure Rating
The specification for ROV working depth changed this year from 15 m to 20 m. Hand calculations
were performed to prove that current 3 mm hulls are capable of working up to a 20 m depth with
a safety factor of 2. It was assumed that the polycarbonate had a maximum yield stress of 10MPa,
as specified on the datasheet which can be found on the accompanying CD. FEA analysis was also
performed using Patran®. Detailed results of this analysis can be found in Appendix C: ROV Hulls.
4.3. End-Cap Modifications
The addition of the sediment sampling and micro-sensor deployment mechanisms to the ROV
required additional cable entry points into both hulls. It was also anticipated that future ROV
developments would require additional cable entry points. It was therefore decided to modify
each end-cap to accommodate as many entry points as possible. Figure 6 illustrates the end-cap

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labelling system. End-caps 2, 3 and 4 all had four existing entry points, hence it was not practical
to add any more. It was however possible to add four entry points to end-cap 1.
It was also necessary to attach a Bulgin
PXP7012/06S/ST connector to one end-cap in
order to enable easy access to the myRIO battery
as discussed in Section 7.2.5. End-cap 3 was
therefore modified to accommodate the Bulgin
connector.
Technical drawings detailing the end-cap
modifications are provided on the CD.
4.4. Hull Interior Modifications
Due to a large array of electronics being used within the ROV, an interior re-design was necessary
to ensure that space was being used effectively and that all the components were fixed securely;
especially, with the onset of further hardware this year.
The original location of all four thruster batteries, each weighing 0.57 kg, in one of the ROV’s
waterproof hulls placed a considerable constraint on their size, which in turn limited their total
capacity. 3D printed holders were designed to hold the batteries but weight distribution wasn’t
given much consideration. There was a significant weight difference between hulls, which caused
the ROV to tip drastically in the direction of the heavier hull.
Figure 6: End-cap labelling system.

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The location of all electronics within one hull
meant securing each component was difficult
due to limited space. Figure 7 shows this
haphazard arrangement and illustrates the risk
of damage to components that this poses.
In order to alleviate size constraints, as well as to create more space for additional hardware, the
thruster batteries were relocated to the buoy. This freed up one of the hulls and allowed
components to be distributed between the two hulls, correcting weight issues. Each component
was positioned such that each wired connection was as short as possible. 3D printed parts were
then designed to hold each component in its place securely. Table 4 below, highlights the final
position of each electronic component within the two hulls. The hulls were labelled A and B at this
point for clarity and will be referred to this way hereafter in the report. Hull A is the one which
situates the myRIO.
Table 4: Distribution of components between each hull.
Hull A Hull B
myRIO Thruster Motor Controllers
myRIO battery (11.1V) Depth Sensor
Camera and LED spotlight Battery for Servo (7.4V)
Stepper Motor Controller PCB B
Ethernet Adapter
USB Hub
PCB A
Figure 7: Exisitng hull shows haphazard arrangement

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4.5. ROV Legs and feet
The ROV legs shown to the top right in Figure 8 had to go
through a number of design iterations before settling into
their final design. Details for the design process have been
provided in Appendix B: ROV Chassis. The final design of
three vertical legs was determined by the choice of
mechanism employed for the sensors and sediment sampler.
Due to the method of attaching the legs to the chassis,
aluminium plate reinforcement was necessary to prevent
the legs from twisting out of place. The sensor assembly
(red) was quite straightforward with two brackets connecting the leg to the sensor assembly. The
sediment sampler assembly (green) employed a pair of servos that needed to be mounted to the
side of the leg. For this purpose, appropriate parts were used to provide the necessary attachment
to the leg. Holes were machined in the foot plate to allow the microsensor and sediment sampler
to penetrate the seabed.
Figure 8: Final leg assembly.

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5. Sensor Deployment System
The customer specification stated that they wished to investigate carbon flux in and out of the sea
bed by using Unisense microsensors to take oxygen and pH readings. The task was to design a
system to deploy these sensors and protect them during the mission.
Two types of microsensor needed to be deployed; an O2 MicroOptode and a pH microelectrode.
The MicroOptode uses glass fibres to measure oxygen concentrations. These would normally be
protected inside a steel needle. The sensor would be inserted into the sample and then the glass
fibres would be pushed out of the end by a button on top of the sensor. The sensor was designed
to be operated by hand. It was soon found that this would be difficult to achieve. It was agreed
with the customer that, as the amount of fibre protruding from the needle could be adjusted, the
fibre would be locked in place with the tip of the fibre just beyond the tip of the needle.
The pH microelectrode required a reference electrode to be deployed at the same time to take
readings. This meant that three sensors would be needed for two measurements. The sensors
were all approximately 170mm in length and had at least 60mm of cylindrical plastic casing at the
top meaning a single system could be designed to accommodate any of the sensors.
Photos of all the microsensors are provided in Appendix F: Microsensor Deployment Mechanism
Design.

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5.1. Final Design
A number of designs were considered for the deployment of the
microsensors. These have been explained in detail in Appendix F:
Microsensor Deployment Mechanism Design. In the end, it was
decided that stepper motors with leadscrews would be used for the
system as they are light, compact and produce linear motion directly.
The final design for the system, with 3D printed securing brackets, is
shown in Figure 9.
5.1.1. Stepper Motor and Controller
As stated above, a stepper motor was used for linear motion. It offers a precise positioning and
repeatability of movement, where all movement errors are non-cumulative between steps,
justifying its appointment due to the sensitive sensor equipment. The stepper motor will be
powered through the motor controller, of which is directly powered from the battery within one
of the hulls.
A Unipolar motor controller has been chosen for the movement of the stepper motor used for the
sensor deployment. The controller provides the ability to control of four separate stepper motors,
so includes the operation of the three Unisense sensors on board as well as the capability of a
fourth stepper motor for other future purposes.
The initial control program design controlled the stepper motors using the Phidget controller by
running a C++ library function through the myRIO. This was done through the myRIO by creating
a VI that calls a library with a “Call library function node” that will read and run a shared library
Figure 9: Final deployment
system design.

19
stored locally on the myRIO. The function runs a program in which moves each motor to the
sediment level for measurement, and will wait for user input before it will retract the sensors back
into the holding system. Appendix F: Microsensor Deployment Mechanism Design provides further
details.
5.1.2. Structure and Waterproofing
The casing for the system comprises of; 3 polycarbonate cylinders of varying diameters, two
polycarbonate end caps and a plunger. It was designed to be disassembled to access the sensor
and the motor. The stepper motor was secured to the top face of the lower end cap. A hull, tall
enough to accommodate the leadscrew, was made from a polycarbonate cylinder with two end
caps. O-rings were used to seal the end caps. The leadscrew went through the lower end cap and
attached to a 25mm diameter polycarbonate plunger which was encased in a 26mm diameter
polycarbonate tube. The plunger was machined to fit a pair
of O-rings which would seal the gap between the plunger
and the tube as shown in Figure 10. Further details including
calculations can be found in Appendix F: Microsensor
Deployment Mechanism Design. A 3D printed holder glued
to the plunger secured the microsensor. The last tube was
added as a protective cover for the sensor.
5.2. Unisense Data-Loggers
A miscommunication with the customer meant that it was initially decided to amplify the signal
from the sensors and store the data on the myRIO. It was eventually discovered that the data from
the sensors had to be sent straight to specific Unisense data-loggers otherwise it would be invalid
Figure 10: Plunger with O-rings.

20
to use in a scientific journal. The data-loggers both amplified and stored the data. This meant that
they had to be on board the ROV as the signal from the sensors was so weak, pico-Amps in the
case of the pH sensor, that it would not reach the surface through 20 metres of cable. The data-
loggers were extremely expensive so would not be available for this project. They were also quite
large compared to the other ROV components. It was therefore decided that the current hulls
would not be modified but new, larger hulls would be designed for future projects. Models and
drawings for the new hulls can be found in Appendix F: Microsensor Deployment Mechanism
Design.
5.3. System Limitations
Testing of the stepper motor showed that while it could easily move the plunger with one O-ring,
two O-rings provided too much friction and the motor was not powerful enough. Waterproof tests
showed that one O-ring around the plunger was sufficient but time limitations prevented
extensive underwater testing.
The O-rings used to seal the plunger were Nitrile O-rings and these were lubricated and given extra
sealant with silicon grease. However over time silicon grease becomes sticky and less effective. A
solution could be to use Viton O-rings. These are more expensive, however they slide much more
easily and do need lubricant such as silicon grease. This could make them a better option to seal
the plunger.
Issues were encountered when transferring the completed program to the myRIO and time
constraints prevented a full validation of the microsensor deployment system.

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6. Sediment Sampling Mechanism
In order to further analyse the results of the Unisense microsensors, the customer required a
system to store and collect a small amount of sediment for testing. Test samples are the easiest
and best way to conduct more detailed and sophisticated tests in the lab. The location of the
sample must be relative to the location of the microsensor deployment therefore the system had
to be assembled close to the microsensor assembly. The customer also specified the need to keep
the sample undisturbed and preferably with its layer intact. For this reason a bespoke soil sampling
system has been developed to meet the requirements of the customer. Due to the complexity of
the problem and the added burden of waterproofing the whole arrangement, the final solution
was reached after a rigorous iteration process. Details of the iteration process is provided in
Appendix G: Sediment Sampling Mechanism Design.
6.1. Chosen System
Deep-sea divers typically collect samples via a syringe capsule by hand. This method was
investigated to see if the syringe could operate remotely. Environmental Sampling Supply ©
produce a LOCK N’ LOAD syringe shown in Figure 11 (Environmental Sampling Supply, 2015) which
was deemed appropriate for the task.

22
Capsules are cheap and designed to collect
sediment, with a bevelled syringe to allow for
easy insertion and incorporated plunger that
creates a vacuum to hold sample inside the
syringe. It was decided that the syringe
method offered a simple, cheap and non-
intrusive solution; the next step moving
forward would be designing the actuation
system for the syringe.
6.2. Testing of Sampling Syringe
Before deciding on any actuation system, the method in which the ESS syringes are used needed
to be studied and tested. Since the syringes are typically meant to be used by hand, the first test
was to establish how effective they were when collecting the required type of sediment. Figure 11
shows the blueprints of the syringe provided by ESS, it can be seen that that within the syringe
body is a plunger that slides up when inserted whilst creating a vacuum. This is highly significant
as the syringe was most effective when it was sucking up i.e. when the plunger was fixed and the
body free to move linearly.
Figure 12 and Figure 13 illustrate the experimental setup that was utilised, the plunger was fixed
while the body was free to move into the mud sample, weights were added to approximate the
required force needed. From the test, it was established that the plunger needed to be fixed and
the force required to insert and withdraw the syringe body was calculated to be 20N-30N.
Figure 11: Blueprints of LOCK N’ LOAD Soil Sampling
Syringe

23
Figure 12 Experimental setup of force test
Figure 13: Syringe under 10N and 20N respectively

24
6.3. Final Design
After a rigorous iteration process a final design was reached using
dual servos as shown in Figure 14. Appendix G: Sediment
Sampling Mechanism Design discusses the preliminary designs
involved before deciding on this one. These include testing and
evaluating with the customer different design solutions in order
to come up with the most feasible, cost effective solution
possible, whilst being considerate to any physical impact it could
have on the design of the ROV.
The servo used is a high torque, Hitec HS7954SH-G2 Servo. A high
amount of torque is required to rotate a link arm. The link arm
needed to be extremely rigid to prevent any torsional effects as
well as be able to resist any damage due to constant salt water
contact. As such, a 10 cm, high density plastic sail arm was
sourced. The length of the link arm is important in order for the syringe to reach the required
insertion depth, Figure 15 illustrates this further.
As you can see from Figure 15, assuming a max insertion depth of 3.5 cm and angle of rotation of
45˚, the servo must be at least 3.5 cm away the contact point of the slider. This means when the
syringe is fully inserted into the seabed, the length of the arm must be at least 4.9 cm.
Figure 14: Final design of sediment
sampling system.

25
The relationship between the servo torque, the force on the syringe and horizontal distance
between the servo and the syringe is given by the following equation:
𝐹𝑜𝑟𝑐𝑒 (𝑁) =
𝑇𝑜𝑟𝑞𝑢𝑒 (𝑘𝑔. 𝑐𝑚)
𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 (𝑐𝑚)
We were able to determine the minimum amount of force the servo could exert on the syringe.
Since the max length of the arm is 10cm and the max torque is 22kg.cm, it was worked out that
the minimum force would be 21.6N, which is within the 20N-30N requirement for an effective
yield.
After a sample is taken, the syringe still needs to be capped to prevent the sample from escaping
when the ROV is moving. Therefore a cap has been designed to allow easy capping of the syringe
following the collection of a sample. A bowl design has been developed where the base on which
the syringe rests has a smaller diameter compared to the mouth. This way, the syringe has a bigger
target and capping is made easier where the syringe can slide in to sit on the base. This prevents
Figure 15: Trigonometric illustration of link arm length in relation to slider.

26
any soil from being washed away after collection thus preventing disturbance of the sample. The
cap will be placed on a link arm operated by a secondary less powerful servo. This servo forms part
of the capping mechanism for the syringe assembly. A number of design ideas were considered
for use here but in the end, a standard low torque servo proved to be the simplest and most cost
effective solution. The servo is attached to the side of the leg and rotates the cap in place to allow
the syringe to lower into position as shown in Figure 16.
6.3.1. Waterproofing
The servos were water proofed by first coating the circuit board and motor in a non-conductive
silicone gel. Secondly, the servo was filled with non-conductive, low viscosity vegetable oil making
sure each servo is fully submerged in the oil when assembled. This prevents water ingression into
the servo through the seams and screw openings. An O-ring was placed around the servo head to
stop oil from escaping. Finally, the outside housing was coated in a liquid epoxy that is resistant to
water and is insulating.
Figure 16: Plan view of capping servo.

27
7. Control System Developments
Based upon the specification outlined in Section 1.1 it was necessary for the ROV’s control system
to provide the following functionality:
1) Enable all ROV actions to be controlled wirelessly by the user from a PC.
2) Facilitate the deployment of the micro-sensor mechanism.
3) Facilitate the deployment of the sediment sampling mechanism.
4) Enable the motion of the ROV to be controlled easily and intuitively.
5) Real-time streaming of video from the ROV to the user PC.
6) Ability to record video and capture photos.
7) Sufficient battery capacity for a 45 minute mission duration.
8) Enable the ROV power supply to be easily connected and disconnected.
9) Enable the ROV power supply to be easily recharged.
In order to achieve these aims the control system’s hardware and software both required
modification.

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7.1. Review of Existing Control System Hardware
Figure 17 is a basic layout of the control system that was developed during the 2013/14 academic
year.
It was found that the desired level of motion control could be achieved by utilising the existing
sensors and thruster controllers. The camera was also found to be sufficient for the streaming and
recording of video and images.
In order to deploy the micro-sensor mechanism, a stepper motor and controller needed to be
added to the control system. Likewise, two servo motors needed to be added to enable the
deployment of the sediment sampling mechanism.
Figure 17: Basic layout of control system developed during the 2013/14 academic year.

29
The requirement of wireless communication between the ROV and its user proved to be a
significant constraint due to the complexities associated with transferring data wirelessly through
water. It was decided that the most effective way of enabling wireless communication was to
position a Wi-Fi router on the surface of the water and connecting it to the myRIO in the ROV via
an Ethernet cable and USB-Ethernet adaptor. This allowed data to be sent from the myRIO to the
router via a wired connection, then from the router to the user PC via a wireless connection, and
vice versa. It was thus decided that along with the thruster batteries, the buoy would also
accommodate a Wi-Fi router. The design of this buoy is detailed in Section 8.
Considerable disassembly of the ROV was necessary to disconnect and reconnect the batteries in
the original control system. This proved to be a major limitation when attempting to connect or
disconnect the ROV’s power supplies in the field. Relocating the thruster batteries to an easily
accessible position on the buoy remedied part of this problem however modifications still needed
to be made to the ROV to enable easy access to the myRIO battery.
7.2. Implementation of Hardware Modifications
7.2.1. Micro-Sensor Deployment Hardware
The micro-sensor deployment mechanism utilises a Portescap 35DBM10B2U-L stepper motor and
a Phidget Stepper Unipolar Motor Controller is used to power the stepper motors whilst also acting
as an interface between the stepper motor and the myRIO. The Phidget controller is in turn
powered by the same battery used to power the myRIO. A USB connection is used to pass
commands from the myRIO to the Phidget controller via the USB hub. The Phidget controller
converts these commands into signals which are then sent to the stepper motor.

30
7.2.2. Sediment Sampling Hardware
A Futaba S3003 servo motor is used to manoeuvre the cap of the sediment sampler. This servo
motor is powered and controlled directly by the myRIO. The red, white and black wires of the
servo motor are connected to the +5V, PWM0 and DGND (MXP A) pins of the myRIO respectively.
A Hitec HS-7954SH servo motor is used to manoeuvre the syringe of the sediment sampler in the
vertical direction. The power requirement for this servo motor was too large for it to be powered
by the myRIO directly and its input voltage of +7.4V was not within range of both the myRIO
battery and the thruster batteries. As such, a separate Storm 7.4 V, 1800 mAh, LiPo battery is used
to power the servo motor. The positive lead from this battery connected to the red lead of the
servo motor, whilst the negative output lead from the battery is connected to the DGND (MXP A)
pin of the myRIO together with the black lead of the servo motor. The yellow lead of the servo
motor is connected to the PWM1 (MXP A) of the myRIO.
7.2.3. Wireless Communication
An Edimax Wireless Router with 4 LAN ports and a maximum connection speed of up to 300 Mbps
was used to facilitate wireless communication. Power is provided to the router from a 2200 mAh
portable charger power bank. An Ethernet cable 25 m in length connects the LAN1 port of the
router to the USB-Ethernet adaptor connected to the myRIO. Once the router has powered up the
name of the router’s Wi-Fi network appears as the available network connection “UAV Submarine”
on the user PC. Selecting this network and then entering the password “esub2015” when
prompted sets up communication between the user PC and the ROV.
A USB antenna was supplied by the University with the aim of extending the signal range of the
user PC if necessary.

31
7.2.4. Thruster Batteries
Four Turnigy, 5000 mAh, 22.2 V, LiPo batteries were connected in parallel and used to supply
power to all five thrusters and their controllers. It was estimated that the combined capacity of
the four batteries would be sufficient to operate three thrusters at full power for a duration of 90
minutes. Calculations supporting this estimation are contained in Appendix L. A length of 25 m,
1.5 mm2, 3 core power cable transferred power from the batteries located on the buoy to the
thruster controllers on the ROV.
7.2.5. Easy Access to the myRIO Battery
It was decided that it should be possible to
connect, disconnect and recharge the
myRIO battery without having to
disassemble the ROV. To achieve this, the
power and balance leads were routed to a
Bulgin PXP7012/06S/ST connector which is
attached to one of the hull end-caps as
shown in Figure 18. Also routed to the connector were the positive and negative leads from the
myRIO, spot light (see Section 7.2.6) and stepper motor controller power inputs.
Figure 18: Connecting the battery to the myRIO via the
Bulgin® connector.

32
When deploying the ROV, a mating Bulgin
PXP7010/06P/ST connector is attached as shown
in Figure 19. Figure 19 also illustrates how the
terminals of this connector are wired together,
completing the circuit between the battery and
the myRIO, spotlight and stepper motor
controller. In order to seal the electrical connections, one end of a dummy cable has been inserted
into the rear of the Bulgin connector and the other end into a spare cable gland on the end-cap.
When the battery requires charging, the Bulgin connector is detached then a second Bulgin
PXP7010/06P/ST connector is attached. This second connector routes the battery’s power and
balance leads to the charging station as shown by Figure 20.
Figure 20: Connecting the battery to the charging station via the Bulgin® connector.
7.2.6. Additional Hardware Modifications
A 4.5 W LED spot light was positioned next to the camera to increase its visibility in low light. Its
power was supplied from the myRIO battery via a switching circuit (PCB C). The switching circuit
was designed to connect or disconnect the power supply to the spot light in response to a high or
Figure 19: Attachment of mating Bulgin connector.

33
low signal from the myRIO respectively. A schematic of the switching circuit is provided in
Appendix J: Electrical Schematics. The black and red leads of the switching circuit are connected
to the negative and positive terminals of the myRIO battery respectively. The green and
green/black wires of the switching circuit are connected to the DIO0 and DGND (MXP B) pins of
the myRIO respectively. The brown and blue wires of the switching circuit are connected to the
terminals of the spot light.
A 6 A fuse was positioned between each thruster and its respective controller. This ensured the
current supplied to an individual thruster could not significantly exceed its maximum rating of 5.8
A.
A 20 A fuse was positioned between the thruster batteries and thruster controllers to prevent
excessive current from being drawn through the power cable. This also limited the maximum
number of thrusters that could be active at any one point in time to three.
A 1.5 A fuse was positioned between the myRIO battery and the myRIO power input. This ensured
the current supplied to the myRIO could not exceed its maximum rating of 1.5 A.

34
7.3. Summary of Hardware Modifications
Figure 21 details all of the implemented hardware modifications. A larger copy of Figure 21 is
provided in Appendix J: Electrical Schematics. Schematics of PCBs A, B and C are also provided in
Appendix J: Electrical Schematics.
7.4. Review of Existing Control Program
As mentioned in Section 2.5, a control program had been written using LabVIEW during the
2013/14 academic year. It was agreed that the method by which this program controlled the
motion of the ROV had room for improvement. In addition to this, a number of critical program
files were found to be missing. As such, it was decided that developing a new control program
would be the best course of action. Not only did this allow a more intuitive motion control strategy
to be implemented, it also allowed additional program functions, such as micro-sensor and
sediment sampler deployment, to be more easily integrated into the control program.
Figure 21: Schematic of the ROV’s control system hardware after modifications.

35
7.5. Summary of New Control Program
The aim of the control program was to coordinate the actions of each hardware component on
board the ROV in order to achieve the objectives outlined at the beginning of this section. The
control program was written in LabVIEW and comprised two main VI’s (User panels) which are
executed simultaneously. The first main VI, referred to as the host VI, is executed on the user PC
whilst the second main VI, also referred to as the target VI, is executed on the myRIO. The functions
performed by the host VI are:
 Acquirement of user commands via a keyboard, mouse or an Xbox control pad.
 Interpretation of user commands and communication of these to the target VI.
 Acquirement of sensor data communicated by the target VI.
 Interpretation of sensor data and communication of relevant information to the user via a
visual user interface.
The functions performed by the target VI are:
 Acquirement of user commands communicated by the host VI.
 Interpretation of user commands followed by sending of appropriate control signals to
relevant hardware components.
 Acquirement of data from the on-board sensors and its communication to the host VI.
Figure 22 illustrates the types of information acquired by both the host and target Vis, as well as
the resulting outputs.

36
Figure 22: Graphical representation of the inputs and outputs of both the host and target VIs.
Detailed descriptions of the communication protocols adopted and the algorithms executed
within the host and target VIs are provided in Appendix K: Detailed Software Information.
7.5.1. User Commands
User commands can be inputted via a keyboard, Xbox control pad or mouse. Key assignments are
provided in Appendix M: List of User Commands.
7.5.2. Visual User Interface
Figure 23 displays the user interface.
Figure 23: Visual user interface.

37
Table 5 details the key features of the user interface labelled in Figure 23.
Table 5: Description of user interface features.
Feature Description
01 Depth gauge with depth limit exceeded warning light.
02 Compass with ACW and CW rotation limit exceeded warning
lights.
03 Video display.
04 Micro-sensor and sediment sampling mechanism information.
05 Vertical thruster power knob.
06 Spot light on/off switch.
07 Create new video file icon.
08 Record video icon.
09 Save video file icon.
10 Screenshot icon.
11 ROV stop icon.
12 Joystick on/off icon.
13 Error display panel.
7.6. Main Limitations of Control System
7.6.1. Batteries On-Board ROV
In its current state, the control system requires two LiPo batteries to be positioned on-board the
ROV. If water ingress were to occur, such positioning would present a serious safety hazard, both
to the batteries and the surrounding components. It is suggested that any future developments of
the control system includes the replacement of these batteries with voltage regulators to step
down the voltage of the 22.2 V thruster power supply.
7.6.2. Leak Detection
There is currently no hardware in place which can automatically detect the ingress of water into
either hull. Potential solutions have been researched but it was not possible to develop any
designs. The most promising solution researched involves the use of two strips of copper tape

38
(Open ROV, 2013). The strips are placed sufficiently close to one another such that droplets of
water are able to bridge the gap, causing an electrical connection.
7.6.3. Vision
The camera on-board the ROV only provides vision in the forwards direction. Additional cameras
would be desirable to provide vision in multiple directions, as well as to confirm correct
deployment of the microsensor deployment and sediment sampling mechanisms. However, it is
unlikely that the current connection between the ROV and user PC would be able to accommodate
multiple image streams. Modifying the control program to allow the user to select between
different cameras is one possible solution.
8. Buoy
Early on in the project it was decided that the ROV would be tethered to a floating base station
that would allow the range of the ROV to be increased. Initially it was envisaged that this would
be in the form of a trailer, towed by the hovercraft. It was decided that this may encompass too
much work for the hovercraft team in the first year of their project. A buoy was chosen to provide
the required base station, giving a stable buoyant platform from which to offer a link between the
ROV and the laptop controller on a boat or the shore.
The buoy was intended to increase the range of the ROV, to the design criteria of 50-200m. This
was achieved by using a Wi-Fi router to create a local wireless network connection from the laptop
to the buoy. An Ethernet cable was then used to connect the buoy to the ROV. The issue of
electrical loses over long lengths of cable was also reduced with this design, with a 25m power and
Ethernet tether being adopted, instead of much longer cables.

39
Due to the addition of the sensor deployment and sediment sampling mechanisms, it was decided
that the second hull on the ROV could no longer be used for housing the batteries that powered
the thrusters. Coupled with the need to purchase new batteries at the beginning of the year, it
was decided that the buoy would also act as the location for the batteries for the thrusters,
therefore freeing up a hull for additional components.
8.1. Final Design
8.1.1. Electrical Components
The buoy had to accommodate four thruster batteries for required mission time. A Wi-Fi router
was needed to transfer data between the controlling laptop and the myRIO on the ROV. An Edimax
BR-6428NS was selected as it allowed connection speeds up to 300 Mbps which was adequate for
the quantity of data transfer. The Wi-Fi router is powered by a separate USB battery, eliminating
the requirement for a step-down voltage circuit in the buoy and creating a secondary system so
that if the thruster batteries fail, there is still a link with the ROV. The USB battery supplied the
required current of 1 Amp and 5 Volts and had twice the capacity required for the mission time.
8.1.2. Dry box
A dry box was used to accommodate all the electronic components for the buoy. A LoMo Medium
dry box was used which had an O-ring design and two lockable catches to ensure waterproofness.
The electrical components described above were accommodated within the dry box. To stop the
components moving around, which could lead to cable connectors being dislodged, a 3D printed
interior was designed and manufactured (Figure 24). The interior was manufactured from twenty
parts due to the size of the printing bed. The parts were designed with lap and peg in hole joints
which gave some structural rigidity. Glue was also used to secure the parts together. The batteries

40
were held in pace with small battery clips which can be bent for the removal of the batteries. The
Wi-Fi router is fixed to the inside of the dry box lid, with the antenna drilled through and sealed.
Figure 24: Drybox interior
8.1.3. Chassis
The final design for the buoy can be seen in Figure 25. The chassis is made from the
aforementioned machine building systems speed frame and the dry box is secured to the chassis
by two bungee cords. The chassis fits together by using T-slots and automatic fastening sets with
M6 bolts. The chassis also adds legs to the buoy which provides a flat base for the buoy to sit on
dry land. The legs were required as the Bulgin waterproof connectors protrude from the base of
the drybox, thus it would be unable to sit flat on dry land.

41
Figure 25: Final Buoy design
8.1.4. Soil pipe
As can be seen in Appendix H: Buoy Design many
designs were considered to supply the buoyancy
for the buoy. Cylinders had been considered but
after the issues with the end caps on the ROV hulls
it was decided to use an off the shelf end cap
sealing system. To create an airtight space four
ninety degree angle connectors were used to
connect four lengths of soil pipe together to from a rectangular shape. The angled connectors have
built in lip seals and are sealed with a push fit. Silicone greases was used to lubricate the lip seals
to protect them and ensure waterproofness. Four off the shelf brackets (Figure 26) were used to
connect the soil pipe arrangement to the chassis. The brackets simply fit around the soil pipe and
were then attached to the chassis by two M6 bolts for each bracket.
Buoyancy hand calculations were used to determine if the quantity of soil pipe used would be
sufficient (Appendix H: Buoy Design, Table 14: Buoyancy hand calculations.). The soil pipe displaces
0.024m3 of water. The volume that needed to be displaced was 0.014m3, this is approximately
Figure 26: Bracket connectors.

42
twice the required displacement. Figure 27 shows that the waterline on the buoy was halfway up
the soil pipe; therefore proving the calculations were correct.
Figure 27: Buoy waterline.
8.2. Centre of buoyancy and gravity
To ensure the stability of the buoy the centre of buoyancy and centre of mass needed to have
similar X and Y values so they are in line with each other in the vertical axis. The centre of mass
was determined by setting all the mass properties within the CAD model and using the centre of
mass function. The water level was determined by making all the parts solid with water properties.
Then a horizontal plane was moved up and down until the mass of water below the plane equalled
the total mass of the buoy. Figure 27 shows the position of the water level line. The centre of
buoyancy is then the centre of mass for water model below the water level line.
Figure 28: Centre of Mass (left), Centre of Buoyancy (Right).

43
Figure 28 shows the position of the centre of mass (left) and centre of buoyancy (right). The centre
of mass and buoyancy co-ordinates are (-145,-238,-27) and (-143,-238,-42) respectively. It can be
seen that the difference in X is 2mm and Y is the same. This difference is minimal; therefore it will
not affect the stability of the buoy. The distribution of mass within the drybox was carefully
thought out to keep it symmetrical; therefore keeping it stable in the water. The centre of mass is
15mm above the centre of buoyancy in the Z direction, this difference is also small. If the buoy
sinks further into the water on one side, due to currents or waves, the centre of buoyancy will
move thus creating a restoring moment which will restore the buoy to its original position.
8.3. Bulgin Waterproof connectors
Two cables are required to transmit power and control signals from the buoy to the ROV. The
power and Ethernet cables need to enter the dry box to connect to the router and batteries. To
provide waterproof connections Bulgin IP68 connectors were used. A hole saw was used to cut
two holes in the base of the dry box for the connectors. The connectors screw together each side
of the dry box to provide a waterproof female port on both sides. The external cables, between
the buoy and ROV, have waterproof ends which attach to the connector on the dry box. The
arrangement adopted enables the cables to be detached from the buoy and the ROV for
transportation. When the buoy
is placed on a flat surface the
legs attached to the chassis
ensure that the protruding
connectors are not bent or damaged. The connectors protrude by 10cm bellow the dry box when
the cables are connected (Figure 29).
Figure 29: Bulgin connector position.

44
8.4. Tether Management System (TMS)
With the ROV now being attached to a floating buoy instead of
being operated from a boat it was decided that a Tether
Management System (TMS) would be required to help prevent the
Ethernet and power cables becoming tangled. The purpose of a
TMS is to lengthen and shorten the tether in order to minimise the
effect of cable drag during use. Work detailed in the ROV Manual (Christ & Wernli, 2011) and by
Abel (1994) was studied and used as a basis for investigating tether design and management.
Significant research was undertaken into commercially available
systems, to gain an understanding of what designs have been
developed. Many simple designs are based upon a manual payout
from a boat, which can be seen in Figure 30 (rovinnovations, n.d.).
A typical design for an automatic system can be seen in Figure 31
(malmorstad, n.d.). There are two main design types of TMS, top
hat and side entry cages. A side entry design is simply a box that the ROV is parked inside of while
it is raised and lowered in the water, Figure 32 (seaeye, n.d.). A Tophat sits on top of the ROV and
does not enclose the ROV as a side entry cage does.
The final adopted solution to the TMS was to use a neutrally
buoyant tether. With a neutrally buoyant tether, the force
required by the ROV to pull the cable underwater or bring it to the
surface is minimal. To achieve a neutrally buoyant tether a floating
rope was platted together with the power and Ethernet cables.
Figure 30: Manual cable reel pay-
out
Figure 31: Commercially available
TMS system
Figure 32: Side entry cage.

45
However, the floating rope did not provide enough buoyancy to counteract the mass of the cables.
Small floats made of foam were available from the previous year’s project. The volume of the
floats was determined by submerging the float in a measuring cylinder filled with water and
recording the increase in volume. It was then calculated that a float was need every 6.2m to
provide the required buoyancy. Appendix I: Tether Management System Design shows the
calculations used to determine how many floats were required and the size of the intervals
between them.
During the third test the neutrally buoyant cable was tested with the buoy. The cable worked as
expected. The ROV was able to pull the tether
underwater with ease and no change in the ROVs
pitch or roll was witnessed. The excess cable floated
near the surface; therefore there was no force on
the ROV from the tether. When the ROV surfaced
the tether followed behind and was not having any
effect on direction or speed. Figure 33 shows the
cable during the third test. It can be seen that the
cable sinks between the floats. To increase the
effectiveness and reduce the quantity of
submerged cable smaller floats at more regular intervals should be used.
Figure 33: Neutrally buoyant cable.

46
To conclude, the tether management system deployed with the ROV is a neutrally buoyant tether
which does not have any effect on speed and direction of the ROV therefore achieving the aim of
the TMS.
9. Full System Validation
9.1. Dry Land Test
9.1.1. Thruster Response
The thrusters were found to respond correctly to user commands inputted using both the
keyboard and Xbox control pad.
9.1.2. Wireless Communication
The range and speed of the wireless communication was tested outdoors. Without the USB aerial
connected it was found that the wireless connection dropped out when the router was moved
more than 20 m from the user PC. The ROV’s response time suffered an approximate 0.5 s delay
when commands were sent using the wireless connection.
9.2. Pool Test
It was necessary to perform a third pool test in order to validate the aspects of the design that
could not be validated during the dry land test. The pool test was performed in a 3.8 m diving pool
located at the Sobell Leisure Centre, Aberdare. The objectives of the test were as follows:
 Validation of the ROV’s waterproofness.
 Correction of any alterations in the ROV’s pitch and roll resulting from chassis
modifications.
 Assessment of the ROV’s buoyancy.
 Validation of the buoy’s buoyancy and waterproofness.

47
 Validation of the tether management system.
 Calibration of the ROV’s depth sensor.
 Assessment of the ROV’s manoeuvrability in three dimensions.
 Assessment of the underwater visibility provided by the spot light and camera.
 Identification of any unforeseen issues.
Originally it was also planned to validate the underwater capability of the sediment sampling and
micro-sensor deployment mechanisms during this pool test. However, due to manufacturing
delays it was not possible to assemble either mechanism before the test.
9.2.1. ROV Waterproofness
The waterproofness of the ROV’s chassis was validated a week prior to the pool test to allow time
for any necessary modifications and to reduce the risk of damage to electronic components. Three
possible points where water ingress could have occurred were identified; the replacement cable
glands, replacement end cap O-rings and Bulgin® connectors. One hull fitted with all three of these
features was filled with weights then lowered to the bottom of the 3.8 m pool. The hull was left
for 45 minutes then removed from the pool. It was found that no water ingress had occurred
therefore it was agreed that a full system test could commence safely.
9.2.2. ROV Pitch and Roll
The ROV exhibited no significant pitch or roll when in the water, as can be seen in Figure 34.

48
Figure 34: ROV exhibiting neither pitch nor roll.
9.2.3. ROV Buoyancy
The ROV was found to be negatively buoyant. It was found that operating the vertical thruster at
50% power enabled the ROV to maintain a constant position in the vertical axis. It was anticipated
that this value of power would be reduced with the addition of the sediment sampling mechanism
due to its extra buoyancy.
9.2.4. Buoy Buoyancy and Waterproofness
The buoy was found to float easily and sat level on the surface of the water as expected. This is
shown in Figure 35.
In order to simulate waves the buoy was
pushed down on one side until the soil
pipe was fully submerged and then
released. Upon release the buoy
returned quickly to its original position,
Figure 35: Buoy floating level on the water’s surface.

49
thus proving that the change in position of the centre of buoyancy gave the required restoring
moment.
The dry box and soil pipe were disassembled after the pool test and examined for any water
ingress. None was found, proving that all seals on the buoy were watertight.
9.2.5. Tether Management System (TMS)
It was found that the floats attached to the
tether provided sufficient buoyancy to
prevent the tether from sinking. Figure 36
shows how the floats remained on the surface
of the water with the cables suspended
between each float.
It was also found that each float provided minimal resistance to the ROV when descending or
moving in the horizontal plane.
Tangling of the tether was found to be a problem with all 25 m of tether released. Appendix I:
Tether Management System Design details possible solutions to this issue with the use of a motor
driven reel.
9.2.6. Depth Sensor Calibration
Voltage readings were acquired from the depth sensor every 0.5 m, starting at a depth of 0.5 m
up to a depth of 3.5 m. The relationship between depth (𝑧, m) and output voltage (𝑉𝑜, V) was found
to be roughly linear between this range and is described by the following equation:
𝑉𝑜 = 0.032𝑧 + 2.06
Figure 36: TMS in action.

50
It was acknowledged that this relationship may not be true for the entire operating depth of the
ROV. It was planned to use a dead weight tester located in the mechanical workshop to calibrate
the sensor up to a depth of 20 m, however this was not possible due to time constraints.
9.2.7. ROV Manoeuvrability
The ROV was able to move in all directions and responded with minimal delay to user commands.
It was decided not to measure the ROV’s velocity in each direction as it was likely that the results
obtained would be affected by the addition of the sediment sampling and micro-sensor
deployment mechanisms.
9.2.8. Unforeseen Issues
It was not possible to assess the underwater visibility of the camera with the spot light due to a
fault in the control program’s code. The fault was rectified at a later date, however there was not
another opportunity to assess the camera’s visibility with the spot light.
The wireless connection between the user PC and Wi-Fi router was lost on numerous occasions
during the test. Reconnection was possible, however this was a time consuming process during
which the ROV could not be controlled. The connection appeared to be more stable when the
Edimax USB aerial was removed but disconnections still occurred. Further investigation after the
test identified an IP address clash on the router. This was due to the fact that the IP address for
the Ethernet adapter had changed following a software update on the myRIO. Once the issue was
rectified, the Wi-Fi connection was found to operate without any issues.

51
10. Future Recommendations
Based upon the system limitations outlined in previous sections of this report, Table # details
recommended areas for future development.
Table 6: Recommended future developments.
Category Development
Buoy Hardware &
Chassis
Motor driven Tether Management System. See Appendix I: Tether
Management System Design for further details.
Control Systems &
Communication
Establish communication between myRIO and stepper motor
controller.
Implementation of a leak detection system.
Replacement of batteries on-board ROV with voltage regulators.
Sensors & Sampling
System Hardware
Replacement of microsensor deployment mechanism Nitrile O-rings
with Viton O-rings.
Validation of microsensor deployment mechanism sealing during
motion.
ROV Hardware &
Chassis
Ease of assembly and disassembly.

52
11. Final Summary
Table 7 details the deliverables agreed upon at the beginning of the project and their status at the
end of the 2014/15 academic year.
Table 7: Status of project deliverables.
Deliverable Status Comments
Resolution of outstanding ROV issues. Achieved
Development of a microsensor
deployment system.
Partly
Achieved
Problems encountered implementing
control code. Full system validation not
performed as a result. Further details
provided in Section 5 and Appendix F:
Microsensor Deployment Mechanism
Design.
Development of a sediment sampling
system.
Partly
Achieved
Waterproofing of system not complete.
Full system validation not performed as a
result.
Modification of ROV chassis to allow
for attachment of microsensor and
sediment mechanisms.
Achieved
Development of buoy for the purpose
of wireless communication and ROV
power supply.
Achieved
Development of Tether Management
System
Partly
Achieved
Floating cable system implemented.
Research performed into passive and
motor driven cable reel mechanisms.
Development of user friendly control
program.
Achieved

53
12. Table of References
Abel, B. A., 1994. Underwater Vehicle tether management systems. Brest, IEEE, pp. 495-500.
Bentley, C. et al., 2014. En410t UAV Project - Autonomous Submarine, Cardiff: s.n.
British Standards Institute, 2008. BS ISO 3601-2: Housing Dimensions for General Applications,
s.l.: British Standards Institute.
Christ, R. D. & Wernli, R. L., 2011. The ROV Manual: A User Guide for Observation Class Remotely
Operated Vehicles. s.l.:Butterworth-Heinemann.
Environmental Sampling Supply, 2015. Products. [Online]
Available at: http://www.essvial.com/Products.aspx?ID=16
fixya, n.d. [Online]
Available at: http://www.fixya.com/support/t13021190-how_can
[Accessed 05 05 2015].
Hobby King Ltd., 2014. Turnigy 2200 mAh 3S 20C Lipo Pack. [Online]
Available at:
http://www.hobbyking.co.uk/hobbyking/store/__8932__Turnigy_2200mAh_3S_20C_Lipo_Pack.
html
[Accessed 4 November 2014].
Hobby King Ltd., 2014. Turnigy 5000mAh 6S 20C Lipo Pack. [Online]
Available at:
http://www.hobbyking.co.uk/hobbyking/store/__9176__Turnigy_5000mAh_6S_20C_Lipo_Pack.
htmh
Home Built ROVs, 2015. Mayfair 750 GPH Bilge Pump Thruster Testing. [Online]
Available at: www.homebuiltrovs.com/mayfair750test.html
homebuiltrovs, n.d. [Online]
Available at: http://www.homebuiltrovs.com/seafoxretrofit.html
[Accessed 05 05 2015].
hozelock, n.d. [Online]
Available at: http://www.hozelock.com/watering/hose-reels/auto-rewind/20m-autoreel-
2490.html
[Accessed 05 05 2015].
malmorstad, n.d. [Online]
Available at: http://www.malmorstad.com/products/tms
[Accessed 05 05 2015].
McLennan Servo Supplies, 2015. [Online]
Available at: http://www.alzanti.com/datasheets/european/stepper/35dbmseriesdla.pdf

54
National Instruments, 2013. User Guide and Specifications. [Online]
Available at: http://www.ni.com/pdf/manuals/376047a.pdf
Open ROV, 2013. Water/Leak Detector Circuit. [Online]
Available at: https://forum.openrov.com/t/water-leak-detector-circuit/251
[Accessed 30 March 2015].
Phidgets, 2015. OS - Linux. [Online]
Available at: www.phidgets.com/docs/OS_-_Linux
Phidgets, 2015. Phidgets Unipolar 4 Motor. [Online]
Available at: www.phidgets.com/products.php?product_id=1062_1
rovinnovations, n.d. cable-reels. [Online]
Available at: http://www.rovinnovations.com/cable-reels.html
[Accessed 05 05 2015].
SeaBotix Inc., 2007. Standard Thruster & 2 Wire Whip. [Online]
Available at: http://www.seabotix.com/products/pdf_files/BTD150_Data_Sheet.
seaeye, n.d. [Online]
Available at: http://www.seaeye.com/tms.html
[Accessed 05 05 2015].
stevenmcclements, n.d. [Online]
Available at: http://stevenmcclements.blogspot.co.uk/
[Accessed 05 05 2015].
Unisense, 2015. [Online]
Available at: www.unisense.com

55
Appendix A: Bill of Materials

56
Appendix B: ROV Chassis
The first design iteration consists of four straight legs as shown in Figure 37. This design was
disregarded, as there would be an insignificant improvement to the stability of the ROV.
Figure 37: From left to right, top to bottom; first, second, third and fourth chassis design iteration.
The second design iteration consists of four legs placed at an inclined angle. This design has a wider
base compared to the first design hence the improvement of overall ROV stability.
The third design iteration consists of only three legs instead of four as in any previous design
iterations. The decision of having three legs was made due to the possibility of having at least one
of the legs (in a four-leg design) not being in contact with the seabed in a worst case scenario (e.g.
on a highly uneven surface), resulting in the possibility of the ROV tipping over. As the sediment
and sensor deployment are integrated as part of the legs, the risk of having one of the legs not
1 2
34

57
being in contact with the seabed would mean the sediment and sensor deployment might not
function properly. Having only three legs can help eliminate such a risk.
The fourth chassis design iteration consisted of three legs arranged in a symmetrical manner. This
design has better overall weight distribution compared to the third design due to its symmetrical
arrangement. This design was also thought to have insignificant effect on the ROV
manoeuvrability, as there was no component in which the direction of each thruster is facing. The
final design was developed mainly based on the fourth design and involved using fabricated
reinforcement plates and machine building systems’ fastener sets. The original chassis frame was
also modified to widen the base and provide a more secure platform to attach the legs.

58
Appendix C: ROV Hulls
Numerical Validation: Hand Calculations
The following equations were used to calculate the stress acting on the 3mm thick hulls at 20m
depth of water.
Circumferential Stress:
σc = [(pi ri
2
- po ro
2
) / (ro
2
- ri
2
)] - [ri
2
ro
2
(po - pi) / (r2
(ro
2
- ri
2
))]
Axial Stress:
σa = (pi ri
2
- po ro
2
)/(ro
2
- ri
2
)
Radial Stress:
σr = [(pi ri
2
- po ro
2
) / (ro
2
- ri
2
)] + [ri
2
ro
2
(po - pi) / (r2
(ro
2
- ri
2
))]
pi = internal pressure in the tube (MPa) = 0.1 (atmospheric pressure)
po = external pressure in the tube (MPa) = 0.3 at 20m water depth
ri = internal radius of tube (mm) = 124
ro = external radius of tube (mm) = 130
r = radius to point in tube or cylinder wall (mm) (ri < r < ro)
Table 8: Stresses at various positional along the hull.
Radial Position (r) At 124mm At 130mm
Axial Stress -2.3178 -2.3178
Circumferential Stress -4.5357 -4.3357
Radial Stress -0.1 -0.3

59
Numerical Validation: FEA Modelling
Figure 38: Von Mises stress distribution.
The pressure hull was modelled by using Patran software. A simple hollow cylinder was created to
represent the pressure hull and uniform rectangular grid cells were generated automatically by
Patran. The displacement of each end of the tube was constrained 20mm from the edge which is
the actual overlapping distance between the end cap and the tube. The material (polycarbonate)
was assumed to have Young’s modulus of 2.3GPa and Poisson’s ratio of 0.37. The inner pressure
of the tube was assumed to be at atmospheric pressure, which is 1 bar whereas the outer pressure
of the tube was set to be 3 bar (at 20m water depth). The end result was plotted as Von Mises
stress distribution and a maximum stress value of 4.43MPa was obtained. The maximum safety
working stress of the material according to the manufacturer is 10MPa and under normal
circumstances the pressure hull would be working at approximately half of the maximum safety
working stress to give a safety factor of 2. The stress concentration is located nearby the region
where the end cap stops overlapping at both end of the pressure hull as shown in Figure 38.

60
Appendix D: ROV Buoyancy calculations
The ROV was designed to be slightly negative buoyant; therefore the mass of the ROV needs to
exceed the mass of water displaced. The total mass of the ROV with all cabling and systems
attached was 16.2Kg. The total volume displaced by the ROV was determined from the
Solidworks CAD model and was 0.015593m3. The mass of water displaced was calculated by
multiplying the volume by the density of water as seen below. The density of fresh water was
taken as 1000Kg/m3 and sea water was taken as 1035Kg/m3.
0.015593 × 1000 = 15.6𝑘𝑔 𝑜𝑓 𝑏𝑢𝑜𝑦𝑎𝑛𝑐𝑦 𝑖𝑛 𝑓𝑟𝑒𝑠ℎ 𝑤𝑎𝑡𝑒𝑟
0.015593 × 1035 = 16.1𝑘𝑔 𝑜𝑓 𝑏𝑢𝑜𝑦𝑎𝑛𝑐𝑦 𝑖𝑛 𝑠𝑒𝑎 𝑤𝑎𝑡𝑒𝑟
The difference between the mass of water displaced and the mass of the ROV determines the
amount of buoyancy.
15.6 − 16.2 = −0.6𝑘𝑔 𝑖𝑛 𝑓𝑟𝑒𝑠ℎ 𝑤𝑎𝑡𝑒𝑟
16.1 − 16.2 = −0.1𝑘𝑔 𝑖𝑛 𝑠𝑒𝑎 𝑤𝑎𝑡𝑒𝑟
This corresponds to a downward force of:
0.6 × 9.81 = 5.886𝑁 𝑖𝑛 𝑓𝑟𝑒𝑠ℎ 𝑤𝑎𝑡𝑒𝑟
0.1 × 9.81 = 0.981𝑁 𝑖𝑛 𝑠𝑒𝑎 𝑤𝑎𝑡𝑒𝑟
In fresh water there is a force of 5.89N downwards and in sea water the force is 0.98N; therefore
the vertical thruster power output will need calibrating depending on the type of water it is
being deployed in.

61
Appendix E: Enlarged Hull Design
Figure 39: ROV with new extended hulls
Table 9: Weight and dimensions of data logger (Unisense.com).
Dimensions (W × D × H) /mm 225 × 125 × 62
Mass (Approx.) /kg 2

62
Figure 40: Drawing for new hull cylinders
Figure 41: Drawing of new end caps

63
Appendix F: Microsensor Deployment Mechanism Design
Photos of Unisense Microsensors
Figure 42: Unisense O2 MicroOptode (Unisense.com)
Figure 43: Tip of MicroOptode with glass fibre partially extended (Unisense.com)
Figure 44: Normal microsensor deployment method (Unisense.com)
Figure 45: Unisense Microelectrode (Unisense.com)
Figure 46: Unisense reference electrode (Unisense.com)
Initial Design Concepts
Linear Actuator Concept
The figures in the previous section show that the microsensors use either glass fibres or glass
needles to take measurements and are therefore extremely delicate. They are also very expensive.

64
This meant that protecting them from damage during the mission was an essential design
consideration. The safest place for the sensors appeared to be inside the ROV chassis, however
there was not enough vertical space to mount them. It was decided that legs would be added and
the sensors would be mounted on sliding mechanisms on the inside of the legs.
The next stage was to decide on a mechanism to provide the
linear motion needed to lower the sensors into the sediment
and then raise them back up. Initially linear actuators were
considered for the task. They were available in a variety of
specifications, including waterproof versions, and could
provide a compact mechanism which would be reasonably
simple to implement. The actuator would be mounted onto
the chassis frame next to the leg with a connecting arm
attached to the sliding mechanism. When the operator
wished to deploy the sensor a command would be sent from
the myRio to the actuator’s controller, called a ‘dumb’
controller as it could only output speed and position commands. A concept of this system is shown
in Figure 47.
It was quickly found however that waterproof actuators were too expensive for the project. A
quote from Vipa gave a cost of £349.98 per actuator. The quote is shown in Table 10. The idea of
using linear actuators was abandoned in favour of a cheaper alternative.
Figure 47: Concept for a deployment
system with linear actuators.

65
Table 10: Quote from Vipa for waterproof actuators.
Rack and Pinion concept
As discussed in the previous section a cheap alternative to linear actuators was needed. The main
reason for the high cost was the need to waterproof electronic components to an IP69 rating which
would allow them to operate at depths of 20 metres. The solution seemed to be to buy a standard
electric motor and then waterproof it in house. This presented two challenges; how to waterproof
the motor and how to translate the rotary motion of the electric motor into linear motion.
Waterproofing Electric Motors
Bilge Pump
In the first design, the modification of a bilge pump was considered for the drive of the sensor
holder. Bilge pumps are designed to run continuously underwater so removing the casing and

66
exposing the shaft would have provided a reliable drive for the gear rack. The bilge pump that was
considered was the Mayfair 750gph bilge pump, tested to show
a capability of running up to 30 meters depth.
There were, however, some design complications in the use of a
bilge pump. First, at depth the high pressures applied to the lip
seals on the shaft would have increased the frictional torque on the shaft, thus the current drive
required increased. This higher force and current requirement would make the calibration of
motion difficult.
This, with the additional factor that dry running of the pump would cause damage to the motor
would mean the delicate motion required for the sensors would not be applicable.
Potting and Capsuling
Potting is a process of which the complete electronic assembly, or the motor coils in this scenario,
are filled with a solid or gelatinous compound for exclusion from moisture. The added benefits
from the system are a simplicity in the design, as well as additional protection from impact, shock,
and vibration. Notable materials include wax, epoxy resin, and plastics.
Capsuling involves a similar process in which the motor electronics are enclosed within a
watertight box with a push rod through a port sealed with the use of O-rings. For additional
security the servo electronics would have been filled with a non-conductive oil.
However, both methods are crude and have a chance of damaging or breaking the motor. In the
case of encapsulating the motor, the oil may even increase the current draw from the motor.
Figure 48: Mayfair 750 Bilge Pump.

67
Magnetic Coupling
As the previous waterproofing designs were found to be crude and damaging to the application of
the motor, complete separation of the motor and drive was considered. In this case, magnetic
coupling.
Magnetic coupling is used to transmit the torque between two unconnected components through
the use of magnetic force. In the interest of the movement of the sensor, magnetic coupling would
be used for the complete separation of the two coupled parts. Thus meaning the motor may be
sealed off from the water whilst still providing the required driving force. Additionally, a lack of
contact between the parts would give an additional benefit in reduced friction, wear, noise, and
removes the requirement of lubrication.
In the design, as shown in Figure 49 a set of magnets may be attached to the motor shaft within a
completely sealed container. The wiring
may enter this housing through the use of
potting as they will not be required to
move. A second set of magnets may be
mounted within the ring with an internal diameter larger than the cylindrical waterproof housing.
Though the design would have provided a long lifetime of use and a fully waterproofed system,
the magnets would interfere with the sensor equipment and amplification attached alongside it.
The Unisense pH meter has an input range of ±4500pA with an input impedance of 1013 Ohm, and
it is recommended by Unisense specification to avoid forms of electronic or magnetic interference.
Due to this, magnetic coupling could not be used.
Figure 49: Magnetic coupling concept.

68
Motion Translation Methods
There were several possible methods of mechanically translating rotary to linear motion which
were considered. Initially variations of the Crank – Slider and the ‘Scotch Yoke’ mechanisms were
investigated. The advantage of these systems was that the amount of travel and the speed of
motion was built in mechanically by the size of the main gear and the lengths of the slider
components. This meant that the motor did not need a controller with position control and could
be controlled by simple on/off commands from the myRio. However both mechanisms would have
been unnecessarily complex to manufacture and would have needed a comparatively long length
of chassis frame to mount them. Due to the thruster layout the amount
of space for deployment mechanisms was limited so a more compact
system was needed.
It was decided that a rack and pinion system was the best option as it was
the most compact and also had the fewest moving parts making it the
simplest to manufacture. Both the rack and the pinion would be
manufactured in house using 3D printing to save the cost of buying
custom made components from an external supplier. A concept for this
system is shown in Figure 50. Unlike the other mechanisms there was no
mechanical limit to the amount of travel so a controller would be needed
to provide position control to ensure that the rack did not move too far
and escape its slide. This was preferable as a compact system that could be easily mounted to the
chassis was more important. However it was eventually decided that even this system was
unnecessarily complex as the pinion, the rack and the rack’s slider would have to be designed and
Figure 50: Concept for a
rack and pinion
deployment system.

69
manufactured and other methods for achieving linear motion would be simpler and more
effective.
Final System Design
It was decided that the best way to achieve linear motion was to
use stepper motors. These are electric motors which rotate what
is effectively a threaded nut. This rotation moves a threaded rod,
known as a lead screw, linearly up and down. Once this motor had
been chosen there were two main tasks. The first was design the
control system of the motor, including defining the positions to
which the motor would have to travel to deploy and retract the
sensor, and to integrate this system with the myRio controller
used to control the ROV. The second was to design and construct
the waterproof casing around the stepper motor and the mechanism which allowed the motor to
deploy the sensor.
Stepper Motor and Controller
In the operation of a stepper motor, the motor drive differs from general DC motors in that it is
driven by current pulses, which generates discrete rotations of the motor shaft.
The stepper motor has input contacts of which allow the current from the supply into the coil
windings. As mentioned, pulsed waveforms in the correct pattern is required to create the
electromagnetic fields needed to drive the motor. Stepper motors may also move an exact amount
of degrees (or steps) giving full control over the motor, which allows motion to an exact position
Figure 51: Stepper motor with
leadscrew (Mclennan Servo
Supplies).

70
and to hold that position. Due to this complexity of the drive, a stepper motor controller was
required to energize the phases in a timed sequence to make the motor turn.
In the decision of the motor controller, a Phidget unipolar stepper motor controller was chosen
for features including the ability to control 4 differing stepper motors through a single chip. In the
case of the project, three of these ports are used for the control of the three Unisense sensors
required. The fourth port is currently unused and thus may be used for implementation into future
developments of the system.
The stepper motor controller has a requirement of a supply of a maximum of 12V with a current
consumption of up to 100mA. This may be easily taken from the batteries on-board the ROV hulls
or elsewhere.
Stepper Motor Connections
To produce the minimum amount of radiated noise, the motor leads are of a twisted construction.
The cable has a requirement to be
screened, with the screen
connected to an earth at the drive
end and to the motor body at the
motor end. The motor lead
configuration is shown in Figure
52.
Figure 52: Six lead motor of unipolar drive.

71
At each node of the stepper motor controller, labelled ports of a range of + A - D + may be found,
which corresponds to specific wiring from the stepper motor. Table 11 shows a simplistic wiring
colour guide for the stepper motor used.
Table 11: Stepper motor controller wiring guide.
Labelled Port + A B C D +
Designated
colour wiring
Red Yellow Black Orange Brown Red
The two red wires corresponding to the centre tap (+) are found grouped alongside the two wires
corresponding to them as three wires will exit from the top and bottom portion of the stepper
motor. Figure 53 below shows the Phidget stepper motor controller with the labelled ports.
Figure 53: Phidget’s 4 Stepper motor controller.
Control Program and myRIO Implementation
The provided libraries from Phidgets are not compatible with LabVIEW on a 64 bit Linux based
operating system. As the myRIO has the capability to program a processor running a real time OS
and a customizable field-programmable gate array (FPGA), the myRIO processor may be
programmed in C/C++ using the default shipping personality. However, it is only possible to
customize the FPGA through the use of LabVIEW. So, the operation of the stepper motors is driven
through the use of C/C++ program code implemented through LabVIEW.

72
In the development of the C++ code for the system, the required libraries were available through
download on the Phidgets website. The code was developed on an external Linux based operating
system using Eclipse CDT (C/C++ Development Tooling) which provides fully functional C and C++
integrated development Environment (IDE) based on the Eclipse platform. The fully implemented
code may be found within the attached CD.
Further Development of the Control Program
As the C++ program developed is not yet fully compatible with the myRIO, further developments
will be required for full integration into the system design. Steps necessary for development of the
code are discussed.
With the developed code provided and with the use of Eclipse, a shared library may be formed,
intended to be shared by multiple executable files. Program modules may be loaded from these
individual shared libraries into memory at run time. Eclipse gives the capabilities of developing
these shared libraries. When directly connected to the myRIO, the shared library form may be
imported into the local directories of the myRIO at ‘/usr/local/lib/’.
To implement the code into the myRIO, the LabVIEW VI ‘Call Library Function Node’ may be used
to directly call the Linux shared library function. This creates an interface to call the existing
libraries written for use in LabVIEW.

73
Waterproofing
Figure 54 shows the final design for the system. It consists of a
waterproof hull containing the motor, a plunger inside a tube and
a tube to protect the sensor. The leadscrew was attached to the
plunger by means of a threaded hole in the plunger. This was
reinforced with glue. The sensor holder was glued to the plunger
so that when the leadscrew moved the plunger, it moved the
sensor holder in turn.
The design of the waterproof hull was based in the design for the
main hulls. The tube used was 5mm thick polycarbonate. This was
chosen to ensure that the hull could withstand the pressure of
depths of 20 metres. The hull used end caps which were sealed
with O-rings conforming to the BS ISO 3601-2:2008. The lower end cap needed to be drilled to
allow the leadscrew down to the plunger. Therefore further waterproofing was needed. At first lip
seals were considered but these were found to be more suited to sealing rotating shafts and may
not have been as effective at sealing the plunger travelling linearly. Instead grooves were
machined into the plunger to house O-rings, in accordance with BS ISO 2601-2-2008, which then
formed a seal against the surrounding tube. The hole in the lower endcap was 15mm in diameter.
By chance this was also the maximum diameter of the microsensor. The tube therefore had to
have a diameter greater than 15mm. To allow for space for the sensor holder and plunger 3mm
thick polycarbonate tube with a 26mm internal diameter was chosen. 3mm wall thickness tube
Figure 54: Final system design with
brackets.

74
was chosen as it was the same thickness of polycarbonate used for the main hulls and this had
been shown by FEA to be sufficient to withstand the pressure at 20m.
O-Ring Calculations
As stated in the previous section O-rings were used to seal the hull and the plunger. The previous
project had sized the O-ring housing grooves incorrectly and this had led to the hulls leaking. It
was important that the correct dimensions for the grooves were found using the equations from
Annex B of BS ISO 3601-2:2008 as shown below.
The first step was to determine the bore, the inside diameter of the tube, denoted as 𝑑4 and the
piston diameter, the diameter of the end cap or plunger, denoted as, 𝑑9. The next step was to
identify the type of application. The O-rings for the end caps were identified as being used in a
hydraulic static application and their compression ranges were found from Figure 55. The O-rings
sealing the plunger were used in a hydraulic dynamic application and their compression ranges
can be found in Figure 56.
Figure 55: Compression ranges of O-rings for hydraulic static applications (BS ISO 3601-2-2008).

75
Figure 56: Compression ranges of O-rings for hydraulic dynamic applications (BS ISO 3601-2-2008).
Once the compression range had been found the depth of the housing, 𝑡 𝑥 could be found.
𝑡 𝑥 = 𝑑2 − [(𝐶 𝑛𝑜𝑚 × 𝑑2)/100]
Where 𝑑2 = the O-ring cross section and 𝐶 𝑛𝑜𝑚 = the nominal compression of the O-ring expressed
as a percentage.
The housing diameter, 𝑑3 could then be found by subtracting double the housing depth from the
bore of the tube.
𝑑3 = 𝑑4 − 2(𝑡 𝑥)
The depth of the groove was found from;
𝑔𝑟𝑜𝑜𝑣𝑒 𝑑𝑒𝑝𝑡ℎ =
𝑑9 − 𝑑3
2
The next step was to find the maximum inside diameter of the O-ring, 𝑑1,𝑚𝑎𝑥. BS ISO 3601-2-2008
recommended stretching the O-ring by 2% so 𝑑1,𝑚𝑎𝑥 was found from;

76
𝑑1,𝑚𝑎𝑥 = 0.98 × 𝑑3
Calculations for End-Cap O-rings
For the end cap O-rings the bore of the tube, 𝑑4, was 60mm and the piston diameter, 𝑑9, was
59mm. Figure 55 showed that for hydraulic static applications the compression range of an O-ring
with a 2.5mm cross section was between 13% and 30% so the nominal compression had to be
found.
𝐶 𝑛𝑜𝑚 = (𝐶 𝑚𝑎𝑥 + 𝐶 𝑚𝑖𝑛)/2
𝐶 𝑛𝑜𝑚 =
30 + 13
2
= 21.5%
The housing depth was then calculated;
𝑡 𝑥 = 2.5 − [21.5 × 2.5)/100] = 1.875𝑚𝑚
This gave a housing diameter of;
𝑑3 = 60 − 2(1.875) = 56.25𝑚𝑚
The depth of the grooves was;
59 − 56.25
2
= 1.375𝑚𝑚
Which led to a maximum O-ring inside diameter of;
𝑑1,𝑚𝑎𝑥 = 0.98 × 56.25 = 55.125𝑚𝑚
Therefore the O-rings chosen to seal the end caps had a cross section of 2.5mm, an inside diameter
of 55mm and were housed in grooves 1.375mm deep.

77
Calculation of Plunger O-rings
The bore of the tube was 26mm and the diameter of the plunger was 25mm. Figure 56 showed
that for hydraulic dynamic applications the compression range of an O-ring with a 2mm cross
section was between 13% and 26%. This gave a nominal compression of 19.5%. However it was
decided to use a larger compression to ensure that there was a good seal between the O-ring and
the tube so a compression of 25% was used.
𝑡 𝑥 = 2.0 − [25 × 2.0)/100] = 1.5𝑚𝑚
𝑑3 = 26 − 2(1.5) = 23.00𝑚𝑚
25 − 23
2
= 1𝑚𝑚
𝑑1,𝑚𝑎𝑥 = 0.98 × 23 = 22.5𝑚𝑚
Therefore the O-rings chosen to seal the plunger had a 2mm cross section, a 22.5mm inside
diameter and were housed in a 1mm deep groove.
Buoyancy Calculations
One of the objectives of the project was to get the ROV to be slightly negatively buoyant. This
meant that the weight and buoyancy of each component had to be found. As the models built in
Solidworks had been assigned material properties they could be used to get an estimate for the
mass of the component. The mass of the whole sensor deployment system including the brackets
was, according to Solidworks, 0.56kg. As the plunger moved up and down the amount of water
displaced changed. It was decided to calculate the buoyancy of the system when the plunger was
fully retracted and displacing the least water as this was where the plunger would be for most of
the mission. This meant that the plunger was approximately 10mm below the lower end cap.

78
Volume Displaced
There were two main volumes to calculate. The first was the motor hull. The second was the
volume displaced by the second tube from the lower end cap to the bottom of the plunger. Below
this was filled with water during the mission so no significant volume was displaced.
The volume displaced by the hull was;
𝜋(35 × 10−3
)2
× 135 × 10−3
= 5.195 × 10−4
𝑚3
The volume displaced by the second tube was;
𝜋(13 × 10−3
)2
× 60 × 10−3
= 3.186 × 10−5
𝑚3
The total volume displaced was;
5.195 × 10−4
𝑚3
+ 3.186 × 10−5
𝑚3
= 5.514 × 10−4
𝑚3
The mass of water displaced was;
1000 × 5.514 × 10−4
= 0.5514𝑘𝑔
The difference between the mass of the system and the mass of water displaced was;
0.56 − 0.5514 = 8.6 × 10−3
𝑘𝑔
This corresponds to a downward force of;
8.6 × 10−3
× 9.81 = 0.084𝑁
Solidworks estimated that the whole sensor deployment system had a mass of 0.56kg. As shown
above the mass of water displaced was 0.5514kg. This meant that the system was slightly
negatively buoyant with an underwater weight of 8.6 grams in fresh water giving a downward

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