3-component force balance and angle of attack actuator

EG3005 3rd Year Project FinalReport 2013/2014

3-component force balance and angle of attack actuator

Tobias Reichold

Date of submission: Friday, 9th of May 2014

University of LeicesterDepartment of Engineering

Contents

1 Introduction 11.1 Overview 11.2 Project background 1

1.2.1 Forces in flight 11.2.2 The Charles Wilson wind tunnel 2

1.3 Core components and functionality 21.3.1 The use of a force balance? 4

2 Manufacturing and Assembly 52.1 Early work 5

2.1.1 Fixed Plate modifications 52.1.2 Floating plate modifications 52.1.3 ”Components to be manufactured” 62.1.4 Gears 72.1.5 Force transfer strips 7

2.2 Initial modifications and assembly 72.3 Final manufactured components 112.4 Final assembly 14

3 Electronics system 163.1 Encoder concept 16

3.1.1 ADC selection 163.1.2 Potentiometer selection 17

3.2 Electrical shielding 173.2.1 ADC 173.2.2 Power cables 183.2.3 Analog signal cables 183.2.4 Stepper motor 18

3.3 Stepper motor driver 18

4 Control and readout software 194.1 Overview 194.2 Individual stages 19

4.2.1 ADC code 194.2.2 LabVIEW code 20

Potentiometer readout program 20

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Contents

Interpolation program 21

5 Installation and calibration 235.1 LUT calibration 235.2 Installation 23

6 Progress vs proposal 246.1 Delays at the start 246.2 Problems during the project 246.3 Conclusion and handover 25

Acknowledgments 26

Bibliography 27

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1 Introduction

1.1 Overview

This report marks the end of the project to construct and calibrate a 3-componentforce balance and angle of attack actuator for the Charles Wilson sub-sonic windtunnel at the University of Leicester. This final report will describe:

1. The complete manufacture and assembly process2. The electrical systems3. The software code for LabVIEW and the Arduino controller and ADC4. The installation and calibration5. A discussion of the actual progress vs the proposal

1.2 Project background

The renovation of the Charles Wilson wind tunnel is an ongoing project. Over thepast 2 years it has been the departments aim to update the capabilities of the windtunnel by improving the working environment and offering more modern amenities[1]. As part of the renovation, the wind tunnel is to receive an updated 3-componentforce balance with an remote controlled angle of attack actuator (AOA).

1.2.1 Forces in flight

If an airfoil is subjected to a flow of air, it will experience various forces. The 3forces we are interested in are lift, drag and pitching moment. They are in figure 1[3]:

Airflow

Figure 1: 3 airfoil forces

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These are the forces that our force balance should measure. In addition it is ableto adjust the angle of attack (AOA) of the wing section enabling a variety of flyingscenarios, for example if the aircraft is climbing rapidly[3].

1.2.2 The Charles Wilson wind tunnel

The Charles Wilson wind tunnel is a closed-loop sub sonic tunnel, which has a fullywooden framework. Its single 1.5m eight bladed axial fan is powered by a 24kWWard Leonard PSU set, permitting a maximum flow speed of 30ms−1. The tunnelis split into two main sections: The environmental section, which is used e.g. fortesting the aerodynamics of parachutes and the performance of small wind turbines,and a high speed section, where the force balance will be mounted[3].

1.3 Core components and functionality

A force balance is assembled from a variety of components. To understand how theforce balance works, we will outline each core component and it’s functionality. Inthis example, we will look at the fully assembled force balance before it was mountedin the Charles Wilson tunnel:

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Figure 2: Assembled force balance

1. Fixed Plate: The fixed plate is the base plate that mounts to the side of thewind tunnel and holds all other components.

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2. Floating plate: The floating plate has a shaft attached to it, which reachesinto the wind tunnel. The wing section is attached to this shaft. Dependingon the forces acting on the airfoil, the floating plate will move with the airfoil,transferring the resulting forces on to the brass shim force transfer strips. Thefloating plate is suspended by the brass shim strips.

3. Lift force arms: The lift force arms will measure the lift component of thetotal acting forces.

4. Drag force arm: The drag force arm does the same as 3. but for the dragcomponent.

5. Tension spring: The tensioning springs purpose is to hold the airfoil shaft inplace when the system is at idle.

6. Angle dial: The angle dial displays the current AOA.7. Brass shim force transfer strips: The force exerted by the moving floating plate

is transferred to the lift and drag arms via the strips to measure them.8. Jointed spacer arms: These jointed spacer arms allow the floating plate to

move parallel to the fixed plate.9. Retention screws: When the force balance is not in use, these screws are

tightened causing the floating plate to be slightly raised. This removes thetension exerted by the floating plate on the brass shim.

10. Mid train shaft: This shaft has one 11 tooth gear on the front and one 80tooth gear (not visible) on the rear. It transmits the motion of the steppermotor to the main 180 tooth gear and therefore onto the airfoil.

11. Stepper motor: The motor supplies the rotational motion to the gear assemblyand is the heart of the AOA actuator.

12. Potentiometer and bracket: The potentiometer will rotate and vary it’s wipervoltage according to the rotation of the 180 tooth gear. This voltage is usedto determine the angular position of the airfoil.

13. BNC bracket: This holds 6 BNC bulkheads which are connected to the po-tentiometer. Via 2 of the channels, the potentiometer is supplied with 3.3Vand the 4 remaining are for measuring the supply and wiper voltage via theArduino.

14. 180 tooth gear: This gear is connected to the angle dial and the airfoil shaft.15. Tightening bolt: When the airfoil shaft is inserted into the balance, it passes

through an internal collet and sticks out the end. When tightening the bolt,the collet clamps down the airfoil shaft and holds it in place.

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1.3.1 The use of a force balance?

The principle use of such a force balance is in testing different airfoils and deter-mining how much lift they can produce and how much drag they generate, undervarying AOA’s and wind speeds. With the updated load cells to measure the forces,this can now be done very accurately. Another benefit over the old system is theremote controlled AOA actuator. You will be able to set the desired angle usinga LabVIEW program, then have a stepper motor maneuver the section into placewith a accuracy of ±0.1° degrees over a total range of −75° to +75° degrees. Forthe given accuracy, this adjustment is reasonably fast at a maximum rotation speedof 5/second. [3].

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2 Manufacturing and Assembly

2.1 Early work

The project started with a thorough study of the provided documentation, includingreports and CAD drawings, from the former 4th year group who started this projectin 2012-2013[2]. The most important pieces of information from all reports were:

1. How far has manufacturing and assembling progressed,2. Are there any known faults, problems or defective components3. A collection of CAD drawings for existing components and for those which

still needed to be manufactured.The reports and CAD drawings mentioned only a single minor design error whichwas a discrepancy between the stepper motor shaft and the first 11 tooth gear. Thereport stated that almost all components were already manufactured and ready tobe assembled. It turns out that the report missed almost all tasks that were actuallyleft to do. The provided CAD drawings almost all had significant numbers of errors[4].

2.1.1 Fixed Plate modifications

The fixed plate acts as the ground plate, which mounts to the wind tunnel wall andholds all other components. The CAD drawing of the modifications to the fixedplate, which indicated the hole positioning for the force and drag arms, was missinga total of 21 holes on the plate [4]!

2.1.2 Floating plate modifications

The floating plate will move according to the applied forces on the airfoil and transferthe forces onto the force transfer strips. The CAD drawing of the modifications to thefloating plate displayed holes that were either non-existent or severely mislocated.The holes for the stepper motor mounting had counter bores two times too widein diameter for the screws used. In addition, the positions of the bearing blockmounting holes were all wrong by 4mm[4].

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2.1 Early work

2.1.3 ”Components to be manufactured”

The collection of CAD drawings provided contained the mid-train gear shaft, whichhouses an 11 & 80 tooth gear, the motor pinion shaft, the collet for gripping theairfoil section shaft and the bearing block. The dimensions provided for the mid-train gear shaft were all incorrect and did not correspond to requirements of thebearing block. It was therefore completely redesigned as seen in figure 3:

Figure 3: Mid train gear shaft CAD drawingThe same applies to the collet, manufactured by the 4th year group. It had tobe turned down by more than 2mm. To address the issue of the gap between thestepper shaft and the 1st 11 tooth gear, a flexible universal joint was proposed bythe 4th years, which however would not keep the gear firmly in place and wouldallow it to droop down and flex away from the above 80 tooth gear. Figure 4 showsthe gear mounting locations [4]:

Figure 4: Back of floating plate

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2.2 Initial modifications and assembly

The mid train shaft was also suffering from a torque problem which caused it tomove about unforeseeable when spinning up. This is another major problem notaddressed in the report. This was solved by manufacturing an additional bracketwhich fitted on the other side of the floating plate, opposite the bearing block asshown in figure 5 [4]:

Figure 5: Side view of the floating plate

2.1.4 Gears

All, except one gear, did not have a boss extrusion, but the ”Modified Force BalanceAssembly” drawing listed all 4 as having one. This meant that the fitting of grubscrews for the 11 tooth gears was very tricky, as they have to be placed between theteeth of the gear and this only allows for an M2.5 or smaller screw to be fitted as thegears would otherwise interfere with each other. In addition, the 180 tooth gear hadto be re bored to accommodate the tightening bolt. It also required non-standardpitch circle diameter screw holes to be added to secure the gear to the angle dial [4].

2.1.5 Force transfer strips

As seen in Figure 2, the brass shim force transfer strips are responsible for transfer-ring the forces which act on the floating plate from the airfoil section onto the liftand drag arms. These components are of major importance to the entire assembly.The end sections of all 3 brass strips had sheared of right outside their mountingmechanism and new strips had to be found and soldered into their mounts [4].


The first modifications were made to the floating plate in order to mount the step-per motor and bearing block to it. The holes for the block were slightly widened to

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correct for incorrect dimensions on the CAD drawing. With floating plate modifi-cations finished, the next task was to manufacture the redesigned mid train shaftand bracket, so that the shaft would fit precisely into the bearing and housing. Thisallows for free positioning of the gears when aligning them (see figure 4&5) and itsolves the torque issue on the shaft. Next the main 180 tooth gear was re-boredand the non standard pitch circle diameter holes drilled to mount the gear andaccommodate the tightening bolt as shown below in figure 6[4]:

Figure 6: Gear and tightening bolt assembly;The collet was then turned down by a total of 2mm in diameter to fit into the hollowshaft of the angle dial. These tasks were done by the workshop technicians. Thenthe holding brackets for the jointed standoffs were installed. Finally, the steppermotor mounted and the bearing block with it’s bracket counterpart was installed asshown in figure 7 [4]:

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Figure 7: Assembled floating plate;As the fixed plate had already been fully modified, the assembly process was fairlystraight forward. The fixed and jointed standoffs were mounted first, followed by thelift and drag force transducer arms. The arm assembly for the lift arms was mountednext. The shaft of the drag arm was too long to fit properly into it’s bearings, so itwas trimmed by about 4mm and then mounted again as shown in figure 8 [4]:

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Figure 8: Assembled fixed plate;A custom adapter has been made for the stepper motor. This mounts directlyto the stepper motor shaft and accommodates one 11 tooth gear. Both 11 toothgears have been fitted with M2.5 grub screws between the teeth. The adapter isthe replacement for the previously proposed universal joint. The brass shim forcetransfer strips have been cut to size and re soldered into their original position afterremoving all leftover shim from the connections [4]. The work described up to thispoint has been done in semester one. The next section focuses on the work done insemester two work.

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2.3 Final manufactured components


In semester 2, a total of 3 more components were manufactured to implement theangular encoder system. This includes:

1. a variable potentiometer bracket with over-torque protection,2. a shortened BNC connector bank3. a modified, electrically shielded, IP67 diecast box which houses the Arduino

Due.The potentiometer bracket is made from 2 L-profiled pieces of aluminum, allowingboth horizontal and vertical adjustment capabilities in order to ensure a good fitbetween the potentiometer and the main 180 tooth gear as can be seen in figure 9:

Figure 9: Potentiometer with bracketThe potentiometer was fitted with a 15 tooth gear which had been re-bored to 1/4inch to fit the potentiometer shaft. It is secured by 2 M2.5 grub screws, located atopposite sides between the teeth. To prevent the potentiometer from taking damagewhen it is turned beyond its end of rotation, two 2 rubber spacers have been fittedat its mounting point. Both have been treated with silicone spray which enables

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sufficient grip during normal operation and allows the potentiometer to rotate withinthe bracket if turned too far.The BNC connector bank houses 6 non-isolated BNC bulkheads, 75Ω. It is madefrom a piece of aluminum with an L profile as can be seen in figure 10:

Figure 10: BNC bracketThis means that the BNC shields are all interconnected with each other to preventground loops. The connector bank is mounted to the left side of the fixed plateto aid the later cable management of the BNC cables, 75Ω, 5m and to ease theinstallation of the cables from the potentiometer to the connector bank.The last component is a diecast box which contains the arduino board as can beseen in figure 11:

Figure 11: Arduino diecast box

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1. 1-6: BNC bulkheads.2. 7: Guarded power switch.3. 8: PSU banana jacks.4. 9: Ground banana jack grounds out the diecast box.5. 10-11: USB programming & native cable. Programming cable is for data

transmission and the native cable needed to run the Arduino as a host ( nativecable currently not in use).

Six isolated BNC bulkheads, 75Ω, have been added. These provide connectors tothe analog input ports on the arduino. External banana jacks provide the arduinowith power from an external PSU which offers much cleaner power than a simpleUSB supply. This is important as it enables the Arduino to make more accuratereadings. A separate ground banana jack, connected directly to the box, groundsout the enclosure, further reducing potential electric interferences. A guarded powerswitch ensures safe operation of the ADC.

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2.4 Final assembly

2.4 Final assembly

Figure 12: Assembled force balanceAfter all components were manufactured, the final assembly was done:

• mounting the floating plate to the fixed plate,• installing the force transfer strips,• mounting of the potentiometer bracket,• the BNC connector bank and the wiring between the BNC bulkheads and the

potentiometer.

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2.4 Final assembly

To ensure the potentiometer bracket can’t rotate when under load, 2 M4 screws wereinstalled with a horizontal offset to each other to ensure a secure fit. All electricalconnections were soldered on and protected with heat shrink tubing. After a finalinspection by myself and workshop staff, the force balance was deemed correctlyassembled and ready to install.

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3 Electronics system

3.1 Encoder concept

The main purpose of the encoder system is to convert the rotation of the poten-tiometer, which varies according to the rotational position of the 180 tooth gear,into angular position information of the AOA as outlined in figure 13:

Figure 13: ADC diagram and functionality outline

3.1.1 ADC selection

As the main computational infrastructure of the Charles Wilson Wind tunnel ispowered by LabVIEW, a NI ADC such as a NI 6008 USB ADC was the first choice. It offers a 12 bit ADC with differential mode voltage readout and it would ensurecompatibility with the existing infrastructure. However at 95 pounds, it was tooexpensive for the remaining budget. Hence, the Arduino Due was chosen as itoffered the same ADC resolution at a lower price. Other Arduino products, such as

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3.2 Electrical shielding

the Uno, can supply higher voltage of 5V but the ADC resolution is only 10 bits.Going from 10 to 12 bits yields a quadruple resolution of 4095 points rather than1023. Hence the use of the Arduino Due.

3.1.2 Potentiometer selection

The main selection criteria for the potentiometer are:1. A high resistance value in order to get good voltage variations across the full

turn spectrum2. A good linearity tolerance and low temperature drift to ensure a good linear

variation in resistance when rotated3. Must have sufficient turns to be able to to cover an angle range from −75 to

+75 degrees angle of attackThe chosen potentiometer is a Vishay 535 50kΩ 5 turn. This potentiometer offers alinearity of 5% at 50kΩ, which is the highest resistance value in the series. Mountinga 15 tooth spur gear to the potentiometer shaft and being driven by the 180 toothgear, results in the utilization of all 5 turns over the full angular range.

3.2 Electrical shielding

The stepper motor and the driver card components which operate at high voltages,consume large amounts of current in operation. The stepper motor has been fittedwith 5m extension wiring, in order for the force balance to be mounted in placeand the stepper being supplied with power, while having sufficient slack in the wiresto avoid damage when pulled. All these are major sources of interference whichcauses noise to be induced into the voltage signals, reducing accuracy and reliability.Therefore, critical components such as the ADC, power cables, data cables and thestepper need to be shielded.

3.2.1 ADC

As the ADC is the heart of the encoder system, the shielding is extra thorough toensure reliable operation. It is mounted into an IP67 Diecast Box with the boardseparately isolated from the chassis. The chassis itself is grounded via an earth plugto ensure any induced voltages are removed from the ADC and the chassis (see figure11).

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3.3 Stepper motor driver

3.2.2 Power cables

Shielding for this component is critical, as the power cables are very long and carrylarge currents. They have been sleeved over the full length in a tinned copper braidand grounded at one end to earth.

3.2.3 Analog signal cables

For data cables, standard 5m BNC coaxial cables,75Ω, were used as they offer goodshielding, are simple to install and were cheap to buy, compared to 50Ω cables.

3.2.4 Stepper motor

The Stepper motor does not have a comparable shielding to the before mentionedcomponents as it can’t be encased due to the resulting increase in temperature. Themotor is fitted with a dedicated ground cable to earth. As the motor face is incontact with the exposed metal surface of the force balance, it has the added effectthat the balance is grounded as well.

3.3 Stepper motor driver

To drive the stepper motor a Gecko G201X driver card was purchased and in-stalled along with the existing Gecko drivers in the wind tunnel. This ensures cross-compatibility should the driver ever fail, there are 2 more on standby that couldreplace it. This component did require additional funding of approx. 96 pounds asit was not purchased by the former 4th year group.

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4 Control and readout software

4.1 Overview

The readout software has multiple stages. The first stage is the Arduino Due which iscoded in Arduino programming language. The continuous voltage signal is digitizedand exported via USB. The 2nd stage is the host computer acquires the exporteddata, via the same USB. The 3rd stage is the LabVIEW program which processesthe received data into the desired angular format. The basic block diagram can beseen in figure 13.The initial plan was to use the LabVIEW toolkit which allows simple interfacingbetween the Arduino and LabVIEW. It supported programming the Arduino in theLabVIEW environment and contained a library of approximately 800 different sam-ple programs, including a potentiometer readout program. However, the ArduinoDue currently uses beta drivers, which are not compatible with LabVIEW. Hence acustom program had to be made.

4.2 Individual stages

Due to the complexity of the programs and the varying platforms, we will take acloser at the individual stages to see how they operate and interconnect to eachother.

4.2.1 ADC code

Figure 14, shows 3 lines of code in which the Arduino is initialized to the maximumADC resolution of 12 bits and a maximum baud rate of 115200 to ensure maximumspeed and accuracy. It receives the raw voltage signal from the potentiometer viaanalog input port A0.

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Figure 14: Code for initialization of arduinoIn the code shown in figure 15, the data points are buffered in memory until a pre-setquantity aveLen is reached and averaged to reduce the effects of noise.

Figure 15: Summation and averaging of data pointsThe final step is to export the averaged data sets via, here named COM10. A timedelay of 1ms is added to the loop to avoid the arduino becoming unstable as seenin figure 16:

Figure 16: Export and delay

4.2.2 LabVIEW code

Potentiometer readout program

The LabVIEW program controls both the stepper motor motion whilst reading andprocessing the ADC data. The host computer obtains the data through USB, onCOM10, by using NI VISA, a package enabling a LabVIEW program to importdata. This gateway is set to the same baud rate and COM port as used by thearduino 1 highlights the NI VISA in figure 17:

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Figure 17: Potentiometer readout programThe received data is sent through a string to number converter in order to be pro-cessed further 2. To remove any accidental data points which are = 0 , a basicBoolean filter is implemented 2. If the data point is greater than 0, the outputis true and the data point is carried forward, otherwise it’s discarded. The filtereddata points are declared as a global variable 3. In 4 the filtered data points areconverted into the measured voltage by multiplying with the ratio of the assumedsupply voltage 3.3V and the ADC resolution of 4095. The measured voltage is alsoplotted in a graph. As no limit switches are implemented, a 2 stage software safetyis used in 5 and 6. In stage 1 5, if the voltage is ≥ 2.5V or ≤ 0.9V a visualwarning is displayed as preliminary caution. In stage 2 6, if the voltage is ≥ 2.8Vor ≤ 0.5V , the program will automatically terminate and therefore cuts out anystepper motor motion.

Interpolation program

In order to obtain an angle from the measured voltage, we need a spreadsheet whichcontains the information about which voltages correspond to which angles. Thespreadsheet is called a look up table (LUT). The used data is obtained during thecalibration of the AOA actuator. The LUT is fed into a subVi which reads out thefile and indexes the voltages and angles as seen in figure 18:

Figure 18: Open LUT sub Vi

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As the measured voltages will never match exactly with the values in the LUT,linear interpolation is used to get an approximate value for the angle. The usedformula used can be seen in figure 19, where A is the LUT’s angle, V the LUT’svoltage and V 0 the measured voltage:

Figure 19: Interpolation programThe final result is an approximate AOA from the measured voltage on the poten-tiometer.

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5 Installation and calibration

5.1 LUT calibration

Before the force balance was mounted, the encoder needed to the calibrated. Itwould still be possible to calibrate the encoder after the balance is mounted, butas there are no physical limit switches, it is important to observe the position asthe angle dial is moved in the range of ±75° in increments of 1°. This gives a highaccuracy LUT. It would still work if the table only had e.g. 20 data points, dueto the linear interpolation capabilities of the LabVIEW code. However, this wouldmake it less accurate.For each angle, approximately 1000 voltage readings were acquired via LabVIEWand averaged in a spreadsheet. This is repeated for every incremental step andrecorded in an excel spreadsheet. This is now the Voltage/Angle look up table.

5.2 Installation

The force balance is now mounted on the rear of the high speed section of the tunnelby 3 M12 steel bolts. This is a 2 person job as one person has to hold the balanceand insert the bolts while the other tightens the nuts from inside the tunnel. In thiscase Mr Dipak Raval helped me mounting. The last task was the cable managementof the power and data cables. It is important to maintain sufficient separation ofthe power and data cables due to the electrical interferences from the stepper powercables and the driver. Despite both cables being shielded, it is good practice to keepthese cables well separated to reduce noise even further.

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6 Progress vs proposal

6.1 Delays at the start

At the beginning of the 3rd year, my former supervisor Dr Xiano Mao had leftthe University meaning that no project work could start. Approximately 2 weeksinto the semester, a re-allocations had been made. At this time, I presented myown project idea to my new supervisor Dr. Rona: Turbulence detection by opticalinterferometry. After weeks of consultation with scientists at Oxford University, itbecame clear that while the project was doable, it was beyond the scope of a 3rdyear project. The new project was the 3 component force balance. Both factorscombined already lead to a significant delay of approximately 3 weeks.

6.2 Problems during the project

As this project was said to be a very well conducted project to this stage, theexpectation was to find a project which was ready to be continued and had gooddocumentation. At first sight, the provided reports looked very promising, howeverit quickly became clear that mechanically, the force balance was not close to beingready for assembly, as stated in the reports. The majority of the CAD drawingsfor ”components to be manufactured” were unusable as the dimensions had littleto no correlation to the existing parts. Some needed complete re-designs. A CADdrawing of the fixed plate missed 21 holes present on the part. Pre-manufacturedcomponents such as the bearing block had it’s mounting hole alignment of by 4mmdiagonally and the collect was 2mm too thick. These problems cost a lot of timeand effort to correct.Another setback was the lack of the Gecko stepper motor driver, around which theelectrical system was built. The fine print in the purchasing list then revealed thatthe driver was not yet purchased. This required requesting additional funding inorder to buy the new driver card as without it, the force balance’s AoA actuatorwould not work. This resulted in an additional cost of 96 pounds. Later, when pro-gramming the software, electrical noise became a major problem. This factor hadnot been considered to be a major problem, hence it caused further delay whilst crit-ical components had to be shielded. Finally, compatibility issues with the ArduinoDue and the LabVIEW specific interfacing code required a new custom program,requiring more time.

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6.3 Conclusion and handover

6.3 Conclusion and handover

It was intended to have the force balance fully manufactured and assembled by theend of semester 1, implemented and calibrated by the end of semester 2. Due tothe a fore mentioned problems and January exam period, the final manufacture andassembly was delayed to mid February, causing the project not the completed asoriginally intended. An important lesson that was learned from these problems isthat you should always expect the unexpected. When a project is handed over, youshould expect there to be errors and/or missing/incomplete parts.Despite the setbacks, major progress has been achieved throughout the year:

1. The force balance received all its necessary modifications and re-designed com-ponents.

2. It’s fully assembled and mounted in its final position.3. Stepper motor and encoder system are fully operational, including their re-

spective software packages and calibration.4. The system is build to allow easy upgrading for a forthcoming project (see

below).The remaining items that need to be completed are:

1. The most important task is to complete the wiring and calibration of the forcetransducers with dead weights and update the existing LabVIEW programwith the new calibration constants. The program is the same as used in the2nd year airfoil experiment.

2. Currently, the force balance doesn’t have physical home or limit switches. Thestepper motor limit and home control is in software only. For a more reliableoperation, physical limit and home switches should be added and implementedinto the existing control software.

3. The arduino reads the wiper voltage of the potentiometer in single ended modeand the LabVIEW software assumes a constant supply voltage of exactly 3.3V.To increase reading accuracy and generate an independence from fluctuationsin the PSU, the arduino code and the LabVIEW software should be modifiedsuch that the system takes a differential reading of the supply voltage andthe wiper voltage. The BNC cables/jacks are already installed to supportdifferential mode.

4. If the system has been idling for a longer period of time, it is necessary tore-check the encoder calibration and, if needed, re-calibrate the system andupdate the look up tables.

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Acknowledgments

First and foremost I would like to thank both my supervisors Dr. Audrius Bag-danavicius and Dr. Aldo Rona for their continuous support and guidance through-out the project. Another big thank you goes to Mr. Alan Wale and Mr. Dipak Ravalfor their support in all manufacturing and installation matters. Whenever neededan expert option on any software or wind tunnel related problems, Mr. AndrewNorman and Mr. Paul Williams would not hesitate to assist to the best of theirabilities. Finally, a big thank you to the Department of Physics at the Universityof Oxford for providing the crucial brass shim for the force transfer strips, withoutwhich the project would still be in pieces today.

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Bibliography

[1] Alex Harris Andy heard Michael Hancock Zihui Dong Ben Doust, Rob Cowlam.Fourth year project executive summary report; Charles Wilson wind tunnel re-port. University of Leicester, first edition, 2012.

[2] Rob Cowlan. Charles Wilson Wind Tunnel Renovation. University of Leicester,2012.

[3] Tobias Reichold. The 3-component force balance and angle of attack actuatorPoster. Tobias Reichold, 2014.

[4] Tobias Reichold. EG3005 3rd Year Project Interim Report 2013-2014 3-component force balance and angle of attack actuator. Tobias Reichold, 2014.

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3-component force balance and angle of attack actuator

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