Autonomous Control of a
Scalextric Slot Car on a
User-Defined Track
Siddharth Kamath
Souma Mondal
Dhaval Patel
School of Electrical and Computer Engineering
Georgia Institute of Technology
http://www.scalextric-usa.com/
What is Slot Car Racing?
Electric Motor
Contacts
Power
Pack
Powered
Rails
Resistor
Handheld
Controller
http://www.wikipedia.com
Project Overview
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Design a system that allows a car to
autonomously race against a human player
Marketed toward existing Scalextric customers
who cannot easily find opponents
The product will keep the user base active and
boost the number of repeat customers
The base station will cost $180 and each car will
cost $50
Design Objectives
Autonomously
control car by:
Monitoring
position of car around track in real-time
Analyzing position data and applying appropriate
voltage to track
Display
the track
Record
last checkpoint passed if slot car falls off
performance metrics such as lap times
and top speed
System Overview
Position Data
Electric Motor
Contacts
Digital In
Powered
Rails
Power
Pack
Analog
Out
USB
http://www.wikipedia.com
Main Subsystems
Position/Speed
Detection
Data
Transmission
Control
Algorithm
Position and Speed Detection
Reflective Strips
5V
Checkpoints
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0V
Time
Position – Increment counter per pair of reflective strips
Velocity – Obtain one velocity per checkpoint
Line Detector
IR
LED
Phototransistor
LOW
Wireless Transmitter
HIGH
Advantages of a Line Detector

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Inexpensive
Easy to use
Digital output – convenient for wireless
transmission
Continuous sensing – no polling necessary
http://www.lynxmotion.com/
Data Transmission

Data transmitted from car to PC
Wireless transfer from Slot Car using Linx
Technologies HP3 wireless transmitter and receiver
 Data read in through NI USB DAQ into LabVIEW
on PC
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Voltage from PC to track
Control Voltage from LabVIEW output through NI
USB DAQ
 DAQ output voltage amplified to meet voltage
specifications of track

Power Supply Selection
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CR2450 Li-MnO2 Cell - Used to power the photointerrupter and wireless modules on the car
Constraints
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Low weight (6gm)
Nominal voltage (3V)
High capacity (600mAh)
Inexpensive
Easily obtainable
http://www.wikipedia.com
Control Algorithm
Track Input by User
Position
Speed
Get
Upcoming
Track Layout
Determine
Optimal Track
Voltage
Calculate
Track
Complexity
Desired Track Voltage
Calculating Complexity
x – distance from the front of the car
K – curvature of the track at that point
50cm – the horizon
The Mysterious Exponent c

Multiplicative constants can be factored out and
therefore do not work

The exponent c therefore helps tune the
importance of the curvature relative to the
distance
Other Software Factors

User selected difficulty – affects the
aggressiveness and the top speed

Learning from crashes – the complexity rating
for that section of track is increased
Demonstration Plan
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System drives slot car around circuit without
falling off track
Race the slot car against an experienced user on
an arbitrary track
Scale system’s performance depending on user’s
difficulty setting
In case of derailing, slot car can be placed onto
last checkpoint and resume normal operation
Problems and Issues

Scaling voltage and power when connecting NI
DAQ to track
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Optimizing algorithm
Empirically determining the constant parameters
 Scaling performance based on difficulty levels
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Project Schedule
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October
November
Interfacing:
Sensors, Control Unit and Race Track
Power Supply, Wireless Transmission, NI-DAQ
Hardware Testing and Software Development:
Crash Tolerance, Control Parameters,
Multiple Difficulty Levels
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December
Additions:
Optional Software Features
Final Demo
Budget and Cost Analysis
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NI USB 6008 (DAQ)
HP3 Series Receiver
Base Station
$150
$30
$180
HP3 Series Transmitter
Line Tracker
Five 3V Coin Batteries
Car
$25
$20
$5
$50
Total
$230
Current Status
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Complete
Line tracker and NI-DAQ tested
 Algorithm simulation
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Upcoming Milestones
Testing of wireless interface by Oct 25th
 Data transfer from car to PC to track by Oct 30th
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Questions?
Position Detection Sensor
http://www.lynxmotion.com/
Spacing Requirements
< 10cm
Checkpoint n
Checkpoint n+1
Max slot car speed = 1000 mm/s
Max distance between checkpoints = 100 mm
Max ping rate = 10 pings/sec
Transmission rate = 56,000 pings/sec