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Bachelor Thesis - Repository TU Delft

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1. DATASHEET MOTOR On the next two pages the datasheet of the used motors 33 are included 51 E DATASHEET MOTOR 919D SERIES SINGLE RATIO METAL GEARBOX RE 540 1 MOTOR al jn pozi om A maan tt ie lt hol bes e en dll RATIOS NOW AVAILABLE AS EX STOCK ITEMS nes 919D2 51 4 5v 15v WITH RE 540 1 MOTOR RATIO 2 5 1 919D61 4 5v 15v WITH RE 540 1 MOTOR RATIO 6 1 919D111 4 5v 15v WITH RE 540 1 MOTOR RATIO 11 1 919D501 4 5v 15v WITH RE 540 1 MOTOR RATIO 50 1 919D1481 4 5v 15v WITH RE 540 1 MOTOR RATIO 148 1 91908101 4 5v 15v WITH RE 540 1 MOTOR RATIO 810 1 pew 919D30001 4 5v 15v WITH RE 540 1 MOTOR RATIO 3000 1 Designed for heavy duty industrial and model applications this robust unit boasts a powerful high quality three pole motor with sintered bronze bearings The ali steel gearbox incorporates bronze output bearings enabling the high torque transfer from the motor to be transmitted through the gearbox The unit is mounted on a 1mm thick plated steel bracket MOTOR DATA aa vate om NO LOAD 6 0v CONSTANT Pc 2 0v CONSTANT 15800 a TABLE R P M a 00 1975 2633 3295 9190111 1077 1436 919D1481 91908101 919D30001 TORQUE TABLE g cm 1 T heoretical rating for motor amp gearbox combined mem Pir enor es ae es am Tresen ro oe am ome RE 540 1 11 1 1300 1698 7370 iz 5910 EA RE 540 1 810 1 95742 125064 542700 81
2. Subject to minimum order quantities of 250 units the following ratios are also available with a six week lead time The physical dimensions of these other gearboxes may vary from the data as illustrated above Details of individual gearboxes are available upon request GEARBOX 18 1 WITH 540 1 MOTOR GEARBOX 30 1 WITH 540 1 MOTOR GEARBOX 60 1 WITH 540 1 MOTOR GEARBOX 70 1 WITH 540 1 MOTOR GEARBOX 75 1 WITH 540 1 MOTOR GEARBOX 90 1 WITH 540 1 MOTOR GEARBOX 100 1 WITH 540 1 MOTOR GEARBOX 120 1 WITH 540 1 MOTOR GEARBOX 180 1 WITH 540 1 MOTOR GEARBOX 200 1 WITH 540 1 MOTOR GEARBOX 250 1 WITH 540 1 MOTOR GEARBOX 300 1 WITH 540 1 MOTOR GEARBOX 350 1 WITH 540 1 MOTOR GEARBOX 400 1 WITH 540 1 MOTOR GEARBOX 450 1 WITH 540 1 MOTOR GEARBOX 500 1 WITH 540 1 MOTOR GEARBOX 600 1 WITH 540 1 MOTOR GEARBOX 700 1 WITH 540 1 MOTOR GEARBOX 900 1 WITH 540 1 MOTOR GEARBOX 1000 1 WITH 540 1 MOTOR GEARBOX 1500 1 WITH 540 1 MOTOR THE ABOVE FIGURES ARE A GUIDE ONLY AND DO NOT FORM ANY CONTRACTUAL OBLIGATION ON THE PART OF MFA COMO DRILLS 1 2 a i 3 4 5 6 T 7 8 9 10 11 12 13 14 15 16 17 18 BIBLIOGRAPHY U S Energy Information Administration FAQ How much of world energy consumption and electricity generation is from renewable energy Washington D C 2013 Online available at http www eia gov tools faqs faq cfm id 527 amp t 4 Mary Rock
3. Laura Parsons Offshore Wind Energy 2010 online Avaiable at http www eesi org files offshore wind 101310 pdf Dr Nicolas Fichaux EWEA Justin Wilkes EWEA Oceans of Opportunity Harnessing Europe s largest domestic energy resource online Avaiable at http www ewea org fileadmin ewea documents documents publications reports Offshore Report 2009 pdf James Gapinski What Are the Best Wind Farm Locations 2014 online Avaiable at http www wisegeek org what are the best wind farm locations htm Matthew Baker ASSESSING OFFSHORE WIND CONDITIONS MEASUREMENT MODELING AND ANALYSIS APPROACHES AWS Truepower Albany NY 2011 online Avaiable at http www law pace edu sites default files PECC Matthew Baker AWS Truepower pdf Airbornel Lidar amp Obliques Los Angeles CA online Avaiable at http airbornel com CMR University of Bergen Statoil Marintek and Fugro OCEANOR Measurements of Wind Profile from a Buoy using Lidar Final Report Reference No 9631 2012 S Navalkar Manoeuvrable Stabilised Buoy for Offshore Wind Assessment online Avaiable at https blackboard tudelft nl bbcswebdav pid 2128737 dt content rid 7464483_2 courses 28205 131404 S_Navalkar BuoyStabilisation pdf Fugro Oceanor Seawatch Wind Lidar Buoy online Avaiable at http www oceanor com related Datasheets pdf SEAWATCH_Wind_LiDAR_Buoy pdf M H G Baas A Pannekoek Bachelor Thesis Bachelor of Scie
4. if the override is enabled 3 6 OVERVIEW DESIGN Figure 3 6 gives an overview ofthe complete autonomous position control system as designed in this chapter The PC power supply that is used to power the system is not part ofthe design since the power management falls outside the scope of the thesis However it is necessary for the system to function 3 6 OVERVIEW DESIGN 23 GPS Module Gyroscope PC Power su pply Navilock 552ETTL GPS module Parallax L364200D 3 3V ground data 3 3V data 3 3V Microcontroller LFC F1343 Control 3 3V Transistor H Bridge circuit 1 Transistor H Bridge circuit 2 IRL640 L298N IRL640 L298N PWM 12V PWM 12V Motor left Motor right 919D2 51 919D2 51 Figure 3 6 Total navigation system scheme TESTING AND RESULTS 4 1 TEST PLAN After completing the design the construction phase starts During the building process tests are performed to check if the process goes right These small tests will not be described The tests that are performed at the completion of the construction of each component are of more value and therefore will be described in following sections The results of these tests are described and compared with the requirements established in chapter 2 Finally the system will be tested while integrated with the buoy 4 1 l MOTORS Three tests were performed on the motors in different stages of the design process to verify that the design w
5. level of integration and low power consumption This microcontroller supports various interfaces such as one Fast mode Plus I C bus interface USB UART SSP in terfaces four general purpose timers a 10 bit ADC On the board are available UEXT Debug Interface user buttons USB device and user LEDs This allows you to build a diversity of powerful software that can be used in a wide range of applica tions BOARD FEATURES e MCU LPC1343 Cortex M3 up to 70 MHz 32 kB Flash 8kB SRAM UART RS 485 USB SSP PC Fast ADC e Power supply circuit e Power on led e USB connector and functionality e USBC LED e Debug interface SWD Serial Wire Debug e UEXT connector e Eight user LEDs e Two user buttons e Reset button e Prototype area e FR 4 1 5 mm red soldermask white component print e Dimensions 80x50mm 3 15 x 1 97 49 ELECTROSTATIC WARNING The LPC P1343 board is shipped in protective anti static packaging The board must not be subject to high electrostatic potentials General practice for working with static sensitive devices should be applied when working with this board BOARD USE REQUIREMENTS Cables The cable you will need depends on the programmer debugger you use For instance if you use https www olimex com Products ARM JTAG ARM TAG COOCOX you will need USB A B cable Hardware Programmer debugger or other compatible programming debugging tool with SWD interface The only Olimex programmer that
6. 4 5 and 15 V The microcontroller that will be used to do the navigation calculations can only supply low power 3 3 V signals however An option is to control the motor speed by modifying the magnitude of the voltage across the connections of the motor But controlling the magnitude of a voltage with the microcontroller requires a digital analog converter that needs to be able to provide enough power for the motors to run at full speed This is an expensive part to buy or a time consuming part to build This is why to control the speed of the motor Pulse Width Modula tion PWM is used by the microcontroller PWM is a technique that switches a DC source on and off with a constant frequency and an adjustable duty cycle to regulate the amount of power supplied to the load Using PWM maintains a large part of the torque produced at DC input while decreasing the rotation speed The frequency of the PWM signal to be sent to the motors is chosen to be 500 Hz This frequency is high enough 18 3 DESIGN PROCESS rs 5 6 7 8 9 to minimize the stutter that occurs when the motor is switched on and off with a frequency that is too low On the other hand 500 Hz is low enough for the effects of the capacitor parallel to the motor to be small at high frequencies the impedance of the capacitor becomes low meaning that a large part of current flows through the capacitor instead of the motor Figure 3 3 Parts of the designed waterproof casing The o
7. Also the rotation one way around was slower than the other way around These effects can be prevented by choosing more suitable PWM values for the affected states All values of the table are obtained with the buoy being stationary at the start of the test The real top speed is therefore higher than the values shown in the table It can be concluded that requirement 2 1 7 is met Duty cycle speed m s Duty cycle Rotation speed degrees second 56 100 0 62 50 left turn 50 0 31 50 right turn 37 Table 4 4 Results of testing the speed and turning of the buoy The test of the entire autonomous positioning system did not yield any results other than the observation that the test setup was flawed The motors rotated far slower in this setup than in previous tests needing the 32 4 TESTINGAND RESULTS full 100 duty cycle on the PWM signals to begin turning and even then they did not always start rotating This can be attributed to the voltage drop that occurs when up to 4 A of current travels through 10 meter of copper wiring The requirements 2 1 10 and 2 1 11 are a combination of the GPS accuracy measurement and the nav igation system tests Requirement 2 1 10 states that the prototype must be able to reach its destination as accurately as the GPS allows and 2 1 11 states that it must be able to keep its position with that same ac curacy Since the GPS measurements revealed that the accuracy of the GPS unit is less then
8. C 100 Vas 10V Vas 10V Ip 17A nm nC Vps 160V Vas 5 0V See Fig 6 and 13 a Voo 100V t Rise Time 83 lo 17A tot Turn Off Delay Time 44 Ra 4 60 tr Fall Time 52 Aps5 70 See Figure 10 O wi Internal Drain Inductance 45 en Pr dei se o H from package ME Internal Source Inductance and center of die contact Vas 0V Output Capacitance Vos 25V ze Reverse Transfer Capacitance Fri IT f 1 0MHz See Fic Source Drain Ratings and Characteristics Parameter I Min Typ Test Conditions As Continuous Source Current MOSFET symbol D g Body Diode A showing the Ism Pulsed Source Current u integral reverse S Body Diode p n junction diode s Vso _ Diode Forward Voltage t 20 Ty 25 C Is 17A Vos 0V O tre Reverse Recovery Time 310 470 ns Ty 25 C Ir 17A LO Reverse Recovery Charge _ 3 2 4 8 C di dt 100A us O pe l Forward Tum On Time Intrinsic turn on time is neglegible turn on is dominated by Ls Lp Notes O Repetitive rating pulse width limited by Iso lt 17A di dt lt 150A us VoD lt V BR DSS max junction temperature See Figure 11 Tj lt 150 C Y Vpp 50V starting Ty 25 C L 3 0mH Pulse width lt 300 us duty cycle lt 2 RG 250 las 17A See Figure 12 2 www irf com 42 B DATASHEET TRANSISTOR International IRL640PbF IGR Rectifier a a 5 E s E i Q
9. Flidar buoy possible in addition to solar panels increasing the time the buoy can do measurements without running out of power The AXYS WindSentinel 13 from figure 1 3b is another existing moored buoy platform modified to do wind measurement The AXYS NOMAD buoy platform on which the WindSentinel is based is shaped more like the hull ofa ship than like a circular buoy This hull shape helps preventing the buoy from turning around its vertical axis This increases the accuracy of wind direction measurements The shape also makes dragging the buoy to a new location easier The buoy does not have sensors for other measurements and the LiDAR device is not stabilized The on board power is supplied by solar panels small wind turbines and a fuel cell While the previously mentioned buoys are commercially available the Neptune Project 14 buoy is still under development A render is shown in figure 1 3c This moored buoy does not consist of a single large 1 3 STATE OF THE ART ANALYSIS 3 floating body but it has four smaller floats connected in a square configuration On top of these floaters the LiDAR device is secure on an actively stabilized platform The buoy has in addition to the LiDAR device a sensor for measuring ocean waves The on board power is generated by small wind turbines and solar panels a Flidar b AXYS WindSentinel c Neptune buoy Figure 1 3 Different LIDAR Buoys Each existing Lidar buoy mentioned above is equip
10. Own input Wires Different colours types Free DUT ma A ECN Table 4 5 components with their prices Delft University of Technology is abbreviated as DUT CONCLUSION In the problem definition chapter 2 a number of requirements were set in order to achieve the goal of this thesis which is designing autonomous position control for the SEAWATCH buoy As can be read in chapter 4 the tests confirmed that all of these requirements are met except for requirement 2 1 13 Since the compen sation of the yaw would not be implemented anyway because of the scope and this requirement was aimed at making such compensation easier possible it can be concluded that a successful prototype has been built The beauty of the design is that it can be seen as a black box If the gyroscope used is included in the package the whole system can be placed on any buoy to create a navigation system When implemented on other buoys characteristics might change like top speed rotation speed and energy consumption Some parts of the system can easily be scaled up the microcontroller can handle the NMEA protocol making it able to communicate with almost any GPS receiver The motor driver can be scaled up if high power H bridges and transistors are used The propellers are scalable and would become 25 cm in diameter but the motors are not scalable while also meeting the full scale buoy requirements If the motors would be scaled up they would consume 1 kW of
11. Q E pu O O g S A O 5 ke Ous PULSE WIDTH 442945 PULSE WID re 250 V Fe 15000 Vos Drain to Source Voltage volts Vos Drain to Source Voltage volts Fig 1 Typical Output Characteristics Fig 2 Typical Output Characteristics Tc 25 C Tc 150 C Ip Drain Current Amps Ros on Drain to Source On Resistance Normalized 30 3 5 40 4 5 5 59 29 39 3 29 40 60 BO 100 129 40 189 Vas Gate to Source Voltage volts T y Junction Temperature C Fig3 Typical Transfer Characteristics Fig 4 Normalized On Resistance Vs Temperature www irf com 3 DATASHEET GPS MODULE On the next three pages the most relevant pages of the datasheet of the GPS module 25 are included 43 44 C DATASHEET GPS MODULE LOCK PCMBN12 970627007 Pin Assignment gt Unpopulated in TTL version Page 3 Date 12 2010 45 NAVILOCK Please refer to u blox5 Receiver Description Protocol Specifications http www u blox com images downloads Product Docs u blox5 Protocol Specifications 28GPS G5 X 07036 29 pdf See the Chapter Navigation Configuration Settings Description on page 42 You can configure it by use of u center or transmit it to the receiver by batch command every time the system starts up GPS modules NL 550ERS NL 551EUSB and NL 552ETTL are designed to forget all user settings when the battery pack is low to be able to meet demands of the broad r
12. are controlled by the navigation system The option to control the yaw will be kept open 3 DESIGN PROCESS The system to be designed will consist of the following parts En Positioning system The controller which is the central element of the system The positioning system which obtains its position and passes it to the controller Controller The propulsion which enables the buoy to relocate The motor driver which uses the signals of the controller to supply the motors with the right voltage The software on the controller required to make the parts work as one system and to calculate the route Propulsion In following sections the choices and considerations made to design these repulsion components are discussed Figure 3 1 Overview diagram 3 1 CONTROLLER To control the whole autonomous position control system a central controlling and computing unit is needed There are several options to fill this place Two options are taken into consideration a Field Programmable Gate Array FPGA chip and a microcontroller A FPGA needs to be programmed using VHDL a hardware de scription language while a microcontroller can be programmed in C C is used much more widely for embed ded programming and hence libraries for many functions are commonly available Therefore programming in it will be preferable Microcontrollers also have built in protocols for for example UART communication which will be use
13. can cover more than 6000 km during the three months it can be at sea at a time It uses satellite communication and GPS for it position ing A schematic representation of the navigation system in an ASV that is used to measure nutrients and fluorescence in seawater is shown in figure 1 5 17 The ASV has a central processing unit CPU that gets the position Figure 1 4 ASV Ltd C Enduro and direction of the buoy from a GPS receiver and electric compass and uses this information to send the right amount of power to the thrusters to move the vessel to its destination The vessel in question does not have a rudder and is therefore steered by the difference in thrust which the thrusters on both sides of the vessel produce The CPU of the vessel also receives DGPS signals via telephone communication and sends that to the GPS unit A DGPS signal contains GPS information of a land station and is used to correct the GPS receiver and make it more accurate The CPU also sends the position of the vessel back to land via satellite communication Using DGPS the position can be calculated with an accuracy of 2 m What the CPU of this vessel does exactly is not described in the paper What is described is that the system has two modes one mode that is active when the vessel is far away from its target In this mode the vessel only determines its position in intervals of 140 seconds The course is also adjusted only once per interval This conserves the energy
14. current develop ments in this area 1 3 STATE OF THE ART ANALYSIS Before formulating the exact requirements of the design an analysis of the existing technologies in the field of the subject is conducted In this analysis the subject is split up into two parts On one hand a buoy that does wind measurements using a LIDAR device and on the other hand the technology that enables the buoy to navigate to a given position autonomously 1 3 1 LIDAR BUOY There are multiple different kinds of buoys both available on the market and under development that use Li DAR technology for wind measurement The most interesting ones will be further examined and compared The Flidar Floating LiDAR buoy 12 is amoored buoy that is large compared to the Seawatch buoy 4 meter diameter versus 2 8 meter This buoy shown in figure 1 3a is more specifically designed for wind measurements The buoy cannot do as many different oceanographic and meteorologic measurements as the Seawatch buoy but is limited to measuring air pressure humidity and temperature in addition to the LiDAR measurements The Flidar uses a passive stabilisation of the LiDAR device for more accurate mea surements The larger platform and weight makes the buoy more stable in the water but also make it more troublesome to reposition the buoy since a larger ship with a larger crane is required to lift it out of the water The larger platform does make the usage of small wind turbines on the
15. displayed in table 4 3 The error might be caused by the gyroscope not being exactly horizontal during the tests If this is the case more accurate orientation measure ments would require to be compensated for the effects of x and y rotation However the source of the error was not conclusively found The directions calculated by the microcontroller was during all tests less than half a degree away from the expected direction Rotation degrees Error without correction degrees Error after linear correction degrees 720 clockwise 34 3 720 counter clockwise 30 2 Table 4 3 The measured angle error after 2 full rotations without and with linear correction The testing of the navigation system showed that the navigation system can direct the prototype success fully to a given destination By turning according to the left and right states and moving straight ahead in the forward state the intended position was approached and when it was close enough the stop state was entered The distance between entering the stop state and the intended position varied between 3 and 10 meters depending on the direction from which the destination was approached Interesting about this test is that the destination was not approached in a straight line but in slight spiral like curve This resulted in a taken path that is 50 meters while the distance between the start and destination was only 40 meters This deviation is most likely caused by the fa
16. e rr MED o ces Gee GE PROBLEM DEFINITION The problem needs to be specified in a more detailed way before a fitting solution can be designed That is why a list of requirements are set to specify a desirable performance for the prototype and the full scaled buoy These requirements are set in section 2 1 1 In section 2 1 2 is described how the prototype requirements are converted to requirements for the full scaled buoy The remaining requirements concerning surrounding topics are added in sections 2 1 3 to 2 1 5 2 1 REQUIREMENTS For setting the right requirement it is necessary to focus on the global problem definition which is set in section 1 2 That is why it is repeated below Besides that communication with the other participants of the project group must ensure that no conflicting requirements are set Designing an actively stabilised platform for the SEAWATCH offshore buoy to account for measurement errors of the ZephIR 300 LiDAR Designing autonomous position control for the SEAWATCH buoy Delivering a working scaled prototype of the buoy with both of these designs 2 1 1 PROTOTYPE REQUIREMENTS In consultation with the other participants of the project group common design requirements are set regard ing the scale of the prototype For the group working on the stabilisation the dimensions of the prototype cannot be too small since some parts of the prototype like the linear actuators are not available at a too small siz
17. either the longitude or latitude of the current position of the prototype is 17 x 107 GPS minutes different from that of the destination This allows a maximum drift either straight north south east or west of 3 23 m and a maximum distance diagonally of 10 4 meter 3120 7555 Measured Position 4 Measured Position 3100 er m Actual Position mi Actual Position 7550 a 3080 os U Qu 3060 2 E E 7545 o 3040 O xa oe z V 7540 amp 3 3020 a El E E o amp 3000 lt NE 2980 s 2960 7530 325 350 375 400 425 450 475 500 9260 9280 9300 9320 9340 Longitude 10 minutes Longitude 10 minutes a Results of the first GPS test b Result of the second GPS test Figure 4 4 GPS location deviation tests The main problem with the result of this test is that the actual coordinates of the position where the tests were done came from a source of which the accuracy is unknown Even when using the satellite images of Google Earth it cannot be verified that the coordinates obtained by requesting the coordinates of a point on the map are the exact coordinates of the testing position This means the amount of distortion on the mea sured position cannot be determined with 100 accuracy The noise on the measured position on the other hand is measurable by calculating the standard deviation of the measurement The conclusion that can be drawn from these measu
18. energy together which is far more than the limitation on the power set by requirement 2 1 16 The tests have shown that the motors on the prototype could be smaller while still achieving the desired top speed but even then the power requirement will most likely not be met on the full scale buoy In the recommendations chapter 6 some suggestions are done to solve this issue The system designed is a rather orthogonal system That means that different components of the system can be adapted or replaced without the other components being influenced The microcontroller for exam ple could be updated with new software or replaced A driver with a H bridge could replace the current driver without consequences 5 1 OVERVIEW SYSTEM The design of the manoeuvring system of the buoy resulted in an autonomous navigation system In table 4 5 all components used in this system are summarised with their price and origin The microcontroller board calculates the route a straight line to it s pre programmed destination It is able to do that on the condition that it receives its current location and orientation After the calcula tion the microcontroller outputs a control signal to the drivers The current location is send by the GPS unit Via an UART connection the location is sent to the mi crocontroller board 4 times per second The orientation is calculated from the data sent by the gyroscope e The drivers turn the 3 3 VPWM control signal
19. implemented method can become inaccurate when the the distance to the destination and the distance of the buoy from the equator increase Implementing an algorithm that utilizes equation 3 5 will solve this problem and ensure that the buoy always sails toward the destination via the shortest path A way can be devised to transmit the coordinates of a new destination to the microcontroller remotely Since both the UART and the IC connections are already used by the microcontroller this could not be implemented in this prototype Research could be done in different hull shapes for the full scale buoy The power required to propel the buoy is far higher than the available power The motors could be smaller when the water drag of the buoy would be a lot smaller A more streamlined hull will decrease the water drag The full scale buoy could also be equipped with a different source of power such as fuel cells to provide the power its needs for its autonomous positioning Possibilities that can be considered is equipping the buoy with a small wind turbine like some of the other existing LIDAR buoys or covering more area of the buoy with solar panels 35 A BUDGET A BUDGET BEGROTING Versie 2 In dit document staat een globale begroting beschreven voor het Bachelor Afstudeer Project BAP met als onderwerp Manoeuvrable stabilised buoy for offshore wind assessment Er is gekozen voor een aanpak waarbij voor het manoeuvreren twee
20. its required power The test is performed outdoors because the GPS module does not have a strong enough signal from enough satellites inside a building to calculate its position reliably During the test ten samples are taken from the GPS output signal over a period of several minutes The coordinates of each of these samples are compared to each other and to the actual position from which the test was done The co ordinates of the positions where the test is done are obtained using Google maps The test is done two times in two different locations to determine the effect of the surroundings in which the test is done The first test is done in a location that is on three sides surrounded by buildings while the second test is done in a location with fewer buildings in the vicinity The main requirement that is tested during this test is requirement 2 1 8 which says that the average deviation of the positioning system should not be more than 10 m 4 1 4 NAVIGATION The navigation system is the combination of the GPS a gyroscope and the microcontroller working together to determine the direction in which the buoy has to go to reach its destination During the design all compo nents were first tested separately The GPS module is attached to the microcontroller and to a pc using a UART to USB cable The micro controller displays the received GPS coordinates on the LEDs which can be checked to the coordinates received by the pc The gyroscop
21. next requirement can be set 2 1 22 The navigation system needs to be compatible with as many existing buoys as possible 2 2 SCOPE It is not realistic to take all prototype and full sized buoy requirements into account due to limited time available for the design process Therefore a few compromises are made regarding the requirements of the prototype The compromises made are listed below A regular buoy such as the Seawatch buoy is not designed for manoeuvring making sailing with it not very efficient However a different hull shape for the prototype will not be designed in this thesis Instead the hull shape of a Seawatch buoy will be used as starting point This decision is made because a buoy shaped hull is more stable on the waves Stabilising the platform is easier when the prototype itself is more stable This stabilizing platform has priority above making it move more efficiently during this project To make sure that the stabilizing platform works on board of a buoy the prototype needs to have a buoy shape For the energy management only rough calculations are done for the full scaled buoy For the proto type power consumption is not taken into account as a requirement A power supply for the prototype is not designed in this thesis Instead a PC power supply with a 12 V and a 5 V connection is used to power the prototype From the six degrees of freedom only the surge and the sway explained in figure 2 1
22. position is at least as large as that Applicable on full scaled buoy Required modifications Requirement 2 1 1 Requirement 2 1 2 Requirement 2 1 3 Requirement 2 1 4 None Requirement 2 1 5 All components need to be fully watertight Requirement 2 1 6 Maximum weight approximately 125 times larger Requirement 2 1 7 Sailing speed scaled to approximately 1 4 m s Requirement 2 1 8 None Requirement 2 1 9 None Requirement 2 1 10 None Requirement 2 1 11 None Requirement 2 1 12 None Requirement 2 1 13 None Requirement 2 1 14 None Table 2 1 Translation of prototype requirements to full scaled buoy Besides these requirements there are some requirements that are only of interest to the full scaled buoy One of those is the time the buoy has to be able to be on the sea autonomously Because wind measurement are often not a snapshot but an observation over longer periods of time the following requirement is set 10 2 PROBLEM DEFINITION 2 1 15 The buoy must be able to be at sea autonomously for at least a month This requirement results in the need for strict energy management The Seawatch buoy has a lithium battery bank of 9792 Ah and a lead acid battery bank of 248 Ah at 12 V These battery banks are fully charged at deployment and can be recharged using the PV cells on the Seawtach buoy These cells can provide a total of 180 W of electrical power 9 The Seawatch buoy will be outfitted with extra equipment of active stabili
23. propeller The value 1 S represents how much of the pitch length the vessel actually moves through water when the propellers move one complete turn The slip is a unitless value and in case of a regular model ship hull this value is approximately 0 30 for the prototype the slip is expected to be higher but could not be measured before choosing the propellers and motors Using equation 3 1 with 2 km h desired top speed 3000 rpm rotational speed and a slip of 0 50 a desired pitch of 22 mm is obtained _ IV w S The diameter of the propeller is chosen in the same way the required power and rotational speed for the motors was by looking at examples of model boats The model of the ship M V Ballyloran 27 uses a propeller of 42 mm in diameter Because the propeller size is often chosen by relating it to the power of the motor a propeller size of 42 mm is assumed to be sufficient for the prototype p 3 1 3 3 3 PLACEMENT OF THE PROPULSION There are different choices concerning the number of motors and propellers and the orientation in which they are mounted on the buoy The first possibility is using one or more propellers with a rudder s behind it This option provides good navigational precision when moving to a new location but compensating the yaw is more difficult for the buoy when a rudder would be used because the buoy need to move away from its position for the rudder to be effective Rudders are most effective when the
24. schroeven worden gebruikt en voor het stabiliseren een platform met pneumatische cilinders Het overzicht van onderdelen is niet compleet omdat we sommige onderdelen in ons klein schaal model weglaten zoals een gps unit of voor sommige onderdelen zoals bijvoorbeeld de accu goedkope of gratis alternatieve oplossingen gebruiken zoals een spanningsbron PRIJS PER STUK PRIJS 20 40 AD DA omzetter 14 10 40 Actuatoren 4 30 4 80 eenmalig 200 Compressor 4 BO 120 Sensoren J3 SO 150 Printplaat J2 20 40 100 100 15 30 100 100 TOTAAL LE Arjan van der Kruijt Copyright 2014 DATASHEET TRANSISTOR On the next three pages the most relevant pages of the datasheet of the used transistors 32 are included 39 B DATASHEET TRANSISTOR PD 94964 International IER Rectifier IRL640PbF HEXFET Power MOSFET e Dynamic dv dt Rating e Repetitive Avalanche Rated D e Logic Level Gate Drive Voss 200V e RDS on Specified at Vas 4V 8 5V e Fast Switching Rps on 0 180 e Ease of Paralleling e Simple Drive Requirements Lead Free Description Third Generation HEXFETs from International Rectifier provide the designer with the best combination of fast switching ruggedized device design low on resistance and cost effectiveness The TO 220 package is universally preferred for all commercial industrial applications at power dissipation levels to approxim
25. section 4 1 3 The absolute distance between the current position and destination could be calculated by the microcontroller to see if the prototype must move but this is not necessary Instead the motors are activated when the current longitude or current latitude differs more than a to be chosen value from the destination longitude or latitude respectively The value must be chosen in such a manner that the maximum difference between the current position and destination is not more than the accuracy ofthe GPS 3 5 5 HE OVERRIDE FUNCTION The last thing the navigation software need to be able to do is be controlled remotely Unfortunately no real time connection between the microcontroller and a computer could be implemented Further research into I C communication with two masters could be done and a USB to I C connector purchased to make such a connection possible And due to the limited amount of pins available on the microcontroller board a system that would control the prototype using for example the buttons on the microcontroller board was also not possible However the function to turn off the autonomous position control and to enable a different piece of software to set the motor driver state of the prototype is implemented This function has two parameters one that enables or disables the override function 1 is enabled 0 enables the autonomous positioning and one that represents what the motor driver state the controller should be in
26. to a 12 V PWM signal and outputs it to the motors The waterproofed motors at last run the propellers making the buoy move 33 RECOMMENDATIONS Reviewing our design a few things can still be improved or need more research A short list of possible developments is given The motor drivers for the prototype need to be able to make the motors rotate both ways For this the design with the first H bridge could be modified with a H bridge that can handle higher currents To make the GPS data more accurate differential GPS DGPS could be considered For this technique stations on land broadcast corrections on the GPS signals These corrections can be used by the buoy to make its positioning more accurate A way to do more accurate surge and sway corrections can be investigated An accelerometer could used to more accurately measure the surge and sway while a configuration with more motors might be able to do these corrections more accurately These sensors could be positioned on the stabilized platform of the buoy to minimize measurement errors that may be caused by surge and sway motion An electrical compass as an addition on the gyroscope will prevent errors cause by integrating the noise on the gyroscope measurements In the next design the yaw correction could be implemented A control system might be necessary to to control this yaw correction The direction in which the destination lies when it is calculated using the
27. 0000 2010000 NOTE To establish Torgue Rating in nM divide g cm by 10 197 0 IMPORTANT NOTICE Due to the wide range of applications for this product itis the users re sponsibility to establish the products suitability for their individual purpose s NA a a Aen PAPE IEEE A mn 6 Aa 93 MEA comopmus 919D SERIES SINGLE RATIO METAL GEARBOX RE 540 1 MOTOR GEARBOX DIMENSIONS D fees E CODE Soor 11 1 EO 919D501 50 1 919D0101 010 4 91903000 1 Part No 1071 Anti vibration mount M3 Part No 919D30 TIMING PULLEYS Bearing Blocks 5mm I D Part No 919D26 Steel shaft 5mmOD x 150mm Part No 919D29 Pulleys Belts Double ended motor mount Length Width 919D15 165 9 Part No 919D30 1 Bearing Blocks 6mm I D Part No 919D26 1 Steel Shaft 6mmOD x 150mm Pt No 919D1 In Line Pt No 919D2 Voltage Regula Pt No 919D3 In line Coupling Pt No 919D4 Pulley Pt No 919D24 Bevel Gear Coupling 6mm 6mm Dia tor 6 15v DC Input 4v 12v out 6mm 8swg Meccano 25mm dia Aluminium box Right Angle 12 67mm x 24 8mm put 26mm x 31mm x 15 5mm Dia 12 67mm x 24 8mm Pt No 919D5 Pulley 16mm Pt No 919D6 Universal Pt No 917D2515 O Ring Pt No 919D27 Gear Adapter Pt No 919D25 Nylon Bevel dia Aluminium Coupling 6mm 6mm 70mmx5mm Dia Gears 1 1 0D30 7mm ID6mm
28. 10 meters the navigation was designed to only kick in when the distance to the destination is more than that Itis also tested that the navigation can notice when it is further than this distance away from its destination This means we can deduce that requirements 2 1 10 and 2 1 11 are met The total navigation system costs 134 22 which not include the gyroscope The budget granted was 70 It must be noted that the estimated budged differed quite a bit with the final expenditure Costs for raw materials were barely made and besides that the other group members chose a design that turned out to be cheaper than expected With shifting some budget the costs stayed under limit Requirement 2 1 3 is therefore met Component amount Microcontroller board Olimex LPC P1343 Borrowed DUT GPS unit Navilock 552ETTL GPS module 39 99 Conrad Electronic Benelux BV GPS cable Aansluitkabel Navilock NV DL Z 9 99 Conrad Electronic Benelux BV Gyroscope Parallax L3G4200D 26 29 RS Components B V Nmos transistor 2 IRL640PbF 2x 3 95 HEC Electronica Delft Brushed motor 2 919D2 51 2x 26 06 RS Components B V Waterproofing materials PVC caps clips and glue 13 94 amp Gamma other material see fig 3 3 free DUT Propeller 2 3 bladen scheepsschroef 2308 50L 2x 3 89 Conrad Electronic Benelux BV Fuse with socket 2 5 A fuse with socket 2x 1 25 HEC Electronica Delft PC power supply Cooler Master RS 380 PMAP Borrowed
29. Bachelor Thesis Manoeuvrable Buoy for Offshore Wind Assessment gt ad 2 O E D Ge O gt ps 09 eb 2 eb QO Delft University of Technology Challenge the future BACHELOR THESIS MANOEUVRABLE BUOY FOR OFFSHORE WIND ASSESSMENT by 1 Hogervorst A van der Kruijt in partial fulfillment of the requirements for the degree of Bachelor of Science in Electrical Engineering at the Delft University of Technology to be defended on Wednesday July 2nd 2014 at 9 00 AM Supervisor Ir S T Navalkar Thesis committee Dr S D Cotofana Delft University of Technology Ir S T Navalkar Delft University of Technology Prof ir L van der Sluis Delft University of Technology An electronic version of this thesis is available at http repository tudelft nl Delft t University of Technology PREFACE This design report describes the design of a prototype of an autonomously manoeuvring buoy with a stabil isation platform on top that provides a stable basis for measurement equipment This design was commis sioned by the Delft University of Technology The focus of this design report will be on the autonomously manoeuvrability Two students out of six will be responsible for this part The other four students ofthe com posed group will be responsible for the stabilisation platform and a scaled version of a buoy In a period of two months different steps where taken A backg
30. Bridge Motor Driver 3A Dual Full Bridge Motor Driver 25W 4 8 to 46V 15 Pin MULTIWATT 15 online Avaiable at http nl rs online com Infineon IPP50CN10N G N channel MOSFET Transistor 20A 100V 3 Pin PG TO 220 3 online Ava iable at http nl rs online com NXP semiconducters I C manual March 2003 online Avaiable at http www nxp com documents application_note AN10216 pdf J E Volder The CORDIC Trigonometric Computing Technique Institute of Radio Engineers Inc 1959 pp 226 230 International Rectifier IRL640PBE N Channel MOSFET Transistor 17A 200V 3 Pin TO 220AB online Avaiable at http nl rs online com MFA Como Drills Geared model motor 4 5 15V 2 5 1 online Avaiable at http nl rs online com
31. DAR emits light in the form of a laser and measures the light that is reflected by the airborne particles to determine how fast and in which direction those particles are travelling 7 LIDAR can measure air currents at multiple heights up to 300 meters making it a very useful tool For offshore measuring a LiDAR device is often placed on a buoy Another way of measuring wind data that is used offshore is using large met masts that are placed on the bottom of the sea Buoys are preferred because they are cheaper to deploy and can be easily relocated by boat 1 2 GLOBAL PROBLEM DEFINITION Using a LiDAR device on a buoy poses a problem A LiDAR needs to be on a completely horizontal platform to perform ac curate measurements Besides that it would be very convenient to have a buoy that doesnt need to be relocated by boat be cause deploying ships to pickup a buoy to place it somewhere else can be expensive and time consuming That is possible when the buoy is designed like some kind of ASV ASV stands for Autonomous Surface Vessel and will be examined in section Lave The assignment description 8 refers to an existing buoy as an exam ple to explain the intention This Seawatch buoy 9 uses a LIDAR module Figure 1 1 LIDAR ZephIR 300 named ZephIR 300 shown in figure 1 1 To limit the scope of our thesis 2 1 INTRODUCTION we use these products as the basis of our design This is because they both are proven in practise Toget
32. Definition 7 DA AMM aves ea ud ee tee ddr 7 2 11 FEN s es a a u En a den and 7 2 1 2 full scaledbuoyreguirementt 9 2 1 3 Production requirements o sooo e AAA 10 2 14 Ecological requirements su 4 eea ette e 11 2 1 5 Business requirements lt gt as s eee READE RR DOES drake he 11 De EE EE A ee ike AAA 11 3 Design Process 13 Sl ONE re bed SA BE eRe 13 32 LG RE EE EE EN 14 33 Propubion denoi coo ek dee eee he ke a G Bk 15 SJ VROM NE EIN 15 SS MARINA EE EE ee ee ee 15 3 3 3 Placement of the propulsion osos 4 za a a de BSE a 16 3 34 H NEN ss nova ka a Een asien 17 305 VEN e e a en AAA 17 3A 0 oe ss aros sacra 17 SE ee a en ee aa 18 351 Communication with the GPS module xicos can ee herre ke ESS 19 3 5 2 Communicationwiththegyroscopes 20 3533 re EAO es eK a hehehe eS 20 334 MotorControl es s asana ewe ee SEER RES OEE EG 22 3 5 5 T v ae er a Ra 22 ETE lt ce esad wi ee AAA 22 4 Testing and Results 25 Al CU ee aaa EE eee eae IIA 25 Ah DIS ae a ce hek ee EE EE 25 JE ICI rev Nr A 25 EE NE mod le EEE EE AAA 26 214 Navigation o s es r eee val dB BE JE Sev e Ude Sk here RE 26 215 Tees eek ae m RE ERE ERE RRA ESE HEE SS 21 216 MENN as A AAA ne 27 42 R s ltsand discussions rasa ewe ee Re ee giare Sana PTE SAG 28 AZ IEA y ks a e a a zd vle AR AA AAA 28 122 LONG o gt a ais ee ie en ee ee e
33. EA 0183 GGA GSA GSV RMC VTG Page 5 Date 12 2010 46 C DATASHEET GPS MODULE NAVILOCK e Serial RS232 Level e Baud rate 38 400 bps e Output protocol NMEA 0183 GGA GSA GSV RMC VTG TTL Level 3 3 Volt Baud rate 38 400 bps 0 to 0 6 Volt TTL Low Level 2 31 to 3 3 Volt TTL High Level 3 3 Volt 2 TTL Level Tolerance Output protocol NMEA 0183 GGA GSA GSV RMC VTG Physical Properties e Dimensions 30 mm x 30 mm x 7 9mm e Cable length none optional connection cable 95843 required 10 cm at open cable ends e Operating temperature range 400 to 85T The USB Serial Bridge is only populated on NL 550ERS Please refer to the ublox5 reference manual for protocol description It is available for download under http www navilock de produkte gruppen 13 Boards und Module 60418 NL 550ERS ublox5 html show datafile amp type 7 The NL 551EUSB requires a ublox5 USB driver which is available for download under http www navilock de produkte gruppen 13 Boards und Module 60419 NL 551EUSB ublox5 html show datafile amp type 3 Page 6 Date 12 2010 DATASHEET MICROCONTROLLER On the next three pages the most relevant pages of the datasheet of the used microcontroller board 23 are included 47 48 D DATASHEET MICROCONTROLLER INTRODUCTION LPC P1343 is a development board with LPC1343 ARM Cortex M3 based microcontroller for embedded applications from NXP LPC P1343 featuring a high
34. M signals are noted The start up current the first few seconds after switching on the motor 4 2 RESULTS AND DISCUSSIONS 29 is not captured in the table Duty cycle Current motor left A Current motor right a Table 4 1 Measurement of currents at different duty cycles and 500 Hzat 12 V 4 2 2 DRIVERS The first test confirmed that the motor controllers work the way they were supposed to The output during this test was a PWM signal of 12 V with the same duty cycle and frequency as the input set by the pulse generator At the second test it was discovered that the transistor 50CN10N is virtualy unable to switch on at the voltage of 3 3 V that the microcontroller supplies After replacing the transistors with the type IRL640 the last test was done Properties of this transistor can be found in appendix B After connecting the motors the current increased and became too big for the H bridge to handle more than 2 A as shown in table 4 1 The H bridge temperature rose up until 100 C and kept rising The large current was caused by the resistance of the casings That is why the choice could be made to use an other H bridge which can handle bigger currents Due to limited time the H bridge was removed from the mo tor drivers during all further tests causing the buoy to rotate around the Z axis with a drift of at most 0 5 m Therefore requirement 2 1 13 is not met but consequences are very limited No other requirements are enda
35. MODULE Setting up the communication with the GPS module is done by enabling the UART of the microcontroller and setting it to the correct baud rate Like mentioned in section 3 2 the GPS module has a baudrate of 38400 The microcontroller has a baudrate generator that requires a input clock of 16 times the baudrate The clock can be set to the desired frequency using a clock divider that controls the clock speed of the baudrate generator Equation 3 2 shows how the value of this clock divider can be chosen ryaud represents the desired baudrate f represents the clock frequency of the microcontroller and div represents the value of the clock divider Solving for the unknow values results in a div of 117 1875 Setting the clock divider to 117 the closest integer to the desired value results in a baudrate of 38462 which deviates 0 16 from the baudrate ofthe GPS module This difference is small enough to ensure successful communication between the GPS module and the microcontroller fe k 3 2 divx 16 ea Tbaud The bytes that are received using the UART form sentences of the NMEA 0183 protocol as mentioned in section 3 2 The bytes represent symbols following the ASCII encoding NMEA sentences always consist of comma separated words The first word of the sentence is a six symbol long word that starts with GP while the three last letters of this word signify what kind of sentence that sentence is A NMEA sentence ends with a sym
36. al a lower efficiency than brushless motors because the brushes cause fric tion The brushes wear out and need to be replaced periodically causing maintenance costs Brushed motors can however be controlled more easily since they require just two control wires with no specifications to the timing of the control signals instead of a three phase control signal with timing that determines its rota tional speed Besides that brushed motors are far cheaper to buy than brushless motors For these reasons the choice for brushed motors is made for the prototype The required power and rotational speed of the motors of the prototype is chosen by comparing the di mensions and specifications of the prototype to a model boat The model boat selected to be compared is a model of the ship M V Ballyloran 27 This boat has a weight of 16 4 kg and uses a 12 V Marx Decaperm motor with a gear ratio of 1 2 75 This motor produces a power of 42 W at maximum efficiency and rotates at a speed of 8400 rotations per minute rpm Because of the gearbox the rotation speed of the propeller ofthe model boat is approximately 3050 rpm The prototype of the buoy is expected to weigh about 10 kg some what less than the model boat The width of the boat is 216 mm while the prototype has a width of 526 mm and while the model boat has a streamlined V shaped hull the prototype has a less streamlined round hull This means the water resistance of the buoy is a lot higher tha
37. al equipment to be placed away from the prototype A disadvantage in relation to other positioning systems e g an acoustic positioning system is that a regular GPS module has a poor indoor performance To communicate its data to a user in this case the microcontroller the GPS module needs to have a suit able communication protocol at its disposal Since the microcontroller has a serial UART 24 connection available this way of serial communication is preferred The size price and compatibility with the system were taken into consideration for the choice for the Navilock NL 552ETTL GPS receiver More information about thid GPS module can be found in appendix C It is in size better than alternatives which are so small that they cannot be soldered into a system easily like the A2200A GPS Module while still being affordable But most importantly it communicates in a way that the microcontroller can easily use it sends bytes using a Universal Asynchronous Receiver Transmitter UART with a baud rate of 38400 The microcontroller has as mentioned in section 3 1 a built in UART component The information sent by the chosen GPS module is represented in the NMEA 0183 protocol This protocol uses sentences formed by comma separated words This kind of sentences can easily be interpreted by the microcontroller The NMEA 0183 protocol is the stan dard for communicating positioning information for naval applications The GPS can also provide
38. ange of private users who make adjustments whose effect they do not know In order not to render the module unusable thereafter the memory is volatile for user settings General Specifications u blox5 GPS amp GALILEO SuperSense UBXG5000 UBXG0010 GPS Chipset High Sensitiv Tracking Sensitivity 160 dBm AssistNow Offline Support 14 Days Almanac Data DGPS WAAS EGNOS and MSAS Support EGNOS Default disable Supports NMEA 0183 Protocol Internal patch antenna Specifications Chipset u blox5 GPS 8 GALILEO SuperSense Frequency L1 1575 42 MHz C A Code 1 023 MHz Channels max 50 channels Position UP DATE Rate 4 Hz Sensitivity 160 dBm Tracking Sensitivity 160 dBm Satfixing Sensitivity 145 dBm Cold Start Positioning accuracy 2 5 m CEP 5 0 m SEP or SBAS 2 0 m CEP 3 0 m SEP Speed 0 1 m s Time 1us synchronized to GPS time Internal CMOS Multi Purpose Flash 2 Byte 13H 19 2 512 KByte SST39VF400A Date e Basic setting WGS 84 Time New acquisition 1 sec on average Hot start 3 5 sec on average Warm start 25 sec on average Cold start 30 sec on average Dynamic Conditions e Altitude of reception Max 18 000 Meter 60 000 Feet e Speed of reception Max 515 Meter Second 1000 Knots e Acceleration Max 4g e Vibration Max 20 m s x 3 Power Supply e Electrical connection 5V DC e Current draw Approx 80 mA Interface Properties e USB 1 1 e Baud rate Auto e Output protocol NM
39. ately 50 watts The low thermal resistance and low package cost of the TO 220 contribute to its wide acceptance throughout the industry Absolute Maximum Ratings Parameter IDG Tc 25 C Continuous Drain Current Ves 5 0 V Ip Tc 100 C Continuous Drain Current Vas 5 0 V lom Pulsed Drain Current Pp Tc 25 C Power Dissipation Linear Derating Factor Gate to Source Voltage Single Pulse Avalanche Energ Avalanche Current lt Peak Diode Recovery dv dt Operating Junction and Storage Temperature Range Soldering Temperature for 10 seconds 300 1 6mm from case Mounting Torque 6 32 or M3 screw 10 Ibfein 1 1 Nem 55 to 150 Thermal Resistance Ec Parameter Units Rec Junction to Case Recs Case to Sink Flat Greased Surface Reva _Junction to Ambient www irf com 1 01 30 04 41 IRL640PbF International IGR Rectifier Electrical Characteristics O Ty 25 C unless otherwise spodje Parameter Min Typ Max Test Conditions Vas 0V Io 2504A Breakdown Voltage Temp Coefficient _ V C Reference to 25 C Ip 1mA Static Drain to Source On Resistance zd a Vas 5 0V Ip 10 l u B 0 27 Ves 4 0V Ip 8 5A Vasih Gate Threshold Voltage 1 lire 2 0 V Vos Ves Ip 2504A E Forward Transconductance 16 S Vos 50V Io 10A Y 7 Drain to Source Leakage Current SS E Vos 200V Vag OV Vos 160V Vas 0V Tj 125
40. ating mode Four general purpose timers counters with a total of four capture inputs and 13 match outputs D DATASHEET MICROCONTROLLER Programmable WatchDog Timer WDT System tick timer Serial Wire Debug and Serial Wire Trace Port High current output driver 20 mA on one pin High current sink drivers 20 mA on two I2C bus pins in Fast mode Plus Integrated PMU Power Management Unit to minimize power consumption during Sleep Deep sleep and Deep power down modes Three reduced power modes Sleep Deep sleep and Deep power down Single 3 3 V power supply 2 0 V to 3 6 V 10 bit ADC with input multiplexing among 8 pins 40 GPIO pins can be used as edge and level sensitive interrupt sources Clock output function with divider that can reflect the main oscillator clock IRC clock CPU clock Watchdog clock and the USB clock Processor wake up from Deep sleep mode via GPIO interrupts Brownout detect with four separate thresholds for interrupt and one threshold for forced reset Power On Reset POR Crystal oscillator with an operating range of 1 MHz to 25 MHz 12 MHz internal RC oscillator trimmed to 1 accuracy that can optionally be used as a system clock PLL allows CPU operation up to the maximum CPU rate without the need for a high frequency crystal May be run from the main oscillator the internal RC oscillator or the Watchdog oscillator Code Read Protection CRP with different security levels
41. be dangerous for anyone who is involved For example the propellers of the buoy may never be turning when the buoy is being hauled aboard because they might injure someone Therefore a reasonable safety margin must be respected 2 1 18 The production and deployment of the buoy happens following the safety regulations of that sector for example the regulations for use of international waters 20 On the end of its life time the buoy still should not be harmful to the environment Therefore another re quirement with respect to its materials is set about recyclability The materials used on the buoy that will be recyclable will be most likely the metals and the high quality synthetics that are used 2 1 19 Atleast 70 of the buoy is recyclable 2 2 SCOPE 11 2 1 4 ECOLOGICAL REQUIREMENTS The full scale buoy will be deployed in the ecological offshore environment so it must not harm that envi ronment Therefore the following requirement is set 2 1 20 The buoy does not contaminate the environment in which it is deployed When malfunctioning the ecological effect must not exceed the limits set by European regulations 2 1 21 The buoy and its components are produced following the European ecological regulations regarding the production of technology 2 1 5 BUSINESS REQUIREMENTS From the perspective of the market the navigation component of the product must be as compatible as possible without losing any of its functionality The
42. bol a checksum number and two end sentence symbols The checksum number is a hexadeci mal number that is used to verify that the received sentence does not contain a bit fault The checksum must be equal to the xor of all received characters between the and symbols If the checksum verifies the sentence the information of that sentence can be used by the microcontroller There are a large amount of NMEA sentences of which several are sent out by the GPS module The com munication is for this purpose one way there is no need to communicate anything back to the GPS module since it already sends useful sentences The sentence that is primarily used to obtain the position and state of the GPS module is the GPGGA sentence This sentence contains the longitude and latitude of the module 20 3 DESIGN PROCESS the amount of satellites in view and whether the module has a fix on its location The longitude and latitude are represented in degrees minutes one sixtieth of a degree and 1074 minutes Since 1 x 107 degree is the smallest value that can be represented in NMEA the longitude and latitude values are stored on the micro controller in a 32 bit register where one bit represents 500000 degree This means the resolution of the stored location is SAN ARGEN times the earth s circumference which results in a resolution of 18 5 cm This resolution is far smaller than the expected average difference between the actual position and t
43. chematic view of the two considered motor placement configurations The choice is made for the prototype to attach the propellers to the motors with shaft that is as short as possible like visualised in figure 3 2 This way the motors can be mounted on the underside ofthe buoy The choice for this placement of the motors is made because it is a solution that is uncomplicated it does not require a shaft to go through the hull of the prototype and requires no joints or gears to connect the motor and propellers to that shaft Another point in favor of this solution is that it increases the modularity of the 3 4 MOTOR DRIVER 17 solution it can be mounted on different vessel without having to integrate the motor and motor shaft into that vessel 3 3 4 SELECTED COMPONENTS For the prototype two motors ofthe type Como Drill 919D with a 2 5 1 gearbox are chosen More information on this motor can be found in appendix E Together the motors have a power rating of 42 4 W 21 2 W each and they have a rotational speed of 5000 rpm at maximum efficiency at 12V DC The motors provide the de sired power although their rotational speed is higher than the value mentioned in section 3 3 The speed of the motor can be easily scaled down using the motor driver see section 3 4 so having a higher maximum rotational speed is not undesirable The motors are equipped with a capacitor of 0 22 uF parallel across its terminals This is to make sure that when the cu
44. consumption of the CPU and the GPS unit The other mode is active when the vessel is closer than 600 m near its target In this mode the course is modified more often to reach the destination accurately 1 4 OUTLINE OF THE THESIS Having described the existing techniques in the field of the subject the designing of a navigating LIDAR buoy is described in the rest of this thesis divided into the following chapters The next chapter chapter 2 holds the objective of this thesis the requirements of the design and the scope of the project Chapter 3 discusses the choices and actions made during the design of the prototype Chapter 4 presents the method of testing of the prototype and the results of those tests The conclusions we draw from the tests are discussed in chapter 5 and chapter 6 contains the recommendations about the project 1 4 OUTLINE OF THE THESIS Buoy System ET A i A A i vn vn nn 9 3 AM A an AE A CA A ii in Ai di Ten nn ee DIRA 7 Buoy Position m DGPS Corrections Heading Thruster oe o Thruster GPS Receiver Electric compass Control unit N Modem and Satellite phone Buoy Position DGPS Corrections Modem and Satellite phone Modem and Telephone Buoy mapping system on research ship DGPS Corrections Service on land Figure 1 5 Schematic representation of a navigation system of an autonomous surface vessel um sm EEE l e gt e eee SAMIM pm ee
45. ct that the gyroscope was not calibrated while the module pointed exactly north This happened because the compass could not be held directly next to the module before cal ibration because the electromagnetic field of the laptop that was used as power source for the navigation system influenced the compass Since the navigation system reached its destination requirement 2 1 9 is met 4 2 5 TOTAL SYSTEM One motor with its cables has a mass of 383 g and the drivers have a mass of 56 g That adds up to 882 g The mass of the microcontroller was not taken into account because the microcontroller is already on site Even if the microcontroller was added the weight would not exceed 1 kg and therefore requirement 2 1 6 is met 4 2 6 INTEGRATED SYSTEM The first test after lowering the prototype into the water is testing if it is still stable on the water s surface with the autonomous position control system attached Since the buoy remained floating right side up even when pushed over it was confirmed that the prototype was still stable With this requirement 2 1 14 is met Each motor driver state is tested and measured twice In table 4 4 the average speeds measured during the tests are shown in case of the forward states or the average turning speeds in case of the turning states are shown One motor was found to provide less thrust than the other The effect of this was that the buoy did not sail in an exact straight line at the slower speed
46. d stations to get a more accurate position measurement vii INTRODUCTION 1 1 BACKGROUND The search and exploitation of environment friendly energy sources is an ongoing topic Fossil energy re sources will only last for a limited period of time Solar energy wind energy and alternative renewable energy resources are becoming more popular and already play a significant role in the current energy production In 2013 about 21 of the world s produced electrical energy was renewable energy while this was 18 in 2003 1 Wind energy is one of those renewable energy resources Especially the offshore application of wind tur bines is a growing market The global growth rate of offshore wind energy is 30 percent installed capacity per year 2 In the future offshore wind turbines can satisfy a huge part of our energy demands In a recent study the European Environment Agency EEA estimates the technical potential of offshore wind energy in the EU to be 30 000 TWh annually The European Commission estimates total EU electricity demand of be tween 4 279 TWh and 4 408 TWh in 2030 3 Before the placement of wind turbines in an offshore environment several measurements are required to calculate the profitability of placing those wind turbines The most interesting factors are the wind speed its direction and continuity 4 5 One technique of measuring this is using a LIDAR Light Detection And Ranging 6 device In essence Li
47. e Making the dimensions too big will result in larger production costs and an unmanageable prototype The following scale is selected 2 1 1 For the prototype a scale of 1 5 is held in relation to the full scaled buoy The start date is the 22th of April 2014 and the deadline of this report is the 18th of June 2014 The proto type needs to be build by then and test must be performed Therefore the following requirement can be set 2 1 2 The prototype is built in a time span of 2 months For this project a budget was allocated To determine the size of the budget a estimation was done This estimation can be found in appendix A This includes the budget for all three subgroups 2 1 3 The prototype does not exceed the budget of 820 euros The buoy must be able to operate while drifting in turbulent waters From this a number requirements can be derived 2 1 4 All buoy components that will be submerged when the buoy is in the water need to be completely water tight 2 1 5 All components above the surface when the buoy is in the water need to be at least splash waterproof This means that the electronics aboard the prototype may not come in contact with any water when water is splashed against it 8 2 PROBLEM DEFINITION For the total weight of the buoy the navigation system can not add too much weight to the buoy because it increases risk of sinking The prototype is able to keep afloat ifits draft increases somewhat A draft i
48. e ae ne 29 423 KROES MOE oaeen N eee eS ESS a 29 124 MORA oot betwee ae eee en es AAA 30 4125 VINU s i e e eS oe Raw RE FASE A 31 vi CONTENTS 426 Integrated system es en aa o IAEA Hs 31 5 Conclusion 33 SL Overview NSL x ane eeraa A a a a a A 33 6 Recommendations 35 A Budget 37 B Datasheet transistor 39 C Datasheet GPS module 43 D Datasheet microcontroller 47 E Datasheet motor 51 Bibliography 55 SUMMARY Offshore electrical energy production out of wind energy is a growing market Wind and water data is needed to measure the most profitable location to set up offshore wind farms Retrieving the required information can be done by placing expensive masts or deploying moored buoys with measuring equipment The prob lem with moored buoys is that they need to be relocated by ship every time wind data from a different position is need which can be time consuming and expensive The goal of this thesis is to design an autonomous positioning system for a scaled prototype of an offshore wind measurement buoy The main requirements connected to this goal is that the system must be able to measure its current position calculate in which direction it must travel to reach its destination and have ap propriate propulsion to move the prototype toward that destination The prototype must also be able to keep its position and prevent itself from drifting off From tests performed on this prototype recommendation for the design of a full scale au
49. e is attached to a flat surface and after calibration it is rotated several times around its z axis The microcontroller displays the measured angle on its LEDs so that the actual rotation can be compared to the measrued rotation The direction calculation is tested by programming several current positions and destinations into the microcontroller and displaying the result on the LEDs to be checked against the expected values After all components were tested to work separately the total navigation system is tested For this test both the GPS and and gyroscope are connected to the microcontroller The GPS module the two gyroscopes and the microcontroller are fastened closely together on a piece of wood as shown in figure 4 1 The system on this piece of wood will be called the navigation module during this test One end of this module is chosen to be the front this would be the direction the buoy would sail if the module was mounted on the prototype Both gyroscopes are present although only one is necessary because the software is designed to initialize and communicate with two gyroscopes Changing this would take time while initializing an extra gyroscope but not using it does not have any negative effects A destination position is chosen the coordinates of that destination are measured using the GPS module and entered into the software Then a start position is chosen a several dozens of meters from the destina tion During thi
50. e performed on the motor drivers in different stages of the design process e The first test is a test on the motor drivers alone to check that they were built correctly This is done as follows Voltage sources are used to power the drivers and to simulate the control signals of the H bridges and a pulse generator is connected on the gate of the NMOS transistor to simulate PWM signals The output of the H bridges is measured to confirm that the motor driver works as expected e If this first test succeeds the same test is done with the PC power supply to power the motor driver and the microcontroller to provide the control signals 29 26 4 TESTINGAND RESULTS e As a last step the motors are connected to the output of the H bridges The motors are inside their waterproof casing during this test By checking if the motors rotate at the expected speed and in the expected direction it can be verified that the drivers work correctly The limitation that needs to be taken into consideration during this test is that the H bridges can only conduct 2 A of current without risking them breaking 4 1 3 THE GPS MODULE The first test conducted with the GPS module is a test to determine the accuracy of the module For this test the GPS module is connected with a PC using a USB TTL serial cable This cable converts the serial signal sent into the USB end to a UART signal and vice versa The 5 VDC on the USB port is also used to supply the GPS unit with
51. een two point less than 20 km apart is negligible The prototype will for testing purposes never be given a destination more than several dozens of meters away because of the limited length of the cable of the power supply and the limited sailing area on the test location This means equation 3 3 can be used to calculate the direction in case of the full scale design as well as for the prototype The main problem that needed to be solved is that the microcontroller has no hardware to do floating point calculations As a result the arctan function needs to be estimated just using integer operations 0 atan2 La Le Aq c 3 3 0 atan2 sin L4 L cos A cos A sin Ag sin A cos Ag2 cos L4 L 3 4 arctan ifx gt 0 arctan2 y x 90 arctan ify Oandx lt 0 3 5 90 arctan ify lt 0andx lt 0 The arctan function can be estimated using the CORDIC Trigonometric Computing Technique 31 The computing sequence that is used by the microcontroller is the vectoring computing sequence This sequence 3 5 SOFTWARE 21 rotates a two dimensional vector with set angles each one smaller than the previous one until the vector lies as close as possible to the positive x axis By adding up all the taken rotation steps the angle of the vector with the x axis is obtained which is equal to arctan y x An example of how the vectoring sequence works is shown in figure 3 5 the original vector red is rotated with increasingly
52. es second with an accuracy of 8 75 millidegree per second degree 26 3 3 PROPULSION DESIGN The buoy needs a way to move itself towards its destination In this section the method of propulsion is chosen the specifications of this propulsion are considered and the components are selected that meet the specifications The propulsion of a large majority of all ships on the sea are realised with propellers outside the hull but there are other methods of propulsion such as sails and pump jets Sails are not a usable option for the buoy because they rely on the wind for their power so the speed of the buoy would be unreliable at best Pump jets use propellers inside the hull to pump water in and expel it through a nuzzle at high speeds Pump jets provide high speed and manoeuvrability for boats but they are less efficient at lower speeds and more expensive to install than regular propellers This is why motors with propellers outside of the hull are selected as the method for propulsion 3 3 1 THE MOTORS A choice must be made between different types of electric motors AC motors brushed DC motors and brush less DC motors For this choice both technical aspects such as power and efficiency and economical aspects such as costs need to be considered Firstly the buoy has a battery as a DC voltage source This is why only DC motors are considered There are two main types of DC motors brushed and brushless motors Brushed motors have in gener
53. ey should While testing each state the forward or rotational speed in that state is measured During this test the PC power supply is placed on the buoy to power the prototype The testing setup is shown in figure 4 3 The 230V cable the leads to the power supply is made sure not to touch the water And to minimize the effects if the cable might touch the water and short circuit through the water a 230 V to 230V transformer with earth leakage switch and fuse is installed between the power supply and the power socket During this test requirement 2 1 14 will be checked This requirement states that the autonomous navigation control can not destabilize the prototype This is tested by checking whether the prototype with the autonomous position control system can be easily capsize If this is not the case the requirement will be met Figure 4 3 Testing the speed and turning of the buoy Another test was done to test the entire autonomous positioning system in combination with the buoy For this test a cable of the pc power supply was extend to 10 meters in length This way the power supply does not need to be on the buoy meaning that the fuse in the power supply will cut off the power if a short circuit occurs due to water The combination of the GPS gyroscopes and microcontroller as shown in figure 4 1 is placed on top of the prototype and the motor drivers are connected to the microcontroller A destination position is pre programmed into the
54. full for communicating with sensors and such while on an FPGA those protocols need to be implemented from the bottom up This is why a microcontroller is selected for the prototype There are two kinds of microcontroller boards that can be provided by the Delft University of Technol ogy to use during this project One board uses a Atmel ATmega8 microcontroller 21 while the other uses a LPC1343 microcontroller 22 Some relevant features of both microcontrollers are shown in table 3 1 IC is a communication protocol that can be used to communicate with multiple devices on the same bus Com munication with sensors like the gyroscopes discussed in section 3 2 is done with I C which is why a micro controller with this function is preferred Based on the features listed in the table the LPC1343 is the more suitable microcontroller of the two Buying another board with a microcontroller with even better specifica tions is an option but since the available microcontroller is already sufficient for our purpose there was no need to buy an other microcontroller The available board that uses this microcontroller the Olimex LPC P1343 board for more information about his board see appendix D has a limited number of available Input Output pins since some of the pins of the microcontroller are used for the USB connection buttons LEDs the I C and UART connections 13 14 3 DESIGN PROCESS of the board The number of remaining pins is expected
55. has SWD interface at the moment is ARM JTAG COOCOX https www olimex com Products ARM JTAG ARM JTAG COOCOX OpenOCD debuggers ARM JTAG TINY ARM JTAG TINY H ARM JTAG OCD ARM JTAG OCD H can also be adapted to work with SWD interface by getting https www olimex com Products ARM JTAG ARM JTAG SWD NOTE that at the current moment only Rowley Crossworks supports this combination PROCESSOR FEATURES LPC P1343 board use ARM Cortex M3 microcontroller LPC1343FBD48 301 from NXP Semiconductors with these features ARM Cortex M3 processor running at frequencies of up to 72 MHz ARM Cortex M3 built in Nested Vectored Interrupt Controller NVIC 32kB on chip flash programming memory Enhanced flash memory accelerator enables high peed 72 MHz operation with zero wait states In System Programming ISP and In Application Programming LAP via on chip bootloader software Serial interfaces USB 2 0 full speed device controller with on chip PHY for device UART with fractional baud rate generation modem internal FIFO and RS 485 EIA 485 support SSP controller with FIFO and multi protocol capabilities C bus interface supporting full I C bus specification and Fast mode Plus with a data rate of 1 Mbit s with multiple address recognition and monitor mode Other peripherals 42 General Purpose I O GPIO pins with configurable pull up down resistors and a new configurable open drain oper
56. he IC bus to 400kHz The specifics of the protocol can be found here 30 and will not be explained into more detail in this thesis 3 5 3 DIRECTION CALCULATION The microcontroller needs to be able to calculate the direction in which the buoy must sail in order to reach its destination When neglecting the effects of the curvature of the earth the direction in which the buoy needs to sail can be easily calculated using equation 3 3 L represents the longitude in this equation while A represents the latitude and 0 represents the direction Subscript c denotes the current position of the buoy and subscript d denotes that of the destination The atan2 function is a function with two arguments that increases the range of the inverse tan function to 7 7 in the way shown in equation 3 5 When the curvature of the earth is not neglected the fact that longitude and latitude are polar coordinates influences the equation resulting in the more complicated equation 3 4 In the full scale design the route the buoy will take is calculated on a computer and sent to the buoy as a series of way points This computer program uses data on sea maps and shipping lanes and does not lie within the scope of this thesis The distance between the way points sent to the buoy will not be more than 20km because the buoy does not sail very fast so it will be travelling a long time between way points The effect of the curvature of the earth when calculating the angle betw
57. he one measured by the GPS unit which means this resolution will not be a limiting factor for the accuracy of the positioning The coordinates sent by the GPS module are expected to be varying to some degree which will result in a rapidly changing current position that is used by the microcontroller To prevent this the current position that is used by the microcontroller will be the average of four received coordinates which mean the position is updated once a second The GPS module can also calculate the orientation and speed of the buoy by comparing a number of previous locations This data is only reliable when the module is moving fast enough for the previously visited points to form a consistent line The prototype is expected not to move this fast this is why the direction in which the prototype moves is measured using the gyroscopes 3 5 2 COMMUNICATION WITH THE GYROSCOPES The communication with the gyroscopes is as mention before done via the I C protocol This protocol allows a master to communicate with multiple slaves over one shared bus 30 In our application the microcontroller acts as the master while both gyroscopes are slaves The IC protocol uses 2 buses one data bus over which the communication happens and one clock bus On the clock bus a clock signal is set by the master all slaves use this clock rate for the communication making it synchronous communication The microcontroller sets the clock rate of t
58. her with the two goals mentioned above the following problem definition is composed Designing an actively stabilised platform for the SEAWATCH offshore buoy to account for measurement errors of the ZephIR 300 LiDAR Designing autonomous position control for the SEAWATCH buoy Delivering a working scaled prototype of the buoy with both of these designs The Seawatch buoy 9 is a wavescan buoy with a LiDAR de vice on top shown in figure 1 2 The wavescan buoy is a circu lar moored buoy that is equipped with several sensors for obtain ing different kinds of meteorological and oceanographical informa tion This buoy has proven successful for purposes like collecting data on ocean currents air and water temperature wave height and direction and solar radiation The LiDAR device is affixed to the top of the buoy without any stabilisation The power required for the measurements can be provided by a battery and by optional so lar panels With this buoy in mind a navigation system will be de signed The design of a platform that actively compensates the buoy s tilting angle caused by the waves can be found in the bachelor theses 10 11 of the four other participants of the project group The second issue is the repositioning of the buoy The goal is to design a system that makes a buoy able to travel to a given position autonomously With this in mind Figure 1 2 Seawatch buoy the search begins to find the situation with regard to the
59. iDAR Buoys with their properties 4 1 INTRODUCTION 1 3 2 AUTONOMOUS NAVIGATION Autonomous navigation on the ocean is not done by buoys Unmanned vessels on the water surface only exist in the form of small boats A collective name for all boats and buoys that navigate without a person driving it on board is Autonomous Surface Vessel ASV ASVs are used in the military commercial and research sectors for a wide range of purposes which include 15 e Military and security purposes such as mine field exploration weapon testing ocean surveillance and marine personnel training Environmental monitoring and underwater positioning for commercial uses such as on off shore oil and or gas sites Gathering of information on seawater and wind on the ocean s surface for scientific purposes One of the commercially available ASVs on the market today is the C Enduro made by the company ASV Ltd 16 The C Enduro shown in figure 1 4 is a long endurance autonomous vessel that can be equipped with different kinds of sensors for monitoring for ex ample the CO rates solar and wind or ocean waves and currents on the surface This particular vessel has the shape of a flat cata maran and is 4 2 m long and 2 4 m wide The large flat top sur face of the vessel is covered almost entirely in solar panels and it is equipped with a wind turbine as wide as its hull Using these power sources in addition to a small diesel generator the vessel
60. ics It could be described as the ratio of the inertia of a ship to the gravitational forces working on it In this case the Froude number is used to describe the amount of drag resistance the buoy has in the water and it can be calculated with equation 2 1 By giving the prototype the same Froude number as the full scaled buoy the amount of drag resistance the prototype has at its top speed is comparable to the amount of drag resistance of the full scale buoy Using equation 2 1 a desired top speed of 2 km s 0 56 msecond is obtained a vsL 2 1 7 The prototype sails at a minimum top speed of 0 62 m s Fd 2 1 2 1 8 The prototype obtains its current position from a positioning system that has an average deviation ofat most 10 m For the navigation of the buoy to its navigation a number of requirements can be set For the requirement below it must be noted that the buoy is only capable of maneuvering in waters with a sufficient depth and a limited current 2 1 9 The prototype calculates the direction to its destination and is able to make it there as long as the destination is reachable in one line 2 1 10 The prototype reaches its destination with a maximum deviation as small as its positioning system allows 2 1 11 The prototype keeps its position with a maximum deviation as small as its positioning system allows For future purposes the buoy gets an override function This way the buoy may be extended with a manual
61. m needs to have an override function for maneuvering the buoy manually or any other purposes The implementation of this function is described in section 3 5 5 This function will not be tested explicitly but it will be used during tests involving the motor driver and the mi crocontroller to simulate the motor driver states calculated by the autonomous positioning This is done by connecting the motor drivers to the microcontroller and using the override function on the microcntroller to set the output signals to a certain motor driver state using the buttons on the microcontroller If those tests are successful requirement 2 1 12 will be met as well 4 1 6 INTEGRATED SYSTEM After the autonomous positioning system has been tested on its own the system is installed on the prototype ofthe buoy which is designed by M Baas amp A Pannekoek 10 The motors are placed in the chosen configu ration on the underside of the buoy as figure 4 2 shows and the microcontroller and drivers are placed inside the PVC drain pipe that forms the center of the prototype The PVC pipe can be sealed making it splash water proof Therefore requirement 2 1 5 is considered met Figure 4 2 The motors attached to the prototype of the buoy 28 4 TESTINGAND RESULTS The buoy is tested in the top end of the towing tank of the faculty 3ME of Delft University of Technology During this test all motor driver states are tested to see if they make the buoy move as th
62. manoeuvre control An other purpose can be the correction of the yaw using the propulsion system In figure 2 1 different movements like yaw are illustrated 2 1 12 The navigation system has an override function that allows another system or a user to control the propulsion of the buoy 2 1 13 The propellers of the buoy are placed in such a way that the buoy can rotate around its Z axis to com pensate the yaw without drifting away 2 1 14 The autonomous positioning system is placed on the buoy in such a way that it does not jeopardize the stability of the buoy 2 1 REQUIREMENTS 9 Figure 2 1 six degrees of freedom 2 1 2 FULL SCALED BUOY REQUIREMENTS Some of the requirements set for the prototype apply to the full scaled buoy as well while others are not relevant to the full scaled buoy Table 2 1 shows what requirements of the prototype can be applied to the full scaled design and what requirements need to be modified before they can be applied Some of these modifications are explained as follows e Since the full scale buoy is 5 times bigger than the prototype the volume and weight of components like the motors and propellers are approximately 125 times larger because of the three dimensions e For the precision of reaching its destination and of staying on one location the buoy is dependent on the accuracy of the GPS unit aboard Since the accuracy of GPS is 7 8 m on average the deviation the buoy can have from its intended
63. microcontroller Then the buoy is laid into the water about 25 m away and then turned on to see if it moves towards its destination 4 2 RESULTS AND DISCUSSIONS The tests described in the previous section are performed and results are described in the this section After the test results the consequences of the results of the tests are discussed 4 2 1 MOTORS The result of the motor tests is that the motors worked fine and the casings are both watertight After rotating for several minutes under water at full speed no water had leaked into the casing The casings do add some friction on the motor shaft making the current that the motors require during their start up more than 2 A To differentiate between the two motors they are mentioned by the position they will be given on the prototype left or right The first seconds the right motor used 2 1 A while the left motor used 2 5 A with peaks at the moment of switching that were even higher After the start up the current through both motors slowly declined toward 1 3 A through the right motor and 1 9 A through the left one This difference in power consumption is caused by the way each motor is fastened into its casing the left motor was placed slightly obliquely with respect to the tube increasing the friction of the rubber ring on the rotor shaft The decrease of the current is due to the warming up of the petroleum jelly which causes less friction In table 4 1 currents at different PW
64. n that of the model ship Although the exact top speed of the model boat is not mentioned in the source it is very likely that the model boat has a higher top speed than the desired 2 km h of the prototype The exact weight of the prototype and its friction in the water were still unknown while choosing the motors but since the example model boat has both a higher weight and higher top speed 42 W is assumed to be enough power to propel the prototype Waterproof motors are not very easy to find but it still is an option to buy an waterproof motor Most motors for model boats use a propeller shaft through the rear bottom of the boat but that concept is unusable for a buoy purpose The costs of a waterproof motor are a lot higher than a regular motor Given the fact that there is a limited budget the choice is made to accept the challenge of waterproofing it by hand The designing of a waterproof housing is described in section 3 3 5 3 3 2 THE PROPELLERS The pitch and diameter are the most important dimensions of the propeller of a boat The pitch of a pro peller is the length the propeller would move forward if it were to do one complete turn in a solid substance 16 3 DESIGN PROCESS The pitch is related to the rotational speed of a propeller and the speed of the boat via equation 3 1 In this equation p is the pitch of the propeller in m v is the speed of the buoy in m s w is the rotational speed of the motor in rad s and S the slip of the
65. nce Thesis Manoeuvrable Stabilised Buoy for Offshore WindAssessment not yet published P L de Goffau J C Mes Bachelor Thesis Thesis BEP Report not yet published Flidar Cost Effectieve Accurate Wind measurement 2013 online Avaiable at http www flidar com wp content uploads 2013 11 FLiDAR_Intro_201311 pdf Axys Technologies Inc WindSentinel Offshore Wind Resource Assesment Buoy 2013 online Ava iable at http axystechnologies com wp content uploads 2013 11 WindSentinel digital Data Sheet pdf Neptune Project Neptune Barcelona Spain 2014 online Avaiable at http neptool eu Autonomous Surface Vehicles Ltd ASV unmanned marine systems Portchester UK online Avaiable at http www asvglobal com Autonomous Surface Vehicles Ltd Long Endurance Marine Unmanned Surface Vehicle Portchester UK online Avaiable at http www asvglobal com files datasheets c enduro datasheet 1 pdf Ken Ishii et al Development of Dynamic Positioning Buoy for vertical sensing National Research Insti tute of Fishery Engineering Kashima Japan 1995 C R Griffiths Extreme residual current speeds upon the uk continental shelf 1996 online Avaiable at http www hse gov uk research othpdf 400 499 0th437 pdf 99 96 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 BIBLIOGRAPHY M Courtney Lidars Offshore
66. ncrease of 10 should be acceptable so an estimation of a reasonable weight comes out to a maximum of 10 of the total allowed weight Since the prototype has an 1 5 scale the weight needs to be scaled with a factor 5 one time in each dimension Since the full scaled buoy has a weight of approximately 1200 kg 9 the following requirement can be set 2 1 6 The navigation system mass may not exceed a total of 1 kg The global problem definition repeated in section 2 1 implies that the prototype needs to able to relo cated itself to a given position and needs to prevent drifting off At first a top speed is argued and defined Besides that the minimum accuracy of the position is set The speed of the prototype is obtained by first setting a desired speed for the full scale buoy A speed of at least 5 km h 1 4 m s is desirable for the real buoy because with such a speed the buoy will be able to move around the area where a new wind farm is planned in a manner of hours since wind farms have a typical surface area of 10 to 30 km Besides that the speed of currents at sea for example the North Sea and the Norwegian Sea rarely exceeds 5 km h 1 4 m s 18 which implies that the buoy is almost always capable of dealing with current Scaling down this desired top speed for the buoy to a desired top speed for the prototype is done using the Froude number The Froude number is a dimensionless value used to describe certain flow characterist
67. ngered and the buoy is still properly maneuverable The test with the transistor as the only component in the driver circuit had a good result The circuit that is instead is shown in figure 3 4 configuration 1 Not all states of the motor controller described in section 3 5 4 be used without the half bridges Table 4 2 shows which states can still be used without the H bridges The states are different in another way from the states from table 3 2 in the way that the left and right states only use a 50 duty cycle Since the rotation speed of the prototype will not be the maximum possible without H bridges the choice is made to reduce the rotation speed even further in favour of higher controllability Duty Cycle Left Duty Cycle Right Forward fast Forward slow Left Right Stop Table 4 2 The PWM duty cycles in each of the motor driver states that remain withou H bridges 4 2 3 THE GPS MODULE During the first test the amount of satellites in the view of the GPS module varied between four and seven averaging 5 5 satellites The coordinates from the ten samples taken during this test are shown in figure 4 4a The measured points have a standard deviation of 0 00336 minutes from the average latitude value and a standard deviation of 0 00318 minutes from the average longitude of the measurements This average co ordinate of the ten samples lies 0 0069 minutes latitude and 0 0013 minutes longitude from the coordinates of the actual mea
68. ngles of both the gyroscopes as the calculated direction need to be encoded in the same way The orientation measured with the gyroscopes is saved in a register with the least significant bit rep resenting 35 2000 degrees This is why the rotation values of the vectoring steps 90 45 26 6 14 0 etc are calculated in the same format and set hard coded into the memory of the microcontroller These values will be used during the vectoring computing sequence after each rotation the value corresponding to that rota 22 3 DESIGN PROCESS tion is added or subtracted to or from the resulting angle With the vectoring computing sequence and equation 3 3 the direction towards the destination can be calculated The last step is using this information to control the motors 3 5 4 MOTOR CONTROL The microcontroller must finally be able to send signals to the motor drivers For each motors there are two H bridge control signals and one PWM signal that need to be sent out by the microcontroller The values of these signals depend on the orientation and the desired direction of the buoy The first step that the motor control algorithm takes is calculating the angle the buoy still needs to rotate which is done by subtracting the orientation from the direction Using this angle the motor control sets the duty cycles of both motors to a desired value In this process six states are defined forward fast forward slow backwards slow turn right and turn lef
69. ould work as expected The first test on the motors is done shortly after the delivery of the motor Supplying the motors with 12 V on their terminals in both ways will reveal if the motors run in both directions and then supplying the motors with a PWM signal supplied by a pulse generator at different duty cycles and frequencies to observe how the motors react to PWM signals e The second test performed on the motors is a test to determine the difference between the two motors inside their casing For this test the motor is placed inside its casing and then directly connected to a voltage source The propeller is not attached to it because it does not contribute on the result While supplying the motors with different voltages the current used by the motors is noted Although the power consumption is not a focus during this design the motors may not use more than the 5 0 A because that is the maximum current that can pass through the safety fuse and the maximum current that may flow through the H bridges is only 2 0 A e The third test is a test to determine if the waterproof casings are actually waterproof Again the pro peller is not attached The motor inside its casing is lowered into water and the source is turned on for several minutes at 12 V Since the motor is the only component of the navigation system that is fully submerged requirement 2 1 4 is tested during this test 4 1 2 DRIVERS Just as with the motors three tests wer
70. ped with a Global Positioning System GPS receiver to measure its current position The position of the buoy is used to correct the wind measurement data with the drifting of the buoy around its anchor point The buoys that have wave measurement equipment can also correct the measured wind data with the angular displacement of the buoy These corrections are done with signal processing software specially designed for this purpose Furthermore all buoys described above have ways of short range and satellite communication to send the measurements back to the main land in regular intervals The different types of LIDAR buoys including the seawatch buoy and their properties are summarised in table 1 1 An important observation that can be made from this table is that none of the buoys can move itself autonomously and only one uses active stabilisation Besides that all systems of which the buoys are a part use software data correction to make their measured data more accurate Wind Sentinel Neptune Project Available on the market X xs B B Active platform stabilisation X Passive platform stabilisation X Software data correction X X x X Wavemeaswemet e KT GPS Receiver x x X Short range communication GSM GPRS amp GPRS modem GPRS 3G information not VHF UHF radio _ amp Wifi released Satellite Communication Moored Buoy Autonomous Positioning PV Cells Optional Wind Turbines Fuel Cells Table 1 1 Existing L
71. rements is that the accuracy of the GPS module is dependent on the amount of satellites in view which in turn is dependent on among others the location of the GPS module The more open the surroundings of the GPS module are the easier the module can pick up signals from satellites In the second test this effect was visible by the lower standard deviation of the the points from the average The full scale buoy will be sailing at sea an environment with very little obstructions like buildings which means the GPS will not be hindered by this kind of obstructions This makes the second test more representable for the conditions under which the buoy will be operating That means that that the requirement 2 1 8 is met the positioning system has an average deviation of less than 10 m 4 2 4 NAVIGATION The tests performed on the separate parts of the navigation system yielded the following results e The communication between the GPS module and the microcontroller works as intended the slight difference in baud rate did not have a noticable negative influence on the communication e The angle measured by the gyroscope has a slight error that is linear to the amount the gyroscopes 4 2 RESULTS AND DISCUSSIONS 31 has turned from the position in which it was calibrated After correcting this error by multiplying the measure angle with a constant value of 1 02 the average measurement error was reduced to around 2 degrees The results of this test are
72. riginal PWM signal is a 3 3 V signal produced by the microcontroller This 3 3 V PWM signal needs to be converted to a 12 V signal for the motors This is achieved by switching a 12 V source on and off with us ing the 3 3 V PWM signal from the microcontroller In figure 3 4 the implementation is shown with a NMOS transistor In this configuration the NMOS transistor is connected to ground and has a job to pull down the voltage at the negative terminal of the motor while the positive terminal is connected with 12 V DC The motor is now able to turn in one direction To make the motor spin in both directions the polarity on the motors needs to be reversed Therefore a half bridge H bridge is used A H bridge is a system of switching transistors used to reverse the voltage across two terminals The H bridge that is used has two input signals When one of those inputs is 1 and the other 0 the voltage across the load becomes positive while when the inputs are inverted the voltage across the load is reversed and becomes negative In figure 3 4 the implementation of the H bridge is shown Two such circuits are used in the propulsion system one for each motor The H bridges that were selected to be used in the motor driver are of the type L298N produced by STMi croelectronics 28 These H bridges can operate with input voltages between 5 and 45 V and can handle currents up to 2 A This is expected to be enough to control the motors since the current
73. round research has been done a design made build and tested All these steps are described in this thesis With some of these steps some extra help was offered Therefore we would like to thank all the people that were involved or contributed in some way to the project A special thanks goes out to the following people for their support advice and commitment to the project Sachin Navalkar our supervisor He came up with the subject and guided us through this project with useful feedback Kees Slinkman he took care of ordering components and came up with some great design ideas Be sides that he took care of the manufacturing of some of the components and supplied us with tools Decosier BV who sponsored the project by making free raw materials available The staff of the towing tank for letting us perform tests on water The people at the faculty of 3ME that made our workspace available The other participants of the group who always where a pleasure to work with Mathieu Baas Paul de Goffau Johan Mes and Annemieke Pannekoek I Hogervorst A van der Kruijt Delft June 2014 ili CONTENTS Summary vii 1 Introduction 1 Lal DN ch ee eee na m na a in SER aan a 1 1 2 Global problem definition i i se soes a rede 1 1 3 State of the art analysis deca ee bee BOERS AAA A 2 ook IMANES eee ee eee ee eee ee Ree EEE AA 2 1 32 AUTONOMOUS HEARD 24 sne en eeN ee ne d a A IA OE Oe cc a idos 4 2 Problem
74. rrent through the motor is suddenly cut off the inductor current does not cause a very high voltage across the connections of the motor for a short period of time The propellers selected have a diameter of 50 mm and a pitch of 26 mm The propellers are larger both in size and pitch than the values mentioned above This is to account for the possibility that the slip of the prototype is higher than the 0 50 assumed while calculating the pitch A larger propeller can provide more forward force per rotation which makes these propellers useful when operating the motors below their max imum rotational speed The propulsion requirements for the full scale buoy can be obtained by scaling up the properties of the motors and propellers of the prototype The scale factor of the power of a motor is typically the scale factor squared making the total power consumed by the large scale buoy if these motors are scaled up 1040 W which would exceed the set 125 W limit The size of the propellers when scaled up will be 25 cm However at this stage of the design process no conclusion can be drawn as to whether the selected motors and pro pellers are sufficient for the prototype The requirements for the motors and propellers are discussed in the recommendations chapter 6 3 3 5 WATERPROOFING The main disadvantage of mounting the motors on the underside of the prototype is that the motors need to be in a small enclosure that needs to be entirely watertight
75. s test the different motor driver states are represented using the LEDs on the microcontroller when the LEDs in the middle of the array of 8 LEDs light up it is in the forward state Light on the left and right op the module when pointing the front side of the module away from you means that it is in the left and right states respectively All LEDs lighting up at once means that the destination has bee reached To let the gyroscope put out the orientation of the navigation module in degrees from true north like the direction calculation does the gyroscope needs to be initialized while the navigation module points straight north This is verified using a compass 4 1 TEST PLAN 27 Figure 4 1 Test setup for the complete navigation system After initialization the navigation module is moved in the same way the buoy would in the motor driver state that is represented on the LEDs The position on which the stop state is entered is compared to the actual destination position If the stop position of is less than the GPS accuracy away from the desired destination then the test is successful and then requirement 2 1 9 is met 4 1 5 TOTAL SYSTEM The total navigation system must be weighed to determine its exact mass to check if requirement 2 1 6 is met This will be done with a kitchen scale Other test on the total navigation system are done with the sys tem integrated with the prototype of the buoy Requirement 2 1 12 states that the syste
76. sation and autonomous positioning and it needs to be close to self sufficient in its energy consumption Therefore the capacity of the battery banks that will be used on the full scaled buoy is doubled Via equation 2 2 the total power the buoy has at its disposal is roughly 400 W The existing systems of the buoy consume around 200 W 19 The remaining available 200 W is divided as follows the active compensation can t use more than 75 W and the autonomous position control can t use more than 125 W 395W 22 7 2 2 Power with Deadacid 9792 Ah Tithium 248 Ah e U 12V e S 180W e h 720 hours month e y 1 3 Fraction of time the solar panel is operational This results in the following requirement 2 1 16 The energy consumption of the navigation and propulsion units may not exceed 125 W 2 1 3 PRODUCTION REQUIREMENTS Should the buoy ever be taken into production the following requirements are set for the production of the buoys The environment friendly image made by providing techniques for wind farms will be reinforced by or dering components or raw materials at companies that have the same reputation or at least not a bad repu tation 2 1 17 Components and raw materials are bought at shops or from companies with a non controversial im age During its lifetime the buoy is handled by multiple people both during its production and during it deploy ment to and recollection from sea These interactions must not
77. smaller steps blue toward the positive x axis AE a VERE Figure 3 5 Example of the vectoring computing seguence The pseudocode representing the CORDIC vector step is as follows angle lt 0 if y is larger than 0 rotate 90 degrees clockwise x y and y x angle angle 90 else rotate 90 degrees counter clockwise x y and y x angle angle 90 iteration counter O while the desired calculation accuracy is not met if y is larger than 0 rotate arctan 2 iteration counter degrees clockwise angle angle arctan 2 iteration counter else rotate arctan 2 iteration counter degrees counter clockwise angle angle arctan 2 iteration counter iteration counter is increased by 1 The angle that is added or subtracted each iteration is 0 arctan 2 because this way each rotation step can be calculated by adding or subtracting a n bit right shifted version of each element of the vector to or from the other one For example a clockwise 45 degree angle is done by adding y to x and subtracting x from y and a counter clockwise rotation of 14 degrees arctan 1 4 is done by subtracting y shifted right by 2 bits from x and adding x shifted right by 2 bits to y During this computing sequence the length of the vector is not kept the same but that information is not required To make the result of the vectoring sequence comparable to the rotation around the z axis measured by the gyroscope the a
78. surement position 107 minute is as mentioned in section 3 5 equal to 18 5 cm when is assumed that the circle of which that length is a part has the circumference of the earth This is the case for the longitude circles which go over both poles and the latitude circles which are perpendicular to the longitude circles near the equator But the circumference of latitude circles decreases as the distance to the equator increases This means when assuming 107 minute is equal to 18 5 cm this will always be a maxi mum value Thus the average distance between the measured positions and the actual position is at most 13 30 4 TESTINGAND RESULTS m y 69 13 x 0 185 During the second test the GPS module had seven satellites in its view during all samples The coor dinates from the ten samples taken during this test are shown in figure 4 4b The measured points have a standard deviation of 0 00057 minutes from the average latitude and 0 00060 minutes from the average longi tude of the measurements The average coordinate of the ten samples lies 0 0041 minutes latitude and 0 0006 minutes longitude from the coordinates of the actual testing position This means that the average distance between the actual position and the measured positions is at most 7 9 m Based on the result of both tests the maximum drift off distance as described in section 3 5 4 is chosen to be 10 m Based on this choice the motor controller will start the motors when
79. t These states are called motor driver states since each state causes a different behaviour of the motor driver The forward fast state is used when the prototype needs to move to a new location while the forward slow and backwards slow states are used when the prototype needs to keep a certain position and when it has almost reached its destination Turn left and right are used to turn the buoy in the right direction before it can begin sailing toward its destination These states will make the buoy turn around its Z axis without moving in the x of y directions Finally the stop state stops both motors The prototype is in this state when it has reached its destination With these six states the prototype can reach any destination that is in a straight line from it Table 3 2 shows the duty cycle of the PWM signals and control signals of the H bridges that are required in each state Duty Cycle Left H Left Duty Cycle Right H Right Forward fast Forward slow Backward slow Left Right Stop Table 3 2 The PWM duty cycles and H bridge control signals in each of the five motor driver states The motor control only needs to direct the prototype to anew location when it is further away from its goal then a set allowable drifting distance This distance needs to be as small as the accuracy of the GPS module allows according to requirement 2 1 11 so it needs to be chosen after the accuracy of the GPS module has been tested see
80. the buoy with data on its speed and direction but this data is only reliable when the GPS receiver is moving at a high enough speed Since the buoy and especially the prototype is not going to be moving that fast a different way of measuring the orientation of the buoy is required To implement the stabilized platform the prototype will be equipped with gyroscopes that measure its rotational speed around all three axis By taking the integral of the rotational speed around the z axis the orientation of the buoy can be obtained This implementation is noise and distortion sensitive since the noise and distortion will be integrated but despite that this method is chosen to measure the orientation of the buoy The distortion on the signal is caused by an average rotational speed that the gyroscope measures while it is completely sta tionary The distortion problem is tackled by calibrating the gyroscope By taking hundreds of samples in a fixed position the average distortion is calculated and subtracted from the output signal of the sensor The main advantage of using the used gyroscope is that no additional sensors are needed This means that no 3 3 PROPULSION DESIGN 15 additional ports of the microcontroller are required to connect that sensor and no separate code has to be written to communicate with that sensor The gyroscope sensors chosen are of the type Parallax L3G4200D This type of sensor can measure rotation speeds of up to 250 degre
81. they need without load is 0 5 A and they load on the motors is not expected to be so large that the 2 A is exceeded The transistor that is chosen for the motor driver is of the type 50CN10N 29 This transistor can handle 20 A drain current and a gate source voltage of 20 V meaning that it can handle the current and voltage that the motors require It also has a typical gate threshold of 3 V meaning the 3 3 V of the microcontroller should be able to switch it 3 5 SOFTWARE Now that all separate components are designed and chosen the next step is to make all parts work together as one system For our purposes the microcontroller has five tasks to fulfill e The microcontroller reads out the location sent by the GPS module e The microcontroller keeps track of the orientation of the prototype using the data from the gyroscopes e The microcontroller calculates the direction the prototype has to face to travel to its destination e The microcontroller sends out the control signals for the motor drivers for the appropriate propulsion in the calculated direction 3 5 SOFTWARE 19 12V Lev 3 3V T A 3 3V en Configuration 1 Configuration 2 Figure 3 4 Implementation of the motor driver with just one NMOS transistor configuration 1 and with an H bridge in addition to the NMOS transistor configuration 2 The microcontroller has a function that can be used to manually control the prototype 3 5 1 COMMUNICATION WITH THE GPS
82. to be sufficient for the prototype and that is why the LPC P1343 microcontroller board is selected However the amount of pins that will be needed for the complete design could not be counted yet at this stage of the design The LPC 1343 microcontroller is not perfect however It has no hardware to perform floating point op erations This is a limitation that needs to be taken into consideration while designing the algorithm for calculating the direction of the buoy in section 3 5 The solution to this limitation will be using fixed point operations to approximate the answers The fact that the number of Input Output pins is limited also needs to be taken into consideration during the rest of the design Clock speed CPU SRAM memory Flash memory In Out pins UART connections I C connections Table 3 1 Comparison of the ATmega8 and LPC1343 microcontrollers 3 2 POSITIONING SYSTEM The prototype need to be able to obtain its position from some kind of sensor The full scale buoy obtains its position from GPS signals To increase the scalability of the program running on the microcontroller GPS would be a smart choice While other positioning systems would use different protocols to send their data a GPS that is placed on the prototype will send data in the same way a GPS module on the life sized buoy would Another reason is that a GPS module is relatively small which makes it easy to fit on the buoy and that it does not require adition
83. tonomous positioning buoy are derived The system that is designed uses a GPS module to measure its location and a gyroscope to measure its orientation A microcontroller uses this information to calculate the direction to a pre programmed destina tion This direction is used to sent signals to two motor drivers which control two DC motors with propellers attached to them The system is designed in such a way that it can be easily added to the scaled prototype of the buoy the motors are attached to the underside of the prototype while the rest is placed inside the prototype The different parts of the autonomous positioning system are tested confirming that they work like they were designed to The prototype with the system attached can move itself in any horizontal direction and the correct signals to control the motors are generated Due to a failing test setup a test that combines these parts was unsuccessfully For the design of the full scale buoy a different hull shape for the buoy is recommended The designed propulsion costs too much power when scaled up to be realizable in full scale For more accurate navigation the use of an electric compass is recommended above a gyroscope An electric compass measures the Earth s magnetic field to calculated which way is north Also techniques like Differential GPS or accelerometers can be considered for more accurate positioning Differential GPS DGPS uses signals with GPS corrections sent by lan
84. vessel they are attached to has a reasonable speed Since the prototype is not very fast a rudder will most likely not be the most optimal solution Also choosing or designing a rudder suitable for the buoy is another design step that is not strictly necessary which would only cost extra time This is why a rudder is not preferred in this case Another option is mounting two motors with propeller on a different place on the buoy A configurations with 3 or more motors do not provide much more controllability and extra cost for the third motor is not worth it With only two motors there are many possible configurations The two configurations shown in figure 3 2 are considered in particular This is because the two configurations are well suited to compensate for a certain aspect of the drifting of the buoy Configuration 1 compensates the yaw especially well while configuration 2 is very suitable for the compensation of surge and sway However surge and sway can be compensated with configuration 1 while configuration 2 has no way of compensating for the yaw When moving to a new location both motors need to be turning at full speed for the highest top speed In this case the motors in the configuration 2 work partially against each other Other configurations are not more efficient or do not provide more controllability than configuration 1 This is why the configuration 1 is chosen for the prototype Configuration 1 Configuration 2 Figure 3 2 S
85. with a few flashbacks 2013 General Assembly of the United Nations Convention on the Law of the Non navigational Uses of Inter national Watercourses 1997 online Available at http legal un org ilc texts instruments english conventions 8_3_1997 pdf Atmel corp ATmega8 L Datasheet 2013 online Avaiable at http www atmel com images atmel 2486 8 bit avr microcontroller atmega8 datasheet pdf NXP semiconductors LPC1311 13 42 43 Datasheet June 2012 online Avaiable at http www nxp com documents data sheet LPC1311 13 42 43 pdf OLIMEX Ltd LPC P1343 development board user s manual February 2013 online K Conway M DeHaan UART Universal Asynchronous Receiver Transmitter February 2011 on line Avaiable at http whatis techtarget com definition UART Universal Asynchronous Receiver Transmitter Maestro Wireless GPS Receivers A2200 A User Manual February 2012 online Avaiable at http www richardsonrfpd com resources RellDocuments SYS 29 GPS Receiver A2200 User Manual VI 0 pdf Parallax Inc Gyroscope Module 3 Axis L3G4200D Datasheet April 2013 online Avaiable at http www parallax com sites default files downloads 27911 Gyroscope 3 Axis L3G4200D Guide v1 1 pdf Tankerman Motor and Prop Survey last accessed on June 18th 2014 online Avaiable at http www modelboats co uk forums postings asp th 45505 amp p 3 STMicroelectronics L298N Full
86. with the rotating motor shaft coming out of it Figure 3 3 shows the parts of the designed solution As watertight capsule a 50 mm diameter PVC drain pipe 1 with two tightly fitting caps 2 and 8 on both ends is used This pipe can be easily attached to the underside of the buoy using PVC fixing clips shown in the figure 1 Two PVC rings 3 and 5 hold the motor 4 in place and the motor shaft exits the capsule through a rubber ring 7 that is fitted into the cap 8 The motor shaft 6 is designed to connect the 6 mm rotation shaft of the motor to the 3 3 mm screw thread shaft on which the propeller 9 can be fastened This motor shaft has a section between the motor and the propeller where it has a smooth surface this part is were it leaves the capsule through the rubber ring The wires of the motor leave the capsule though the other end 2 A hole is made in the cap just large enough for the wires and after they are pulled through that gap the wires are glued into place To prevent the water from dripping in slowly through the rubber ring when the motor shaft is rotating some petroleum jelly is applied between the shaft and the ring This also reduces the friction of the shaft caused by the rubber ring The last step of the waterproofing is adding a 5 0 A fuse to the motor circuit If there occurs a leakage the resulting short circuit will only blow the fuse 3 4 MOTOR DRIVER The motors can be powered by a DC voltage signal of between

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