senior design

Development of a Wheel Force/Torque Sensor for Autonomous Ground Vehicles

Development of a Wheel Force/Torque Sensor for

Autonomous Ground Vehicles

A Project work

Presented to

The School of Engineering and Engineering Technology

Federal University of Technology

Akure, Ondo State

In Partial Fulfillment of the requirements for the degree

of Bachelor of Engineering (B.ENG) in Electrical and Electronics Engineering

FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE.

By

OLALEYE OLUWATOSIN OLUWADAMILOLA (EEE/10/0710)

MAY, 2015.


CERTIFICATION

I certify that this project was carried out by OLALEYE, OLUWATOSIN OLUWADAMILOLA

and other team members in both the department of Electrical and Mechanical Engineering of the

FAMU-FSU College of Engineering.

………………………………… …………………………….

Dr. M.P Frank Dr. M.P Frank

Senior Design Supervisor Senior Design Advisor

……………………………….. ……………………………..

Dr. Peter Kalu Dr. Simon Foo

Program Coordinator ECE Departmental Chair

(4-1-1 FUTA-FAMU)


SPONSOR AND TEAM MEMBERS

COMPILED AT:

FLORIDA A & M UNIVERSITY AND FLORIDA STATE UNIVERSITY

COLLEGE OF ENGINEERING (FAMU-FSU COE)

SPONSORED BY:

AEROPROPULSION MECHATRONIC & ENERGY CENTRE

CENTRE FOR INTELLIGENT SYSTEMS CONTROLS AND ROBOTICS

TEAM MEMBERS:

John Gregulak [email protected] Oluwatosin Olaleye [email protected]

Matthew Russo [email protected] Marc Saint-Fleur [email protected]

Randall Veliky [email protected]

Project Website: http://eng.fsu.edu/me/senior_design/2015/team23/


DEDICATION

This project work is dedicated to the Almighty God for giving me the needed inspiration and

strength to accomplish this task. I also want to appreciate my family members (Olaleye J. O.,

Olaleye M. T., Olaleye Ifeoluwa, Olaleye Oluwapelumi), and everyone who had contributed

immensely to the success of this project. God bless you all.


ACKNOWLEDGEMENT

All glory and honor to the Almighty God for the grace and opportunity to successfully complete

my first degree, without him the completion of my final year project would not have been

possible.

I would like to also appreciate the management of the Federal University of Technology Akure,

for given me the rare opportunity to be part of the FUTA-FAMU cohort program in the United

States. Special thanks to Florida Agricultural and Mechanical University (FAMU) for admitting

me to complete my undergraduate degree program, and the FAMU-FSU College of Engineering

for providing me with the necessary facilities to carry out my project design.

I would also like to acknowledge all those who assisted in realizing the goals of this project.

First, acknowledgement goes out to my advisors, Dr. Chuy and Dr. Frank, who were

immeasurably helpful throughout the course of this design. Special thanks also go to our

instructors, Dr. Gupta, teaching assistants, Ricardo Aleman, Samuel Botero, and Yuze Liu, and

the overall senior design coordinator, Dr. Shih. The staffs of the department of Electrical and

Electronics Engineering, Federal University of Technology Akure, Nigeria are also duly

appreciated for their help and support throughout these five years programme.

This project would not have been possible without the help of the sponsor, Dr Oscar Chuy, who

gave his full fledge support financially and materially to see that this project is a big success. Big

thanks to Dr. Chuy for his support in achieving this goal as well as his encouragement to

maintain progress in track.

Finally, my special appreciation goes to all staffs of the College of Engineering’s machine shop

and the Centre for Intelligent System Controls and Robotics (CISCOR) for their all-round

support. My profound gratitude goes to my team members, John Gregulak, Marc Saint-Fleur,

Matthew Russo and Randall Veliky, friends and colleagues in persons of Bolufawi Omonayo,

Tolulola Adeyewa, Omoniyi Gabriel amidst others. Thank you all for making this project a

success. God bless you all (Amen).


ABSTRACT

Over the last few decades, doldrums of research have gone into the development of a system that

allows autonomous ground vehicle to better live up to its all-terrain designation. Outcomes from

these researches have shown that the core concept of the assembling strain-gauges, converting

measured strain into torque or another force, is a sound theory, one that has been implemented

for more than 30 years.

The objective of this project is to devise a way to quantify the interaction between the wheel and

ground of CISCOR's autonomous all-terrain vehicle (ATV), called the Gas operated land

intelligent all terrain hub (GOLIATH). In the interest of making GOLIATH more capable of

living up to its all-terrain designation, this project aim is to design, fabricate and integrate an

economically friendly wheel force/torque sensor to detect forces or torques applied to the wheels

of the ATV. This is essential in maintaining traction and stability of the vehicle during off-terrain

transit. This force/torque sensor unit will be mounted between the wheels and hub of the

autonomous vehicle. This technique provides the best medium to quantify the axial forces acting

on the wheels of the ATV.

Currently, there are already fabricated wheel torque sensor units commercially available in the

market. The major drawbacks to these units are that they are produced specifically for certain

applications and highly expensive to procure. These drawbacks make large scale production and

adoption for all terrain vehicles difficult.

Like any design project, several designs were initially looked at and properly verified before

selecting an appropriate design. The chosen design went through several alterations to better

realize the goal of the project.

This design has theoretically proven to be the best bet due to its portability, high system

compatibility, ease of fabrication, and its economic viability.

However, in a bid to achieve this, there are pertinent technical constraints that must be factored

into the design requirements for effective measurement of torque, calibration of measurements,

and intermittently communicating with the ATV's computing systems. Additionally, this sensor

unit need to able to withstand extreme conditions (shock, temperature, terrain, etc.) that the ATV

operates in.

Finally, the realization of this economically friendly wheel force/torque sensor resulting from its

comparatively low production cost and large scale production will help increase the full scale

adoption of wheel torque sensors for ATVs.


TABLE OF CONTENTS Certification…………………………………………………………………..................................i

Sponsor and Team members………………………………………………………………………ii

Acknowledgement…………………………………………………………………………......…iii

Abstract………………………………………………………………………………………….. iv

Dedication…………………………………………………………………………………………v

Table of contents ………………………………………………………………………………....vi

List of Figures… ………………………………………………………………………………...vii

List of Tables… ……………………………………………………………………..………….viii

1.0 Project Overview .......................................................................................................... 12

1.1 Background ............................................................................................................................................ 12

1.2 Problem Statement ................................................................................................................................. 13

1.3 Design Requirements ............................................................................................................................. 14

1.2.1 Design Specifications ..................................................................................................................... 14

1.2.2 Performance Specifications ............................................................................................................ 15

CHAPTER TWO ............................................................................................................... 15

2.0 Background Research ................................................................................................... 15

CHAPTER THREE ........................................................................................................... 17

3.0 Project Management ..................................................................................................... 17

3.1 Schedule ................................................................................................................................................. 18

3.2 Resources ............................................................................................................................................... 18

3.3 Procurement ........................................................................................................................................... 18

3.4 Communications .................................................................................................................................... 19

CHAPTER FOUR .............................................................................................................. 19

4.0 Concept Generation ...................................................................................................... 19

CHAPTER FIVE ................................................................................................................ 24

5.0 Final Design .................................................................................................................. 24

5.1 Mechanical Design ................................................................................................................................ 24

5.2 Electronics ............................................................................................................................................. 25

5.2.1 Microcontroller .............................................................................................................................. 25

5.2.2 Code Description ............................................................................................................................ 25

CHAPTER SIX .................................................................................................................. 27

6.0 Operations Manual ....................................................................................................... 27

6.1 Operation of unit .................................................................................................................................... 29


CHAPTER SEVEN ............................................................................................................ 30

7.0 Design of Experiment .................................................................................................... 30

7.1 Mechanical Experiments ....................................................................................................................... 30

7.1.1 Digital Testing ................................................................................................................................ 30

7.1.2 Material Testing ............................................................................................................................. 30

7.1.3 Full Scale Test ................................................................................................................................ 30

7.2 Electrical Experiments ........................................................................................................................... 31

7.2.1 Electrical Test................................................................................................................................. 31

7.2.2 Wi-Fi test ........................................................................................................................................ 31

7.2.3 Sampling test .................................................................................................................................. 31

7.2.4 Voltage test ..................................................................................................................................... 31

7.3 Completed Assembly Testing ................................................................................................................ 31

CHAPTER EIGHT ............................................................................................................ 33

8.0 Considerations for Environment, Safety, and Ethics .................................................... 33

CHAPTER NINE ............................................................................................................... 34

9.0 Conclusion .................................................................................................................... 34

CHAPTER TEN ................................................................................................................. 35

10.0 References ................................................................................................................... 35

CHAPTER 11 ..................................................................................................................... 36

11.0 Appendix ..................................................................................................................... 36

11.1 Parts Procured ...................................................................................................................................... 36

Rechargeable Nickel Metal Hydride Battery Pack Cs (3000 MA), 6 Batteries (3W x 2D) ........................ 38

11.2 Gantt Chart........................................................................................................................................... 40

..................................................................................................................................................................... 41

11.3 Code ..................................................................................................................................................... 42


LIST OF FIGURES

Figure 1 GOLIATH ...................................................................................................................... 13

Figure 2 The Forces and the Moments Acting on the Wheel in a Static Frame ............................. 5

Figure 3 A Wheatstone Bridge Where the Top Half of the Bridge Represents Strain Gauges and

the Bottoms are Resistors.............................................................................................................. 17

Figure 4 Budget Used to Manufacture Force/Torque Sensor Prototype ....................................... 19

Figure 5 Original Force/Torque Assembly Prior to Modification .................................................. 8

Figure 6 Design After Wheel Spacer Was Added .......................................................................... 8

Figure 7 Side by Side Comparison of the New Sensor Design(Right) Versus the New One(Left)

....................................................................................................................................................... 21

Figure 8 Original Electrical Circuit Design .................................................................................. 22

Figure 9 Electrical Circuit Diagram (Left) and Final Product (Right) ........................................... 9

Figure 10 Exploded View of Assembly ........................................................................................ 24

Figure 11 Sensor Cross ................................................................................................................. 24

Figure 12 Sensor Cross Finite Element Analysis ......................................................................... 26

Figure 13 SPI Channels(Top), Transmitted/Received Data(Bottom) ........................................... 26

Figure 14 Hub Adapter ................................................................................................................. 27

Figure 15 Inner Plate ..................................................................................................................... 27

Figure 16 Cross Section ................................................................................................................ 28

Figure 17 Outer Plate .................................................................................................................... 28

Figure 18 Wheel Spacer ................................................................................................................ 29


LIST OF TABLES

Table 1 Electrical Component Decision Matrix ........................................................................... 10

Table 2 Complete Bill of Materials .............................................................................................. 21

Table 3 Gantt Chart, October - January ........................................................................................ 40

Table 4 Gantt Chart, January - April ............................................................................................ 41


CHAPTER ONE

1.0 Project Overview

The objective of this project is to devise a way to quantify the interaction between the

wheel and ground of CISCOR's autonomous ATV, GOLIATH. This is to be achieved via the use

of a force/torque sensor mounted between the right front wheel and hub.

1.1 Background

As technology advances, increasingly more systems are becoming automated, requiring

less and less human interaction and input. One of the more ambitious goals of this automation is

to have fully autonomous vehicles. The Defense Advanced Research Project Agency (DARPA)

hosts many competitions with the sole purpose of creating such vehicles and furthering their

progression into everyday life [1]. Many of the advances tested and pioneered at these

competitions have already made it into the mainstream markets. Systems such as adaptive cruise

control and lane departure systems are already offered as features on many vehicles, and

capabilities will increase as other systems such as networked collision avoidance are perfected

[2]. One of these fully autonomous systems being developed is the Center for Intelligent Systems

Control and Robotics’ (CISCOR) Gas Operated Land Intelligent All Terrain Hub (GOLIATH),

shown in Figure 1. GOLIATH started out as a 2012 Polaris Sportsman 550 all-terrain vehicle.

Previous projects with this vehicle led to the addition of actuators on the throttle, brake, steering

and shifter. Last year, additional sensors and computer systems were added and interfaced

together to give GOLIATH the ability to navigate autonomously [3]. The goal this year is to

further the capabilities of this unmanned vehicle.

In order to complete this task, it will be necessary for the vehicle to be able to detect

when wheel slip is occurring. A human driver can easily ascertain if wheel slip is occurring; the

lack of forward motion and sound of the wheel spinning often leads to visual confirmation of the

event. For an autonomous vehicle, visually detecting wheel slip is too cumbersome and

inefficient to work, so other electronic means are required.

One of the main problems with the current state of the vehicle is that is cannot effectively

determine the best way to traverse rough terrain utilizing a combination of GPS based course

selection and forward faced imaging. Should the vehicle be able to detect wheel spin and loss of

traction, it will be able to change the control input, just as a human driver would, in order to

overcome the obstacle.


Figure 1 GOLIATH

To determine if wheel slip occurs, the use of strain gauges to measure the torque on the

axle will be needed. A strain gauge is designed to convert mechanical motion into electrical

signal [4]. The most common strain gauges have a flexible backing with a metal wire

pattern attached. A voltage is applied to the gauge that runs through the wire, as the gauge bends

under strain the resistance through the wire changes as a function of the strain. Using this

function and measuring the resistance change leads to an accurate calculation of the strain. To

measure the resistance change the gauge is attached to a Wheatstone bridge. Many types of strain

gauges have been made and are used on axles; however, most gauges only measure the weight

experienced by the axle [5]. This gauge will measure forces in all directions, as well as

accompanying moments.

It should be noted that there are commercially available units that can be purchased that

are capable of measuring the forces that this project aims to. However, these units have several

problems which prevent them from easily integrating into the GOLIATH. Primarily, these units

are expensive; at $10,000 to $15,000, they are two to three times the budget of this project.

These units typically mount on the outside of the wheel, which could interfere with terrain or

other obstacles. Finally, there is still the issue of communication between the unit and the ATV

which would need to be addressed. While commercial units could be integrated into the systems,

a better alternative is to make one that expressly integrates, and does so at a fraction of the cost

[6].

1.2 Problem Statement

The ability to sense the force or torque applied to a wheel is essential to maintaining

traction and stability of autonomous ground vehicles. In the interest of making GOLIATH more


capable of living up to its all-terrain designation, the objective of this project is to design,

fabricate and integrate a wheel force/torque sensor for the vehicle.

Sponsored by CISCOR, this project aims to add more input systems to GOLIATH.

Currently, the vehicle is capable of remote operation through use of the throttle, brake, and

steering, along with GPS navigation and object avoidance via laser rangefinders. While this is

acceptable for paved or relatively smooth terrain, the current inputs cannot modulate the three

outputs effectively over rough terrain. In its current state, the GOLIATH is not as capable in all-

terrain situations as a human driver.

The objective of this project is to design and test a way to improve the GOLIATH’s off

road capability, allowing the vehicle to better navigate rough terrain through use of a wheel

force/torque sensor that will wirelessly communicate with the computer control system. In order

to realize this goal, the team will need to design a system that:

Measures forces and moments on the ATV's wheel

Communicates wirelessly with the ATV

Is strong enough to not break or fail during use of the ATV during normal use

1.3 Design Requirements

The design will function via the use of strain gauges mounted to the arms of the cross

member that sits in the middle of the unit, shown in Error! Reference source not found.. These

gauges will then need to transmit the strains in each arm to a controller, which can then take the

signals, convert them from voltages to forces, and wirelessly transmit them to the vehicle.

The unit is constrained both in its overall design as well as how it performs in collecting

and distributing data, and how it converts the data into a more usable form.

1.2.1 Design Specifications

The overall design will have to fit within a 7.5 in (19 mm) to 11 in (28 mm) diameter as

7.5 in is the distance between the bolts in the hubcap and 11 in is the inside diameter of the

hollow portion of the wheel. The height of the assembled gauge along the shaft is 5 in (12 cm).

This height is more than was originally planned for, and was selected to ensure that each section

will be strong enough to handle any forces on the wheel. The overall effect of moving the wheel

out will increase the turning radius, but testing has shown that the overall ride and capability is

not hindered.

The unit will only have to sustain a quarter of the total weight that the ATV experiences,

but for safety each wheel will be experiencing the full weight and applied factor of safety of 1.5

to the forces and 2 to the torques. The maximum force with these added constraints is 4800 lbf

(21,360 N) and a torque of 2049 lbf*ft (1760 N*m). The team decided to go with Aluminum

7075 for the build material. While this material was not as strong as some stainless steels or

titanium, it was still capable of handling the forces, and its anticorrosion properties as well as it

resistance to fatigue made it a good candidate for the purposes of this project.

The weight of the unit is not an immediate concern, as the final product is of a testing

nature. The unit is being mounted on the steering knuckle, so any weight added will be unsprang,

and will not affect vehicle handling or suspension; however, a lighter final product is still more

desirable, as it will induce less momentum on the wheels and axle.


This being said, it is possible that the unit could be made shorter by going to a stronger

material and making the sections thinner. However, these materials proved to be more costly

than the Al7075, anywhere between three and five times the cost, and could not be fit into the

budget. [7]

1.2.2 Performance Specifications

The unit will have to withstand normal to extreme use of the ATV. The unit will have to

work under shock, fatigue, water, and dirt conditions. The sensor will have to pick up very

minute to extremely large forces to be able to get readings.

There must be enough sensors placed inside the unit so as to read all forces happening in

all directions. The readings will pass through a microcontroller where the readings will be

analyzed with dynamic equations to output the exact forces in every given direction and resulting

torques. The data will then be transmitted with a wireless router to the main controller of the

ATV so it can do with it as it wants.

This unit will work continuously for 6-10 hours of normal operation, which is long

enough to cover most ATV excursions. The gauge will also have the ability to be removed from

the wheel in the most convenient way for the consumer.

CHAPTER TWO

2.0 Background Research

The scope of this research is to develop a sensor to measure force and moment that will

be experienced by a vehicle’s wheel. The medium used to develop these values is done by a


means of measuring strain at specific points of the sensor. Given that the calculated forces

experienced by the assembly stay within the range of elastic behavior (an elastic region on the

stress strain curve where any deformation is not permanent) for the material, there is a linear

relation between the internal strains and the external forces and moments.[8] The concept of the

force torque sensor is as follows; consider a structure with an applied load (input) at a particular

point of it by an unknown force vector in the range of linearity represented by Equation 1. Then,

on the surface of the structure there must produce (output) a vector of number of n strain signals

in specific locations based on the geometric shape of the structure, 𝑆 = (𝑆1𝑆2𝑆3 ⋯ 𝑆𝑛). Given

the principle of elasticity, Equation 2 can be produced [9].

�⃗� = (𝐹𝑋, 𝐹𝑦 , 𝐹𝑧 , 𝑀𝑥, 𝑀𝑦 , 𝑀𝑧) Equation 1

Equation 1 represents force and moment in the respective direction.

𝑆 = [𝐶] ∙ �⃗� Equation 2

Equation 2 represents the value of strain generated by an n x 6 compliance matrix where n

represents the value of strain multiplied by the force vector in the linear range.

Through algebraic manipulation, a

calibration matrix can be multiplied by the strain

value in order to find the force vector input of the

sensor. A calibration matrix is the inverse of the

previously defined compliance matrix. Equation 3

represents the force input in the form of a vector

after manipulation.

�⃗� = [𝐶]−1 ∙ 𝑆

Equation 3

The general concept of the force/torque

sensor is to capture the forces and moments

transmitted between the vehicle and the tire

contact patch. Error! Reference source not

found. represents all of the forces at the point of

contact of the tire and the ground.

The strain used in order to find the forces

for application needed is done by using strain

gauges, which are used in a Wheatstone bridge.

The bridge is configured to be a half bridge set

up, where there are two strain gauges and two

resistors in each bridge used to find the change in resistance between a coupled set of strain

readings. Figure 4 (below) shows an example of the configuration of a Wheatstone bridge.

Strain gauges initially output deflection through voltage, which is then converted by

Figure 1: Forces and Moments acting on the wheel in a

static frame.


Figure 2 A Wheatstone Bridge Where the

Top Half of the Bridge Represents Strain

Gauges and the Bottoms are Resistors

Equation 4 into a value of strain in a degree of micro strain(10−6).

𝜀 = 𝑉𝑜

𝐾𝑉𝑖 Equation 4

The conversion of voltage into strain 𝑉𝑜 is the output voltage and 𝑉𝑖 is the input voltage

and K is the gauge factor based on the strain gauge used in application.

Similar projects have been experimented in its entirety in the past. The main factor that

sets this project apart is the fact that it is intended for use on an autonomous vehicle. In the past,

this project has been researched to apply for situations nearly the same as this, as well as

application for robotic arms and structure integrity. The key

concepts behind this project have been presented in many

similar manners due to the fact that the principal concept does

not change. The main difference is the form of data

communication and transmission. In this project the movable

components such as the circuit amplifier and the

microcontroller which will control the sampling rate and the

wireless communication are much smaller and more efficient

than that of which discussed in the past and previous literature.

Some of the main concepts used in this design are that of

which were read from previous versions of this design.

CHAPTER THREE

3.0 Project Management

Like all other design projects, this one was no small task. It took the entire team working

towards the same goals together to complete it. Utilizing resources effectively was paramount to

realizing the end goal.


3.1 Schedule

Several individual and collective milestones were adopted to ensure proper completion of

the project. Some of these were completed independently and were not reliant on other aspects of

the project, while others were necessary to be completed in order.

An aggressive schedule was initially proposed, leaving the team ample time after

completion for any problems that arose. While this turned into an inaccurate Gantt chart, it was

beneficial to be able to use the extra budgeted time at the end. Several factors that pushed to

team behind the proposed schedule included shipping on obscure or specialized electronic

components, delays in the machine shop, and redesigns performed on both the circuit and the

hub assembly.

An updated Gantt chart with every major and minor step of the project is detailed in the

Appendix.

3.2 Resources

Several resources were available to the group through the school. Arguably, the most

important were the two advisors assigned to the project. Both were immensely helpful in

assisting with the design process, as well as any problems that were discovered.

Another resource would be the available facilities from the school. The machine shop

was an invaluable resource, in spite of month delay arbitrarily imposed. While the pieces were

not made in a timely manner, nor were the machinists always the most pleasant or productive

people to talk to, the parts were made with the necessary precision and specifications. The only

time this was not true was when the eight holes for the center cross section were not correctly

tapped. This was a simple mistake on their part, but was rectified by ordering different bolts to fit

the incorrect threads.

Finally, the CISCOR lab was utilized by the team near the end of the project. Several

members were able to get access to the lab, and were then certified to use the tools and shop

there. This allowed the team to perform tasks such as creating the circuits with greater ease. As a

psychological boost, when working there, the team was always in sight of GOLIATH, which

provided a clear picture of the end goal.

3.3 Procurement

The breakdown of the cost incurred on products purchased for the prototype are

represented and discussed. $5000 was the allocated budget for the prototype and the total direct

and indirect costs incurred on the project is just under $3400. This value includes the costs of

both mechanical and electrical parts purchased in the course of the project. It also compensates

for other ad-hoc and add-on costs resulting from part inadequacies and design revision. The pie

chart shown in Figure 3 illustrates the complete breakdown of the overall resource allocation for

the project prototyping as well as auxiliary components needed for calibration and assembly.

It is worthy to note that the entire wheel force sensor unit designed was within the

allotted budget, thus signifying the economic viability of the prototype. If eventually produced

on a large scale, the product will be rolled out at market friendly prices as a result of its minimal

production cost. Although there are several commercially available products, the fact remains

that they are not plug and play units. This means that commercially, each of these units must be


custom made for a specific application. Consequently, the force/torque sensors currently

available commercially, have prices ranging from a minimum of $10,000 which are more

expensive to procure and are not designed for harsh terrain as this design.

Figure 3 Budget Used to Manufacture Force/Torque Sensor Prototype

3.4 Communications

Overall, communications throughout the project were not a major issue for the group.

Intra-group communications were handled mainly via phone and text. As members typically had

their phones on or close by, there was very little lag when using this method.

Outside communications were mainly handled through emails, which were not as rapid as

phone, but generally were adequate for setting up meetings with advisors or getting specific

questions answered about reports or presentations.

Weekly or biweekly meetings with advisors were set up at the beginning of the project,

and followed throughout both semesters.

CHAPTER FOUR

4.0 Concept Generation


Unlike some concepts generated

during the design phase, a mechanical

design was provided to the force/torque

sensor project in its initial phases. With

that in mind, there were some

modifications to the design throughout

the project. The first design change was

to the addition of spacers in order to

reduce concentrated stress on the sensor

assembly. Figure 3 represents the

original design before any

modifications. Figure 4 represents the

second version design with the space

addition.

The final modification was done to

the actual sensor which is modify the

geometric shape of the sensor in order to

provide more spacing to insert the

moveable parts for the sensor. Figure 5

displays a before and after of the sensor

design. It should be noted that all designs

changed to the mechanical aspect of the

design were done using the solid works

software before manufacture.

Figure 4: Original mechanical design

Figure 5: Modified mechanical design


Figure 6 Top and down comparison of the New Sensor Design (Right) Versus the New One (Left)

In the electrical aspect, the circuit design has been modified significantly since the

beginning of the project. Nearly all of the involved with the circuit has been modified. To begin,

the original circuit was made on a breadboard using and compatible op-amp and non-precision

resistors and capacitors. This design was changed due to the lack of integrity of the breadboard

and the instability of the circuit due to non-precision resistors. The second version of the circuit


Figure 7: Original Electrical Circuit Design

was made using linear strain gages and 350ohm resistors. This design was not made with the

power supply fully considered. Figure 6 shows the first circuit design.

Through various new

modifications and trial and error the final

design for the electrical circuit was

developed. In figure 9 a diagram of the

final electrical circuit as well as a

physical representation of the final

product is displayed. In brief, the

significance of the electrical circuit is to

properly amplify the micro strain signal

received from the strain gauges.

The components that contributed

to the final circuit design were a part of a

decision matrix. This matrix was created

with the fact that this is meant to be a

version 1 prototype and the main goal is

to develop a working product.

The values of the decision matrix were rated on a scale of 1-5 with 1 being a low score

and 5 being the highest. The categories, which were chosen were those of that throughout the

design phase were found to be the most important. For the voltage regulators, the switching

regulator was chosen over the linear regulators due to its capability to resist a higher voltage

change without damaging the entire system. High precision resistors and capacitors are in

reference to components that were designed specifically for this application opposed to low

precision resistors that can be used for a variety of applications meaning the tolerance and

voltage range falls along the lines on the desired values needed. Material is important in terms of

longevity and stability of the component.

Figure 9: Revised Electrical Circuit Design Figure 8: Sensor circuit on prototyping board.


Table 1: Table 1 Electrical Component Decision Matrix

Voltage Regulators

Efficiency Voltage output Total

Linear

Regulator

2

2

4

Switch

Regulator

5

5

10

Resistors/Capacitors -

Tolerance Material -

High Precision 5 5 10

Low Precision 3 3 6

Boards -

Availability Efficiency -

Protoboard 5 4 9

Printed Circuit

Board

2

5

7

Bread Board 5 1 6

Wiring -

Efficiency Size -

30 gage 4 4 8

22 gage 4 3 7


Figure 10 Exploded View of Assembly

Figure 11 Sensor Cross

CHAPTER FIVE

5.0 Final Design The final design of the assembly consists of mechanical and the electrical side. The

mechanical side is primarily focused on the picking up the forces from the ground or vehicle and

being able to handle them. The electrical side focuses more on converting and measuring these

forces, and then transmitting them to the ATV.

5.1 Mechanical Design

The final mechanical design, shown

right, contains a total of five parts as well as a

spacer, several bolts, nuts, and studs. The parts

from left to right are: wheel spacer, wheel

plate, sensor cross, hub plate, and hub mount.

The wheel spacer was created to account for a

non-threaded portion of the over-the-counter

studs that were bought directly from Polaris.

The wheel and hub plates are for protection of

the electronics as well as adaptors so the cross

can be mounted to different size wheels. The

hub mount is used to securely attach the

assembly to the Polaris 550 Sportsman’s axle

hub. The final part is the sensor cross, drawling

below. The cross is attached to the hub plate at its

outer ring while attached to the wheel plate at the

center of the cross. Each part is made from

aluminum 7075. The material tests show this

material has a yield strength of 505MPa and a

density of 2.81 g/cm3.

The cross is the central part of the sensor.

The cross’ empty space will be used to house the

electronics and microcontroller. There will be

rubber mats on either side of the cross that the

electronics will be attached to and that will help

isolate the electronics from damage. All

components were chosen and made to fit within

the spaces provided by the cross. The cross will also act as the source of strain that the strain

gauges will measure. As mentioned before, the wheel plate is attached to the sensor on the inner

part of the cross and the hub plate is attached to the outer part of the cross. This will cause

several moments and forces to act upon the cross. These moments will cause a strain upon the

cross that will be felt most at the corners where the inner part of the cross meets the spokes of the

cross as shown in the FEA below. The strain gauges will be placed at these points as well as the


front and back of the spokes at the same distance. The cross and these strain gauges will

constitute the sensor itself.

The cross was made through digital prototyping. The finite element analysis, FEA, of the

cross shows that the strain is concentrated at the inner base of the spokes. The scale shows that

the strain encountered will be in the mill-strain range when the torque applied is in the 5kN*m

which is five times as large as the maximum torque the ATV’s motor can apply. Displacement of

the cross under this torque is within the elastic range of the material and is in the tens of

micrometers range.

The rest of the assembly is for protection and mounting, while the electronics are for

measuring, powering, amplifying the gauges output, and digitizing the signal. Lastly the

microcontroller processes the data and transmits the computed data to the ATV’s hub.

5.2 Electronics

5.2.1 Microcontroller

The selected microcontroller, the BeagleBone Black, was chosen primarily due to its low

cost, as well as it high processing power (1GHz) and ability small form factor. This was kept

consistent throughout all design revisions, as it was more than capable of handling any

computations we needed.

5.2.2 Code Description

mcp3208Spi.h

This file is just a generic header file that is used to declare objects. It includes the public

and private class, destructor, constructor and even some integer declarations.

mcp3208Spi.cpp

This file is also a generic C++ code file that ensures that everything is running correctly.

For example, if the correct SPI mode could not be used, it would exit(1), meaning it would exit

with an error. Same thing with bytes per word, and SPI speed. Other declarations as well.

mcp3208SpiTest.cpp

This is the file in which the reading in of the data is actually done and then the conversion

to a digital value takes place. First, all declarations are made and initial values are set to 0. Next,

inside an infinite while loop, the data on channel 0 is initialized. The first byte transmitted is

data0[0] which is in the form 00000[START BIT][SGL/DIG][D2]. In the case of this program,

START BIT is always 1, SGL/DIF is always 1 as well which signifies that single ended

conversion is being used. Next data0[1] is sent to the A2D which consists of [D1][D0]000000, 6

other bits which are don’t cares. For this program, D2, D1 and D0 are a binary representation of

which channel is being read. For example 000 for D2, D1 and D0 represent channel 0 while 111

represents channel 7. Next, the value is read from the A2D and then stored on the device

registers. The a2dvalue is reset and then bitwise manipulated to produce the correct digital value.

In order to receive proper digital values, bitwise manipulation must occur. As shown in the


Figure 12: Sensor Cross Finite Element Analysis

Figure 13 SPI Channels(Top), Transmitted/Received Data(Bottom)

Figure Below, the data is received in data0 [1] and

data0 [2] with data0 [0] being full of don’t cares.

The data from data0[1] must be shifted left 8 bits

to make it twelve bits long and bitwise anded with

0b111100000000 to ensure that the last 8 bits are

indeed 0. Next, the twelve bit result is put through

a bitwise or operation with the remaining 8 bits to

get the full 12 bit result. This same process is

repeated for all 8 channels, in succession.

Communication between Microcontroller and A2D

Communication between the Beaglebone Black and the Analog to Digital converter is

made possible by using the SPI or Serial Peripheral Interface communication method. This is a 4

wire connection that allows rapid transfer of data. The four wires are Data Out, Data In, Chip

Select/ Shut Down and also the Clock line. The Analog to Digital converter can support 100ksps

when powered with 5V in the Vdd port. After calculation and testing, the maximum sampling

rate achieved was around 700 samples per second per channel. This equated to 80,000 samples

on all 8 channels of the Analog to Digital converter in just over 13 seconds.

A wireless adapter has been installed to the available USB port on the Beaglebone Black

which will eventually enable this data to be transferred wirelessly to the main control station of

the ATV.


CHAPTER SIX

6.0 Operations Manual The following is the procedure for mounting the assembly to the ATV:

1. Using a 17 mm socket with appropriate ratchet, loosen the four lug nuts on the ATV. DO

NOT REMOVE THE NUTS AT THIS TIME.

2. Using a suitable lift point, preferably on the frame, place a jack underneath the ATV and

lift it so that the wheel is off the ground. Support the ATV with a suitable jack stand. DO

NOT WORK ON OR UNDER ANY VEHICLE THAT IS SUPPORTED ONLY BY

A JACK.

3. Remove the lug nuts and the wheel.

4. (Figure 16) Place hub adapter on hub, and attach with provided short lug nuts. Torque lug

nuts to 45 lbf ft with a 17 mm socket.

5. (Figure 17Error! Reference source not found.) Place inner plate on hub adapter and

attach with M8x1.25 bolts. Tighten bolts to 25 lbf ft with a 13 mm socket.

Figure 14 Hub Adapter

Figure 15 Inner Plate


6. (Figure 18) Attach cross section to inner plate with M10x1.25 x 60mm bolts through the

back of the inner plate. Tighten bolts to 35 lbf ft with a 13 mm socket. Be careful to not

strike or crush electrical components when placing and securing section. Microcontroller,

circuit boards and battery should fit within blank areas of section with ample room on all

sides.

7. Connect strain gauges to circuits. Pay attention to what connections are made; connect

plugs 1 and 1, 2 and 2, etc.

8. Turn on system.

9. (Figure 19)Place outer plate and attach with M10x1.25 x 70mm bolts. Torque bolts to 35

lbf ft with 17 mm socket.

10. (Figure 20) Place spacer on studs.

Figure 17 Cross Section

Figure 16 Outer Plate


11. Place wheel on studs and install supplied long lug nuts.

12. Lower ATV

13. Tighten lug nuts to 45 lbf ft with 17 mm socket.

6.1 Operation of unit

Unit requires no further user input when operating ATV. However, the operator should

always drive operate ATV responsibly, never driving recklessly or in hazardous conditions.

Furthermore, before any driving, the ATV should be checked for proper operation (oil and gas

level, tire pressure, etc.). The unit does not impede driving or operation of the ATV, but it does

affect the driving characteristics. Care should be taken when first driving the ATV until user is

familiar with handling characteristics.

Figure 18 Wheel Spacer


Figure 10: Tension

Testing of Al 7075

CHAPTER SEVEN

7.0 Design of Experiment The mechanical, electrical, and computing aspects of the project were all tested

separately and then assembled and tested as a complete unit. The mechanical tests consist of

digital testing, material testing, and a full scale test. The electrical test is a model strain test while

the computing tests were code compatibility tests.

7.1 Mechanical Experiments

7.1.1 Digital Testing

Digital testing was required by the FEA. These tests were conducted on the sensor cross

as well as the entire assembly itself. The test on the full assembly was done in a static

environment with a maximum torque of 30 kN*m and a weight force of 16 kN. Both of these

numbers were pulled from the maximum torque and weight possible of the ATV with our factor

of safety of 3, the maximum torque was the maximum output of the motor times the factor of

safety doubled and then multiplied by the factor of safety again to account for a wheel getting

stuck as the ATV is in motion. The results of the test showed no mechanical failure as well as

ample strain within the cross itself.

7.1.2 Material Testing

Aluminum 7075 is an aircraft aluminum that possesses a high yield

strength and low density; it is because of these qualities that the material

was chosen for the base material. The metal’s properties were under

discrepancy at the beginning of the project so test sheets were ordered and

cut. The tension test was performed as shown to the right to determine that

the yield strength of the material was around 505 MPa and a strain of .2

(unit-less). These parameters allowed for a considerable amount of stress

and strain before plastic deformation occurs. This fact allowed us to

confidently choose this material as the material for not only the sensor

cross but also the rest of the assembly parts.

7.1.3 Full Scale Test

The full scale test was done on the entire mechanical assembly. The test consisted of

assembling all the parts and attaching it to the ATV. Then operating the ATV under real life

conditions we determined that the unit was mechanically sound. During this test several aspects

were tested to see if the performance of the ATV was hindered by the sensor. The turn radius

was found to have increased by a few inches but no conclusive measurement was made due to

variables and non-consistency with the tests. The rest of the ATV’s functions had not

experienced any detectable changes.


7.2 Electrical Experiments

7.2.1 Electrical Test

The electrical test preformed was an exact setup of the circuit outside of the sensor. The

strain gauges were bent and outputs from the Wheatstone bridge were amplified and recorded.

This showed the workings of the electrical circuit as well as the centering and calibration that

needed to be done to the Wheatstone bridge.

7.2.2 Wi-Fi test

A wireless adapter was inserted into the USB port on the Beaglebone Black to enable

wireless capabilities. Using the file under /etc/network/interfaces, the wireless configuration

settings were inserted. Once applied, the Beaglebone Black could successfully connect to

wireless. This was verified by pinging several different websites multiple times. The results from

the pinging shows all packets of data (64 bytes) were successfully sent and received with a 0%

packet loss with over 100 transmissions per website pinged.

7.2.3 Sampling test

The Analog to Digital converter supports a maximum of 100ksps when powered with 5V.

After conversion from an analog to digital value, the output sampling rate turned out to be

approximately 700 samples per channel per second. How long it took to reach 80,000 samples

was timed and the results show that it took approximately 13 seconds for these 80,000 samples

for all 8 channels.

7.2.4 Voltage test

To verify the accuracy of the analog to digital converter, a voltage test was conducted.

The digital output value represents a DC voltage value on the input. By using a simple formula,

𝐷𝑖𝑔𝑖𝑡𝑎𝑙 𝑜𝑢𝑡𝑝𝑢𝑡 = 4095∗𝑉𝑖𝑛

𝑉𝑟𝑒𝑓 Equation 5

where your digital output is the value after conversion, the Vin is the input voltage to the

converter and the Vref is the reference voltage in which the Analog to Digital converter is

connected; in this case, 5V. Also, the digital value 4095 is represented by the resolution of the

Analog to Digital Converter. This number is calculated by 2#𝑏𝑖𝑡𝑠 − 1, which is 212 − 1 = 4095.

Calculating for Vin, the formula results in

𝑉𝑖𝑛 = 𝐷𝑖𝑔𝑖𝑡𝑎𝑙 𝑂𝑢𝑢𝑝𝑢𝑡 𝑉𝑟𝑒𝑓

4095 Equation 6

By comparing these values using a multimeter and the output value from the Analog to Digital

converter, the results were verified that the conversion is accurately producing proper digital

values.

7.3 Completed Assembly Testing

At the time of this writing, the assembly has been completed and all associated

components have been tested individually. However, there still is the need for tests on the

completed assembly with all associated systems integrated. The first test is calibration of the


unit. Following a successful calibration, the team then needs to operate the vehicle and sensor

over different terrain types and verify that the interactions between the wheel and terrain is being

picked up by the assembly.


CHAPTER EIGHT

8.0 Considerations for Environment, Safety, and Ethics While developing the force/torque sensor for the GOLIATH ATV, safety was the group’s

top priority. Safety is key to every group member as every group member was needed to work on

the project. Should a member miss any time due to an easily avoidable injury suffered from

negligence or carelessness, the risk of not completing the project goes up considerably. Every

time a member of the team was working on the ATV, soldering a circuit, attaching a strain

gauge, or other, similar work, they were never alone and always had another group member in

close range, if anything were to go wrong. Proper safety precautions were taken and the

appropriate safety gear was always worn while operating the ATV or simply working on the

ATV. The safety and well-being of others around us was the next priority. Ensuring that no

others were hurt during the process was key to making this project a success. Finally, the safety

of the ATV was always considered and never taken lightly. Had the ATV been broken or

damaged during the project, a successful prototype could not have been delivered. For the design

of the actual project, a large factor of safety was included while doing all calculations that

pertained to any part that was being designed and eventually going to be fitted to the ATV. A

large factor of safety in the final design means that while the ATV was being operated, whether

remotely or autonomously, it was going to be absolute certain that the parts would not fail under

normal operating circumstances.

Many considerations for the environment were taken during this project. The main

consideration being that no fluids from the ATV were leaked nor discharged from the ATV into

the ground causing potential harm to animals and the environment. All fluids going into the

ATV were transported in approved containers, the main fluid being gasoline for the ATV to run

on. Also, the ATV was not left idling for extended periods of time which releases large amount

of Carbon Dioxide into the atmosphere. Next, while testing the ATV with the Force Torque

Sensing unit installed, the ATV was driven in a professional manner to ensure that no damage to

any property resulted from simply testing the ATV in off road conditions.

During the course of this project, ethical decisions were always made. It was important

for the team to always make ethical decisions regardless of the circumstances. The consequences

of making an unethical decision outweighed any potential benefits. Although, what others may

see as an ethical decision or ethical action, other may see as a completely unethical situation. For

this exact reason, any trouble with unethical behavior or decisions was clearly avoided.


CHAPTER NINE

9.0 Conclusion Keeping with the growing demand of vehicles being able to autonomously

perform the tasks they were designed to perform, CISCOR has created the GOLIATH. The

purpose of GOLIATH is to accomplish the same goals as an ATV driven by a human, navigate

rough terrain with a passenger and cargo. This project's goal is to add the force/torque sensor in

order to detect torque and allow the vehicle to operate better in uneven terrain. This falls in line

with the overall goal of the project, which is to develop a sensor that can quantify interaction

between the wheel and the ground.

A final design has been selected, as well as an accompanying electronics circuit, which

will function with the design. The design has been selected to best complete the objective, while

ensuring reliability and reducing the chance of failure as much as possible. All parts for the final

designs are in from delivery and used toward the final design. What this means is that the final

design for the mechanical aspect of the sensor is complete as well as the design for the electrical

circuit. This also means that both components have been fabricated as well.

For future recommendations, the final mechanical design lacks the proper infrastructure

to secure the movable parts mounted within the sensor, a design to do so is ideal. Also, for the

wireless communication, once the assembly is compiled onto the ATV, the will be inference

causing a weaker signal than expected. A modification will be needed in order to provide a

stronger signal for communication. Balancing of the wheel after the sensor is mounted onto the

ATV is necessary, in order to ensure optimal performance and prevent premature damage. The

final future recommendation for the force/torque sensor is to have the circuit printed onto a PCB

(Printed circuit board) to increase its durability and resilience to adverse conditions.


CHAPTER TEN

10.0 References 1. Darpa Robotics Challenge. DARPA, n.d. Web. 26 Sept. 2014.

2. Parks, Bob. "Taking It to the the Street." Popular Science 270.5 (2007): 58-66. Print.

3. Akbar, Marc, Merrick Salisbury, Michael Brazeau, Lester Kendrick, Omesh Dalchand,

Jeremy Hammond, and Nahush Kulkarni. "Gas Operated Land Intelligent All Terrain

Hub." FAMU FSU COE, 17 Apr. 2014. Web. 26 Sept. 2014.

4. Brier, Hyman. Strain Gauge Load Indicator. Ohio Commw Eng Co, assignee. Patent US

2813709 A. 19 Nov. 1957. Print.

5. "The Strain Gauge." The Strain Gauge. N.p., n.d. Web. 10 Oct. 2014.

6. Vehicle Test Sensors. Sensor Developments, n.d. Web. 01 Dec 2014

7. McMaster Carr, n.d. Web. 9 Apr 2015


CHAPTER 11

11.0 Appendix

11.1 Parts Procured

Table 2: Complete Bill of Materials

Item Qty Price Total Vendor Link

Strain Gauge

#KFH-6-350-C1-11L1M2R

5 $125 $375 Omega http://www.omega.com/pptst/KFH.ht

ml

Mouser

Amplifier

#584-AD8620ARZ 5 $15 $75

Analog

Devices

http://www.mouser.com/Semiconduct

ors/Amplifier-ICs/Precision-

Amplifiers/_/N-

9rtls?Keyword=8620&FS=True

Aluminum

7050(Tempered

)

#1281T22

1 $13 $13 Online

Metals

https://www.onlinemetals.com/mercha

nt.cfm?pid=17925&step=4&showunit

s=mm&id=1042&top_cat=60

Strain Gauge

Adhesive

#SG493

1 $30 $30 Omega

http://www.omega.com/pptst/Strain_G

age_Adhesives.html?ttID2=Strain_Ga

ge_Adhesives

Aluminum

7075 Sheet

12”x12”x.5”

#9478T137

2 $227 $454 McMaster

Carr

http://www.mcmaster.com/#standard-

aluminum-sheets/=vngkqw

Aluminum

7075 T6 Bare

(308 x 308 x

3.18)

1 $29 $29 Online

Metals




Mouser

Amplifier

#584-AD620AN

20 $9 $90

Mouser

Electronic

s

http://www.mouser.com/Cart/Cart.asp

x

Aluminum

7075 T6 Bare

(308 x 308 x

3.18)

1 $29 $29 Online

Metals




ADC 12bit SPI

8 CH

#579-

MCP3208CIP

10 $4 $40

Mouser

Electronic

s


x

Aluminum

7075 Sheet

12”x12”x2”

#1190T788


Carr




Aluminum

7075 Sheet

12”x12”

x1.25”

#1190T768


Carr



Vibration

Dampening

Pads 12”x12”

x1/8”

#5940K57

2 $36 $36 McMaster

Carr


vibration-damping-pads/=vngpea

Beagle Bone

Black Micro

Controller

BB-BBLK-

000-REVC-ND

2 $55 $110 DigiKey

http://www.digikey.com/product-

search/en?lang=en&site=us&keyword

s=BB-BBLK-000-REVC-

ND&WT.z_slp_buy=TI_BeagleBoard

Bolt

M10x1.5x75 2 12.52 25.04

McMaster

Carr 95327A643

Nut M10x1.5 1 12.65 12.65

McMaster

Carr 92497A450

Bolt

M10x1.5x60 2 10.38 20.76

McMaster

Carr 90854A213

Bolt

M8x1.25x60 2 7.05 14.10

McMaster

Carr

90854A180

Washers M10 1 4.36 4.36

McMaster

Carr 91166A280

Washers M8 1 3.23 3.23

McMaster

Carr 91166A270

Wheel Studs

M10x1.25x58

#7518671

12 0.99 11.88 Polaris

http://www.polaris.com/en-us/atv-

quad/shop/parts#/Polaris/A12ZN55A

A%2f%2fAQ%2f%2fAZ_SPORTSM

AN_550_%282012%29/WHEELS%2

c_FRONT_and_HUB_-

_A12ZN55AA%2f%2fAQ%2f%2fAZ

/84969/85039

Wheel Nuts

Mx10x125

#7547363

8 1.68 13.44 Polaris

http://www.polaris.com/en-us/atv-

quad/shop/parts#/Polaris/A12ZN55A

A%2f%2fAQ%2f%2fAZ_SPORTSM

AN_550_%282012%29/WHEELS%2

c_FRONT_and_HUB_-

_A12ZN55AA%2f%2fAQ%2f%2fAZ

/84969/85039


Rechargeable Nickel Metal Hydride Battery Pack Cs (3000 MA), 6 Batteries (3W x 2D) # 6964T74

1 $76 $76 McMaster

Carr

http://www.mcmaster.com/#6964t74/=

w5g0fm

Plier-Nose

Wire Stripper

for 30-22 AWG

Solid/32-24

AWG Stranded

# 7294K15

1 $17 $17 McMaster

Carr

http://www.mcmaster.com/#7294k15/

=w5gf02

Electronic

Torque

Wrench : 1/2"

Square Drive,

300-3000 in-

lbs., 25-250 ft.-

lbs. Torque

#8976A12


Carr

http://www.mcmaster.com/#8976a12/

=w5gero

Multi-Current

Universal

Smart Charger

for 2.4V - 7.2V

NiMH/ NiCad

Battery Pack ---

CE listed

# 1480

1 $18 $18 Battery

Space

http://www.batteryspace.com/multi-

currentuniversalsmartchargerforany24

-72vnimhnicdbatterypack.aspx

Voltage

References 2.5-

V Precision

Micropower

Shunt

#595-

LM4041D12IL

P

10 $0.69 $6.90

Mouser

Electronic

s


x

Metal Film

Resistors -

Through Hole

1/8watt

350ohms .1%

5ppm

#71-

16 $3.00 $48

Mouser

Electronic

s


x


PTF56350R00

BZEK

CAP TANT

0.1UF 35V

10% RADIAL

#399-3526-ND

10 $0.82 $9.00

DigiKey

Electronic

s

http://www.digikey.com/classic/Order

ing/AddPart.aspx

Voltage

Regulator

Breakout Board

4 $10 $40

Dimension

Engineerin

g

https://www.dimensionengineering.co

m/products/vreg-breakout


Table 3 Gantt Chart, October - January

11.2 Gantt Chart


Table 4 Gantt Chart, January - April


11.3 Code /*********************************************************************** * mcp3208SpiTest.cpp. Sample program that tests the mcp3208Spi class. * an mcp3208Spi class object (a2d) is created. the a2d object is instantiated * using the overloaded constructor. which opens the spidev0.0 device with * SPI_MODE_0 (MODE 0) (defined in linux/spi/spidev.h), speed = 1MHz & * bitsPerWord=8. * * call the spiWriteRead function on the a2d object 20 times. Each time make sure * that conversion is configured for single ended conversion on CH0 * i.e. transmit -> byte1 = 0b00000001 (start bit) * byte2 = 0b1000000 (SGL/DIF = 1, D2=D1=D0=0) * byte3 = 0b00000000 (Don't care) * receive -> byte1 = junk * byte2 = junk + b8 + b9 * byte3 = b7 - b0 * * after conversion must merge data[1] and data[2] to get final result * * * * *********************************************************************/ #include "mcp3208Spi.h" using namespace std; int main(void) { mcp3208Spi a2d("/dev/spidev1.0", SPI_MODE_1, 200000, 8); int a2dVal0 = 0; //initialize all the channel values to 0 int a2dVal1 = 0; int a2dVal2 = 0; int a2dVal3 = 0; int a2dVal4 = 0; int a2dVal5 = 0; int a2dVal6 = 0; int a2dVal7 = 0; unsigned char data0[3]; //Set up arrays to store data unsigned char data1[3]; unsigned char data2[3]; unsigned char data3[3]; unsigned char data4[3]; unsigned char data5[3]; unsigned char data6[3]; unsigned char data7[3]; while(1) { //CHANNEL 0 CONVERSION------------------------------------------------------------------------------------------------- data0[0] = 0b00000110; // first byte transmitted -> 00000(STARTBIT = 1) (SGL/DIF = 1) (D2)


data0[1] = 0b00000000; // second byte transmitted -> (D1)(D0)000000 data0[2] = 0; // third byte transmitted....don't care a2d.spiWriteRead(data0, sizeof(data0)); a2dVal0 = 0; a2dVal0 = (data0[1] << 8) & 0b111100000000; //merge data[1] & data[2] to get result a2dVal0 |= (data0[2] & 0xff); //--------------------------------------------------------------------------------------------------------------------- //CHANNEL 1 CONVERSION------------------------------------------------------------------------------------------------- data1[0] = 0b00000110; // first byte transmitted -> 00000(STARTBIT = 1) (SGL/DIF = 1) (D2) data1[1] = 0b01000000; // second byte transmitted -> (D1)(D0)000000 data1[2] = 0; // third byte transmitted....don't care a2d.spiWriteRead(data1, sizeof(data1)); a2dVal1 = 0; a2dVal1 = (data1[1] << 8) & 0b111100000000; //merge data[1] & data[2] to get result a2dVal1 |= (data1[2] & 0xff); //--------------------------------------------------------------------------------------------------------------------- //CHANNEL 2 CONVERSION------------------------------------------------------------------------------------------------- data2[0] = 0b00000110; // first byte transmitted -> 00000(STARTBIT = 1) (SGL/DIF = 1) (D2) data2[1] = 0b10000000; // second byte transmitted -> (D1)(D0)000000 data2[2] = 0; // third byte transmitted....don't care a2d.spiWriteRead(data2, sizeof(data2)); a2dVal2 = 0; a2dVal2 = (data2[1] << 8) & 0b111100000000; //merge data[1] & data[2] to get result a2dVal2 |= (data2[2] & 0xff); //--------------------------------------------------------------------------------------------------------------------- //CHANNEL 3 CONVERSION------------------------------------------------------------------------------------------------- data3[0] = 0b00000110; // first byte transmitted -> 00000(STARTBIT = 1) (SGL/DIF = 1) (D2) data3[1] = 0b11000000; // second byte transmitted -> (D1)(D0)000000 data3[2] = 0; // third byte transmitted....don't care a2d.spiWriteRead(data3, sizeof(data3)); a2dVal3 = 0; a2dVal3 = (data3[1] << 8) & 0b111100000000; //merge data[1] & data[2] to get result a2dVal3 |= (data3[2] & 0xff); //--------------------------------------------------------------------------------------------------------------------- //CHANNEL 4 CONVERSION------------------------------------------------------------------------------------------------- data4[0] = 0b00000111; // first byte transmitted -> 00000(STARTBIT = 1) (SGL/DIF = 1) (D2) data4[1] = 0b00000000; // second byte transmitted -> (D1)(D0)000000 data4[2] = 0; // third byte transmitted....don't care


a2d.spiWriteRead(data4, sizeof(data4)); a2dVal4 = 0; a2dVal4 = (data4[1] << 8) & 0b111100000000; //merge data[1] & data[2] to get result a2dVal4 |= (data4[2] & 0xff); //--------------------------------------------------------------------------------------------------------------------- //CHANNEL 5 CONVERSION------------------------------------------------------------------------------------------------- data5[0] = 0b00000111; // first byte transmitted -> 00000(STARTBIT = 1) (SGL/DIF = 1) (D2) data5[1] = 0b01000000; // second byte transmitted -> (D1)(D0)000000 data5[2] = 0; // third byte transmitted....don't care a2d.spiWriteRead(data5, sizeof(data5)); a2dVal5 = 0; a2dVal5 = (data5[1] << 8) & 0b111100000000; //merge data[1] & data[2] to get result a2dVal5 |= (data5[2] & 0xff); //--------------------------------------------------------------------------------------------------------------------- //CHANNEL 6 CONVERSION------------------------------------------------------------------------------------------------- data6[0] = 0b00000111; // first byte transmitted -> 00000(STARTBIT = 1) (SGL/DIF = 1) (D2) data6[1] = 0b10000000; // second byte transmitted -> (D1)(D0)000000 data6[2] = 0; // third byte transmitted....don't care a2d.spiWriteRead(data6, sizeof(data6)); a2dVal6 = 0; a2dVal6 = (data6[1] << 8) & 0b111100000000; //merge data[1] & data[2] to get result a2dVal6 |= (data6[2] & 0xff); //--------------------------------------------------------------------------------------------------------------------- //CHANNEL 7 CONVERSION------------------------------------------------------------------------------------------------- data7[0] = 0b00000111; // first byte transmitted -> 00000(STARTBIT = 1) (SGL/DIF = 1) (D2) data7[1] = 0b11000000; // second byte transmitted -> (D1)(D0)000000 data7[2] = 0; // third byte transmitted....don't care a2d.spiWriteRead(data7, sizeof(data7)); a2dVal7 = 0; a2dVal7 = (data7[1] << 8) & 0b111100000000; //merge data[1] & data[2] to get result a2dVal7 |= (data7[2] & 0xff); //--------------------------------------------------------------------------------------------------------------------- sleep(1); cout << "The Result CH0 is: " << a2dVal0 << endl; cout << "The Result CH1 is: " << a2dVal1 << endl; cout << "The Result CH2 is: " << a2dVal2 << endl; cout << "The Result CH3 is: " << a2dVal3 << endl; cout << "The Result CH4 is: " << a2dVal4 << endl; cout << "The Result CH5 is: " << a2dVal5 << endl;


cout << "The Result CH6 is: " << a2dVal6 << endl; cout << "The Result CH7 is: " << a2dVal7 << endl; } return 0; }


11.4 ATV CALCULATIONS

Dry Weight : 733 lbs ➔ 3260 N

Max Payload : 575 lbs ➔ 2558 N

Gross Weight : 1308 lbs ➔ 5818 N

Wheel and Tire Radius : 8 inches ➔ 0.203 m

Factor of Safety: 1.5

Wheel Torques

Tmax x = Tmax y = 4364 N * 0.203 m = 1663 N*m

Tmax z = 2000 N * 0.203 m = 763 N*m

Wheel Forces

Fx = Fy = 4364N

Fz = 2000 N

11.5 VERTICAL CROSS-SECTION OF THE SENSOR SHOWING THE

ELECTRONICS


11.6 MECHANICAL TESTING ON SENSOR


11.7 STRAIN GUAGE CALLIBRATION


11.7 DIGITAL OUTPUT FROM THE SENSOR

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