NATCAR
Design Team 10
Prairie Barger – Archivist, Funding Manager, EE Ma7 Carr – Hardware Manager, EE Stephen King – Team Leader, SoBware Manager, EE Dr. Hartley and Dr. Tran 12/2/11 Need
•  NATCAR is an autonomous vehicle competition
held every year at the University of California in
Davis, Ca.
•  The competition calls for an autonomous vehicle
capable of quickly and safely navigating an
unknown course while adhering to regulations in
order to ensure a competitive environment.
•  The car that can navigate and complete the
course in the fasted time of 3 runs will win the
competition.
Goal
•  Design a 1/10th scaled model, fully
autonomous car, which will adhere to the UC
Davis NATCAR rules.
•  WIN
Design Requirements
Engineering requirements
System capable of measuring
displacement from the track to
within ½” accuracy.
The system must have zero
steady state error.
The system must have a setting
time of less than 2 seconds.
The car must use a custom DCDC converter and motor driver
(no bricks).
The motor should be a DC
brushed motor
The motor should be capable of
outputting 50W.
Function
Interprets both electromagnetic sensor info and
optical sensor info to get a distance offset.
This will allow the system to accurately stay on
the track.
This ensures that the car will complete the
course quickly
This allows the car to easily fit within the size
regulations.
A brushed DC motor allows for the use of a
simple H-bridge motor driver and gives a linear
response of speed to voltage input.
A 50 W output ensures that the motor can drive
the car to achieve the necessary speed fast
enough.
Design Requirements
Engineering requirements
Battery capable of 2700mAh of
charge
Battery costing less than $30
The wheels must be less than
4.25" in diameter and 2.5" wide.
Function
2700mAh will allow the vehicle to run for the
duration of the competition
The price of the battery is limited to $30 by the
official NATCAR rules.
The wheel base must have: length
≤ 14” width ≤ 14”.
The car must have height ≤
9” (except for the flag, width ≤
1”, and length ≤ 3’.
The car should have a rigid,
opaque flag that will trigger a
timer. The flag must be 3”X6”
and be located 9.5” above the
ground. This flag should double
as an emergency stop so that
when it is tripped a hard stop will
cut power to the car.
These dimensions allow the car to easily fit
within the size regulations.
In order to meet safety standards the car must
have an emergency stop. A hardware stop
allows the car to be stopped regardless of the
problem encountered. The rigid flag required for
timing purposes is an excellent way to
accomplish this.
Hardware Block Diagram
LED
Array
Optical
Sensors
DC Battery
Power
DC-DC
Convertor
Steering
Servo
PIC
Magnetic
Sensors
H-Bridge
Motor Driver
Motor
Drive
Emergency
Shut-Off Switch
6 H-Bridge Motor Controller
A B C D Function 0 0 0 0 Free Roll 1 0 1 0 0 1 1 0 0 1 0 1 1 0 0 1 1
1
1
1
Forward Reverse Brake Brake Fireballs &
Explosions
7 DC/DC Converter
•  Adjustable Voltage Regulator
LM350 •  For Vout = +5V
•  For Vout = +10V
8 DC/DC Converter
9 NATCAR Layout
7” 12” 10 Optical Sensor
SFH9240 IC •  Designed to detect the
presence white paper
making it suited for the
application of detecting
the white tape marking
the course…
•  Operates under the
Infrared (IR) spectrum,
allowing it to be
unaffected by the ambient
light.
11 Optical Sensor Setup
•  14 IC’s
•  spaced out 2 cm from each other
•  spanning approximately 23 cm This spacing
ensures the tape (1 inch wide) will constantly be
inside the array and trigger at least 2 photo
detector outputs
12 Magnetic Sensors
To Rectif ier
L2
68mH
C29
66.2pF
13 Magnetic Sensors
14 Precision Rectifier
GND_0
V3
15Vdc
0
Input From Magnetic Sensors
R80
GND_0
5k
R74
GND_0
U20A
3
+
2
LM833
1
D4
-
D1N4448
5.1k
4
15Vdc
8
V2
D3
D1N4448
R51
C35
200n
R52
10k
GND_0
10k
•  Super Diode •  High full power bandwidth amplifier •  Fast switching diodes •  Balance of speed and voltage ripple on output 15 Rectifier Output
16 Butterworth Filter
C37
R54
2k
10k
GND_0
U20B
5
+
C36
10n
6
LM833
7
To PIC
4
R53
8
20n
17 Filter Response
18 Filter Response
19 Peak Detector Circuit
C37
V2
15Vdc
0
V3
R80
GND_0
5k
R74
U20A
3
+
2
LM833
1
-
5.1k
D4
R53
R54
D1N4448
2k
10k
D3
D1N4448
R51
C35
200n
R52
10k
GND_0
8
20n
8
GND_0
U20B
5
+
C36
10n
6
LM833
7
To PIC
4
GND_0
Input From Magnetic Sensors
4
15Vdc
GND_0
10k
20 Software Block Diagram
Power Up/ Brownout Reset
Initial Setup
Enter Main loop
Gather Sensor Information
Raw Optical Data
Sample
Optical Data
Sample
Magnetic Data
Interpret
Sensor Data
Choose State
Vehicle Control
System
Raw Magnetic Data
ADC
Acceleration Signal
Steering Angle
21 PIC Microcontroller
22 Minimal Connections for PIC
23 Initial Setup Flowchart
Declare Global Variable Init Servo PWM Init Servo PWM Init Bargraph Init Motor PWM (Pulse Width ModulaZon) Init Input Capture Module Init ADC (Analog to Digital Converter Init Timers Init Main ISR (Interrupt Service RouZne) Init MagneZc (Analog input) Init OpZcal (Digital Input) 24 Main ISR Flowchart
Gather Sensor Data Gather OpZcal Data Gather MagneZc Data ADC ADC Complete? 1 ms passed? Interpret LocaZon Data LocaZon 25 Input Capture ISR Flowchart
Get Velocity Flag Tripped? Yes Stop Car No Set Velocity Motor PWM 26 Questions/Comments?
27