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Autonomously Controlled Vehicles with Collision Avoidance

Mike Gregoire Rob BeauchampDan HolcombTim Brett

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Motivation

Follow and Avoid Collisions Simulated Highway Driving Environment Autonomous Not Centralized

Centralized System Not Practical for Today's Highways Predictable Vehicle Behavior

First Car Moves, Others Follow

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System Block Diagram

Ultrasonic Sensor Scans Area in Front of Vehicle for Objects

Controller Receives Distance and Angle Information from Sensor and

Decides what to do

The Controller Interfaces to the Platform to Drive the Vehicle

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Overview MDR Deliverables Sonar Sensor Vehicle Interface Specification of Control Behavior Costs Spring Goals

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MDR Deliverables Functional Sonar Sensor

Distance Direction

Platform Interface to Control Vehicle Motor (Speed) Actuator (Turning)

Specification of Control Behavior

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Functional Sonar Sensor• Sonar vs. Optical

• Chose Sonar• Precise Distance

Measurement Is Not As Important as Relative Distance

• Minimum Range is 1.1 ft due to Ringing in Receiver

• Maximum Range is > 8.36ft (for a ceiling) but a Software Limit of 5.5ft is imposed

Sonar

Optical

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Sensor Graphs – Ceiling (Stationary)

Speed Of Sound = 1100 ft/s

Left Channel Median

~ 7550µs

=49.83 Inches

Right Channel Median

~ 7570µs

=49.96 Inches

150µs Error is a 1 Inch Error in Measured Distance

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Sensor Graphs – 2x4 (Moving)

Distance

0

5

10

15

20

25

0 100 200 300 400 500 600 700 800

Inch

es

L

R

Difference (Left - Right)

-250

-200

-150

-100

-50

050

100

150

200

250

0 100 200 300 400 500 600 700 800

Tim

e (uS

ec)

2x4 Board Moving Left to Right over Sensor

The Difference Graph Shows Discreteness in Time. Differences Are Equal to 1 Period (25µs)

Can See Precise Angle Change using Difference Modulo Period

Difference Modulo 25

0

5

10

15

20

25

0 100 200 300 400 500 600 700 800

Tim

e (uS

ec)

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Sensor Graphs – Error and Reliability

-12 -6 0 6 1212 Inches

18 Inches

24 Inches

Distance Off Center (Inches)

Contour - Percentage of Good Data Points

0.950-1.000

0.900-0.950

0.850-0.900

0.800-0.850

0.750-0.800

0.700-0.750

0.650-0.700

0.600-0.650

0.550-0.600

0.500-0.550

• 15 Discrete Distances – 1000 Measurements at Each

• Software Filter on Sensor Qualifies each Point. Counter has to be between 2000us and 8000us with a Difference between -160us and 160us.

• Contour Shows Percentage of Points out of 1000 that are within Filter Limits

• Recreation of position has large error because of inaccuracy in the angle measurement. This is because the same wave front doesn’t trigger both sensors. Using Mod 25 gives accurate change in angle but not an absolute angle.

Measured Position vs Calculated

0

5

10

15

20

25

30

-20 -15 -10 -5 0 5 10 15 20

Inches

Inch

es

Calculated

Measured Left

Measured Middle

Measured Right

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Platform Interface No Schematics Available Need to Reverse Engineer Controls

Motor for Speed Actuator for Steering

Direct Interface Simplest Solution

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Platform Interface - Speed Motor Interface Uses Two Wires

One Wire Tied to Ground One Wire Connected to PIC Through Current Driver

PIC Outputs Using Pulse Width Modulation (PWM) 24µs PWM Period → 41.667kHZ Frequency 96 Discrete Duty Cycles with 4MHZ PIC Clock

Need to Overcome Motor Inertia when Stopped

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Platform Interface - Turning Actuator Interface Uses Four Wires

2 Wires Used For VDD and GND 2 Wires From PIC Output Control Left / Right Turns

Control Wires at Opposite Voltage Steps Actuator Length of Voltage Differential → Length of Turn 20ms For Turn From Center to Full Left / Right Angle Turned is Surface Dependent

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Platform Interface Movie

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Platform Interface Movie

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Control Behavior

Follower should Not Always Drive Directly Towards Leader

Follower should Trace the Path of the Leader

Bad Turn Good Turn

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Control Behavior

Proposal: Use a FIFO Instruction Queue For each Sensor Data Point, a New

Instruction is Loaded into FIFO When Instruction Reaches Head, Follower

Occupies the Same Point as Lead Car When Instruction Entered FIFO

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MDR Deliverables

Functional Sonar Sensor Distance Direction

Platform Interface to Control Vehicle Motor (Speed) Actuator (Turning)

Specification of Control Behavior

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Product Costs $500 Total Budget Fall Expenses ≈ $150

3 Vehicles For Free Ultrasonic Transducers ≈ $50 Op-Amps, PICs, Drivers, Etc. ≈ $100

Spring Expenses 2 More Vehicles ≈ $100 Ultrasonic Transducers ≈ $50 $200 for Unforeseen and Misc. Parts

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Spring Goals Integration of Systems

Communication From Sensor to Platform Controller Three Functional Vehicles

2 With Our System Refine Sensors

Variable Gain to Help Filter Noise Perform Demonstration

Lead Car Driven via Remote Two Autonomous Vehicles Accurately Follow

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Thank You

Questions?

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SupplementalDifference vs Angle

3 Inch Receiver Seperation - 36 Inches Away

0.00

50.00

100.00

150.00

200.00

250.00

0 10 20 30 40 50 60 70 80 90

Angle (Degrees)

Tim

e (u

Sec

)

Amplifier 2 Stage -5V to +5V Amp With a Maximum Gain of 1406 V/V With A DC offset of -1V Output Put into a GND to +5V Amp With a Maximum Gain 37.5 V/V