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TEAM SOLBOT
CRITICAL DESIGN REVIEW
Martin Carbajal
Curtis Porter
Mike Mellman
Erik Zurinskas
Project Description Review
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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 user’s mowing process
High Level View
Microcontroller Design
Microcontroller
MSP430F2418
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Low power for a
wireless/remote system
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Zigbee/RF optimized
AD converter for
input/output control
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Code Composer
development environment
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Compass
3-Axis Compass HMC6343
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Mounted on microcontroller PCB
I2C communication to
microcontroller at pins 30 and 31
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Outputs 3 bytes of data:
heading, pitch, and roll
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Typical 2° Heading Accuracy
with 1° Pitch and Roll Accuracy
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On breakout board due to size
of chip
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Compass Functionality
Wireless Communications
The Xbee will provide communications between our
computer and the lawn mower
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Initiation of lawn mower via computer
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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
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Sending to microcontroller through RS232 ASCII
characters at a baud rate of 9600bps
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The Xbee module will be hooked up on pins 32 and
33 of the microcontroller
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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
Microcontroller UART code
Demo of Microcontroller and
Xbee Communication
Software
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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
Motor Control Circuit Schematic
Prototype Motor Control Board
LMD18200 H-Bridge
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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
Optoisolators
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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
Demo of Motor Control Board
Chassis
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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
Drive Motors
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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
Mower Motor
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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
Power Supply
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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
Solar Power System (tentative)
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Small solar (RV)
panel continuously
charges 24V
battery at charging
station
When mower returns
to charging station,
the on-board
batteries are
recharged
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
Updated Division of Labor
TASK
CURTIS
ERIK
MARTIN
MIKE
Hardware
Frame retrofit
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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
Microcontroller path control
X
X
Communication coding
X
X
Memory management
X
X
System testing
X
X
X
X
Preliminary User’s Manual
X
X
X
X
Final Technical Manual
X
X
X
X
Final User’s Manual
X
X
X
X
Software
Documentation
Updated Schedule
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
Questions?