1. EG3005 3rd Year Project Final
Report 2013/2014
3-component force balance and angle of attack actuator
Tobias Reichold
Date of submission: Friday, 9th of May 2014
University of Leicester
Department of Engineering

2. Contents
1 Introduction 1
1.1 Overview 1
1.2 Project background 1
1.2.1 Forces in flight 1
1.2.2 The Charles Wilson wind tunnel 2
1.3 Core components and functionality 2
1.3.1 The use of a force balance? 4
2 Manufacturing and Assembly 5
2.1 Early work 5
2.1.1 Fixed Plate modifications 5
2.1.2 Floating plate modifications 5
2.1.3 ”Components to be manufactured” 6
2.1.4 Gears 7
2.1.5 Force transfer strips 7
2.2 Initial modifications and assembly 7
2.3 Final manufactured components 11
2.4 Final assembly 14
3 Electronics system 16
3.1 Encoder concept 16
3.1.1 ADC selection 16
3.1.2 Potentiometer selection 17
3.2 Electrical shielding 17
3.2.1 ADC 17
3.2.2 Power cables 18
3.2.3 Analog signal cables 18
3.2.4 Stepper motor 18
3.3 Stepper motor driver 18
4 Control and readout software 19
4.1 Overview 19
4.2 Individual stages 19
4.2.1 ADC code 19
4.2.2 LabVIEW code 20
Potentiometer readout program 20
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3. Contents
Interpolation program 21
5 Installation and calibration 23
5.1 LUT calibration 23
5.2 Installation 23
6 Progress vs proposal 24
6.1 Delays at the start 24
6.2 Problems during the project 24
6.3 Conclusion and handover 25
Acknowledgments 26
Bibliography 27
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4. 1 Introduction
1.1 Overview
This report marks the end of the project to construct and calibrate a 3-component
force balance and angle of attack actuator for the Charles Wilson sub-sonic wind
tunnel at the University of Leicester. This final report will describe:
1. The complete manufacture and assembly process
2. The electrical systems
3. The software code for LabVIEW and the Arduino controller and ADC
4. The installation and calibration
5. 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 the
past 2 years it has been the departments aim to update the capabilities of the wind
tunnel 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-component
force 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 3
forces we are interested in are lift, drag and pitching moment. They are in figure 1
[3]:
Airflow
Figure 1: 3 airfoil forces
1

5. These are the forces that our force balance should measure. In addition it is able
to adjust the angle of attack (AOA) of the wing section enabling a variety of flying
scenarios, 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 fully
wooden framework. Its single 1.5m eight bladed axial fan is powered by a 24kW
Ward Leonard PSU set, permitting a maximum flow speed of 30ms−1
. The tunnel
is split into two main sections: The environmental section, which is used e.g. for
testing 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 the
force balance works, we will outline each core component and it’s functionality. In
this example, we will look at the fully assembled force balance before it was mounted
in the Charles Wilson tunnel:
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3
4
5
6
7
7
8
8
8
9
9
10
1112
13
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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 the
wind tunnel and holds all other components.
2

6. 2. Floating plate: The floating plate has a shaft attached to it, which reaches
into the wind tunnel. The wing section is attached to this shaft. Depending
on 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. The
floating plate is suspended by the brass shim strips.
3. Lift force arms: The lift force arms will measure the lift component of the
total acting forces.
4. Drag force arm: The drag force arm does the same as 3. but for the drag
component.
5. Tension spring: The tensioning springs purpose is to hold the airfoil shaft in
place 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 the
tension 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 80
tooth gear (not visible) on the rear. It transmits the motion of the stepper
motor to the main 180 tooth gear and therefore onto the airfoil.
11. Stepper motor: The motor supplies the rotational motion to the gear assembly
and is the heart of the AOA actuator.
12. Potentiometer and bracket: The potentiometer will rotate and vary it’s wiper
voltage according to the rotation of the 180 tooth gear. This voltage is used
to 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 3.3V
and the 4 remaining are for measuring the supply and wiper voltage via the
Arduino.
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.
3

7. 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, under
varying 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 the
remote controlled AOA actuator. You will be able to set the desired angle using
a LabVIEW program, then have a stepper motor maneuver the section into place
with a accuracy of ±0.1° degrees over a total range of −75° to +75° degrees. For
the given accuracy, this adjustment is reasonably fast at a maximum rotation speed
of 5◦
/second. [3].
4

8. 2 Manufacturing and Assembly
2.1 Early work
The project started with a thorough study of the provided documentation, including
reports and CAD drawings, from the former 4th year group who started this project
in 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 components
3. 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 which
was a discrepancy between the stepper motor shaft and the first 11 tooth gear. The
report stated that almost all components were already manufactured and ready to
be assembled. It turns out that the report missed almost all tasks that were actually
left 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 and
holds all other components. The CAD drawing of the modifications to the fixed
plate, which indicated the hole positioning for the force and drag arms, was missing
a 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 transfer
the forces onto the force transfer strips. The CAD drawing of the modifications to the
floating plate displayed holes that were either non-existent or severely mislocated.
The holes for the stepper motor mounting had counter bores two times too wide
in diameter for the screws used. In addition, the positions of the bearing block
mounting holes were all wrong by 4mm[4].
5

9. 2.1 Early work
2.1.3 ”Components to be manufactured”
The collection of CAD drawings provided contained the mid-train gear shaft, which
houses an 11 & 80 tooth gear, the motor pinion shaft, the collet for gripping the
airfoil 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 the
bearing block. It was therefore completely redesigned as seen in figure 3:
Figure 3: Mid train gear shaft CAD drawing
The same applies to the collet, manufactured by the 4th year group. It had to
be turned down by more than 2mm. To address the issue of the gap between the
stepper shaft and the 1st 11 tooth gear, a flexible universal joint was proposed by
the 4th years, which however would not keep the gear firmly in place and would
allow it to droop down and flex away from the above 80 tooth gear. Figure 4 shows
the gear mounting locations [4]:
Figure 4: Back of floating plate
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10. 2.2 Initial modifications and assembly
The mid train shaft was also suffering from a torque problem which caused it to
move about unforeseeable when spinning up. This is another major problem not
addressed in the report. This was solved by manufacturing an additional bracket
which fitted on the other side of the floating plate, opposite the bearing block as
shown 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 Balance
Assembly” drawing listed all 4 as having one. This meant that the fitting of grub
screws for the 11 tooth gears was very tricky, as they have to be placed between the
teeth of the gear and this only allows for an M2.5 or smaller screw to be fitted as the
gears would otherwise interfere with each other. In addition, the 180 tooth gear had
to be re bored to accommodate the tightening bolt. It also required non-standard
pitch 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 lift
and 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 mounting
mechanism and new strips had to be found and soldered into their mounts [4].
2.2 Initial modifications and assembly
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
7

11. 2.2 Initial modifications and assembly
correct for incorrect dimensions on the CAD drawing. With floating plate modifi-
cations finished, the next task was to manufacture the redesigned mid train shaft
and bracket, so that the shaft would fit precisely into the bearing and housing. This
allows for free positioning of the gears when aligning them (see figure 4&5) and it
solves the torque issue on the shaft. Next the main 180 tooth gear was re-bored
and the non standard pitch circle diameter holes drilled to mount the gear and
accommodate 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 hollow
shaft of the angle dial. These tasks were done by the workshop technicians. Then
the holding brackets for the jointed standoffs were installed. Finally, the stepper
motor mounted and the bearing block with it’s bracket counterpart was installed as
shown in figure 7 [4]:
8

12. 2.2 Initial modifications and assembly
Figure 7: Assembled floating plate;
As the fixed plate had already been fully modified, the assembly process was fairly
straight forward. The fixed and jointed standoffs were mounted first, followed by the
lift and drag force transducer arms. The arm assembly for the lift arms was mounted
next. The shaft of the drag arm was too long to fit properly into it’s bearings, so it
was trimmed by about 4mm and then mounted again as shown in figure 8 [4]:
9

13. 2.2 Initial modifications and assembly
Figure 8: Assembled fixed plate;
A custom adapter has been made for the stepper motor. This mounts directly
to the stepper motor shaft and accommodates one 11 tooth gear. Both 11 tooth
gears have been fitted with M2.5 grub screws between the teeth. The adapter is
the replacement for the previously proposed universal joint. The brass shim force
transfer strips have been cut to size and re soldered into their original position after
removing all leftover shim from the connections [4]. The work described up to this
point has been done in semester one. The next section focuses on the work done in
semester two work.
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14. 2.3 Final manufactured components
2.3 Final manufactured components
In semester 2, a total of 3 more components were manufactured to implement the
angular encoder system. This includes:
1. a variable potentiometer bracket with over-torque protection,
2. a shortened BNC connector bank
3. a modified, electrically shielded, IP67 diecast box which houses the Arduino
Due.
The potentiometer bracket is made from 2 L-profiled pieces of aluminum, allowing
both horizontal and vertical adjustment capabilities in order to ensure a good fit
between the potentiometer and the main 180 tooth gear as can be seen in figure 9:
Figure 9: Potentiometer with bracket
The potentiometer was fitted with a 15 tooth gear which had been re-bored to 1/4
inch to fit the potentiometer shaft. It is secured by 2 M2.5 grub screws, located at
opposite sides between the teeth. To prevent the potentiometer from taking damage
when it is turned beyond its end of rotation, two 2 rubber spacers have been fitted
at its mounting point. Both have been treated with silicone spray which enables
11

15. 2.3 Final manufactured components
sufficient grip during normal operation and allows the potentiometer to rotate within
the bracket if turned too far.
The BNC connector bank houses 6 non-isolated BNC bulkheads, 75Ω. It is made
from a piece of aluminum with an L profile as can be seen in figure 10:
Figure 10: BNC bracket
This means that the BNC shields are all interconnected with each other to prevent
ground loops. The connector bank is mounted to the left side of the fixed plate
to aid the later cable management of the BNC cables, 75Ω, 5m and to ease the
installation of the cables from the potentiometer to the connector bank.
The last component is a diecast box which contains the arduino board as can be
seen in figure 11:
Figure 11: Arduino diecast box
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16. 2.3 Final manufactured components
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 ( native
cable currently not in use).
Six isolated BNC bulkheads, 75Ω, have been added. These provide connectors to
the analog input ports on the arduino. External banana jacks provide the arduino
with power from an external PSU which offers much cleaner power than a simple
USB supply. This is important as it enables the Arduino to make more accurate
readings. A separate ground banana jack, connected directly to the box, grounds
out the enclosure, further reducing potential electric interferences. A guarded power
switch ensures safe operation of the ADC.
13

17. 2.4 Final assembly
2.4 Final assembly
Figure 12: Assembled force balance
After 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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18. 2.4 Final assembly
To ensure the potentiometer bracket can’t rotate when under load, 2 M4 screws were
installed with a horizontal offset to each other to ensure a secure fit. All electrical
connections were soldered on and protected with heat shrink tubing. After a final
inspection by myself and workshop staff, the force balance was deemed correctly
assembled and ready to install.
15

19. 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 is
powered 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 ensure
compatibility with the existing infrastructure. However at 95 pounds, it was too
expensive for the remaining budget. Hence, the Arduino Due was chosen as it
offered the same ADC resolution at a lower price. Other Arduino products, such as
16

20. 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 than
1023. 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 spectrum
2. A good linearity tolerance and low temperature drift to ensure a good linear
variation in resistance when rotated
3. Must have sufficient turns to be able to to cover an angle range from −75 to
+75 degrees angle of attack
The chosen potentiometer is a Vishay 535 50kΩ 5 turn. This potentiometer offers a
linearity of 5% at 50kΩ, which is the highest resistance value in the series. Mounting
a 15 tooth spur gear to the potentiometer shaft and being driven by the 180 tooth
gear, 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 fitted
with 5m extension wiring, in order for the force balance to be mounted in place
and the stepper being supplied with power, while having sufficient slack in the wires
to avoid damage when pulled. All these are major sources of interference which
causes noise to be induced into the voltage signals, reducing accuracy and reliability.
Therefore, critical components such as the ADC, power cables, data cables and the
stepper need to be shielded.
3.2.1 ADC
As the ADC is the heart of the encoder system, the shielding is extra thorough to
ensure reliable operation. It is mounted into an IP67 Diecast Box with the board
separately isolated from the chassis. The chassis itself is grounded via an earth plug
to ensure any induced voltages are removed from the ADC and the chassis (see figure
11).
17

21. 3.3 Stepper motor driver
3.2.2 Power cables
Shielding for this component is critical, as the power cables are very long and carry
large currents. They have been sleeved over the full length in a tinned copper braid
and 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 good
shielding, 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 mentioned
components as it can’t be encased due to the resulting increase in temperature. The
motor is fitted with a dedicated ground cable to earth. As the motor face is in
contact with the exposed metal surface of the force balance, it has the added effect
that 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 could
replace it. This component did require additional funding of approx. 96 pounds as
it was not purchased by the former 4th year group.
18

22. 4 Control and readout software
4.1 Overview
The readout software has multiple stages. The first stage is the Arduino Due which is
coded in Arduino programming language. The continuous voltage signal is digitized
and exported via USB. The 2nd stage is the host computer acquires the exported
data, via the same USB. The 3rd stage is the LabVIEW program which processes
the received data into the desired angular format. The basic block diagram can be
seen in figure 13.
The initial plan was to use the LabVIEW toolkit which allows simple interfacing
between the Arduino and LabVIEW. It supported programming the Arduino in the
LabVIEW environment and contained a library of approximately 800 different sam-
ple programs, including a potentiometer readout program. However, the Arduino
Due currently uses beta drivers, which are not compatible with LabVIEW. Hence a
custom program had to be made.
4.2 Individual stages
Due to the complexity of the programs and the varying platforms, we will take a
closer at the individual stages to see how they operate and interconnect to each
other.
4.2.1 ADC code
Figure 14, shows 3 lines of code in which the Arduino is initialized to the maximum
ADC resolution of 12 bits and a maximum baud rate of 115200 to ensure maximum
speed and accuracy. It receives the raw voltage signal from the potentiometer via
analog input port A0.
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23. 4.2 Individual stages
Figure 14: Code for initialization of arduino
In the code shown in figure 15, the data points are buffered in memory until a pre-set
quantity aveLen is reached and averaged to reduce the effects of noise.
Figure 15: Summation and averaging of data points
The final step is to export the averaged data sets via, here named COM10. A time
delay of 1ms is added to the loop to avoid the arduino becoming unstable as seen
in 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 and
processing the ADC data. The host computer obtains the data through USB, on
COM10, by using NI VISA, a package enabling a LabVIEW program to import
data. This gateway is set to the same baud rate and COM port as used by the
arduino {1} highlights the NI VISA in figure 17:
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24. 4.2 Individual stages
Figure 17: Potentiometer readout program
The 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 basic
Boolean filter is implemented {2}. If the data point is greater than 0, the output
is true and the data point is carried forward, otherwise it’s discarded. The filtered
data points are declared as a global variable {3}. In {4} the filtered data points are
converted into the measured voltage by multiplying with the ratio of the assumed
supply voltage 3.3V and the ADC resolution of 4095. The measured voltage is also
plotted in a graph. As no limit switches are implemented, a 2 stage software safety
is used in {5} and {6}. In stage 1 {5}, if the voltage is ≥ 2.5V or ≤ 0.9V a visual
warning is displayed as preliminary caution. In stage 2 {6}, if the voltage is ≥ 2.8V
or ≤ 0.5V , the program will automatically terminate and therefore cuts out any
stepper motor motion.
Interpolation program
In order to obtain an angle from the measured voltage, we need a spreadsheet which
contains the information about which voltages correspond to which angles. The
spreadsheet is called a look up table (LUT). The used data is obtained during the
calibration of the AOA actuator. The LUT is fed into a subVi which reads out the
file and indexes the voltages and angles as seen in figure 18:
Figure 18: Open LUT sub Vi
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25. 4.2 Individual stages
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 used
formula used can be seen in figure 19, where A is the LUT’s angle, V the LUT’s
voltage and V 0 the measured voltage:
Figure 19: Interpolation program
The final result is an approximate AOA from the measured voltage on the poten-
tiometer.
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26. 5 Installation and calibration
5.1 LUT calibration
Before the force balance was mounted, the encoder needed to the calibrated. It
would still be possible to calibrate the encoder after the balance is mounted, but
as there are no physical limit switches, it is important to observe the position as
the angle dial is moved in the range of ±75° in increments of 1°. This gives a high
accuracy LUT. It would still work if the table only had e.g. 20 data points, due
to the linear interpolation capabilities of the LabVIEW code. However, this would
make it less accurate.
For each angle, approximately 1000 voltage readings were acquired via LabVIEW
and averaged in a spreadsheet. This is repeated for every incremental step and
recorded 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 tunnel
by 3 M12 steel bolts. This is a 2 person job as one person has to hold the balance
and insert the bolts while the other tightens the nuts from inside the tunnel. In this
case Mr Dipak Raval helped me mounting. The last task was the cable management
of the power and data cables. It is important to maintain sufficient separation of
the power and data cables due to the electrical interferences from the stepper power
cables and the driver. Despite both cables being shielded, it is good practice to keep
these cables well separated to reduce noise even further.
23

27. 6 Progress vs proposal
6.1 Delays at the start
At the beginning of the 3rd year, my former supervisor Dr Xiano Mao had left
the University meaning that no project work could start. Approximately 2 weeks
into the semester, a re-allocations had been made. At this time, I presented my
own project idea to my new supervisor Dr. Rona: Turbulence detection by optical
interferometry. After weeks of consultation with scientists at Oxford University, it
became clear that while the project was doable, it was beyond the scope of a 3rd
year project. The new project was the 3 component force balance. Both factors
combined 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, the
expectation was to find a project which was ready to be continued and had good
documentation. At first sight, the provided reports looked very promising, however
it quickly became clear that mechanically, the force balance was not close to being
ready for assembly, as stated in the reports. The majority of the CAD drawings
for ”components to be manufactured” were unusable as the dimensions had little
to no correlation to the existing parts. Some needed complete re-designs. A CAD
drawing of the fixed plate missed 21 holes present on the part. Pre-manufactured
components such as the bearing block had it’s mounting hole alignment of by 4mm
diagonally and the collect was 2mm too thick. These problems cost a lot of time
and effort to correct.
Another setback was the lack of the Gecko stepper motor driver, around which the
electrical system was built. The fine print in the purchasing list then revealed that
the driver was not yet purchased. This required requesting additional funding in
order to buy the new driver card as without it, the force balance’s AoA actuator
would 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 had
not 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 Arduino
Due and the LabVIEW specific interfacing code required a new custom program,
requiring more time.
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28. 6.3 Conclusion and handover
6.3 Conclusion and handover
It was intended to have the force balance fully manufactured and assembled by the
end of semester 1, implemented and calibrated by the end of semester 2. Due to
the a fore mentioned problems and January exam period, the final manufacture and
assembly was delayed to mid February, causing the project not the completed as
originally intended. An important lesson that was learned from these problems is
that you should always expect the unexpected. When a project is handed over, you
should 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 force
transducers with dead weights and update the existing LabVIEW program
with the new calibration constants. The program is the same as used in the
2nd year airfoil experiment.
2. Currently, the force balance doesn’t have physical home or limit switches. The
stepper motor limit and home control is in software only. For a more reliable
operation, physical limit and home switches should be added and implemented
into the existing control software.
3. The arduino reads the wiper voltage of the potentiometer in single ended mode
and the LabVIEW software assumes a constant supply voltage of exactly 3.3V.
To increase reading accuracy and generate an independence from fluctuations
in the PSU, the arduino code and the LabVIEW software should be modified
such that the system takes a differential reading of the supply voltage and
the wiper voltage. The BNC cables/jacks are already installed to support
differential mode.
4. If the system has been idling for a longer period of time, it is necessary to
re-check the encoder calibration and, if needed, re-calibrate the system and
update the look up tables.
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29. 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 Raval
for their support in all manufacturing and installation matters. Whenever needed
an expert option on any software or wind tunnel related problems, Mr. Andrew
Norman and Mr. Paul Williams would not hesitate to assist to the best of their
abilities. Finally, a big thank you to the Department of Physics at the University
of Oxford for providing the crucial brass shim for the force transfer strips, without
which the project would still be in pieces today.
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30. 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 actuator
Poster. 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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