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Development of a Multi-Level Emergency Stop System for Unmanned Vehicles Development of a Multi-Level Emergency
Stop System for Unmanned Vehicles
Michael Vincent Avitabile
Thesis submitted to the faculty of the Virginia Polytechnic Institute
and State University in partial fulllment of the requirements for
the degree of
Master of Science
In
Electrical Engineering
Dr. Alfred L. Wicks, Chairman
Dept. of Electrical Engineering
Dr. Charles F. Reinholtz
Dept. of Mechanical Engineering
Dr. Peter M. Athanas
Dept. of Electrical Engineering
December 7, 2006
Blacksburg, Virginia
Keywords: Emergency Stop, Multiple Level, Unmanned Vehicles Development of a Multi-Level Emergency
Stop System for Unmanned Vehicles
Michael Vincent Avitabile
Abstract
As the use of unmanned vehicles continues to grow, so does the need for
systems to safely test and operate these vehicles. While there are safety sys-
tems designed for this purpose, they are often developed for a specic vehicle
platform. The Multi-Level Emergency Stop (MLES) system provides three user-
dened emergency response contingencies that can be adapted to a wide variety
of unmanned vehicles.
The Multi-Level Emergency Stop system is designed to be an ad-on safety
system that can be integrated into ground, air, or surface unmanned vehicles. A
complete MLES system consists of a hand held transmitter and a vehicle mounted
receiver. The three levels of contingencies are controlled by three switches on the
transmitter. These switches engage and disengage contacts located in the receiver
via a wireless link. The function of these contacts is determined by the user for
each unique application.
Presented in this thesis is the detailed hardware design and software layout
of the Multi-Level Emergency Stop system. Also included are the performance
results and operational tests. Acknowledgments
I would like to thank the many people that have contributed to this thesis and
my graduate studies. Without the love and encouragement of my parents, Bob
and Karen Avitabile, none of this would have been possible. Their support has
provided me with incredible opportunities for which I am forever grateful.
Dr. Reinholtz has had a tremendous inuence on my college career. Since the
rst week of my undergraduate studies, he has given me the opportunity to work
with the Autonomous Vehicle Team where I gained invaluable experience over the
years. Dr. Wicks has always provided guidance throughout the years both in and
out of school. Despite the occasional side project, Dr. Wicks has kept me focused
and provided the motivation needed to nish my degree. Together Dr. Reinholtz
and Dr. Wicks have provided me with many great opportunities.
I would also like to thank all my fellow researchers a Virginia Tech. I am lucky
to have had the experience of working with such talented and motivated individu-
als. Spanning the course of several years, there have been many people that have
contributed to the development of the Multi-Level Emergency Stop system.
This project was initially a joint effort with Ben Hastings. Ben was responsible
for the initial hardware design, and has helped advance the development of the
project throughout. The evolution of the enclosures was the work of Sean Baity.
His designs have transformed this project into a nished product. I would also
like to thank Dave Anderson and Shane Barnett for their assistance with the nal
enclosure design and Cheryl Bauman for her help with the nal testing. It was also
important that the connectors used on the Multi-Level Emergency Stop satised
the strict requirements of Brett Gombar.
iii Contents
Chapter 1:
Introduction
1
1.1
Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
1.2
Existing Safety Systems . . . . . . . . . . . . . . . . . . . . . . .
5
1.3
Disclaimer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10
Chapter 2:
Transmitter Hardware Design
11
2.1
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11
2.2
Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14
2.2.1
DC/DC Converter . . . . . . . . . . . . . . . . . . . . . .
15
2.2.2
Battery Charger . . . . . . . . . . . . . . . . . . . . . . .
18
2.2.3
Battery Protection Circuitry
. . . . . . . . . . . . . . . .
20
2.3
Microcontroller . . . . . . . . . . . . . . . . . . . . . . . . . . .
21
2.3.1
A/D Converter
. . . . . . . . . . . . . . . . . . . . . . .
22
2.3.2
UART . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24
2.3.3
I
2
C
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25
Chapter 3:
Receiver Hardware Design
27
3.1
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
27
3.2
Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . .
28
3.2.1
Protection Circuitry . . . . . . . . . . . . . . . . . . . . .
29
3.3
Vehicle Interface
. . . . . . . . . . . . . . . . . . . . . . . . . .
30
3.3.1
High Current Outputs . . . . . . . . . . . . . . . . . . . .
31
3.3.2
Digital Logic Outputs . . . . . . . . . . . . . . . . . . . .
32
3.3.3
Analog Outputs . . . . . . . . . . . . . . . . . . . . . . .
33
3.3.4
Serial Output . . . . . . . . . . . . . . . . . . . . . . . .
34
Chapter 4:
Wireless Communications
35
4.0.5
Spread Spectrum Communications . . . . . . . . . . . . .
38
4.1
Wireless Protocol . . . . . . . . . . . . . . . . . . . . . . . . . .
40
iv Chapter 5:
Software Design
41
5.1
Transmitter Command Mode . . . . . . . . . . . . . . . . . . . .
42
5.2
Receiver Command Mode . . . . . . . . . . . . . . . . . . . . . .
45
5.3
TX Firmware . . . . . . . . . . . . . . . . . . . . . . . . . . . .
49
5.4
RX Firmware . . . . . . . . . . . . . . . . . . . . . . . . . . . .
52
Chapter 6:
Revision History
56
6.1
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
56
6.2
Version 1.0
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
57
6.3
Version 2.0
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
57
6.4
Version 3.0
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
59
6.5
Version 4.0
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
62
6.6
Version 5.0
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
64
Chapter 7:
Analysis and Testing
67
7.1
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
67
7.2
Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . .
68
7.2.1
Battery Charger . . . . . . . . . . . . . . . . . . . . . . .
73
7.3
Battery Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
75
7.4
Latency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
76
7.5
Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
77
7.6
Error Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
82
7.7
Cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
84
Chapter 8:
Conclusions
85
8.1
Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
86
References
88
Appendix A:
Schematics
90
v List of Figures
1.1
Futaba FRF-0302U 3-Channel R/C System [14] . . . . . . . . . .
6
1.2
Omnitech ORI-SR safety radio system [15]
. . . . . . . . . . . .
7
2.1
Multi-Level Emergency Stop Transmitter . . . . . . . . . . . . . .
12
2.2
E-Stop Transmitter Hardware Block Diagram . . . . . . . . . . .
13
2.3
Power Supply Overview . . . . . . . . . . . . . . . . . . . . . . .
14
2.4
Simplied buck converter model . . . . . . . . . . . . . . . . . .
16
2.5
DC/DC Converter Schematic . . . . . . . . . . . . . . . . . . . .
17
2.6
Lithium Polymer Charger Schematic . . . . . . . . . . . . . . . .
18
2.7
Lithium Charge Prole [10] . . . . . . . . . . . . . . . . . . . . .
19
2.8
Estop Switch Schematic . . . . . . . . . . . . . . . . . . . . . . .
21
2.9
PIC18F6722 Block diagram [7] . . . . . . . . . . . . . . . . . . .
23
2.10 I
2
C Bus Conguration . . . . . . . . . . . . . . . . . . . . . . . .
25
3.1
MLES Receiver . . . . . . . . . . . . . . . . . . . . . . . . . . .
28
3.2
Emergency Stop Receiver Hardware Overview . . . . . . . . . . .
29
3.3
Reverse voltage protection circuit . . . . . . . . . . . . . . . . . .
30
3.4
High Current Relay Output Schematic . . . . . . . . . . . . . . .
32
3.5
Simplied Digital to Analog Converter [12] . . . . . . . . . . . .
33
4.1
Block Diagram of 9XTend Radio Modem [11] . . . . . . . . . . .
36
4.2
Filtration information contained within each RF packet header [11]
38
4.3
Frequency Hopping Spread Spectrum pseudo random sequence
example [8] . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
39
4.4
Wireless Protocol . . . . . . . . . . . . . . . . . . . . . . . . . .
40
5.1
Transmitter ISR Flow Diagrams
. . . . . . . . . . . . . . . . . .
50
5.2
Transmitter Main Loop Flow Diagram . . . . . . . . . . . . . . .
51
5.3
Receiver Software Flow Diagram . . . . . . . . . . . . . . . . . .
54
5.4
Receiver ISR Flow Diagrams . . . . . . . . . . . . . . . . . . . .
55
vi