Autonomous Control of Scalextric
Slot Car on
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
Contacts
Motor
Power
Pack
Rails
Controller
Resistor
http://www.wikipedia.com
Project Overview

Race slot car autonomously against human
player

Target existing customers who cannot easily
find opponents

Keep user base active and boost number of
repeat customers
System Implementation
Position Data
Electric
Contacts
Motor
Digital In
Powered
Rails
Power
Pack
Analog
Out
http://www.wikipedia.com
USB
Design Advantages

Line detector and reflective strips
Cheap to implement
 Easy for end user
 Scalable


LabVIEW and NI DAQ
Rapid prototyping environment
 Integrated data collection
 Potential software updates

Main Subsystems
Position/Speed
Detection
Data
Transmission
Control
Algorithm
Position and Speed Detection
Reflective Strip
50mm
Δt
5V
0V


Time
Position – Increment counter once per checkpoint
Velocity – 50mm (One value per checkpoint)
Δt
Spacing Requirements
< 17cm
Checkpoint n
Checkpoint n+1
Max slot car speed = 2500 mm/s
Max distance between checkpoints = 170 mm
Max ping rate = 15 pings/sec
Transmission rate = 56,000 bits/sec
Checkpoint Detect
HIGH
5V
0V
Time
Checkpoint Pass
LOW
5V
0V
Time
Data Transmission

Data transmitted from car to PC
Wireless transfer using Linx HP3
 Data read in through NI DAQ into LabVIEW on
PC


Voltage from PC to track
Control voltage from NI DAQ
 DAQ output voltage amplified to meet voltage
specifications of track

http://www.linxtechnologies.com
http://www.ni.com
Wireless Transmission Captures
16 pulses/lap
Crack within
pulse
Power Supply


CR2450 Button cell – Powers the line detector, wireless
transmitter on car
5V Voltage regulator – Power efficient, steady output
Voltage Regulator
http://www.wikipedia.com
Amplifier



LM 741
Input
Output
–
–
–
Non-inverting amplifier circuit
0-5V from NI DAQ
0-12V to track
Amplifier Screen Capture
Output from Amplifier (0-12V)
Input to Amplifier (0-5V)
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
c - Tunes the importance of the curvature
relative to distance from car
Complexity Implementation

Currently
Precision of position is one track segment
 Next three track segments considered
 Single voltage calculated per track segment


In progress
Estimate position between checkpoints
 Consider fixed distance ahead of car
 Attain more accurate speed profile

Data Errors
Problem
Solution
Missing a checkpoint
– Change batteries
– Adjust line detector
False checkpoint detection
– Apply noise filter
(10ms threshold)
– Recombine cracked pulses
(2ms threshold)
Example Data
Voltage
Time
Pulse due to noise
Crack in Pulse
(<10ms)
(<2ms)
Race Replay Feature

Sample track voltage during a race
Data acquired at 10,000 Hz
 Save profile to file
 Plays profile back


Potential uses of race replay feature
Compete against their own race profiles
 Compete against other competitor saved profiles

Budget and Cost Analysis





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
Unit Cost
$230
Demonstration Plan

Main demo
System drives slot car around circuit without
derailing
 In case of derailing, slot car can be placed onto last
checkpoint and resume normal operation


Supplemental demo
Race slot car against a human opponent
 Scale system’s performance based on difficulty
setting

Results
Parameter
Value
Position Sensing – Checkpoint detection
99.4%
Velocity Sensing Error
0.6%
Pulse Error Rate
12.5%
Control Voltage onto Track
0-12V (DC)
Speed Range
0-2500mm/s
Failures per Lap
0.1
Car Development





Original weight of car
New weight of car
=
=
85g
110g
Attach line detector and circuit board to slot car
with Velcro
Line detector no more than 0.5’’ above track
Optional use of antennae for receiver and
transmitter
Car Dimensions
Car Views
Battery with
Switch
Voltage
Regulator
Line
Detector
Wireless
Transmitter
System Overview
Position Data
Electric
Contacts
Motor
Digital In
Powered
Rails
Power
Pack
Analog
Out
http://www.wikipedia.com
USB
System Hierarchy
Position Data
Analog
Out
USB
Demonstration Video
Current Tasks

Better position estimates required to improve
control

Ability to differentiate start checkpoint from
other checkpoints

Control algorithm needs more fine tuning
Current Status
Position detection
Velocity detection
Data transmission
Applying amplified voltage to track
Display last checkpoint passed
Car development
Record and play voltage profile
Improve control algorithm
Questions?
Position Detection Sensor
http://www.lynxmotion.com/
Line Detector
IR
LED
Phototransistor
LOW
Wireless Transmitter
HIGH
Car Components