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

What is Slot Car Racing? Electric Contacts Motor Rails Resistor Controller Power Pack

Project Overview Race slot car autonomously against human player Race slot car autonomously against human player Target existing customers who cannot easily find opponents Target existing customers who cannot easily find opponents Keep user base active and boost number of repeat customers Keep user base active and boost number of repeat customers

System Implementation Position Data Digital In USB Analog Out Electric Contacts Motor Power Pack Powered Rails

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 Control Algorithm Data Transmission Position/Speed Detection

Position and Speed Detection Position – Increment counter once per checkpoint Position – Increment counter once per checkpoint Velocity – (One value per checkpoint) Velocity – (One value per checkpoint) 5V 0V Time Reflective Strip 50mm ΔtΔt Δt

Spacing Requirements 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 < 17cm Checkpoint n Checkpoint n+1

Checkpoint Detect HIGH 5V 0V Time

Checkpoint Pass LOW 5V 0V Time

Data Transmission Data transmitted from car to PC Data transmitted from car to PC Wireless transfer using Linx HP3 Wireless transfer using Linx HP3 Data read in through NI DAQ into LabVIEW on PC Data read in through NI DAQ into LabVIEW on PC Voltage from PC to track Voltage from PC to track Control voltage from NI DAQ Control voltage from NI DAQ DAQ output voltage amplified to meet voltage specifications of track DAQ output voltage amplified to meet voltage specifications of track

Wireless Transmission Captures Crack within pulse 16 pulses/lap

Power Supply CR2450 Button cell – Powers the line detector, wireless transmitter on car CR2450 Button cell – Powers the line detector, wireless transmitter on car 5V Voltage regulator – Power efficient, steady output 5V Voltage regulator – Power efficient, steady output Voltage Regulator

Amplifier LM 741 –Non-inverting amplifier circuit Input – 0-5V from NI DAQ Output – 0-12V to track

Amplifier Screen Capture Input to Amplifier (0-5V) Output from Amplifier (0-12V)

Control Algorithm Get Upcoming Track Layout Position Speed Calculate Track Complexity Determine Optimal Track Voltage Desired Track Voltage Track Input by User

Calculating Complexity x – Distance from the front of the car K – Curvature of the track at that point 50cm – The horizon Tunes the importance of the curvature relative to distance from car c - Tunes the importance of the curvature relative to distance from car

Complexity Implementation Currently Currently Precision of position is one track segment Precision of position is one track segment Next three track segments considered Next three track segments considered Single voltage calculated per track segment Single voltage calculated per track segment In progress In progress Estimate position between checkpoints Estimate position between checkpoints Consider fixed distance ahead of car Consider fixed distance ahead of car Attain more accurate speed profile Attain more accurate speed profile

Data Errors ProblemSolution Missing a checkpoint – Change batteries – Adjust line detector False checkpoint detection – Apply noise filter (10ms threshold) – Recombine cracked pulses (2ms threshold)

Example Data Pulse due to noise (<10ms) Crack in Pulse (<2ms) Voltage Time

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)$150 NI USB 6008 (DAQ)$150 HP3 Series Receiver $30 HP3 Series Receiver $30 Base Station$180 HP3 Series Transmitter $25 HP3 Series Transmitter $25 Line Tracker $20 Line Tracker $20 Five 3V Coin Batteries$5 Five 3V Coin Batteries$5 Car$50 Unit Cost$230

Demonstration Plan Main demo Main demo System drives slot car around circuit without derailing System drives slot car around circuit without derailing In case of derailing, slot car can be placed onto last checkpoint and resume normal operation In case of derailing, slot car can be placed onto last checkpoint and resume normal operation Supplemental demo Supplemental demo Race slot car against a human opponent Race slot car against a human opponent Scale system’s performance based on difficulty setting Scale system’s performance based on difficulty setting

Results ParameterValue Position Sensing – Checkpoint detection99.4% Velocity Sensing Error0.6% Pulse Error Rate12.5% Control Voltage onto Track0-12V (DC) Speed Range mm/s Failures per Lap0.1

Car Development Original weight of car=85g New weight of car=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 75mm

Car Views Battery with Switch Line Detector Wireless Transmitter Voltage Regulator

System Overview Position Data Digital In USB Analog Out Electric Contacts Motor Power Pack Powered Rails

System Hierarchy Position Data Digital In USB Analog Out

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

Line Detector LOW HIGH IR LED Phototransistor Wireless Transmitter

Car Components