SD 270X Thesis project for the degree Master of...

Development of an automatic autonomous sensor

carrier for sound profile measurement in deep sea

Produktutveckling utav automatiserad

undervattensond för ljudprofilsmätning i havsmiljö

SD 270XThesis project for the degree Master of Science

Niklas Mö[email protected]

KTH, The Royal Institute of TechnologySweden

September 2016

i

Abstract

This Master Thesis main purpose was to answer the question "Can you measure orcalculate the velocity sound profile while performing a bathrymetric survey in an offshoreenvironment like the North Sea, without any interaction nor modification of the existingequipment?".This, since today underwater surveys are a complex and expensive operation to performwhere you either are mapping the sea floor or on a searching mission for a sunken wrecks.To achieve this successfully, one has to ensure that the accuracy of the position for everydiscovery or created map over the sea floor is entirely correct. This is an identifiedproblem since the bathrymetric device sends its position by sonar, which relies in thesound propagation velocity, which in return varies with the water density. In order toincrease the accuracy one need to determine the water density for all depths, i.e measurethe salinity and temperature between the towing ship and the device that travels closeto the sea bed. This because of layers consisting of fresh water and saltwater that neverentirely mixes with each other in the ocean.

The outcome of this project is a manufactured conceptual design of an autonomoussensor carrier that has the ability to measure temperature to a theoretical maximumdepth down to 150m. It ascends and descends autonomously with an propagation speedof 0.54m/s in a static condition along an existing tether line, connected to a bathrymetricdevice that follows the sea floor. The sensor carrier ascend and descends its motion withhelp of two connected drive wheels powered by an electric motor, combined with twohall sensors to to reverse its movement when reaching desired depth. It has the abilityto store sampled data onto a removable SD card, with a theoretical maximum enduranceof 6,2km and it can be handled by one single person.

Unfortunately, the concept as a whole is not entirely successful, and must thereforebe supplemented within some areas. The major occurrence is that the drive mechanismtender to slip along the tether when climbing in vertical direction with a risk of damagingthe tether coating. Furthermore one needs to increase the operational depth rating. Thisto be able to utilize the sensor carrier at all depths in the North Sea and also the BalticSea. However, the project as whole has achieved a solid framework and platform readyto be developed further in a future second version.

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Sammanfattning

Denna uppsats huvudsyfte var att på ett ingenjörsmässigt sätt kunna besvara frågan"Kan man mäta eller beräkna ljudets utbredningshastighet under en pågående djuphavs-mätning i exempelvis Nordsjön utan att behöva påverka eller att modifiera redan in-stallerad utrustning?"Denna fråga ligger till grund då dagens djuphavsmätningar är mycket komplexa ochkostsamma operationer där man kartlägger havsbotten eller att man genomför sökoper-ationer efter vrak. Detta kräver hög tillförlitlighet på utrustningen och dess noggranhetvid ett fynd eller när man mäter ut topografiska undervattenskartor. Ett identfieratproblem med detta är att med mycket hög noggranhet kunna säkerställa positionen påden aktiva undervattenssonden. Detta då den anger sin position via sonar, som direktberor utav ljudets utbredningshastighet, vilket i sin tur beror utav vattnets densitet. Föratt kunna förbättra noggranheten måste man således bestämma vattnets densitet för detaktuella djupet, indirekt genom att mäta salthalt samt temperatur. Dessa två parame-trar varierar berorende på rådande förhållanden då sötvatten och saltvatten skiktar sigi olika lager varav densiteten också varierar med detta.

Slutprodukten är ett koncept byggt i full skala med möjligheten till att mäta vattnetstemperatur ner till ett teoretiskt maximalt djup av 150m. Sonden klarar självständigtatt färdas upp och ner med en hastiget utav 0.54m/s i statiskt tillstånd längst en vajersom bogserar ett instrument för högupplöst sjömätning. Sonden transporterar sig medhjälp utav två drivhjul som drivs utav en elmotor och som styr sin riktning med hjälputav två hall-sensorer. Vidare så lagras all data på ett flyttbart SD kort, där sondenhar en teoretisk uthållighet på 6.2km som med enkelhet kan handhavas utav endast enperson.

Tyvärr så är konceptet ej helt framgångsrikt och måste såldes kompletteras inom ett parområden för att kunna bli operativt för industrin. Drivmekanismen uppvisar tendensertill att slira på vajern och skada denna vid horisontell uppstigning. Vidare så måstesonden designas så att den klarar att stå emot högre tryck för att kunna nå djupare.Detta krävs så att man kan nyttja detta instrument i både hela Nordsjön samt Östersjön.Projektet i sin helhet uppnått en stabilt ramverk och plattform som kan ligga till grundför att vidareutvecklas i en andra version.

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Acknowledgments

This thesis has been one of my biggest challenges so far. Mainly because I did not haveany previous experience within robotics design, CAD environment nor 3D-printing inthe start of this project. Thus, I had to use all available previous gathered knowledge tore-educate myself all over again.

At first I want to thank my neighbor officemates Elias Erstorp and Sebastian Thuné foryour technical support, good mood and especially all the help throughout this project.I have a hard time to believe that this thesis had come to its extent today without youtwo guys. Elias, I owe you a special thanks with your support regarding the electronicsand your educational way to teach me the basics regarding the Arduino environment.This since I did not have any experience at all in the beginning of this project and itturned out to be a major part of it. Many thanks to you Sebastian who always have beenavailable for answering questions and being supportive. Especially when the 3D-printerdecided to resign at the eleventh hour and also your feedback on the report. Thanksto Fredrik Wikerman for your help and contribution to all the endless discussions andthoughts that I had in the start of this project. Especially for all your support regardingLaTeX related questions, when the computer almost went through the window some-times in pure frustration.

Many thanks to my supervisor, Professor Jakob Kuttenkeuler for your support, patienceand understanding when life encounter setbacks. This in combination of giving me theright push when needed, has meant a lot to me.

Finally, I want to raise a big thanks to my girlfriend Jana who despite medical rea-sons, been able to put up with me and all my late nights and constant change of plansthrough out this entire thesis work, this with a lot more that could be added to it! Allheder åt dig!

Contents

List of Figures vi

List of Tables viii

1 Introduction 1

1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Objective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.3 Delimitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.4 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Frame of Reference 5

2.1 The Baltic Sea and the Gulf of Bothnia . . . . . . . . . . . . . . . . . . . 52.2 The North Sea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.2.1 Appearance of the tether line . . . . . . . . . . . . . . . . . . . . . 72.3 General Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.4 Existing Solutions and Systems today . . . . . . . . . . . . . . . . . . . . 92.5 Hypothesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3 Ideation and Concept Development 10

3.1 Initial concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103.1.1 Tether Climber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113.1.2 Torpedo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133.1.3 Frog Walker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143.1.4 Paddle Wheel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153.1.5 Buoy Ascender . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163.1.6 The Paraglider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173.1.7 Self-chargeable sensor carrier . . . . . . . . . . . . . . . . . . . . . 18

3.2 Pugh Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193.2.1 Pugh Evaluation Results and Conclusion . . . . . . . . . . . . . . . 20

3.3 Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223.4 Forces acting on the sensor carrier . . . . . . . . . . . . . . . . . . . . . . 23

3.4.1 Forces due to current . . . . . . . . . . . . . . . . . . . . . . . . . . 233.4.2 Frictional forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233.4.3 Gravity and Buoyancy Forces . . . . . . . . . . . . . . . . . . . . . 233.4.4 Irregular Disturbances . . . . . . . . . . . . . . . . . . . . . . . . . 24

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Contents v

4 Evaluation of Concepts 27

4.1 Evaluation of Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274.1.1 Paddle Wheel Evaluation . . . . . . . . . . . . . . . . . . . . . . . 284.1.2 Paraglider Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . 314.1.3 Tether Climber Evaluation . . . . . . . . . . . . . . . . . . . . . . . 324.1.4 Re-chargeable sensor carrier Evaluation . . . . . . . . . . . . . . . 33

4.2 Evaluation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344.3 Final Choice of Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

5 Final Concept Design 36

5.1 Wheel mechanism and transmission . . . . . . . . . . . . . . . . . . . . . . 375.1.1 Gear ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

5.2 Watertight Compartment . . . . . . . . . . . . . . . . . . . . . . . . . . . 395.3 Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

5.3.1 Data sampling and Data Acquisition components and sensors . . . 415.4 Hardware system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425.5 User Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

6 Evaluation of Design 45

6.1 Initial setup and usability . . . . . . . . . . . . . . . . . . . . . . . . . . . 456.1.1 Weight and dimensions . . . . . . . . . . . . . . . . . . . . . . . . . 46

6.2 Dry test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 466.3 Live test in the Archipelago . . . . . . . . . . . . . . . . . . . . . . . . . . 476.4 Results from test-run in the Archipelago . . . . . . . . . . . . . . . . . . . 47

6.4.1 Alternative drive wheels . . . . . . . . . . . . . . . . . . . . . . . . 496.4.2 Power consumption . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

6.5 Specification results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

7 Discussion 53

7.1 Transmission, gears and roller bearings . . . . . . . . . . . . . . . . . . . . 537.2 Alternative design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 547.3 Watertight compartment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 557.4 Reverse propagation direction with Hall sensors and magnets . . . . . . . 557.5 Software and sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

7.5.1 Sound velocity measurement device and data transmission . . . . . 567.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

A Appendix A 58

B Appendix B 68

Bibliography 70

List of Figures

1.1 Overview of todays operation. The green curves represents the sonarsignal transmitted to the three antennas at the ship. The Tow-Fish istowed behind the ship while scanning the sea floor. . . . . . . . . . . . . . 2

2.1 Map over the Baltic Sea. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.2 Map over the North Sea. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.3 FEM model for the tether line @ 1 knot. . . . . . . . . . . . . . . . . . . . 82.4 FEM model for the tether line @ 4.5 knots. . . . . . . . . . . . . . . . . . 8

3.1 Schematic overview of conceptual idea. An arbitrary sensor carrier ismarked in yellow on the tether cable with the Tow-Fish marked in black. . 11

3.2 Graphic illustration of the Tether Climber concept. The yellow cone marksthe stop where the carrier should reverse it movement before the Tow-Fish. 12

3.3 Graphic illustration of the Torpedo concept. . . . . . . . . . . . . . . . . . 133.4 A standard climbing ascender . . . . . . . . . . . . . . . . . . . . . . . . . 143.5 Linkage system from the previous clamping mechanism in the human rope

climbing project. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143.6 Principle drawing of the Paddle wheel concept. The three circles illustrates

the paddle wheel which is directly connected to the driving wheels on thetether. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.7 Graphic illustration of the Paraglider concept. . . . . . . . . . . . . . . . . 173.8 Conceptual illustration of the free-rolling Self-charging sensor carrier. . . . 193.9 Pugh matrix evaluation and results. . . . . . . . . . . . . . . . . . . . . . 203.10 Graphic illustration of Pugh Matrix results. . . . . . . . . . . . . . . . . . 213.11 Free Body Diagram for the sensor carrier. . . . . . . . . . . . . . . . . . . 24

4.1 Free body Diagram over the the Paddle Wheel concept. . . . . . . . . . . 294.2 Free Body Diagram for a 2D-foil. [Source] . . . . . . . . . . . . . . . . . . 31

5.1 Overview over the conceptual design, left side. A timing belt connects thetwo drive wheels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

5.2 Overview over the conceptual design right side. A timing belt transfersthe power from the motor to the first drive wheel. . . . . . . . . . . . . . . 36

5.3 Overview over the wheel mechanism. Plate springs are marked in red,contact wheels in gray, drive wheels in green and FL08 bearings in Blue. 39

5.4 Overview over the watertight compartment without the covering acrylictube. The battery is marked in green, sensors in red on the flanges, theArdulog in yellow and ESC-unit in pink. . . . . . . . . . . . . . . . . . . . 40

5.5 Software flow chart schematics. . . . . . . . . . . . . . . . . . . . . . . . . 41

vi

List of Figures vii

5.6 Software state diagram with all stages and log command illustrated. . . . 425.7 Circuit board with connectors for sensors and also the Ardulog micro con-

troller. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425.8 The Bar30 sensor developed by Blue robotics, mounted on one of the flanges. 425.9 Wiring schematics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

6.1 Tether placed on the two contact wheels with the mechanism open. . . . . 456.2 Tether in place with the mechanism locked. . . . . . . . . . . . . . . . . . 456.3 Chosen design of the Magnetic stop. . . . . . . . . . . . . . . . . . . . . . 466.4 Temperature curve from one static test run in the Archipelago. . . . . . . 496.5 Overview of the different manufactured driving wheels. . . . . . . . . . . . 496.6 Damaged housing on tether when using the manufactured gear drive wheels. 506.7 Summary of measurements for energy consumption. . . . . . . . . . . . . . 51

7.1 Conceptual design idea of an auto corrected timing belt. . . . . . . . . . . 55

List of Tables

3.1 Summary of pros and cons for the Tether climber concept. . . . . . . . . . 123.2 Summary of pros and cons for the Torpedo concept. . . . . . . . . . . . . 143.3 Summary of pros and cons for the Frog walker concept. . . . . . . . . . . . 153.4 Summary of pros and cons for the Paddle wheel concept. . . . . . . . . . . 153.5 Summary of pros and cons for the Buoy ascender concept. . . . . . . . . . 163.6 Summary of pros and cons for the Paraglider concept. . . . . . . . . . . . 183.7 Summary of pros and cons for the Self-charging concept. . . . . . . . . . . 19

4.1 Input data for the model with estimated values. . . . . . . . . . . . . . . . 284.2 Results for the model with constant inclination angle '. . . . . . . . . . . 284.3 Frictional components and energy dispersion. . . . . . . . . . . . . . . . . 304.4 Frictional components and energy dispersion. . . . . . . . . . . . . . . . . 33

6.1 Table of different drive wheels. . . . . . . . . . . . . . . . . . . . . . . . . 506.2 Summary of the results compared to the specification list. . . . . . . . . . 52

viii

Chapter 1

Introduction

Todays underwater surveys are a complex and harsh industry to operate within withvarying conditions when mapping the sea-floor. One major obstacle is the fluctuationsof the water density in terms of salinity and temperature differences.This variation cre-ates uncertainty regarding determination of the exact position of underwater measuringequipment since the technique with sonar relies upon the sound propagation velocity.

1.1 Background

Marin Mätteknik, also known as MMT is a measurement company stationed in Gothen-burg, Sweden. They are specialized in high-resolution hydrographic surveys for marineindustry and defense that needs mapping with extremely dense bathymetric data, forprojects within lakes, rivers and sea environments. MMT currently employs about 220employees with leading expertise within barometric and harbor surveys [1]. Throughoutthe years of surveys one has identified the issues with determine the sound profile dueto varying sea condition in terms of both salinity and temperature fluctuations. MMTuses a deep sea instrument towed in a tether line, referred as "Tow-Fish" in this reportwhen performing an underwater survey. It has the ability to document the sea floor andcollect and send requested data. This data is transmitted through the towing tetherto a vessel, see Figure 1.1. The Tow-Fish uses a sonar signal to send its position tothe ship, which is received by three antennas, that triangulates the received signal tocalculates the actual position. The distance between the three antennas is considered tobe relative short compared to the distance between the ship and the Tow-Fish, thus thesystem becomes sensitive to the sound propagation velocity for the signal when triangu-lating. To prevent miss-correlation when receiving the sonar signal from the Tow-Fish,MMT uses a technique called “dragging” where sensors are lowered down manually with

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Chapter 1. Introduction 2

a rope from the towing ship to collect information about temperature and salinity atthe towing ship position to correct the sound profile. The problem occurs when thetowing survey equipment is at far distance and depth from the towing ship, traveling onthe bottom of the littoral or offshore seabed where it transmitting its position and thedragging technique can’t reach. Thus the density is almost undetermined along the pathsince the different segment of both salinity and temperature are constantly varying andunknown where the sound profile changes with the density. The “dragging” technique isa time consuming operation to execute and it requires additional staff performing theextra task. Furthermore there is a high uncertainty regarding the position of the draggedsensors relative to the Tow-Fish and thus has the combined risk of developing incorrectand deviated data when calculating the position. There is also an aspect of entanglingthe rope with the towing line. Furthermore there is also a risk to entangle the rope intothe propellers that causes an overall major malfunction for the survey operation. Theidea is to prevent this situation when using the dragging technique and instead use theexisting towing tether for the survey instrument and from there calculate or measure thesound profile for all depths between the ship and the Tow-Fish. This to eliminate theexcessive staff used for the dragging technique and far-most eliminate all the combinedrisks of uncertainties regarding position but also to avoid to entangle todays auxiliaryequipment.The mission will be to design and develop some sort of equipment that can be used, butat the same time not affect today’s equipment, and completely independent collect anddeliver the needed data.

Figure 1.1: O verview of todays opera t ion. T he green curves represents t he sonarsignal t ransmit ted to t he t hree antennas a t t he ship. T he Tow- F ish is towed behind

t he ship while scanning t he sea floor.


1.2 Objective

The objective is to design, evaluate and develop a conceptual operational and waterproofautonomous sensor carrier with the ability to carry sensors designed for measuring salinityand temperature in deep-sea water environment. The sensor carrier should be designedto reach and operate at a maximum required depth of 1000m. Furthermore it should bedesigned with depth orientation and ability to independently return to the ship whenreaching the Tow-Fish. At close range to the towing ship the sensor carrier shall havethe ability to transmit collected data to for processing. The specification demands highrobustness to be able to withstand a cold harsh environment and with an endurance ofminimum 24 hours of operation. A final conceptual design will be evaluated and readyto be presented by the end of this project. The primal focus shall rely on robustness andusability for the operators and foremost clarify the potential of implementing a designedconceptual idea into reality.

1.3 Delimitations

The project will be limited to include a conceptual design of a functional autonomoussensor carrier, tested to fulfill stated requirement suited for MMT. Thus, the project islimited to not include a final product for the survey industry. Furthermore the concep-tual design will not include a validation of how to send and process information at theoperating ship. Also, it is not specified that the data should include any global positionof the sensor carrier more than depth orientation.

1.4 Methodology

The initial phase in this project is focused upon collecting essential information aboutdeep-water survey operations and the environment to be able to identify vital parametersand to identify problems connected to it. A research and literature study is carried outto collect essential and extensive information regarding different systems and solutionstoday, where references are to be found in literature and eventually throughout inter-views with professionals within the survey industry. From the information research andthe literature study several concepts will be presented, where a final concept is chosenthroughout a simple validation cycle. Last is the design and engineering developmentphase. The development phase will include a full-scale constructed concept model, detail


designed and validated to see if it is doable to implement regarding operational require-ments. In the end of this thesis, a recommendation will be given as a base in order tofurther develop a final concept.

Chapter 2

Frame of Reference

In this chapter one examinees the prior area, mainly the Baltic Sea and the North Seaconditions to identify the parameters that is of vital interest for the project. Mainly oneaims to collect data in terms of salinity and temperature variation and operational depthsfor the region.

2.1 The Baltic Sea and the Gulf of Bothnia

The Baltic Sea and Gulf of Bothnia is usually referred to the same region but correctlyit is separated from each other in the region of Åland, see Figure 2.1 [2]. The BalticSea is situated in middle of Scandinavia with Sweden on the west and Finland on theeast side and the north Europe coast line in the south. Its breach water characterizesthe marine area and it is one of the most harshest marine environmental places on earthto operate within. This in terms of extreme weather and freezing temperature includingice drifts during the winter season due to its near location to the artic circle. The watertemperature strongly correlates with the ice melting seasons where it can drop down toonly 1 °C in the Gulf of Finland in May to over 16 °C in August. [3]. The salty Atlanticwater flows through Skagerak and Kattegatt and is mixed with the contribution of freshwater from rivers and streams. The fresh water flows from the coast-land, mainly fromthe Gulf of Bothnia in the north where the main rivers from the Swedish and Finnishhighlands has their main outlets. Salt and fresh water have different density where saltwater is the heavier one and thus located on the bottom of the sea floor with freshwater located on the surface. The boundary between these water masses occurs in theBaltic Sea in two or more layers at depths of 40-80 meters, where these layers never mixcompletely with each other. The permanent salinity stratification varies between 6-8 hat surface level and 11-20 h in bottom waters [4].

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Chapter 2. Frame of Reference 6

Figure 2.1: M ap over t he B alt ic Sea.

2.2 The North Sea

The North Sea is located in the northwestern part of Europe surrounded by Great Britain,the west Norwegian coast line and the north Europe coastline. It connects with theAtlantic ocean in the north, English Channel in the southwest and with the Baltic Seathrough Skagerak and Kattegatt, see Figure 2.2 [5]. The topography of the North Seais quite unique with an average depth of only 95m but with a maximum depth of 700m,located along the Norwegian Trench in Skagerrak combined with very shallow parts in theopen regions, especially around Dogger Bank. The water climate is mainly influenced bythe main inflow of salt water from the Atlantic Ocean which has a large annual variationcausing great fluctuations. There is also a small contribution of salt water inlet fromthe English channel and the average salinity concentration at open water areas is yearlyaround 35 h. This with an addition of 32-34,5 h variation for the coastal regions dueto the contribution of the fresh water outlets from the English highlands and the largerrivers Rehn, Elbe, Wesser and also from the European and Norwegian coast lines. Dueto the brackish water inflow from the Baltic region the salinity level is much lower near


the Skagerrak inlet and varies between 10-34 h. The average yearly temperature isaround 9,5°C for the north part close to the Atlantic with an addition of a large seasonalfluctuations in the south regions due to the massive addition of fresh water in combinationwith shallow regions, creating a complex environment for underwater surveys [6].

Figure 2.2: M ap over t he Nor t h Sea.

2.2.1 Appearance of the tether line

The appearance of the tether line is of vital interest, this since it form how steep thecurvature of the tether is and thus the climbing elevation. By utilizing a FEM softwaredeveloped by MSY [7] one simulates the wire appearance for different dynamic loadconditions. The load of interest is when a ship has a propagation speed of about 5 knotswith a side current acting on the Tow-Fish. The applied side force is assumed to be 100Nin Surge direction and -300N in Sway direction (I.e, the force is acting on the port sideobliquely directed toward the bow as seen from the boat’s perspective.) The wire weightis estimated to 1.48kg/m with a diameter of 12mm and a total length of 2000m. The


case addresses two different velocities for the ship, 1 and 4.5 knots. The result for thetether appearance can be obtained in Figure 2.3 and 2.4.

Figure 2.3: F E M model for t hetet her line @ 1 knot .

Figure 2.4: F E M model for t hetet her line @ 4.5 knots.

2.3 General Requirements

From Figure 2.3 and 2.4 one can conclude that the sensor carrier needs to be able toclimb both horizontal and in an almost vertical direction. Hence one can set up an overallgeneral requirement list, which follows below.

The sensor carrier must:

• - be robust enough to operate independently between the Tow-Fish and the shipwithout any aiding or interference with the crew, regardless weather conditions,along a 2000m tether

• - have a minimum endurance of at least 24 hours of operation, this excludes re-charging of batteries

• - be able to carry sensors to measure a depth of maximum 1000m and a minimumsalinity variety of 0-35 h

• - not affect the Tow-Fish when neither sweeping nor moving

• - have the ability to transmit data between itself and the command bridge and notinterfere with the data acquisition from the Tow-Fish

• - not affect the towing tether casing

• - be able to collect and storage data for at least 24 hours of operation

• - be easy to handle, carried and ability to be installed by only one person


• - be designed to reach a maximum required depth of 1000m

• - be designed to resist smaller ice floes and ice fouling

2.4 Existing Solutions and Systems today

There is a large variation of developed robots today, designed to climb horizontal or ina vertical direction through different means. It can be achieved by either arm climbingan obstacle, clamping mechanisms, rope ascenders, piston mechanisms or wheels. Onearea of interest is within Search and Rescue Operations where robots are designed toovercome obstacles and to operate in harsh environments and dangerous terrain. TheR.E.S.C.U.E robot designed by TEAM RESCUE is remote controlled and have four in-dependent arms to climb obstacles, designed to withstand water and dust and to operatein disaster areas [8]. Furthermore, a rope climbing robot inspired by copying the motionof a sloth bear climbing has been developed by a team in Kanpur as a design project toclimb an inclined rope, similar to the tether line but above water level [9]. Similar tothis is a piston-mechanism rope climbing robot, designed by Y.C. Koo et. al [10]. Thesetypes of configuration is considered to not be suitable for underwater operation since itwould too great of a challenge to maintain contact with the tether and will thereforenot be evaluated in this project. Another concept developed by Wolfgang Fischer andRoland Siegwald is inspired by utilizing the clamping mechanism in human rope climb-ing [11]. This type of set-up is of interest and it will be taken into consideration duringthe preliminary conceptual designs.

There has not been found any similar or applicable concepts during the initial feasi-bility study that entirely fulfills the requirements and the overall concept of ascending arope or a tether line underwater.

2.5 Hypothesis

The hypothesis for this Master Thesis is stated that the general outcome will be anevaluated concept that can be further developed for market implementation. The concepthas the ability to solve its task by measuring the sound-profile and have the ability tooperate independently for a minimum 24 hour endurance. The concept will be designedto transfer requested information for processing and analysis. The sensor carrier will bedesigned in a suitable size to be handled and mounted by one person at the towing ship.

Chapter 3

Ideation and Concept Development

The Ideation and Concept Development stage is necessary and important since all gen-erated ideas will be presented and evaluated against each other. This is truly importantsince it is difficult to reverse the process and go back and redo the work later throughthe project. All ideas are presented and evaluated against each other with a methodologydeveloped by Pugh [12].

3.1 Initial concepts

The main idea is to use the existing towing line to reach the desired depth to measuresalinity and temperature for the operation area. This can be achieved by designing a self-propelled sensor carrier which travels along the tether to a desired depth; simultaneouscarries sensors for sampling temperature and salinity data. The conceptual idea includesthat the sensor carrier starts from a dock station at the towing ship at Position (1)according to Figure 3.1. From there it travels along the tether, where it will reverse itsmovement at its end Position (2) near the Tow-Fish, and then turn back towards theship at Position (1) again. This configuration enables data acquisition while performingan underwater survey at the same time with no demands of external wires nor anyintervention on the existing towing tether. Thus one eliminates the risk of tangling thatotherwise would interrupt the survey operation.

10

Chapter 3. Ideation and Concept Development 11

Figure 3.1: Schema t ic overview of concept ual idea. A n arbit rary sensor carrier ismarked in yellow on t he tet her cable wit h t he Tow- F ish marked in black .

3.1.1 Tether Climber

The Tether Climber concept climbs with help of two wheels connected to an electricalmotor, sealed in a watertight compartment with room for sensor and a battery package.Four wheels will be in immediately contact with the tether where two are free rolling andtwo are drive wheels, according to the illustration in Figure 3.2. The major advantagefor such a configuration is the simplicity in transferring power from the electric motor tomove it using friction from the wheels that acts against the tether. Furthermore one canreverse the direction of motion by reversing the motor rotation. The major disadvantageis the risk of disturbances along the tether regarding fouling and icing and thus a risk ofslipping due to lack of friction against the tether. A summary of all pros and cons arepresented in Table 3.1.


Figure 3.2: G raphic illust ra t ion of t he Tet her C limber concept . T he yellow conemarks t he stop where t he carrier should reverse i t movement before t he Tow- F ish.

Table 3.1: Summary of pros and cons for t he Tet her climber concept .

Advantage Disadvantage

+ High friction between wheels andtether.

- Driving wheels could affect and dam-age the protective cover on the tetherif low friction occurs. (Driving wheelsstarts to slip)

+ Simplicity in both direction move-ments and ability to reach above sealevel.

- Uncertainties regarding disturbancesalong the tether due to icing and foul-ing.

+ The body can be built in two half’s,assembled and mounted homogeneousaround the tether.+ The design can be very compact dueto less auxiliary equipment.


3.1.2 Torpedo

Similar to the Tether Climber is the Torpedo that is also directly attached to the towingline but with a free rolling wagon four free spinning wheels. Here a electric propeller isused instead of a direct gear transmission as main propulsion. The sensor carrier willhave the ability to turn at Position (1) and Position (2) respectively by a motorizedturntable. The main advantage is that the concept is entirely free rotating around thetether, hence the it has the potential to handle side acting currents better than theTether Climber. An obstacle to overcome is to solve how it should be able to follow thetether and not drift sideways. Another main drawback is the lower efficiency by utilizea propeller and also its lack of ability to reach above sea level. A summary of all prosand cons are presented in Table 3.2.

Figure 3.3: G raphic illust ra t ion of t he Torpedo concept .


Table 3.2: Summary of pros and cons for t he Torpedo concept .


+ Free rotation around towing line. - Low efficiency compared to direct fric-tion propulsion.

+ The body can be built in one rigidbody mounted on an external platformattached to the tether.

- Uncertainties regarding disturbanceslong the tether due to icing and fouling.

+ Could be designed to “sink” with helpof currents and ascend with help of pro-peller/s.

- Rather complex solution for both di-rection movements. (Ability to turn)

- Demands a more complex mechanicalsolution in terms of drive line comparedto contact wheels, hence increasing therisks of malfunction.-Problem to follow the tethers naturalappearance with a risk to drift side-ways.

3.1.3 Frog Walker

Climbers who use the technique Frog walking while ascending a climbing rope is theinspiration for the conceptual idea. In simple terms one connects two rope ascenders toa linkage arm. The procedure is to lock one ascender and simultaneously slip the secondone. When the second ascender has reached its end position, it locks and the secondslips after. This creates the frog walking pattern where the linkage is controlled withan electrical servo. The drawback of such configuration is that ascenders are generallydesigned to only lock against a tether in one particular direction. The main advantageis that one can utilize the currents from the towing boat propulsion velocity and sinkdown to desired depth and from there climb up, hence it has a potential of being a veryenergy efficient concept. A summary of all pros and cons are presented in Table3.3.

Figure 3.4: A st andard climbing as-cender

Figure 3.5: L inkage system from t heprevious clamping mechanism in t he

human rope climbing pro ject .


Table 3.3: Summary of pros and cons for t he Frog walker concept .


+ Tremendous high friction againsttether due to ascender lock mechanismthat allows heavy loads.

- Rather complex solution for both di-rections of movements (To reverse theclimb step function).

+ Energy efficient concept due to one-way electrical propelled climb direction(ascending).

- Uncertainties regarding disturbanceslong the tether due to icing and fouling.(Investigate further)

+ Could be designed to “sink” with helpof currents when ascending.

- Demands a more complex mechanicalsolution in terms of drive line, increas-ing the risks of malfunction.

+ Simplicity in measuring the positionof the sensor carrier on the tether byutilizing the distance for each ascender.

- very complex to use servos underwa-ter. (Keep watertight)

3.1.4 Paddle Wheel

The conceptual idea is to use the acting current that is directly proportional to the shipspropagation velocity as a main propulsion source for a one way ascending motion alongthe tether between Position (1) and Position (2) according to Figure 3.1. This couldbe achieved by designing a Paddle Wheel mechanism that is directly connected to thewheel mechanism on the tether. When returning from position (2) to start ascendingone engages the paddle and thus only utilize the current to propel the sensor carrier. Todescend the paddle wheel, the paddle is disconnected and the sensor carrier self-sinks byits own weight. This configuration is considered to be high effective in terms of efficiencybut rather complex in terms of mechanical design. A summary of all pros and cons arepresented in Table 3.4.

Table 3.4: Summary of pros and cons for t he Paddle wheel concept .


+ Energy efficient concept due to one-way mechanically propelled climb di-rection (ascending) and free falling forthe descending motion.

- In reality it will be complicated to de-sign the propeller to be efficient enoughsince it has to interact perpendicular tothe free stream where the cable’s anglevaries along its length.

+ No demand for a power pack de-signed for propulsion, i.e. save weightand space to make the hull light andsmall.

- No ability to reach above sea level. Apractical concern in terms of data ac-quisition and inspection.

- Entirely dependable on the shipspropagation velocity.


Figure 3.6: P rinciple drawing of t he Paddle wheel concept . T he t hree circles illus-t ra tes t he paddle wheel which is direct ly connected to t he driving wheels on t he tet her.

3.1.5 Buoy Ascender

Instead of using mechanical power as main propulsion source, one could utilize gravityto descend and the buoyancy force for the reverse ascending movement. This could beachieved by designing an expandable bladder that will adjust the buoyancy force for thesensor carrier by using compressed air. The main advantage is that there is no needof electrical power for propulsion. The drawback is that the depth rating, i.e. higherpressure for decreasing latitude, which will affects the bladder in terms of compres-sion. Furthermore the expandable bladder requires to be dimensioned to withstand thetremendous pressure at a 1000m depth. A summary of all pros and cons are presentedin Table3.5.

Table 3.5: Summary of pros and cons for t he B uoy ascender concept .


+ Free mounted along the tether (con-trol loops instead of spinning wheels incontact with the tether).

- Requests a complex construction ofthe bladder to be able to withstand thepressure at a 1000m depth.

+ Rather energy efficient propulsionsystem due to no friction losses compo-nents in terms of a drive line for propul-sion.

- No ability to reach above sea level. Apractical concern in terms of data ac-quisition and inspection.

- Rather complex solution for both di-rections of movements. Need of an ad-vanced control system to correct thebuoyancy for varying depth.


3.1.6 The Paraglider

The main idea is to take advantage of the occurring current due to the propagationvelocity of the towing ship by utilize a sensor carrier with a main foil to create a liftingforce to move along the tether. By assuming that the direction of the tether has itsdirection according to the resultant of the propagation direction with an assumption ofa stationary condition for a foil to operate within. By this one simply implies that thereare no direct side current acting upon the foil since the tether will strictly follow theresultant stream. Thus the sensor carrier will act directly against the current, and thefoil would create a lift force. By mounting the power package on a far distance belowthe foil one would also create a righting moment for the sensor carrier to be able tomaintain stable along its operation route. The sensor carrier will be attached with freespinning wheels on the tether with a frame that attaches the foil. A small gyroscope willmeasure the angle to adjust the foil attack angle with a small electric servo. The maindrawback for the concept is the concerns regarding the turbulence dispersed from thepropellers from the towing ship. There is a major risk of failure for the sensor carrierwhen operating in such a condition. A summary of all pros and cons are presented inTable3.6.

Figure 3.7: G raphic illust ra t ion of t he Paraglider concept .


Table 3.6: Summary of pros and cons for t he Paraglider concept .


+ Can be designed for both ascent anddescending motion without any electricpropulsion i.e. a highly efficient solu-tion.

- There is an imminent risk that thesensor carrier affects the cable’s natu-ral appearance by lifting it or move itsideways.

+ Free mounted along the tether (freespinning wheels).

- Uncertainties regarding the sensitivityregarding disturbances along the tetherdue to possible irregular currents, espe-cially the turbulent region behind thetowing ship.

+ Simple construction in terms of adrive line, which will consist of a foiland a battery pack for the servo.

- Requires towing velocity relative thecurrent from the ship to be able to op-erate.

3.1.7 Self-chargeable sensor carrier

The main idea is to use the advantages from the Tether Climber concept with the robustdrive line and the ability to operate in the turbulent region behind the towing ship andalso reach above sea level in order to easy transmit information on deck level. This incombination with the benefits from the Paddle Wheel where the design allows energyextraction from the acting current. Instead of transfer the energy into mechanical workone uses it to transfer the circular motion from a propeller and transfer it into electricityfor recharging the battery pack. The advantage of such a configuration is the potentialto significantly increase the sensor carriers durability. When the sensor carrier does nothas the required amount of power to ascend itself upward it will descend to Position(2) to recharge until sufficient power level is reached to start descend again. In orderto maintain the propeller perpendicular to the acting stream the concept needs to beentirely freely moving. The main drawback is the significant risk of increased resistancedue to the interaction of the propeller that will disturb the flow. Hence it is a risk thatthe net beneficial effect from the propeller is negative and the result would be that theascending motion will cost more than it will generate in terms of re-charging ability.


Figure 3.8: C oncept ual illust ra t ion of t he free-rolling Self-charging sensor carrier.

Table 3.7: Summary of pros and cons for t he Self-charging concept .


+ Increased durability due to self-charging ability.

- Risk of increased resistance duringpropulsion because of the propeller ef-fect.

+ Ability to reach above sea level,which simplifies data acquisition at thetowing ship.

- Uncertainties regarding disturbanceslong the tether due to icing and fouling.(Investigate further)

+ Due to extra resistance it would beeasy to design the sensor carrier to sinkwith help of currents and ascend withhelp of the wheel platform.

- Rather complex solution with addi-tional equipment in terms of propeller,generator and a transformer, risk formalfunction.

3.2 Pugh Evaluation

In order to be able to choose the most favorable concept to one performs a study toconfront each concept with each other. This in order to choose the best concepts forfurther investigation. This is performed by constructing a rational method accordingto Stuart Pugh and rate each concept and its properties against a main existing designas a reference object. By doing so one can determine if a concept has more favorable-, equal or less favorable properties compared to a baseline concept. By setting up amatrix with all relevant criteria and engineering characteristics by which the conceptswill be evaluated against. As a reference concept one has chosen the current design withdragging the sensors. Also, there is a three grade level scale for comparison with weight


level for each criterion. If the engineering characteristic is better gives a (+), worse (-)or equal characteristic is set to (S) into the ranking matrix. Furthermore, each criterionhas a 13-grade number scale of importance to meet customer needs, which is multipliedwith the engineering character. The sum of all (+), (-) and (S) with its number scale willhand back the overall score for each concept in a matrix, see the next chapter. Thus onewill be provided with a weighted overall score obtained in the matrix for each concept asa basis for choosing the best option to design. Some of the engineering characteristics arenot comparable with the current Dragging design due to a different types of operationmode and has then been marked as Not comparable. The inputs for the Pugh evaluationcan be obtained from Figure 3.9 and the results are clarified and illustrated in Figure3.10 on the next page.

3.2.1 Pugh Evaluation Results and Conclusion

Figure 3.9: P ugh ma t rix evalua t ion and results.

From Figure 3.9 and Figure 3.10 one can obtain that the Self-chargeable sensor carrierconcept is the most promising alternative with the Tether Climber as the second and theParaglider as third. The Paddle Wheel concept comes out as number forth comparedto the reference concept with todays Dragging technique. Thus shall these concepts be


Figure 3.10: G raphic illust ra t ion of P ugh M a t rix results.

further investigated after the first round of rating. The Frog Walker concept is not con-sidered to not be able to reverse its movement with the current design and is phased outin the first round of evaluation. The last concept with the Buoy Ascender is consideredto be a non sufficient solution and also its overcomplexity to withstand the pressure at1000m depth and to follow the tether and thus scrapped entirely.


3.3 Model

In order to evaluate each concept in terms of efficiency and power output, one has toderive a method to calculate the total required energy it takes to finish one route alongthe cable. The initial step is to set up a mathematical model where a local positivedefined coordinate system is implemented that follows the cable direction. The modelwill take into account hydrostatic - and hydrodynamic forces and also friction. Oneassumes an incompressible fluid and body, thus the density is set to be constant for alldepths. Furthermore it is assumed that all currents in the fluid are acting in one setdirection with constant flow proportional to the ships propagation velocity, vs. A FreeBody Diagram for the sensor carrier can be obtained from Figure 3.11. All assumptionsfor the model is summarized below.

1. Incompressible fluid.

2. All irregular disturbances are neglected in the model.

3. Constant mass flow acts straight toward the sensor carrier.

4. Constant propagation velocity vs for the towing ship and constant propagationvelocity vp for the sensor carrier.

5. Constant inclination angle ' for the tether, i.e. one assumes the tether to be in astraight line.

6. Laminar flow.


3.4 Forces acting on the sensor carrier

When deployed in water the sensor carrier will experience a combination of differentloads that will affect the behavior and its movement. These loads can be consideredas forces acting on an arbitrary rigid body in equilibrium state. The forces depend oncurrents, propagation velocity of the ship, size of the sensor carrier and also the sensorcarriers weight.

3.4.1 Forces due to current

Due to the fact that a ship maintains a constant propagation velocity, vs it will tow thesensor carrier when mounted on the tether. This in addition with the sensor carrierspropagation velocity vp along the tether contributes to increased viscous forces. Theseviscous forces acts on the body and varies depending on the shape, surface finish andsize of the sensor carrier. Hence it is taken into account when designing the hull, wherethe designer must consider and pursue a streamlined and symmetric hull-body to lowerthe viscous forces.

3.4.2 Frictional forces

The frictional force occurs between the correcting wheels or control loop that is in contactwith the tether while moving at constant a velocity. It is assumed that the frictionalforce, Fµ will act in direct opposite direction of the propagation velocity, vp and thuswith the same inclination angle as the driving force, FT .

3.4.3 Gravity and Buoyancy Forces

Gravity affects the sensor carrier due to its body mass, which is assumed to be constantover its operational cycle since there is no variation in changing auxiliaries or loss interms of fuel or similar. Furthermore the buoyancy force, FD will act as an lifting forceaccording to Archimedes principle. It is assumed that the body is incompressible andthus the buoyancy force is considered as constant. It is beneficial to design the carrierwith a neutral ratio between gravity and buoyancy to prevent the sensor carrier fromfloating or sinking. A large gravity force will deflect the natural shape of the tether witha risk of disturbing the Tow-Fish. A dominant buoyancy force will affect the towingtether in the same perspective by lifting the tether and affect its natural shape. Oneshall consider a neutral buoyancy condition as preferable as a base to avoid undesiredbehaviors.


3.4.4 Irregular Disturbances

One has to take into account that besides the above stated forces there will also beelements of other irregular disturbances like: waves, wind, sea grass and also turbulencesfrom propellers, just to mention a few. These types of irregular disturbances are notconsidered in the model for the sensor carrier.

Figure 3.11: Free Body D iagram for t he sensor carrier.

From Figure 3.11 in an equilibrium state for the sensor carrier the thrust force FASCENDTfollows the tether direction when ascending with a global coordinate system orientatedaccording to Figure 3.11 one derives:

F

ASCENDT = FD · cos(') +mg · sin(') + Fµ � FB · sin(') (3.1)

And for the case when the sensor carrier is descending (the reversed direction accordingto Figure 3.11) one can derivate the following expression for the descending thrust force,F

DESCENDT according to:

F

DESCENDT = �FD · cos(')�mg · sin(') + Fµ + FB · sin(') (3.2)

Where the buoyant force FB is defined according to Archimedes principle, which impliesa body immersed in a fluid with a density, ⇢w actuated by a lifting force is equal to theweight of the liquid displaced:


FB = ⇢w · g · V (3.3)

Here g represents the gravity acceleration and V is the volume of the body immersed inthe fluid. The drag force in the ascending direction FASCENDD occurs due to dynamicpressure from the acting current [13] generated by the ship propagation velocity vs witha surplus of the sensor carrier velocity vp moving against the current, thus:

F

ASCENDD =

1

2CD⇢wAp(v

2s + v

2p · cos(')) (3.4)

And for the case when the sensor carrier is descending, one as to adjust Equation 3.4and instead subtract the sensor carrier velocity vp according to:

F

DESCENDD =

1

2CD⇢wAp(v

2s � v2p · cos(')) (3.5)

Where CD is the drag coefficient on non-dimensioned form, vp is the sensor carriers prop-agation velocity while moving along the tether and vs is the ship propagation velocity.Ap is the reference area of the immersed body, perpendicular to the acting current field.Finally the frictional force Fµ occurs since there is friction between the towing tetherwhere µ varies with the number of contact points, acting in opposite direction of therequired thrust force FT , directly proportional to the normal force N :

Fµ = µ ·N (3.6)

The total energy required to ascend the sensor carrier is equal to the total work Q,demand to move the sensor carrier from Position (1) to Position (2) along the tetheraccording to Figure 3.11.When all acting forces are known one can derive an expression for the total work requiredto ascend and descend along the path. Work is defined as the amount of energy convertedwhen a transfer takes place under the action of a force integrated over an arbitrary web.The total required work Q when ascending is then equal to the thrust force FASCENDTwhich previously has been derived in Equation 3.1 and integrated over the web:

Q

ASCEND =

2Z

1

(FASCENDT ('))dS (3.7)


Together with Equation 3.1 one gets the following expression:

Q

ASCEND =

2Z

1

(FASCENDD · cos(') +mg · sin(') + Fµ � FB · sin('))dS (3.8)

In a similar matter, with the thrust force FDESCENDT derived from Equation 3.2 thetotal work for descending the sensor carrier is then equal to:

Q

DESCEND =

2Z

1

(�FDESCENDD · cos(')�mg · sin(') + Fµ + FB · sin('))dS (3.9)

Equation 3.3 - 3.6 have been left out for a more transparent expression for the reader tounderstand.

Chapter 4

Evaluation of Concepts

In this chapter one analyzes the previous rated concepts to determine the most favorableconcept. The evaluation consists of rather simplified calculations together with engineer-ing point assumptions to give an indication of the theoretical range and also efficiency.In the end of the chapter one decides upon the most suitable design to continue with.

4.1 Evaluation of Concepts

In order to further be able to evaluate all concepts one assumes a number of values foran arbitrary sensor carrier, that is implemented into the model. The input values inTable 4.1 are considered reasonable for rough estimate calculations to give a hint of thetotal required energy needed for propulsion in order to ascend respectively descend thesensor carrier. Furthermore, a rough approximation is that the tether is considered as astraight line between the towing boat and the Tow-Fish. Thus the inclination angle ' isassumed to be constant for the entire tether length.

27

Chapter 4. Evaluation of Concepts 28

Table 4.1: Input da t a for t he model wit h est ima ted values.

Variable Abbreviation Value

Weight, sensor carrier m 5, 5kgVolume, sensor carrier vp 0, 005m3Friction coefficient µ 0, 6[�]Normal force N 5, 0NDensity, Brecht water ⇢ 1001, 0kg/m3Gravity constant g 9, 81m/s2Length of sensor carrier LASC 0, 3mTowing ship speed vs 2, 1m/ssensor carrier speed vp 0, 5m/sDrag coefficient for ASC CD 0, 5[�]tether length Ltether 2000, 0mFront area of ASC A 0, 015m2Inclination angle ' ⇡/4

From Table 4.1 one calculates all active forces for a constant inclination angle, ' withEquation 3.1 -3.9. All results can be obtained in Table 4.2.

Table 4.2: R esults for t he model wit h const ant inclina t ion angle '.

Variable Abbreviation Value @constant ' Eq.

Buoyancy force FB 49, 1N 3.3Viscous resistance, Ascending FASCENDD 27, 7N 3.5Viscous resistance, Descending FDESCENDD 25, 3N 3.4Frictional resistance Fµ 3, 0N 3.6Req. Thrust Force, Ascending FASCENDT 26, 0N 3.1Req. Thrust Force, Descending FDESCENDT �18, 3N 3.2Total Energy, Ascending QASCEND 52 · 103J 3.8Total Energy, Descending QDESCEND �36, 7 · 103J 3.9

From Table 4.2 one can conclude that there is a surplus of external forces acting in thedirection of motion for the descending motion. Hence, there is a possibility to use theacting current to self-sink to Position (2) regardless design.

4.1.1 Paddle Wheel Evaluation

To evaluate the Paddle wheel concept one aims to verify if there is enough power output interms of kinetic energy for a free stream acting on a solid disc with an area Ac and transferit into kinetic mechanical work for a one dimensional system. In the simplified model, oneassumes a free flow according Momentum theory, based on physics fundamental principleswhich idealizes propeller like a thin disc which momentarily slows in the fluid-pressuredifferential, and thus creates a reaction force which is proportional to the quantity ofmotion, that generates a resistance force R. Furthermore the fluid is considered as


incompressible whereof area ratios varies to maintain constant mass flow due to thevelocity loss. However, using this theory and approach does not consider the geometryof the actual propeller and thus in if needed in a second stage it has to be supplementedwith blade element theory or similar. This investigation is only carried out to give anindication of the theoretical potential power output from a free stream to validate if itfulfills the requirements in terms of enough power to be able to ascend.

Figure 4.1: Free body D iagram over t he t he Paddle W heel concept .

For a one dimension system Power is defined as Force times Velocity. Thus for the modelaccording to Figure 4.1 one can derive:

Pin = R · (vA + vP · cos(')) (4.1)

Where the resistance R can be rewritten as a function of the dynamical pressure actingon the sensor carriers circular disc:

R = q ·Ac (4.2)

Ac is the disc area defined as a solid circular plate with a radius r and the dynamicalpressure q is defined according to Equation 3.4 from the previous chapter 3.3. Thus,one can derive from 4.1, 4.2 the following expression for the maximum theoretical inputpower from the free stream:

Pin = q ·Ac · (vA + vP · cos(')) =1

2CD · ⇢w · ⇡ · r2 · v3A · (1 + vp · cos(')) (4.3)

The total shaft power for propulsion is equal to the utility effect and it has to be equalor greater than the required effect:


Pshaft = Pin · ⌘tot � Preq (4.4)

Where all the internal losses ntot are explained in Figure 4.1:

ntot = nprop · ntrans · nshaft · nfric · nwheel (4.5)

All values for ntot can be obtained in Table 4.3 below.

Table 4.3: Frict ional components and energy dispersion.

Variable Abbreviation Value @constant '

Propeller efficiency nprop 0, 3Transmission efficiency ntrans 0, 6Shaft transmission efficiency nshaft 0, 95Frictional loss, wheel to wire nfric 0, 8Frictional loss, wheel mechanism nwheel 0, 9Total propulsive efficiency ntot 0, 12

The estimated required power to move the sensor carrier from Position (2) to Position(1) according to Figure 3.1 with a constant inclination angle ' = ⇡4 inserted with statedvalues from the result Table 4.2 is equal to:

Preq =EnergyTime

=52000 Joule

2000 m0,5 m/s

⇡ 13W (4.6)

Thus one can solve for the radius r for the propeller whit Equation4.3 inserted in Equation4.4 and set equal to Equation 4.6, gives:

r =

sPreq

12 · CD · ⇢w · v

3A · ⇡ · ⌘tot(1 + vp · cos(

'4 ))

r =

s13

12 · 1.28 · 10012, 13 · ⇡ · 0, 12(1 + 0, 5 · cos(

'4 ))

⇡ 7cm

This very simplified model indicates that it is plausible to use a propeller with a estimated30 % efficiency that will assist to propel the sensor carrier and theoretically achieve therequisite power with a CD = 1, 28 for a flat plate [14]. However with an auxiliary propellermounted on the sensor carrier with a diameter of around 14cm one will rapidly increasethe resistance which is not included in the calculations. Furthermore one has assumedlaminar flow where there is no interaction with the sensor carriers hull. The main issue


with such configuration is to maintain the propeller wings perpendicular to the flowwhen the sensor carrier ascends along the tether. Finally, when approaching Position (1)the free flow becomes extremely turbulent due to the propellers from the towing ship.Thus, the concept is considered to be very inefficient close to surface level. Hence, itis considered that the concept is somewhat plausible due to the previous estimationsand also that it has been successfully completed trials of vehicles on land that travelswith the help of the wind straight against the wind direction. But to utilize the sameconceptual idea underwater with an addition of a large number of variables interactingis still considered to be a large risk for failure.

4.1.2 Paraglider Evaluation

By making the assumption of that a free current occurs due to the ships tow speed vsone could extracts its energy for propelling the sensor carrier. The theoretical maximumlifting force that one could extract from the free current is by modulate the conceptby assuming a solid non-compressible thin foil that creates a controlled lifting force Lproportional to the angle of attack according to Equation 4.7 and illustrated in Figure4.2 [15] below.

Figure 4.2: Free Body D iagram for a 2D-foil. [Source]

L = q ·Awing · CL↵ · ↵ (4.7)

Where q is the dynamic pressure, defined for the ship towing speed, vs stated in Equation3.4 and ↵ is the foils angle of attack in radians. Furthermore Awing is the area of thewing profile assumed to be an arbitrary thin symmetric profile defined by its sectionalspan c and width b. For a thin foil one can set the 2D lifting coefficient slope CL↵ to itsits theoretical value 2⇡ according to Thin airfoil theory. Hence it is the variable Awingthat shall be determined to overcome the required thrust force FT . For a equilibriumstate with a right orientated coordinate system that follows FT one derives:


FT � FTOT · cos( )� Fµ = 0 (4.8)

Where is the inclination angle between FT and the Drag component D. From Figure4.2 one can conclude that the argument goes towards 90 degrees for a decreasing angle' when the tether angle is flatten out to a horizontal position. Thus one can’t solveEquation 4.8 since FT ? FTOT . Hence the practical issue and result whit this conceptis that a foil solution will lift the tether instead of moving itself against the acting freestream.

To overcome this issue it is required to more or less eliminate the drag component Dto ascend the sensor carrier with a forward motion, yet still with a very small resul-tant lifting force. Furthermore it would be of great challenge to make the foil conceptsuccessful to operate steady without getting affected by the turbulent region behind thetowing ship. With all potential disturbances taken into account the concept is consideredto be ineffective and unreliable with a high risk of affecting the towing tether naturalappearance.

4.1.3 Tether Climber Evaluation

In order to further investigate the first concept with the Tether Climber one analyzesthe required need of a power package to powering the unit. For the case with a constantinclination angle, ' it is previously estimated the total needed energy for one round trip.To put this in relation a 6 pole Lithium Polymer battery pack from Dualsky [16] is usedwith the following specifications: 16 000mAh/ 355,3Wh (2,06kg) for comparison. Thisis the most high density in terms of energy and size on the market today. Differenttypes of losses must be considered in the process, such as thermal loss in the batterypack, due to the cold and harsh environment when submerged. It is assumed that abattery will typically deliver only 50 % at –18 °C compared to 100% at 27 °C in air[17]. Hence one can assume that for a battery in a cold environment at 4 °C with ahigher cooling factor due to water surrounding it, one assumes that it is in the sameregion in terms of thermal losses. In addition to this there will be losses regarding thetransmission and also the electric motor. It is reasonable to assume an overall efficiencyof 80% for a 0-1,5hp electrical motor [18] and an overall 60% efficiency for transmissionand shaft connections. Regarding friction between the driving wheels and the tether itis reasonable with a 20% loss due to the tether roughness. The total loss coefficient ntot2is then equal to all upcoming friction losses multiplied:


ntot2 = ncold · nmotor · ntrans · nshaft · nfric · nwheel (4.9)

All input values for Equation 4.9 can be obtained in Table 4.4 below.

Table 4.4: Frict ional components and energy dispersion.

Variable Abbreviation Value @constant '

Cold factor ncold 0, 5Motor efficiency nmotor 0, 8Transmission efficiency ntrans 0, 6Shaft transmission efficiency nshaft 0, 95Frictional loss, wheel to wire nfric 0, 8Total propulsive efficiency ntot 0, 18

The following number of trips for a 18% overall efficiency is then equal to:

ntrip =Total Energy stored [J ] · ⌘totOne trip required energy [J ]

⇡ 355, 3 · 3600 · 0, 1852000

⇡ 4, 4 Rounds (4.10)

4.1.4 Re-chargeable sensor carrier Evaluation

From the previous Section 4.1.3 it is stated that a climbing concept could be possible.Furthermore it is also stated in Section 4.1.1 that there is a possibility to extract enoughenergy from the acting stream to propel the sensor carrier. Hence there is a need ofinvestigate how much resistance an installed auxiliary propeller would create. One as-sumes that the propeller size in Section 4.1.1 with a radius of 7cm is considered to besufficient enough for this concept without further analysis. A configuration like thatwould theoretically extract:

Pin = q ·Ac · vA =1

2CD⇢w · ⇡ · r2 · v3A · (1 + vp · cos(')) (4.11)

Pin =1

2· 1, 28 · 1001 · ⇡ · 0, 072 · 2, 13(1 + 0, 5 · cos(⇡

4) ⇡ 124W (4.12)

With an assumed utility effect equal to Equation 4.5 the generated power for the batterypack is then :

Pgen = Pin · ⌘gen = 124 · 0, 12 ⇡ 15W (4.13)


For a high energy density battery it would require a total time to fully charge the batterywith a 40% added resistance in battery pack:

Tgen =Battery charge [Wh] · ⌘resistance

Charge Power [W ]⇡ 355, 3 · 1.4

15⇡ 33hours (4.14)

It is plausible to let the sensor carrier hold its position and charge its batteries whenneeded before ascending if one allows a tremendous long charging time. It is noteworthythat only half the time is needed to charge the sensor carrier for one ascending motion.Also there is a possibility to increase the propeller diameter to further increase the poweroutput and lower the charging time. However 15 hours of charging time is not consideredto be not sufficient when the main task is to collect data throughout a 24 hour operation.

4.2 Evaluation Results

From Section 4.1.1 one can conclude that it could be somewhat plausible to propel thePaddle Wheel design mechanically with a propeller acting in the free stream. Howeverthe assumptions are quite loose regarding the investigation and thus not accurate enough.Furthermore, if one considers the added resistance that occurs due to the auxiliary pro-peller in combination of a non laminar flow due to interaction with the sensor carriershull will most likely reduce the efficiency further. Finally, a main aspect of not beingable to operate in the turbulent region behind the towing ship and and absence to notreach over the water level makes the concept somewhat limited and too over-complex toachieve in this project cycle. This would be of a practical issue to not be able to bring upthe sensor carrier for data acquisition and inspection without bring up the entire tetherline or use auxiliary equipment to reach the sensor carrier. The promising aspect of thisconcept is the usage of the free stream and no need for energy storage.

The Paraglider concept is considered as not plausible at all due to the fact that a foilwould lift the tether cable instead of ascend the sensor carrier along it. Thus this conceptis of the list entirely.

The most robust alternative is the Tether Climber concept. It seems fairly reasonableto perform four routes before recharging is necessary and it does not requires a lot ofauxiliary equipment to do so. The Tether Climber is a simple and robust concept butwith a limit of four rounds of ascending motion before it needs to be recharged. Thereis some possible margins to choose multiple battery-packs to increase the endurance fur-ther. The drawback is the lack of extracted energy from the acting free stream and thusthe concept is somewhat inefficient compared to the Paddle Wheel concept.


The Self-chargeable sensor carrier concept would solve this issue when combining theidea of the Paddle Wheel concept with the Tether Climber concept, using the rotationalmovement for a propeller from the free stream to re-charge the battery pack. This sinceit is proven that one could use the acting stream for energy extraction. Such type ofconfiguration is more complex and questionable regarding the robustness criterion. Amain aspect is the increased resistance from the propeller where a “slipping” scenariocould occur with the tether, i.e the propeller will decelerating the propulsion movement.

4.3 Final Choice of Concept

The Tether Climber sensor carrier has the highest potential to fulfill all stated require-ments and with sufficient long lasting operation time underwater and also its high ro-bustness. Thus it is concluded that the concept is the most promising alternative toproceed with in this project due its ability to reach above sea level, and foremost its sim-plicity. Self-chargeable sensor carrier is neglected due to the overcomplexity and maindrawback of the added resistance and increased weight due to the auxiliary propellerand generator. Also, one has to perform numerical simulations to ensure the plausiblemaximum power output in the realistic turbulent operating regions.

Chapter 5

Final Concept Design

It this chapter the author explains in detail about the chosen hardware components andalso the developed software for the conceptual design. This to declare all abilities andlimitations together with its overall functionality. The chapter is divided into severalsections where both software and hardware are presented together with the system set-up.Although the final material is very concise, a tremendous amount of time has been spendon research and just to find suitable components. The main task for the final conceptis to test the system as whole to validate if one can sample data in order to calculatethe sound profile without interact or theoretically disturb the existing equipment. Hereit is room for improvements within several areas, but this has been left out for a secondversion, which is discussed in the next chapter.

Figure 5.1: O verview over t he con-cept ual design, left side. A t iming bel t

connects t he two drive wheels.

Figure 5.2: O verview over t he con-cept ual design right side. A t imingbel t t ransfers t he power from t he mo-

tor to t he first drive wheel.

36

Chapter 5. Final Concept Design 37

5.1 Wheel mechanism and transmission

The wire wheel mechanism is built upon the idea of having two driving wheels linkedtogether. This is achieved by connecting one driving wheel with a timing belt to main-tain two independent contact points for propulsion. A chain solution was considered notsufficient due to the corrosive environment. The main design was inspired after someresearch where one founded a patented solution for a Self-propelled cable supported car-riage designed by Lonnie E. Meek, to climb along a wire, designed to carry an extensiveload [19]. This patent was combined with a design-mechanism from a welding machinethat feeds the metal wire into the welding handle. Figure 5.3 displays the design whereit has been modified so each contact wheel instead is supported by plate springs to beself-adjusted along the wire surface roughness. The transmission from the motor to thedriving wheels consist of two rubber BANDO STS 3M timing belts. It is a polyurethanebelt made out of chloroquine rubber with nylon fabric on the teeth side which is consider-ably more resistant to corrosive fluids like: oil, petrol and certain chemicals, compared tostandard belts made of pure rubber. The belt is insensitive to to temperature differenceswith a operating range from -30ºC to + 70ºC [20].

The main belt transfers power from the motor to the first drive wheel where a sec-ond longer belt connects onto the shaft that transmits power to the second drive wheel.The motor is mounted onto an adjustable plate in order to be able to tension the firstbelt. For the second belt a tension wheel is mounted to obtain the stretch, this sinceboth bearing seats are mounted solid.

The contact wheels are designed with double SKF 445 roller bearings in hardened steelfor low internal friction and rubber sealing. Each wheel pair is independently resilient,hence if one loses its traction to the tether the second wheel will still maintain driving.The driving wheels are mounted directly onto a stainless steel shaft with axial floatingFL08 bearing. For the concept design the housing has been 3D-printed in PLA-plastic tokeep the budget low. Due to limitations in time for the project, one decided to neglect acover casing to cover the moving parts like motor, transmission and foremost make thesensor carrier more streamlined.

The wheel mechanism is driven by an electrical M100 brushless motor designed for oceanapplications and extreme environments, developed by Blue Robotics [21].


5.1.1 Gear ratio

The gear ratio i is defined as:

i =n1

n2(5.1)

where n1 is the drive pinion speed and n2 is the driven gear speed measured in rotationsper minute, rpm. In a similar way the gear ratio also corresponds to the ratio of the geartooth numbers zi according to:

i =z2

z1(5.2)

The peripheral velocity for a rotational movement is then equal to:

vp =⇡ · d · n2

60(5.3)

Thus, one obtains an gear ratio i = 4 from equation 5.1 when using a 12 tooth gear onthe pinion shaft together with a 48 tooths onto the driven gear shaft. With an estimatedrotational speed of 2000rpm that delivers around 40W for the motor with a desiredpropagation speed of vp = 0.5m/s one can calculate the diameter d for the drive wheel.The drive wheel is mounted onto the driven gear with the rotational speed n2, hencewith equation 5.1, 5.2 and 5.3 the diameter d is equal to:

d =vp · 60 · i⇡ · n2

=0.5 · 60 · 4⇡ · 2000 = 19mm (5.4)

Since the ESC unit does not have the ability to measure the rotational speed for theconnected motor one can change the rotational speed by adjusting the the PWM signalin the software if needed.


Figure 5.3: O verview over t he wheel mechanism. P la te springs are marked in red,cont act wheels in gray, drive wheels in green and F L08 bearings in B lue.

5.2 Watertight Compartment

Figure 5.4 displays the watertight compartment is an acrylic plastic tube from BlueRobotics [22] with a diameter of 3", sealed with double o-rings flanges and grease withepoxy-sealed cable bushings. The 3" tube fits a Dualsky 10 000mAh/14.8V Li-POL 4SBattery pack inside [23], together with ESC module, power switch and also an Ardulogmicro controller. The first alternative with the Dualsky 6S Battery was neglected sinceit did not fit any of the acrylic tubes that where available and also because the batteryvoltage was to high for the ESC unit that is used. The tube and cable bushing is ratedfor a maximum depth of 150m [24]. For the first concept version a smaller Graupner4000mAh/9.9V LiFE 2S battery since it was the only battery available. The Bar30sensor is mounted directly on the acrylic flange in one of the existing cable bushings,sealed with a o-ring. Furthermore a ventilator is installed that fulfills two main purposes.Firstly, to be able to ensure that the compartment is watertight by connecting a vacuum-pump where the vacuum inside represents the pressure acting from the outside. Second,to vent out air to avoid excess pressure inside the compartment and to be able to mountthe air and watertight o-ring flange.


Figure 5.4: O verview over t he wa ter t ight compar t ment wit hout t he covering acrylict ube. T he ba t tery is marked in green, sensors in red on t he flanges, t he Ardulog in

yellow and E S C-unit in pink .

5.3 Software

The Software is a vital part of the platform and the program environment for the entiresystem is Arduino. The structure is rather simple due to the lack of time when developingit with the focus on the main task of autonomously read sensors, log data from the sensorand to store it onto an SD card. The system simultaneously controls an ESC module,connected to the electrical motor for forward and reverse motion controlled by two Hallsensors. Figure 5.5 illustrates the main loop structure of how the system operates.


Figure 5.5: Software flow char t schema t ics.

5.3.1 Data sampling and Data Acquisition components and sensors

To sample data the Bar30 Sensor developed by Blue Robotics is used and illustrated inFigure 5.8. It has the feature of a depth resolution of 2 mm combined with a temperaturesensor with an accuracy of +/- 1°C [25] where it samples data every second, i.e everyhalf meter of the tether wire. The sampled data is logged onto a removable SD cardwith a real time clock (RTC), saved in a .csv format. This setup provides time and datefor the data sampling, together with the measured parameters consisting of pressure andalso temperature. An external temperature sensor with higher accuracy from the samedeveloper has been neglected due to lack of cable bushings and digital ports, but it isrecommended for a future second design.

In order to be able to precisely calculate the sound propagation speed one needs tomeasure the salinity. However this first version of the software program did not haveenough internal memory to store code for the chosen salinity sensor and thus been ne-glected for the first conceptual design. To be able to switch between the different stagesthe software communicates through digital ports with two Hamlin™ 55110 Hall-sensors[26] in order to determine its end positions. The Hall sensors are favorable due to their


rather small size, robustness and lack of mechanical parts that could malfunction under-water. The software platform is built as a stage structure where the autonomous sensorcarrier handles different tasks depending on its stage. In Figure 5.6 below one can obtainthe three stages STOPPED, DOWN and UP where the stages also controls the log. I.ewhen the autonomous sensor carrier is STOPPED no log is active until a signal from aHall sensor is detected and the stage is set to be UP or DOWN. This to log data whiledescending or ascending.

Figure 5.6: Software st a te diagram wit h all st ages and log command illust ra ted.

5.4 Hardware system

The hardware for the system is built around the micro controller where the ESC unitpowers the control board through a 5V BEC output. It communicates through a digitalinput port that has been modified to an digital output port for PWM control in thesoftware program. An interface connector is installed to be able to connect the Ardulogto a USB port and simultaneously run the software on the sensor carrier if needed.The SD card reader and the RTC clock is directly mounted on a ATMEGA 328 microcontroller card, developed by Hobby Electronics [27] mounted on a self-made circuitboard with connections for all sensors, see Figure 5.7 below.

Figure 5.7: C ircuit board wit h con-nectors for sensors and also t he Ardu-

log micro cont roller.

Figure 5.8: T he Bar30 sensor de-veloped by Blue robotics, mounted on

one of t he flanges.


The Bar30 Sensor illustrated in Figure 5.8 above communicates through an I2C port andis powered by the micro controller at 3.3V. The two Hall sensors communicates throughtwo analog low-voltage output signal ports with the micro controller at the same voltageas the Bar30 Sensor, see Figure 5.9. For the sake of clarification one has modified thedigital output port D4 to an digital input port, in order to control the ESC-unit. Forfurther understanding regarding the software design, see the software program code inAppendix A.

Figure 5.9: W iring schema t ics.

For a complete wiring diagram of the ATMEGA 328 Ardulog with all available ports, seeAppendix B .


5.5 User Manual

1. The initial step is to remove vacuum nut together with the top flange with allcables connected to it, this to make the power switch available. When the device isswitched on the Ardulog will flash a green LED signal when the SD-card is bootedcorrectly. You will hear a few beeps from the ESC when the Ardulog sends a stopsignal to initialize the ESC. If booth units are booted correctly you will hear along tone together with a flashing orange LED light, if not a orange LED light willfollow.

2. When the system is booted close the watertight compartment by fitting the flangeinto the acrylic tube. Ensure that the ventilator nut is removed and also that theo-rings are greased and that there is no dust, hair, or other particles that couldcause a leak.

3. Connect a vacuum pump to the ventilator with the vacuum plug and decrease thepressure to about 400 mmHg and monitor for about 5-10 minutes. If the pressuredoesn’t drop more than 10 mmHg the compartment is considered watertight downto 150m. Remove the vacuum plug and insert the ventilation nut.

4. Open the wheel mechanism the by removing the pin to lock and carefully mountthe tether to the two contact wheels. Close the top and affix the pin.

5. To initialize the data sampling sequence and movement, place a magnet close theHall sensor that facing the opposite drive direction of the tether.

6. To stop the movement at any time, place magnets on both Hall sensors and open themechanism according to step 4 above and power of the sensor carrier by followingthe previous steps in reverse sequence.

Chapter 6

Evaluation of Design

The chapter evaluates the usability, functionality and robustness of the concept as a wholetogether with result from the measurement rounds. The evaluation part consists of resultsboth from dry tests and live tests made underwater.

6.1 Initial setup and usability

It turned out that the concave wheels was insufficient in terms of adjusting the tether andcorrect it when moving. Hence, the tether cable "climbed out" and locked itself betweenthe wheel pair. This issue was corrected by design contact wheels with an increasedconcave track. The design for mounting the sensor carrier onto the tether and to adjustthe leaf spring (center screw) is considered convenient and easy for one person to handle,see Figure 6.1 and 6.2.

Figure 6.1: Tet her placed on t hetwo cont act wheels wit h t he mecha-

nism open.

Figure 6.2: Tet her in place wit h t hemechanism locked.

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Chapter 6. Evaluation of Design 46

6.1.1 Weight and dimensions

The sensor carrier has a overall length/ width /height of 355/ 110 /240mm and a totalweight of 3.0kg. According to the CAD drawing one can obtain a total volume of 1.85dm

3. Consequently, the sensor carrier is slightly negative in terms of buoyancy.

6.2 Dry test

The first test rounds consisted of testing the sensor carrier on dry land in order to val-idate all functions. It turned out that the chosen M100 motor from Blue Robotics wasto weak regarding delivering momentum, hence one choose to upgrade it to the M200motor from the same manufacturer [28]. This since there where no other gear wheelsavailable and also a lack of space to be able to mount them. The gear ratio turned outto be sufficient for the over-sized motor but still limited.

Initially the concept with the Hall-sensors where very convincing when applying a singlemagnet to the sensor during development. Trouble occurred when applying multiplemagnets onto the tether to cover for all possible positions that the sensor carrier couldreach the magnetic stop since it freely rotates around the tether. When applying multi-ple magnets close to each other

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