Laser-Guided Turret

1
Laser-Guided Turret

• ECE 445 Senior Design
• Group 6
• Ryan Nevell, Smit Shah, Sharlene Wu

2
Introduction

• Capture laser dot and control an Airsoft turret
  to fire at target
• Designed for fun - Targeted towards Airsoft
  audience
• Could be expanded to infrared detection, motion
  detection, live firearms, etc

3
Features

• Uses 2 cameras for 3D world view
• Works with ordinary laser pointers
• Serial communication between system and turret
• Accurate up to 16 ft.
• Harmless projectiles

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System Overview
5
Turret

• Built by machine shop
• American Precision Stepper motors (23H-502U)
• Soft Air Defender of World Peace

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Turret Schematic
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Circuit Components

• Allegro SLA7060M Motor Drivers
• PIC16F877
• HIN232CP RS-232 transmitter/receiver
• NTP75N06 Power MosFET for firing mechanism
• F1100E 20MHz Oscillator
• TXM-900-HP-2 RF Wireless Transmitter
• RXM-900-HP2 RF Wireless Receiver

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Circuit Design
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American Precision Stepper motors

• Pan Motor driver draws about 0.35 A current at 11
  Volts
• Tilt Motor driver draws about 0.25 A current at
  11 Volts
• Motors has each step of 1.8
• Pan Motor has freedom of 360
• Tilt motor has freedom of 40

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Motor Drivers

• SLA7060M Allegro Stepper Motor Drivers
• Operates both motors in Half Step Mode giving
  0.9 of precision
• A reference Voltage and Sense resistors are used
  to specify current through motor windings.

11
Firing Mechanism

• Uses a 5V DC Motor to reload and fire.
• It requires up to 2A current when firing
• Generates noise
• Uses a power MOSFET controlled by PIC
• Switch needed to stabilize firing current

12
PIC16F877 Functions

• Receives serial data sent by system
• Decodes the data and check for errors
• Send back information to system about operation
• Controls both motor driver direction and clock
  inputs to motor Driver

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PIC16F877 (cont.)

• Controls firing mechanism
• Monitors reset position and performs positions
  correction

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Wireless
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Wireless Schematic (Removed)

• LINX HP-2 Series receiver and transmitter
• Encoding and decoding algorithm
• Operating frequency 921.37MHz

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Communication Protocol

• 3 or more identical bits in a row (000 or 111)
  drops accuracy over wireless
• A bit is always followed by its inverted bit
• Contains 3 data bits and 1 command/data specify
  bit
• For example in 10101010

Command/Data Specifier
Command Code (000Move Pan Motor to right)
17
Cameras

• Labtec Webcam Pro
• 640 by 480 pixel resolution, 24 bit color
• Facing in generally the same direction and level

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Laser Detection Algorithm

• Existing algorithms rely on laser to be red or
  significantly brighter than rest of scene
• Looks for increases in brightness
• Box method used to check appropriate size
• More efficient and simpler than blob method

19
Laser Processing Process
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Matlab Configuration

• Our program takes picture pairs from cameras, one
  for left camera, one for right camera
• Matlab program by Jean-Yves Bouguet (Caltech)
• Pinhole camera model

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Matlab (cont.)

• Express point P in space to camera coordinates
• Project point P to image plane
• Obtain image coordinates in pixels

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Matlab (cont.)

• A coordinate system is initialized with the left
  camera being at the origin
• Rotation and transformation matrices relate the
  right camera to the left
• Intrinsic parameters (focal length, principal
  point) are sent to the program as well

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Stereo Triangulation
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Stereo Triangulation

• Uses pinhole method
• Draws a line from image planes to the point
• Utilizes least-squares method to determine depth
  of point (Z)
• Calculates the disparity

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Targeting Process
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Targeting Process - Trajectory

• Adjustable Pan Plane and Zero vector
• Allows cameras to be out-of-level to turret
• Allows fine-tuning of turret aim
• More complicated ballistic calculations abandoned
  when Nerf gun failed

27
PC Software

• Decided to use Linux
• Thought Video4Linux would be easiest
• x86 Linux drivers support only 1 camera
• Use network to combine 2 PCs
• Multi-threaded, written in C
• Sleep time between camera frames, turret commands

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PC Software (cont.)

• Modular design
• Various input/output plug-ins
• Easily expandable to 3 cameras
• Simple console UI to change parameters at runtime
• Specially built version of Knoppix used for
  development

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PC Software (cont.)
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Wireless Transmitter/Receiver Testing

• Best performance when operated on separate
  breadboard from Crystal Oscillator
• Firing mechanism adds noise to receiver circuitry
  causing false detection
• Tried to disable receiver while firing

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Targeting Accuracy

• At distances between 7 and 10 feet, targeted
  point averaged within 0.548 of laser point
• Depth accuracy much worse than horizontal/vertical
  especially at long range
• Might clear up with larger calibration grid

32
Targeting and Firing Accuracy
26 Shots fired at various positions at distances
between 10 and 16 feet.
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Original Design Specifications

• Accurate up to 30 ft from cameras
• At 30 ft, BBs will hit target within 1 ft radius
• Wireless configuration

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Current Design

• Accurate up to 16 ft from cameras
• At 16 ft, BBs will hit target within 1 ft radius
• No Wireless due to noise

35
Challenges

• Laser detection
• Cameras saturated by laser
• Laser cannot be seen at 30 ft
• Camera driver limitation
• Defective equipment
• Finding correct stereoscopic algorithm
• Firing circuit generated too much noise

36
Future Hardware Development

• Stronger motors
• Timing belts
• Enhance wireless performance
• Better cameras
• Infrared cameras
• Sell cameras pre-mounted and calibrated

37
Future Software Development

• GUI interface
• Infrared detection
• Motion detection
• Implement camera calibration into program
• Calibrate cameras before production

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Cost Analysis
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Production Cost Analysis
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Credits

• Professor Jonathan Makela
• TA Jason Skowronski
• Professor Seth Hutchinson
• TA Jonathan Holm