our design specifications refer to a previous document...

© 2015, Veroptimal Solution

November 9, 2015 Dr. Andrew Rawicz School of Engineering Science Simon Fraser University Burnaby, BC V5A 1S6 Re: ENSC 440W Design Specification for Auto-adjustable Spoiler System Dear Dr. Rawicz: The enclosed document to this letter is a design specification for an “Auto-adjustable Spoiler Control System”. We intend to design and implement a spoiler control system that makes driving safer, more fuel efficient and more enjoyable. Our design is a cross-disciplinary engineering project which involves aerodynamics, electronics, mechanical system, programming and control theory. Our design specifications refer to a previous document “Functional Specification for

Auto-adjustable Spoiler Control System”, and discuss the design details to achieve the functional

requirements for three parts, includes Front Panel, Main Controller and Spoiler System .Our engineers at Veroptimal Solution will also use this document to stay focused on the project development progress and on the implementation of the desired functionality in a safe and reliable manner. Sincerely,

Zhendong Cao President and CEO Veroptimal Solutions Enclosure: Design Specification for Auto-adjustable Spoiler Control Systems


Auto-adjustable Spoiler Control System

Design Specification

Project Team: Zhengdong Cao CEO Yueying Li COO Tianye Zhou CFO Tianlin Yang CTO Contact Person: ZhengDong Cao E-mail: [email protected] Phone: 778.317.4405 Submitted to: Dr. Andrew Rawicz Mr. Steve Whitemore School of Engineering Science Simon Fraser University Issued Date: Nov 9, 2015 Revision: 1.3


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Executive Summary There are mainly two types of car spoiler in the market. One of them is a fixed car spoiler installed onto the surface of a car back trunk. Another type is a car wing which is held a distance above the car back trunk. When a car is travelling at high speed, more than 80% of the total drag applied on the vehicle is caused by air. Also, the rear body of the car is suffering from an aerodynamic lift in range of hundred pounds which leads to reduced grips of vehicle’s back wheels onto the ground. Therefore, it lowers the vehicle’s stability and maneuverability. Moreover, car spoiler installed on the surface of the trunk lid is to lower fuel consumption through reducing the drag. While a car wing which is held a distance above the car back trunk is aiming for a better safety performance with the usage of applying higher downforce to decrease the lift force. Veroptimal Solution is able to solve both the drag and lift issues with the latest product “Auto-adjustable Spoiler Control System”, or ASCS. It is an intelligent feedback control system which allows users to control the spoiler. Our product provides a friendly-looking user interface panel which allows the driver having full control of the spoiler: the operation mode of the entire system can be set to either automatic or manual depends on user preference. More specifically, with automatic mode, the ASCS will automatically adjust itself until the vehicle has reached to the optimal aerodynamic state. Particular scenarios can be detected, such as hitting emergency brake, driving downhill and being in a slippery road condition. With manual, the ASCS will listen to the user’s command during security scope. The design specification for ASCS provides a set of detailed descriptions for implementations and developments of our prototype. In this document, design improvements for future iteration of ASCS are also discussed. Detailed system operations and aerodynamic principles are discussed with flowchart and analysis. As the user interface, our front panel is designed to have the RF module, LCD circuit, and different control buttons on the layout. All circuit designs, modules and board layout in the main controller are specified with details. A DC motor and a linear actuator are used for height and angle adjustments. This document also provides the test plans for future function verifications.


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Table of Contents

Executive Summary ............................................................................................................... ii

List of table .......................................................................................................................... vi

List of Glossary ..................................................................................................................... vi

1 Introduction .................................................................................................................... 1

2 System Specifications ...................................................................................................... 1 2.1 System Level Diagram ..........................................................................................................1 2.2 System Operation ................................................................................................................2 2.3 Aerodynamics ......................................................................................................................3

2.3.1 Downforce Improvement ............................................................................................................. 3 2.3.2 Drag Reduction ............................................................................................................................. 4

2.4 Mechanical Design ...............................................................................................................5 2.5 Electronics System Design ....................................................................................................5 2.6 Safety Design .......................................................................................................................6

3. Front Panel .................................................................................................................. 7 3.1 Electronic Hardware Design ..................................................................................................7

3.1.1 Central Processing Unit ................................................................................................................ 7 3.1.2 Power Tree .................................................................................................................................... 7 3.1.3 Control Buttons ............................................................................................................................ 8 3.1.4 RF Module .................................................................................................................................... 9 3.1.5 LCD Circuit .................................................................................................................................... 9 3.1.6 Board Layout Design ................................................................................................................... 10

3.2 Firmware Design ................................................................................................................ 11 3.2.1 Control buttons .......................................................................................................................... 11 3.2.2 RF Module .................................................................................................................................. 13 3.2.3 LCD display.................................................................................................................................. 13

3.3 Enclosure Design ................................................................................................................ 13 3.3.1 Exterior Enclosure ...................................................................................................................... 13 3.3.2 Interior Enclosure ....................................................................................................................... 14

4. Main Controller ......................................................................................................... 15 4.1 Electronic Hardware Design ................................................................................................ 15

4.1.1 Power Tree .................................................................................................................................. 15 4.1.2 Motor Driving Circuit .................................................................................................................. 16 4.1.3 Angle Measuring Circuit ............................................................................................................. 17 4.1.4 Force Measuring Circuit.............................................................................................................. 18 4.1.5 Brake Detection Circuit ............................................................................................................... 20 4.1.6 GPS Module ................................................................................................................................ 20 4.1.7 Board Layout Design ................................................................................................................... 21

4.2 Firmware Design ................................................................................................................ 22 4.2.1 RF Module .................................................................................................................................. 22 4.2.2 Angle sensors and pressure sensors ........................................................................................... 22


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4.2.3 GPS Module ................................................................................................................................ 22 4.2.4 LA, Motor and Motor driver ....................................................................................................... 22 4.2.5 Auto mode and Manual mode ................................................................................................... 22

4.3 Enclosure Design ................................................................................................................ 23 4.3.1 Exterior Enclosure ...................................................................................................................... 23 4.3.2Exterior Enclosure ....................................................................................................................... 24

5. Spoiler System ........................................................................................................... 25 5.1 Electrical Design ................................................................................................................. 25

5.1.1 Power Line .................................................................................................................................. 25 5.1.2 Signal Line ................................................................................................................................... 26

5.2 Mechanical Design ............................................................................................................. 26 5.2.1 Mechanical Power Source .......................................................................................................... 26 5.2.2 Arm Mechanism ......................................................................................................................... 27 5.2.3 Hand Mechanism........................................................................................................................ 29 5.2.4 Rigid-body Dynamics .................................................................................................................. 30 5.2.4 Building Materials ....................................................................................................................... 33

6. Test Plan ....................................................................................................................... 34 6.1 Units Test ................................................................................................................................ 34 6.2 System Test ............................................................................................................................. 35

7. Conclusion ....................................................................................................................... 36

Reference ............................................................................................................................ 37

Appendix ............................................................................................................................. 40 Appendix A: Complete Circuit Schematic ....................................................................................... 40 Appendix B: Coast Down Method for Drag Estimation ................................................................... 40 Appendix C: Motor Driver Test ...................................................................................................... 42 Appendix D: Angle Sensor Test ...................................................................................................... 43


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LIST OF FIGURES Figure 1: System Level Diagram ............................................................................................................................ 2 Figure 2: System Flowchart ................................................................................................................................... 2 Figure 3: Simulation of airflow around a high speed car ...................................................................................... 3 Figure 4: Downforce coefficient vs AOA ................................................................................................................ 4 Figure 5: Drag Reduction by Adding a Spoiler ....................................................................................................... 4 Figure 6: General Design of the Spoiler System .................................................................................................... 5 Figure 7: Installing a real spoiler onto the ASCS ................................................................................................... 5 Figure 8: Front Panel Power Distribution .............................................................................................................. 7 Figure 9: Mode Selection Switch ........................................................................................................................... 8 Figure 10: Spoiler Height and Angle Control Circuit ............................................................................................. 8 Figure 11: Set Preference Button circuit ............................................................................................................... 9 Figure 12: RF Module Circuit Design ..................................................................................................................... 9 Figure 13: I2C conversion of the 16x2 LCD.......................................................................................................... 10 Figure 14: LCD Circuit Design .............................................................................................................................. 10 Figure 15: Component Layout (showing only faces) ........................................................................................... 10 Figure 16: Arduino Nano ..................................................................................................................................... 11 Figure 17: Flow diagram of Manual Control of the Spoiler Height and Angle .................................................... 12 Figure 18: Exterior view of Front Panel Enclosure .............................................................................................. 14 Figure 19: Interior view of Front Panel Enclosure ............................................................................................... 14 Figure 20: Main Controller Power Tree ............................................................................................................... 16 Figure 21: Dual Bridge L298N Motor Driver Breakout Board .............................................................................. 16 Figure 22: Motor Driving Circuit design .............................................................................................................. 17 Figure 23: Components used for Angle Measuring Circuit design ...................................................................... 18 Figure 24: Angle Measuring Circuit Design ......................................................................................................... 18 Figure 25: Force Sensing Resistor used for measuring the downforce ............................................................... 19 Figure 26: Non-inverting Summing Amplifier Circuit .......................................................................................... 19 Figure 27: Brake Detection Circuit ...................................................................................................................... 20 Figure 28: GPS Module ....................................................................................................................................... 20 Figure 29: GPS Module circuit design in Main Controller ................................................................................... 21 Figure 30: Layout of Main Controller Components............................................................................................. 21 Figure 31: Flowchart for Automatic Mode .......................................................................................................... 23 Figure 32: Exterior view of Main Controller Enclosure ....................................................................................... 24 Figure 33: Interior view of Main Controller Enclosure ........................................................................................ 24 Figure 34: Typical Boot Lid Design ...................................................................................................................... 25 Figure 35: Linear Actuator .................................................................................................................................. 27 Figure 36: DC Motor ............................................................................................................................................ 27 Figure 37: General Arm Design Prototype of Spoiler System ............................................................................. 28 Figure 38: Lowest Elevation (a) and Highest Elevation (b) .................................................................................. 28 Figure 39: Spoiler Components, (a) Linear Actuator (b) Linear Actuator Stand ................................................. 29 Figure 40: General Hand Design Prototype of Spoiler System ............................................................................ 29 Figure 41: Hand Mechanism Design ................................................................................................................... 30 Figure 42: Hand Mechanism Angle Adjustment ................................................................................................. 30 Figure 43: Spoiler System Detailed Dimension Front View ................................................................................. 31 Figure 44: Spoiler System Detailed Dimension Top View .................................................................................... 32


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List of table Table 1: System Mode Pin Definition .................................................................................................................. 11 Table 2: Array elements from Front Panel to Main Controller ............................................................................ 13 Table 3: Array elements from Main Controller to Front Panel ............................................................................ 13 Table 4: Detailed Dimensions of Front Panel Enclosure ...................................................................................... 15 Table 5: Motor Control Logic ............................................................................................................................... 17 Table 6:Detailed Dimension of Main Controller Enclosure ................................................................................. 25 Table 7: Wires for Signal Line between Main Controller and Spoiler System ..................................................... 26 Table 8: Steel Properties ..................................................................................................................................... 33 Table 9: Material Choices .................................................................................................................................... 33

List of Glossary AOA Angle of Attack

ASCS Auto-adjustable Spoiler Control System

CAN Controller Area Network

FS Function Specification

FS-R# Functional Specification – Requirement #

FSR Force Sensing Resistor

GPS Global Positioning System

I2C Inter-integrated Circuit

I/O Input and Output

KPH Kilometers per Hour

LCD Liquid Crystal Display

PCB Printed Circuit Board

ROM Read Only Memory

SDA Serial Data Line

SCL Serial Clock


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1 Introduction

The Auto-adjustable Spoiler Control System (ASCS) is a feedback control system in which drivers are capable of

adjusting the elevation and angle of attack (AOA) of the car spoiler manually or automatically. As research indicates,

the car spoiler, which stays very close to the surface of the boot lid, helps to decrease the drag and increase the fuel

efficiency with the method of spoiling out the undesirable flows and reshaping airflow streams around the vehicle. In

addition, the AOA of the spoiler with high elevation plays a crucial role in determining how much air will be deflected

upwards, which lead to the generation of down force at the rear of the vehicle [1], [2], [3]. As consequence, higher safety

performance can be achieved with car spoiler being held a distance above the trunk. Our goal is to enable a single car

spoiler to be multifunctional, not only to provide better safety performance but also reduce the fuel consumption.

This design specification provides detailed technical descriptions for the design of each component of the ASCS.

1.1 Scope

This document provides detailed design of the ASCS and specifies implementations to meet the functional

requirements proposed in the previous Auto-Adjustable Spoiler Control System Functional Specification. All

requirements for a proof-of concept system and a partial set of requirements for the final product are included in the

design specification.

1.2 Intended Audience

This document is intended to be used by all engineers of Veroptimal Solution for product development including the

project manager, the hardware designers, the mechanical designers, the firmware developers and the test engineers.

It will be reference as a design guideline throughout the development stage of the product. The project manager shall

refer to the design requirements as consistent criteria and ensure all requirements are met in the final product. The

test engineers will use this document to implement the test plans and confirm that the product follows the design

goal.

2 System Specifications

The ASCS product is transitioning from proof-of-concept phase to prototype phase. With more funding and time,

further modifications and improvements will be implemented in the final production stage. This document provides

the design details that are only for prototyping of the project. Particular functions for the production stage of the

design will be briefly mentioned in the following sections.

2.1 System Level Diagram

A system level diagram of ASCS is shown below as Figure 1. The power lines are marked with red color; signals are

represented by black arrows – solid line is for wire signals whereas dashed line indicates wireless signals.


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Figure 1: System Level Diagram

The design of ASCS can be divided into three major subsystems: Front Panel, Main Controller and Spoiler System

based on their designated functionalities. The Front Panel will be used as a media for the user to control the system

therefore it focuses on the wireless communication and user interface design. The Main Controller is an electronics

system which involves most of the circuit design and programming. The Spoiler System is essentially a mechanical

system controlled by the Main Controller to adjust the spoiler movements therefore it focuses on the mechanical

design.

2.2 System Operation The system flow chart below in Figure 2 describes the behavior of the system. The functional blocks marked with

orange represent the operations done by the Front Panel; operations executions marked by blue are commands from

the Main Controller and Spoiler System.

Figure 2:System Flowchart


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2.3 Aerodynamics As shown in the function blocks in Figure 2, when the system is try to activate “Economy Mode” or “Safety Mode”, the

vehicle aerodynamics, in which we interpreted in the form of downforce and drag in this context, are the crucial

factors that determine the system performance. In “Economy Mode”, the system should reduce the drag applied on

the vehicle; in “Safety Mode”, the system attempts to increase the downforce applied on the rear of the vehicle.

2.3.1 Downforce Improvement In analogous to an airplane wing, the car spoiler is able to generate downforce by “flipping” the wing. The

downforce, FDOWN, of the spoiler can be numerally evaluated by,

FDOWN =1

2ρv2ACDOWN (1)

Where,

ρ is 1.255kg/m3 (air density at 15°C)

v is the air flow speed in m/s

A is the spoiler area in m2

CDOWN is the downforce coefficient

The simulated airflow around a high speed car is shown in Figure 3 where the color represents the speed (red

means fast and blue means slow). It is clear that the air speed is faster at position above the boot lid surface;

therefore, in “Safety Mode”, the ASCS should lift the spoiler to a reasonably high position off from the boot lid in

order obtain large downforce.

Figure 3: Simulation of airflow around a high speed car

From the downforce equation (1) above, we can see that the other variable CDOWN also determines the downforce.

Though both the wing shape and AOA can affect the downforce coefficient, AOA of the spoiler is the major

determinant parameter [4]. The ASCS is able to control AOA of the spoiler, and the resultant downforce can be

monitored by the sensors. To achieve the “Safety Mode”, the system will adjust the AOA until the measured

downforce reaches to maximum.


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For theoretical approximation, we assume the car spoiler area to be 0.225m2 (1.5m x 0.15m) and it is driving at

120kph (or 34m/s); for simplicity we also assume the air flow speed is same with the car speed, so we obtain

that,

FDOWN = 163CDOWN (2)

Figure 4 shows the relationship between the downforce coefficient (interpreted as coefficient of lift) and AOA for

a particular airfoil [5]. The downforce coefficient reaches to maximum (about 1.7) when AOA is about 17 degrees

which will result a 277N downforce in this situation. Based on multiple research results and take consideration of

higher speed situations [6], we expect the maximum downforce applied on the spoiler to be 400N.

Figure 4: Downforce coefficient vs AOA

2.3.2 Drag Reduction The “Economy Mode” should reduce the drag of the vehicle. By comparing the two pictures in Figure 5, adding a

spoiler on the surface of the boot lid can “spoil out” the undesirable flows and thus reshape airflow streams

around the vehicle to decrease drag.

Figure 5: Drag Reduction by Adding a Spoiler

The amount of the reduced drags very difficult to be theoretically approximated since we have to model the

mechanical design of the car as well. Another issue to quantify the air drag reduction is due to the unavailability


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of a large power wind tunnel which simulates the airflow around the car. As an alternative solution, we will use

coast down method to estimate the reduction of the air drag once we build the prototype, see Appendix B for

method details.

2.4 Mechanical Design The Spoiler System occupies most of the mechanical design portion which involved with power source, structural

design, rigid body mechanics and engineering materials. Figure 6 shows the general mechanical design of the ASCS

Spoiler System when it stays at a specific instance of movement. Technical details regarding are provided in section 5.2

which illustrating the mechanical design of the Spoiler System.

Figure 6: General Design of the Spoiler System

The Spoiler System is designed with a specific manner such that it can “grip” an additional spoiler as shown in Figure 7

instead of having a spoiler as an integrated part of the system. In this way, we do not need to spend money and time

on fabricating a spoiler; also it makes the ASCS being more compatible, that is, users can “upgrade” their old spoiler (if

they had one) to a more versatile and intelligent version by simply mount it onto our system.

Figure 7: Installing a real spoiler onto the ASCS

2.5 Electronics System Design The electronics system in ASCS involved with hardware circuit design, board prototyping and firmware programming.


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When designing the circuit two options were considered:

• Microcontroller based circuit design

• PCB based circuit design

Eventually we decided to follow the microcontroller based circuit design scheme and particularly we will use Arduino

microcontroller as the central processing unit. Arduino microcontroller is small, light, inexpensive and reliable. As a

well-developed open source device, Arduino is highly compatible with many hardware shields such as the RF module,

motor driver and GPS module used in our project; much hardware and coding support can be found online. More

importantly, the time spent on the design, debugging and prototyping of a microcontroller based breakout circuit

board is much faster than designing a PCB board. As ASCS is a complex system which involves cross-disciplinary

engineering fields, we have very limited time spending on the electronics system design.

Some market available modules such as H bridge motor driver, GPS module, angle sensor module and RF module can

be directly used for the hardware circuit design. Also there are circuitries with particular functions need to be

specifically designed, e.g. downforce measuring circuit, break detection circuit and many control buttons. The

performance of each circuitry will be first verified by using power supply, multi-meters and oscilloscope on

breadboard; then a small test programs will be uploaded into the microcontroller circuit to validate the functions of

the circuitry. Once the functions of all modules are tested on the breadboard, we will arrange the layout of

components on perf-boards for soldering and prototyping. Suitable mechanical enclosures will be designed for the

circuit boards for protection. The complete circuit schematic is in Appendix A.

2.6 Safety Design

Design for safety is a crucial part of this project. We identified the major hazards or disasters that could be caused by

this system as:

• Fracture of the structural materials under heavy loads

• Vehicle instability caused by improper adjustment of the spoiler AOA

• System operation failure due to the interference of the wireless communication

Structural materials must be chosen carefully to prevent fracture. Quantitative analysis and justifications in terms of

structural mechanics and material properties will be addressed in the Spoiler System design section. The factor

causing instability of the vehicle is the aerodynamic lift generated by the spoiler due to the improper adjustment of

the AOA of the spoiler. The instability scenario is most likely happened in the manual operation mode where the user

mistakenly adjusted the Spoiler Angle Knob. Such mistakes could by avoided by providing user with clear and easy

understandable instructions about the device control in the user document. Lastly, reliance on wireless

communication is another potential for system operation failures. To prevent cascading failures, if the wireless

communication is lost, the system will remain its previous states and will not do any further dangerous movements.


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3. Front Panel

This section specifies the Front Panel design in the prototype stage including electronics design, programming and

enclosure. In the production stage of the project, the electronics will be integrated to the CAN bus of the vehicle

computer which has higher stability in data transmission.

3.1 Electronic Hardware Design The hardware design of the Front Panel in the proof-of-concept stage is divided into two subjects: circuit design and

board prototyping which can be further break down into smaller design pieces. The hardware design for the future

production product will be mentioned in the last part of this section.

3.1.1 Central Processing Unit We will use Arduino Nano microcontroller as our central processing unit. Nano is small (45mm x 18mm) and light

(5g) therefore is a perfect candidate used in the Front Panel design. The electrical specification of Nano is given in

Table 4.

Table 1: Arduino Nano Electrical Specification

3.1.2 Power Tree The power flow diagram in Figure 8 below highlights the current flow direction in the Front Panel circuitry. There

are three components: Arduino Nano, LCD and RF Module are consuming power; the power consumption of

other units such as switch and potentiometer is insignificant as others; therefore, they are not shown in the

diagram. In the diagram, it shows that the LCD and RF Module are taking power from the 5V and 3.3V power rail

from Nano whereas Nano is powered by the battery.

Figure 8: Front Panel Power Distribution


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The regulator on Nano is type of 7805 therefore the regulator is able to deliver 1A when the input power is 12V.

Since the operation current of LCD is normally below 30mA and the maximum current for the RF Module is 20mA [7], [8], therefore using the regulator on Nano as the power source of LCD and RF Module will be sufficient.

3.1.3 Control Buttons The Mode Selection Switch, as shown in Figure 9, is a 3-way switch with pull-up resistors R14, R15 and R16. By

closing the switch on one of the three terminals, e.g. the middle terminal as shown in the picture, then the node

U1_D1 will be short to ground therefore is 0V; the other two nodes are pulled up by the VCC1_5V which is the

Nano 5V rail. The three nodes, U1_D0, U1_D1 and U1_D2 will be connected to Nano digital I/O pins to indicate

the selection of modes.

Figure 9: Mode Selection Switch

The circuit for Spoiler Height and Spoiler Angle adjustment is shown in Figure 10. The Spoiler Height Lever uses a

slide potentiometer and the Spoiler Angle Knob is a rotary potentiometer. The output voltage, U1_A1 and U1_A0

will be fed into Nano analog input pins.

Figure 10: Spoiler Height and Angle Control Circuit

The last control button is the Set Preference Button. When this button is pressed, the Nano shall record the

current spoiler position information and save it in ROM so that this information can be retained even the Nano is

rebooted. In Figure 11, we again use a pull-up resistor for the SET_PREF button; also we shunt a capacitor so that

R17 and C6 consist of a low pass filter to eliminate high frequency bounce when the switch is pressed.


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Figure 11: Set Preference Button circuit

3.1.4 RF Module We use a pair of nRF24L01 of 2.4GHz for wireless communication. To prevent current surges of the module

during transmission, we connect a 10uF capacitor at its 3.3V power rail. Also, some special pins such as CS, SCK,

MOSI and MISO of the nRF24L01 shall be reserved and mapped to the same family pins on Nano. As a result, the

pin connection is given as in Figure 12.

Figure 12: RF Module Circuit Design

3.1.5 LCD Circuit A 16x2 LCD will be displaying information such as the downforce and spoiler angle for user’s knowledge. For the

purpose of saving I/O pins, we will use the LCD with I2C adapter such that all communication can be achieved via

the I2C bus line (SCA and SCL). The I2C adapter circuit connection is shown in the left of Figure 13. The three

address pins, A2, A1 and A0 are pulled up by the 10KΩ resistors which correspond to the slave address of 27 in

hexadecimal value.


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Figure 13: I2C conversion of the 16x2 LCD

The LCD circuit, after being converted into I2C communication, ends up being a very simple circuit seen by the

microcontroller. Note that the SDA and SCL should be specifically connected to analog input pins A4 and A5 on

the Nano which support for I2C communication [9].

Figure 14: LCD Circuit Design

3.1.6 Board Layout Design We will use a perf-board of 15cm x 9cm for prototyping the circuit. The layout of the components by showing

their faces is shown in Figure 15 below.

Figure 15: Component Layout (showing only faces)


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For wiring, due to the availability of resources, we do not many different types of wires; however, we will stick

with some basic rules to ensure the hardware is reliable:

• Use thick wires (22AWG or less) for power lines

• Red wires for positive terminals and black wires for ground

• Use thin and flexible wires for signals

• Minimum wire crossing is desired

• All connections will be nicely soldered (good contact, smooth and shiny soldering surface)

3.2 Firmware Design The main idea of developing Front Panel firmware is to program on Arduino Nano microcontroller, pictures are shown

in Figure 16, which functions with hardware circuit, Knob, switch, button, and lever respectively. Also, we will program

on a RF2.4MHz to complete data exchange. The Main controller feedback information will be displayed on the LCD

Screen.

Figure 16: Arduino Nano

3.2.1 Control buttons

Mode Selection Switch: A 3-way switch is used to connect the 3 digital pins D0, D1 and D3 of the Nano. As

explained in section 3.1.3, D0, D1 and D3 have digital value of 1 by default and will be digital 0 when one of the

pins is connected to the switch. Based on the property specified above, the program defines the three modes,

Automatic, Manual and Preference in the given Table 2.

Table 2: System Mode Pin Definition

Angle Knob & Height Lever: the spoiler height and AOA can be manually adjusted by using the Angle Knob and

Height Lever which correspond to the A1 and A0 pin of the microcontroller on the Front Panel. The actual spoiler


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height and angle are reflected by analog feedback signals which fed to the analog pins of the microcontroller on

the Main Controller. As described in the flow diagram, by comparing the control signal value sent from the user to

the feedback signal values measured from sensors, the system can execute the correct operations.

Set Preference Button: this button will work only under the manual mode. Once the button is pushed, the

microcontroller ROM will be updated to the latest spoiler position including the spoiler height and angle. Even if

the system is power cycled the recorded information will not be lost. When the Preference Mode is being

activated, the system will adjust the spoiler according to the spoiler position data read from the ROM.

Figure 17 is flow diagram to show the system chain of the spoiler Height and angle in manual control.

Adjust spoiler height and angle

Compare desired Height and angle

with Current positon

Is current height and angle - current positon >

2(tolerance)

Raise spoiler height or spoiler angle

Is current height and angle - current positon <= 2 or >=

-2(tolerance)

Is current height and angle - current positon <

-2(tolerance)

Stop moving

Lower spoiler height or angle

Manual Mode

Mode Selection

Figure 17: Flow diagram of Manual Control of the Spoiler Height and Angle


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3.2.2 RF Module The data packages exchanged between the Front Panel to the Main Controller are two arrays – A and B – of both

size 5 described in Table 3 and Table 4.

Table 3: Array elements from Front Panel to Main Controller

Table 4: Array elements from Main Controller to Front Panel

The nRF24L01 has to be defined as either a transceiver or receiver before data transmission proceeds therefore

cannot achieve a real time 2-way communication. In practice, the program swiftly switches the role as a

transceiver/receiver of the RF module on each side.

3.2.3 LCD display The information that the user shall acquire are stored in array B in Table #. Signals and information will be

displayed by the LCD installed on the Front Panel. The program will also intentionally lower the refresh frequency

of the LCD to ensure the driver not being distracted.

3.3 Enclosure Design

The ASCS product will have an enclosure for Front Panel to prevent unintentional damages. More importantly, it will

provide a user-friendly interface for customers to understand and operate the system. The case is designed to be

manufacture with 3D printer. Details for Front Panel enclosure design are illustrated as below.

3.3.1 Exterior Enclosure The exterior of the enclosure aims to provide users an instructional panel to operate the ASCS. Figure 18 shows

the actual design from CAD drawings. Front Panel will fit the circuit layout design to allow users operate the

system. The front is intended to expose adjustments from circuit board, which are LCD screen, Set Preference

Mode Button, Mode Selection Switch, Spoiler Height Level Adjuster and Spoiler Angle Knob.


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Figure 18: Exterior view of Front Panel Enclosure

3.3.2 Interior Enclosure The Figure19 shows the detailed dimensions for Front Panel.

Figure 19: Interior view of Front Panel Enclosure


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Actual measurements and design dimensions are listed in Table 4 below.

All measurements are in centimetre

Letter d is stand for diameter

Table 1: Detailed Dimensions of Front Panel Enclosure

(Unit: cm) ACTUAL DESIGNED

LCD Width 2.3 2.5

LCD Length 7.0 7.4

Mode Selection Switch d=4.0 d=4.5

Set Preference Button d=1.0 d=1.6

Spoiler Angle Knob d=3.0 d=2.0

Spoiler Height Lever Width 0.6 0.7

Spoiler Height Lever Long 4.5 4.7

Case Width 9.2 9.4

Case Long 15.1 15.3

Case Round Depth

0.2

4. Main Controller

The electronics design of the Main Controller in the prototyping stage are microcontroller-based which will be

changed to a PCB-based design in the production stage.

4.1 Electronic Hardware Design

The circuit design of the Main Controller involves Microcontroller, RF Module, GPS Module, Brake Detection Circuit,

Force Measuring Circuit, Angle Measuring Circuit and Motor Driving Circuit. The Microcontroller and RF Module have

the same hardware design as in Front Panel therefore will not be included in this section.

4.1.1 Power Tree Figure 20 shows the Main Controller power tree diagram. The power source of the Main Controller will be the car

battery. As specified in FS-R11, the maximum power required by the system is 40W. Car batteries are lead-acid

type and they can deliver over 100W therefore will be sufficient for powering our Main Controller.


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Figure 20: Main Controller Power Tree

There are two major current branches flow out from the battery: microcontroller branch and motor driver branch.

The Motor Driving Circuit is most power thirsty as it will be driving the mechanical power sources on the Spoiler

System. The Motor Driver Circuit is consisted with two L298N Dual H-Bridge motor drivers with total maximum

power near 40W [10]. Other circuits such as RF Module and GPS are much less power thirsty than the motor driver

therefore can be directly powered by the Arduino Nano regulator outputs (5V and 3.3V).

4.1.2 Motor Driving Circuit The Motor Driving Circuit contains two L298N Dual H-Bridge motor driver breakout boards as shown in Figure 21.

Each driver can only supply up to 20W, therefore we will use two motor drivers to control the Linear Actuator and

DC motor individually.

Figure 21: Dual Bridge L298N Motor Driver Breakout Board

The Motor Driving Circuit design is shown in Figure 22. The ENABLEA pin shorted to the 5V output to have to

motor driver stay at the stand-by mode as long as the Main Controller is powered. The logic inputs, INPUT1 and

INPUT2 are PWM signals which control the current flow direction as well as the average output power. The logical

table is summarized in Table 5.


17

Figure 22: Motor Driving Circuit design

Table 2: Motor Control Logic

ENABLEA INPUT1 INPUT2 Motor Direction

HIGH LOW LOW STOP

HIGH LOW HIGH TURN LEFT

HIGH HIGH LOW TURN RIGHT

HIGH HIGH HIGH STOP

When the motor driver is running at 20W, the heat is dissipated from the heat sink; our pre-test shows that the

heat sink temperature can exceed 100°C at this condition see Appendix C. The design of Main Controller

Enclosure shall have “windows” near the heat sinks to allow thermal dissipation. More details will be given in

section 4.3 about Enclosure Design.

4.1.3 Angle Measuring Circuit We will be using an SCA60C based angle sensing breakout board for our Angle Measuring Circuit. SCA60C is

accelerometer consists of a sensing element chip and a signal conditioning circuit which gives the analog signal

indicating the change of angle respect to horizon. The breakout board model is shown in Figure 14 (a) and the

SCA60C schematic is shown in Figure 14(b).


18

(a) Breakout Board (b) SCA60C Schematic

Figure 23: Components used for Angle Measuring Circuit design

By performing the test of the breakout board (Appendix D), we concluded that the output analog voltage and the

angles of the module are able to sense has a linear relationship within 50 degree. Based on the test result, we

confirm that the SCA60C based breakout board is appropriate for our application of angle measuring. Figure 24

shows the circuit in our design. We only power the module with 5V and take feed its output to the analog input

pin of the Nano. It is important to note that when the breakout board is placed horizontally, the output voltage

will be half the VCC therefore is 2.5V in this case.

Figure 24: Angle Measuring Circuit Design

4.1.4 Force Measuring Circuit We will use three force sensing resistors (FSR) as shown in Figure 25 to measure the downforce applied by the

spoiler. Each FSR is electrically equivalent to a variable resistor of which the resistance changes linearly with

respect to the force applied on its active region (the inner rectangular area). The resistance of each FSR is 10kΩ

when no force applied and close to 100Ω when 100N is applied. Since each FSR is only able to accurately

measuring up to 100N force, we will use three of them for measuring the downforce.


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Figure 25: Force Sensing Resistor used for measuring the downforce

The Force Measuring Circuit is shown in the circuit diagram Figure 26 below where the three FSRs are modeled as

variable resistors R4, R5 and R6. The FSRs along with the 10KΩ resistors R3, R2 and R1 consist of three pairs of

voltage divider. The divided signals v1, v2 and v3 will be summed by the summing amplifier.

Figure 26: Non-inverting Summing Amplifier Circuit

We used LM358 Op-amp for the design due to its single rail supply structure and cheap price. The output U2_A4

is a function of the three inputs described in the equation:

U2_A4 = (1 +R11

R10)(

v1+v2+v3

3) (3)

In this circuit, the ratio of R11 and R10 is 2 which leads the output of the Op-amp U2_A4 essentially equal to the

sum of three voltage divider signals. Therefore, the output of the Force Measuring Circuit represents the sum of

the forces applied onto the three FSRs.


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4.1.5 Brake Detection Circuit The Brake Detection Circuit in Figure 27 is able to tell if the car is braking by sending a triggered pulse at the

output U2_D1. The triggering mechanism is achieved using a comparator circuit shown in Figure 18. The input

signal, Brake_Sig, will be taken from the vehicle brake light. When the driver brakes, the brake light turns on

immediately and the Brake_Sig will also rise from 0V to 12V within 1ms. The Brake_Sig will be divided by a ratio

of 2.5 to feed to the non-inverting input of the LM311. The inverting input of the LM311 is the trigger level which

stays at 0.45V. The output stage of LM311 is an open drain mechanism so we add a pull up resistor R25 in the

circuit design.

Figure 27: Brake Detection Circuit

4.1.6 GPS Module The GPS Module is used to sense the car speed. We use the Ultimate GPS Breakout v3 in out circuit as shown in

Figure 28. To receive better signals from the satellite we also need an antenna.

Figure 28: GPS Module

The connection of GPS Module in our circuit is straightforward: need two pins for power and two pins for

communication as shown in Figure 29.


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Figure 29: GPS Module circuit design in Main Controller

4.1.7 Board Layout Design The layout of components on Main Controller is shown below. Additionally, 2 cables will be sticking out. One

cable is used as the power cord for powering the Main Controller. We refer the other cable as the Spoiler System

Cable which will be mentioned more specifically in section 5.1. The Spoiler System Cable serves as a bridge

between the Main Controller and Spoiler System for both power delivery and signal transmission.

Figure 30: Layout of Main Controller Components


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4.2 Firmware Design The main idea of firmware development of the Main Controller is to control the hardware circuits by Arduino

programs. Also, we will program on an RF2.4MHz to complete data exchange. Meanwhile, one of the most important

function is controlling Spoiler position by adjusting LA length and Motor angle.

4.2.1 RF Module The module will send information to front panel to display, as well as receive data packages from front panel.

When data package received, the micro-controller will determine which mode is selected, what the height and

angle of the spoiler would the driver like. Then, the micro-controller will send signals to motor drivers to

complete adjustment action.

4.2.2 Angle sensors and pressure sensors Those sensors will be connected with analog input pins through the electric circuits. The micro-controller will

read those analog voltage value and convert them into 0-255 unsigned char data and store into package. Then,

those data will be transmitted and displayed on the LCD display at front panel. However, the micro-controller will

process those data to adjust LA and Motor under Auto mode.

4.2.3 GPS Module Since it is very hard to get car speed directly form car, we will use GPS module to get car speed information. The

GPS Module will connect with analog pins to send the speed information to the micro-controller to process. Also,

the information will pack into packages and send to front panel to display.

4.2.4 LA, Motor and Motor driver The micro controller cannot provide enough power to drive LA and motor, so we will use external power source

combined with motor driver to drive them. The LA and Motor will connect with Motor drivers, and Motor drivers

will connect in PWM pins on the micro-controller. The micro controller will send signal to let LA and motor work.

The signal will also include the moving speed of LA and Motor.

4.2.5 Auto mode and Manual mode Under Manual mode, the logic of the firmware will be in the following Figure 31, which controlled by height lever

and angle knob. However, the whole logic of auto mode firmware will be controlled by main controller. The

Figure 31 is shown the control logic of main controller under auto mode.


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Figure 31: Flowchart for Automatic Mode

4.3 Enclosure Design The ASCS product will have an enclosure for Main Controller to keeps all the components together and protect

components from unintentional damages. The case is designed to be manufacture with 3D printer with material of

Figure 32. Details for Main Controller enclosure design are illustrated as below.

4.3.1 Exterior Enclosure The enclosure is designed to be light weight to fit the Main Controller components circuitries compatibly inside.

However, rooms are left intentionally for circuitries to dissipate excess heat. Figure 32 shows the appearance of

the interior design to house the Main Controller circuit board. The upper bound is left unseal for the wire

connections.


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Figure 32: Exterior view of Main Controller Enclosure

4.3.2Exterior Enclosure

The Figure 33 below is the detailed dimensions for Main Controller. Besides, detailed data are list in Table 6.

Figure 33: Interior view of Main Controller Enclosure


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Table 3:Detailed Dimension of Main Controller Enclosure

Unit:cm ACTUAL DESIGNED

Case Long 9.15 11.4

Case Width 15.05 17.3

Case Round Depth

0.25

5. Spoiler System

5.1 Electrical Design The hardware design involved in the Spoiler System focuses the Spoiler System Cable design as mentioned in section

4.1.7. The cable has multiple wires serving for power delivery and signal transmission; different types of wires must be

designed for different purposes. Design details are addressed in the following subsections.

5.1.1 Power Line According to FS-R97, the wire loss from Main Controller to Spoiler System shall be less than 2%. Since the Spoiler

System will be installed on top of the car boot lid whereas the Main Controller stays in the boot trunk, we must

not use thick wires for connections to meet the requirement. Figure 34 is a typical boot lid design. When the

boot lid is closed, the very small slot marked by red color tends to be the best place for which the cable can sneak

in, thus the wire dimensions shall not be large.

Figure 34: Typical Boot Lid Design

The length of the cable is about 1 meter. The have the cable loss less than 2%, the maximum power on the cable

shall be less than 0.8W when the Main Controller is delivering 40W to the Spoiler System. When a 4A current

passing through the wire, the wire resistance by ohm’s law is calculated by equation (4):


26

R <Pcable

I2 = 0.8 W

16 A2 = 50mΩ (4)

By referring to the standard AWG table [11], we should use wires less or equal to AWG22 in order to have the wire

resistance about 50mΩ when its length is 1 meter. Meanwhile we want to minimize the cross section area of the

wire, therefore the AWG22 wires which have sectional area of 0.33m2[12] will be best option for the power line

material.

5.1.2 Signal Line As shown in the system level diagram in Figure 1, the signal lines between the Main Controller and Spoiler

System contain Motor Control signals and Sensor Output signals. There are 13 wires in total for signal

transmission listed in Table 7.

Table 4: Wires for Signal Line between Main Controller and Spoiler System

Given the fact that wire resistance does not produce significant effects at low current low frequency signals, we

are allowed to use thin wires for each signal line to keep the total area small. As a result, we will be using Ribbon

Cable with 14 conductors for our signal line. The end of the Ribbon Cable shall have connector which allows the

Spoiler System to be electrically disconnected from the Main Controller in a simple and easy way.

5.2 Mechanical Design The general mechanical design of the Spoiler System was presented in section 2.4. This section contains technical

details which illustrate the design progressively and comprehensively.

5.2.1 Mechanical Power Source A Linear Actuator and a DC Motor are used in the Spoiler System design serving as mechanical power sources.

Linear Actuators are able to provide translational or linear motion whereas DC Motors generate rotational

motion. They will be used to control the ASCS system outputs – Spoiler Elevation and Spoiler Angle – respectively.

The Linear Actuator we used along with its technical specifications is shown in Figure 35. We refer the stationary

part as body and the movable portion as stroke. The pushing force of the stroke is linearly proportional to the

current draw; the moving speed of the stroke can be varied by the PWM control signals sending from the Main

Controller.


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Figure 35: Linear Actuator

The specification of the DC Motor is marked with yellow color in Figure 36. It has remarkably large rated torque

by satisfying the angular speed which is perfectly suitable to control the AOA of the spoiler.

Figure 36: DC Motor

Both mechanical power sources have self-lock mechanism, that is, they can sustain the previous states without

feeding any electrical power.

5.2.2 Arm Mechanism The Spoiler Mechanism has two parts: Arm Mechanism and Hand Mechanism. Figure 37 below shows the

general arm design prototype of Spoiler System.


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Figure 37: General Arm Design Prototype of Spoiler System

The arm mechanism is driven by the Linear Actuator and it is responsible for adjusting the spoiler height. The

moment when the Arm Mechanism reaches to the lowest position and highest position are presented in the two

pictures in Figure 38. As highlighted, the lowest position is 6.5cm and highest position is 25cm which meet the

FS-R106 and FS-R107.

(a) Lowest Position: 6.5cm (b) Highest Position: 25cm

Figure 38: Lowest Elevation (a) and Highest Elevation (b)

Detailed parts and the related functionalities will be listed as below. Figure 39 shows the parts overview of the

arm mechanisms.


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Figure 39: Spoiler Components;

(a) Linear Actuator (b) Linear Actuator Stand (c) Arm Bracket (d) DC Motor (e) Motor Stabilizer (f) Motor Shaft Couple

The Base of the Spoiler System is designed as shown in Figure# above. It is made with plywood and will be

installed in the surface of the car trunk lid. The base has a square shape which will take up whole system weight

and evenly distribute along its square surface. Linear Actuator is bridged between two Linear Actuator Stands

(Figure 39.b) fixed in the Base with the flexible rotatory ability. DC motor will be mounted on the tip of the arm

support link with the handmade DC motor stabilizer as shown in Figure 39. (e). Two arm support links will be

fixed in the base used Arm Brackets, Figure 39. (c). The Motor Shaft Couple is planned to manufactured with 3D

printer The Alloy Hand Link will be fixed though Motor Shaft Couple, Figure39. (f), with DC Motor, which is the

connector of DC motor and arm link.

5.2.3 Hand Mechanism The Hand Mechanism controls the AOA of the spoiler. According to FS-R4, the ASCS should be compatible with

any type of car spoilers with different width and thickness. As shown in Figure 121, the two horizontal Supporting

Rods along with the Horizontal Stabilizers are able to stabilize a spoiler with arbitrary width; the two vertical

Supporting Rods along with the Vertical Stabilizers can immobilize the spoiler with arbitrary thickness. The

structure shown in Figure 40 is named as a spoiler clamper.

Figure 40: General Hand Design Prototype of Spoiler System


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A Hand Mechanism consists of two spoiler clampers, a Hand Link and some components for connection purposes.

As shown in Figure 41, the entire Hand Mechanism is driven by the DC Motor. The Motor Shaft Coupling and

Motor Coupling Connectors can transfer the mechanical power of the DC motor to the movement of the Hand

Link. Since the Hand Mechanism is attached onto the Hand Link, the mechanical power of the DC Motor will

eventually be translated to the angular movement of the car spoiler.

Figure 41: Hand Mechanism Design

Refering to the picture below, the upper angle and lower angle of the Hand Mechanism movement are 40 degree

and 1 degree respectively which also satisfy the FS-103 and FS-104. The angle of the Hand Mechanism will be

exactly same with AOA of the spoiler. Figure 42 shows the Hand Mechnism flexible angle adjustments.

Figure 42: Hand Mechanism Angle Adjustment

5.2.4 Rigid-body Dynamics Based on the aerodynamic theory explained in section 2.3, we expect the maximum down force occurred when

the spoiler has some distance off from the ground surface and the AOA is approximated 17 degrees. In this case,

we expect a down force, Fd about 300N.


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Figure 43: Spoiler System Detailed Dimension Front View

Figure 43 shows free body diagram of the Spoiler System at an instance of movement. Assuming the 300N to be

the worst case scenario, by using Newton’s Equation, we obtained the result as in equation (5):

FLA ∗ (sin12.87) ∗ (188) = 300 cos(12.87 + 17.3) ∗ (188 + 98) (5)

Where FLA is the pushing force for the Linear Actuator. Solving the equation above we obtained that FLA = 1750N.

That is, with 300N exerted onto the system, the Linear Actuator must provide 1750N to be able to move the

spoiler. Due to the fact that the Linear Actuator can only provide 900N thrust force, we obtained result in

equation (6) that:

900 ∗ (sin12.87) ∗ (188) = Fd ∗ cos(12.87 + 17.3) ∗ (188 + 98) (6)

And Fd is solved to be 155N. In other words, the ASCS in this proof-of-concept stage is only able to lift 155N load.


32

Figure 44 shows the top view of the Spoiler System, the position and geometry is same as in Figure 43.

Figure 44: Spoiler System Detailed Dimension Top View

The two linkages, Arm Link and Hand Link, are suffering most of the load. The 300N down force will be uniformly

distributed onto the two Spoiler Base hence F1 = F2 = 150N; in this case, we use our worst scenario calculation,

FLA = 1750N to evaluate the torque and bending torque (twice of the torque) applied onto the two linkages.

For the Arm Link,

τcenter = 1750N ∗ 244mm = 427N ∙ m (7)

τbending = 854N ∙ m (8)

For the Hand Link,

τcenter = 150N ∗ 98.94mm = 15N ∙ m (9)

τbending = 30N ∙ m (10)

From the calculation as in equations (7) (8) (9) (10), we see that the Arm Link is suffering a much larger bending

force than the Hand Link. Reasonably we should use high stiffness material as the Arm Link and it should be

thicker than the Hands Link. Details for materials are mentioned in next section.


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5.2.4 Building Materials From research [13], four types of steels have the best matches and their properties are listed as the below table.

Table 5: Steel Properties

Properties

Plywood

(Hardwood

core)

Aluminum

Alloy -7178 Stainless Steels Tool Steels

Density (1000 kg/m3) 0.58-0.62 2.83 7.75-8.1 7.72-8.0

Elastic Modulus (GPa) 10.9 70-80 190-210 190-210

Poisson's Ratio 0.37 0.33 0.27-0.3 0.27-0.3

Thermal Expansion

(10-6/K) 6.89-13.1 23.4 9.0-20.7 9.4-15.1

Tensile Strength (MPa) 31-130 607 515-827 640-2000

Yield Strength (MPa) 186-758 538 207-552 380-440

Percent Elongation (%) 11-12.4 10 12-40 5-25

Hardness (Brinell 3000kg) 540 90-205 137-595 210-620

Based on the worst case scenario analysis, decisions have been made to choose the following materials. Rated

the stiffness, hardness and density from level 1 to 5, which has the properties from low to high. The table below

has summarized the materials decided according to their required stiffened, hardness and density.

Table 6: Material Choices

Components Material Stiffness Hardness Density

Arm Bracket Steel 5 5 5

Arm Supporter Aluminum Alloy 4 3 2

Arm Link Steel 5 5 5

Base Plywood 4 3 2

Bracket Pin Steel 5 5 5

DC Motor Stabilizer Plywood 4 3 2

Hand Link Aluminum Alloy 4 3 2

Linear Actuator Body Steel 5 5 5

Linear Actuator Stroke Aluminum Alloy 3 3 2

Linear Actuator Stand Stainless Steel 5 5 5

Linear Actuator Pin Steel 5 5 5

Motor Shaft Couple Aluminum Alloy 4 3 2

Shaft Hand Link Stabilizer Wood 3 2 2

Spoiler Base Wood 3 2 2


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Firstly, for the arm bracket, arm link, bracket pin, Linear Actuator Body and Linear Actuator Link, tool steel will be

the selection. Next, for the reason that tool steel has a related high density and tensile strength compared to the

other three type of steels. More importantly, tool steel is the lowest cost among the other three. Then, for the

Linear Actuator Stand, we choose Stainless Steel to secure the lifetime of the component. In addition, for the

Arm shorter, Arm Longer, Hand Link, Linear actuator Stroke and Motor Shaft Couple, Aluminum Alloy is

considered to use. Because Alloy steel has similar properties as tool steel. Lastly, for the rest of the components,

Bas, DC Motor Stabilizer, Shaft Hand Link Stabilizer and Spoiler Base, wood will be the replacement of steel uses.

Poplar wood will be the best choice for Spoiler System. It is because the properties of wood will be similar to

steel. Especially, wood has much lower cost than steels.

In sum, with aim of higher safety and lower cost, Veroptimal manage to balance the choices of material used.

6. Test Plan

6.1 Units Test In general, our individual module testing consists of separately testing, which include GPS Module testing, Downforce

measurement module testing, Angle measurement module testing, Wireless communication module testing, and

Mechanical part testing.

In order to test every individual module, an Arduino program will be written for every single module. According those

tests, the following results are expected:

Circuit board power test

o Set power supply to 12V, 3A current limit then power up the circuit board with power supply

o The actual current draw of the circuit is the current reading on the power supply

Individual electronics modules test

o GPS module test:

Design a speed comparison test for GPS when it is installed on the car

Compare GPS output value with real car speed

o Downforce and Angel measurement modules tests:

Design test cases to read actual load and rotated angel

Compare actual load and angel values with tested output values

o Wireless Communication module test:

Design a test for the processes of sending and receiving in every 0.1 second

Determine the percentage of error occurs during transmissions

o Mechanical part tests:

No fractures on mechanical structure when 300N load is applied


35

The measurements of the GPS Module, Downforce measurement module, Angle measurement module shall

be accurate (less than 2% of error comparing with the physical measurements)

6.2 System Test

To verify the manual mode system will meet the requirement, the following results are expected:

When the driver selects manual mode, spoiler height controller, spoiler angle controller and set preference

button will be enabled.

Under manual mode, the driver can change to other modes in any time.

When the driver adjusts spoiler height controller, the Arm Mechanism in Spoiler System will raise or descend.

When the driver adjusts spoiler angle controller, the Hand Mechanism in Spoiler System will rotate clockwise

or counter-clockwise.

Once the driver press set preference button, the latest profile of angel and height data of Spoiler System will

be stored in Arduino ROM.

To verify the automatic mode system will meet the requirement, the following results are expected:

When the driver selects automatic mode, spoiler height controller, spoiler angle controller and set preference

button will be disabled.

Under automatic mode, the driver can change to other modes in any time.

The ASCS will perform routinely following the flow chart in Figure 31.

To verify the preference mode system will meet the requirement, the following results are expected:

When the driver selects preference mode, spoiler height controller, spoiler angle controller and set

preference button will be disabled.

Under manual mode, the driver can change to other modes in any time.

Once preference mode is selected, the spoiler height and angle will adjust to a stored value in Arduino ROM.

To verify the ASCS will help the car to reduce drag force while driving:

The coast down test method will be applied.

The detail test information will be attached in the Appendix B.


36

7. Conclusion

As a detailed design guideline, the design specification specifies design goals, design details about each component,

and solutions to meet the function specification. This design specification will be used as consistent criteria

throughout the actual developing phase. Most of the hardware designs are finished except for some board layouts.

Therefore, we will mainly focus on the firmware and mechanical design of the ASCS later on. The amount of expense

and time that we invested in designing the hand and arm mechanism is beyond our expectation. As a result, we are

re-designing some of the mechanical components in order to reduce the cost and increase the easiness for us to make.

Due to the fact that it is rather crucial to ensure all required functionalities of the ASCS are achieved, test plans listed

in the design specification will be well prepared and implemented. This design specification will be strictly followed to

fulfill the design goals.


37

Reference

[1] Y. Xu. (2009, March 08). Qi Che Feng ZuShuo Ming [Aerodynamics Analysis of Vechicles] [Online].

Available: http://designer.mech.yzu.edu.tw/articlesystem/article/compressedfile/(2009-03-08)%20%E

6%B1%BD%E8%BB%8A%E9%A2%A8%E9%98%BB%E8%AA%AA%E5%88%86%E6%98%8E.aspx?ArchID=945

[Accessed 19 October 2015].

[2] A. K. Mathews et al.(2014, June 02) Study of Aerodynamic Effect Of Spoiler On A Car [Online].

Available: http://www.slideshare.net/knightabyn/study-of-aerodynamic-effect-of-spoiler-on-a-car?related=6


[3] Oppositelock.(2014, Dec.01).Wings/Spoilers: You're probably doing it wrong [Online].

Available: http://oppositelock.kinja.com/wings-spoilers-youre-probably-doing-it-wrong-1665312667


[4] Abbott, Ira H (2012, April 26) Theory of Wing Sections. Appendix IV [Online]

Available: https://zh.scribd.com/book/271527757/Theory-of-Wing-Sections-Including-a-Summary-of-Airfoil-Data

[Accessed 11 November 2015].

[5] Abbott, Ira H (2012, April 26) Theory of Wing Sections. Appendix IV [Online]

Available: https://zh.scribd.com/book/271527757/Theory-of-Wing-Sections-Including-a-Summary-of-Airfoil-Data

[Accessed 11 November 2015]

[6] Journal of Jiamusi University (2014, May) Aerodynamic optimization of sedan spoiler based on experimental

design method [Online]

Available: http://www.docin.com/p-1055912742.html



38

[7] XIAMEN AMOTEC DISPLAY CO.,LTD (2008, October 29). Specification of LCD Module [Online]

Available: https://www.sparkfun.com/datasheets/LCD/ADM1602K-NSW-FBS-3.3v.pdf


[8] Nordic Semiconductor. nRF24L01+ Singel Chip 2.4GHz Transceiver Preliminary Product Specification v1.0 [Online]

Available:https://www.sparkfun.com/datasheets/Components/SMD/nRF24L01Pluss_Preliminary_Product_Specificati

on_v1_0.pdf


[9] Arduino. Arduino Nano [Online]

Available: https://www.arduino.cc/en/Main/ArduinoBoardNano


[10] Instructables. Arduino Modules –L298N Dual H-Bridge Motor Controller [Online]

Available: http://www.instructables.com/id/Arduino-Modules-L298N-Dual-H-Bridge-Motor-Controll/


[11] Stranded Wire Chart (AWG) [Online]

Available: http://www.seas.gwu.edu/~ecelabs/appnotes/PDF/techdat/swc.pdf


[12] HM Wire International, Inc. American Wire Gauge Square MM Cross Sectional Area Chart [Online]

Available:http://www.hmwire.com/New%20PDFs/American_Wire_Gauge_to_Square_mm_Cross_Sectional_Area_Cha

rt_1.3.15.10.pdf



39

[13] Efunda. General Properties of Steels [Online]

Available: http://www.efunda.com/materials/alloys/alloy_home/steels_properties.cfm



40

Appendix

Appendix A: Complete Circuit Schematic

Figure A shows the schematic of the ASCS.

Figure A: Circuit Schematic of the ASCS

Appendix B: Coast Down Method for Drag Estimation

Test Condition (for all Test cases: 1, 2, 3)

1. Same weather condition and road condition (wind speed, dry road and no elevation)

2. The initial velocity where measurement takes place should be same for all test cases

3. The car weight should be same (same passenger numbers during all cases)

Test Cases Setup

There are three cases in this test: without spoiler, with spoiler at Economy Mode (lowest drag) and with spoiler at

Safety Mode (largest downforce). For each test case, we drive the car until it reaches to the initial velocity v1, then the

car accelerator will be released so the car is free running. Then we will record the car velocity for every certain

amount of time. We will repeat recording for 10 times in each test case.


41

Figure B: Test Cases for Coast Down Method

Test Result

After test, we will create a data spreadsheet as similar in Table B, the numbers are just examples for demonstration

purpose.

Table B: Data Recording

The data in Table B indicate the drop of car speed in the same time period. We can process these numbers to calculate

deaccelerate of the car hence to compute the total drag force applied on the car based on Newton’s equation:

F = Ma

Where,

M is the mass of the car

a is the deceleration calculated from Table B

Using this method, we can obtain many different sets of F and hence to approximate the changes of drag by

comparing these forces. The estimation can be very accurate if we repeat the test many times.


42

Appendix C: Motor Driver Test

Test Condition:

Rail Power = 12V, ambient temperature = 22°C, 100% duty cycle

The test is conducted in the test condition specified above. Then we use rheostat to pull current from the motor driver.

The setup is shown in Figure C1.

Figure C1: Test Setup

The test results are summarized in Table C. At load of 500mA, 1000mA, 1500mA and 2000mA and soaking for 10

minutes, the heat distribution of the motor driver is reflected by the 4 pictures in Figure C2.

Table C: Power Test of the Motor Driver

Figure C1: Thermal Dissipation of Motor Driver at 500mA, 1000mA, 1500mA and 2000mA


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Appendix D: Angle Sensor Test

Test Condition:

Vcc = 5V, ambient temperature = 22°C

Figure D1: Angle Sensor Test Setup

The test results are recorded and processed as shown in Figure D2. The plot shows that the relationship between

voltage and angle is linear when the angles are between -50° to 50°.

Figure D2: Voltage and Angle Relationship of the Angle Sensor

our design specifications refer to a previous document...

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