TEAM SOLBOT CRITICAL Design Review

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TEAM SOLBOTCRITICAL Design Review

• Martin Carbajal Mike Mellman
• Curtis Porter Erik Zurinskas

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Project Description Review

• Solar Operated Lawnmower Bot
• Our project is a battery powered automatic lawn
  mower
• The user will be able to wirelessly control the
  mower along a desired path
• The mower will record the path and be able to
  autonomously replicate the users mowing process

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High Level View
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Microcontroller Design
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Microcontroller

• MSP430F2418
• Low power for a wireless/remote system
• Zigbee/RF optimized
• AD converter for input/output control
• Code Composer development environment

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Compass

• 3-Axis Compass HMC6343
• Mounted on microcontroller PCB
• I2C communication to microcontroller at pins 30
  and 31
• Outputs 3 bytes of data heading, pitch, and roll
• Typical 2 Heading Accuracy with 1 Pitch and
  Roll Accuracy
• On breakout board due to size of chip

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Compass Functionality
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Wireless Communications

• The Xbee will provide communications between our
  computer and the lawn mower
• Initiation of lawn mower via computer
• Send a if tilt data exceeds a predetermined
  safety value, which will shut off all power to
  mower and, when received at computer, will
  display warning message
• Sending to microcontroller through RS232 ASCII
  characters at a baud rate of 9600bps
• The Xbee module will be hooked up on pins 32 and
  33 of the microcontroller
• For testing with the USB to Xbee we are using
  X-CTU software that came with the Xbee

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XBee UART Data Flow
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Microcontroller UART code
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Demo of Microcontroller andXbee Communication
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Software

• Code Composer will be the development environment
• Computer will be used to load code to
  microcontroller on mower through JTAG connection
• Software receives characters and based on which
  character it will perform the various functions
  (speed, brake, direction, and blade motor)
• Currently working on the path recording
• Error correction with compass and velocity records

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Motor Control Circuit Schematic
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Prototype Motor Control Board
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LMD18200 H-Bridge

• Rated to 55V 3A, which will allow control of
  different sized motors
• Our project will use 20V supply and 0.3A per
  motor
• Input from microcontroller is PWM signal (PWM
  square wave) direction/brake (high/low logic
  signals)
• Change in duty cycle will vary motor speed

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Optoisolators

• PS2501 Photocoupler (16 pin DIP) has 4 separate
  optoisolators
• Used to electrically isolate the control signals
  from motor control board, which prevents noise
  from motors getting onto microcontroller board

To Motor Board
From Microcontroller Board
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Demo of Motor Control Board
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Chassis

• Constructed small prototype with small DC motors
  to test and debug motor control circuit
• Will scale up to full sized lawn mower chassis
  with larger motors

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Drive Motors

• Prototype uses small DC motors
• Final version will be Pittman GM9236S018 DC
  motors
• Peak Torque 6.1 N-m
• No-Load Current 0.33 A

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Mower Motor

• We will use a single DC motor that will spin
  faster than the drive motors
• Motor is controlled (on/off signal) from
  microcontroller using two MOSFETS
• Will also run on 20V supply and use 0.3A

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Power Supply

• Microcontroller board will be run off of a 12V
  (7.5 AH) battery which is regulated at 3.3V using
  an LM317 voltage regulator
• Motor control board will be run off of a 24V (12
  AH) battery which will have two regulated
  supplies 3.3V for optoisolator control voltage
  and 20V for motor supply voltages

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Solar Power System (tentative)

• Small solar (RV) panel continuously charges 24V
  battery at charging station
• When mower returns to charging station, the
  on-board batteries are recharged

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Updated Project Cost
Part Vendor Price (USD)
Microcontroller TI samples Free
Xbee Sparkfun.com 100
Compass Sparkfun.com 150
Chassis Retrofit existing model Free
Wheels TBD 50
Wheel Encoders Sparkfun.com 30
Drive Motors Pittman 100
Mower Motor Pittman 50
Mower Batteries Donation Free
Base Station Battery Donation Free
Solar Panel Siliconsolar.com 130
Misc. Components EE store / Sparkfun.com 100
PC Boards TBD 100
TOTAL 810
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Updated Division of Labor
TASK CURTIS ERIK MARTIN MIKE
Hardware
Frame retrofit X X
Motor Control X X
Power system design X X
RF Communication design X X
PCB Layout X X X X
Electronics mounting/soldering X X X X
Software
Microcontroller path control X X
Communication coding X X
Memory management X X
System testing X X X X
Documentation
Preliminary Users Manual X X X X
Final Technical Manual X X X X
Final Users Manual X X X X
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Updated Schedule
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Critical Dates

• Milestone 1
• Complete control of mower from computer
• Milestone 2
• Record a given path and be able to reasonably
  reproduce path
• Expo
• Fully completed mower with all hardware mounted
  and functional path reproduction
• Any possible additional features that time permits

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Questions?