TEAM SOLBOT
PRELIMINARY DESIGN REVIEW
Martin Carbajal
Mike Mellman
Curtis Porter
Erik Zurinskas
Project Description
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Solar Operated Lawnmower Bot
Our project is a battery powered automatic lawn
mower
Initially the user will wirelessly control the mower
along a desired path and the mower will record the
movements in order to later replicate them
autonomously
It will have a solar powered charging station that
will act as the starting and ending point of the
mowing process
Function List
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Mower will have the ability to be controlled remotely
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It will be able to store the desired mowing path in memory
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It will have wheels that control forward and backward movement as
well as turning
Wireless interaction between mower, base station, and control unit
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Solar power to large battery to mower batteries
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Automatic shut-off if it tips over
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Micro-controller to interact with and control other components (motors
for blades/wheels, wireless component, compass, and power
management)
Possible Extra Features
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Integrated scheduling of mower
Disable the mower if it leaves its designated mowing
area
Collision detection
Integrate an automated sprinkler system with humidity
and temperature sensors
Automatic path creation
Feasibility
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Our members consist of two EE students and two
ECE students with CS minors
We have previous experience with microcontrollers
and power conversion from prior classes
Extensive programming experience
Met with mechanical engineers to discuss
mechanical aspects and possible outsourcing of
chassis construction and mechanical functionality
High Level View
More In-depth Look
System Implementation
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I2C will be the communication protocol used for the
compass
RS232 XBEE wireless communication (2.4 GHz)
Battery voltages will be monitored using the A/D
converters via op-amps into the microcontroller
Microcontroller
MSP430 F5xx 25MHz Series
(MSP430F5418)
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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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Very versatile for future
upgrades or additional accessory
options
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Wireless Communications
The Xbee will provide
communications between our
Base station and the Lawn
mower
Initiation of lawn mower via
base station
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Current location in mower
pattern to base station
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Send an alarm if tilt switch
activated
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Controlled by micro controller
through RS232
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300ft outdoor range
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Navigational Equipment
3-Axis Compass HMC6343
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Mounted on mower
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Compass Heading
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Tilt Outputs to detect tip over
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3 axis Accelerometers
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I2C communication to Microcontroller
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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Chassis
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Will retrofit an existing
lawn mower chassis
We will use the front wheels
to drive, and attach a
caster wheel in the back
middle
We will find suitable drive
wheels with adequate
traction and size
Drive Motor Choice
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Stepper motor or DC motor?
Stepper motor operates in discrete
steps, while DC motor operates
continuously based upon voltage
level
Steppers harder to control, DCs are
simple
Steppers have less torque at high
speed than DCs
We will use 2 DC motors to control
mower movement
DC Motor Specifications
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Force = µk x N
µk is the coefficient of friction between rubber and grass ~0.35
N is the normal force on the wheels ~50 lbs
→ Force = 0.35 x 50 lbs = 17.5 lbs
Torque = F x r
r is the wheel radius ~4 inches
→ Torque = 17.5 lbs x 0.33 ft = 5.78 lb-ft
Desired torque per motor is ~6 lb-ft for adequate movement
Mower Motor
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We will use a single DC motor that will spin faster
than the drive motors
We won’t attach a real blade unless operated
outside due to safety concerns
For demonstration purposes, will attach a plastic RC
airplane propeller
Power System
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Small solar (RV)
panel continuously
charges 12V
battery at charging
station
When mower returns
to charging station,
the on-board
batteries are
recharged
On board batteries
will be Li-Ion packs
to provide enough
power
Power Distribution
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Three separate power systems on mower
Two high power (~24V) systems: one for mower
motor and one for drive motors
One low power (~3.3V) system for microcontroller
and other accessories (noise prevention)
Monitor high power systems; upon low power, return
to charging station to recharge
Utilize switching converters
Software
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Base station will be used to load code to mower
ECE team members to manage this aspect of project
Code Composer will be the development
environment
Project Cost
Part
Vendor
Price (USD)
Microcontroller
Digikey.com
$6.60
Xbee
Sparkfun.com
$45.90
Compass
Sparkfun.com
$149.95
Chassis
Retrofit existing model
Free
Wheels
TBD
$50
Wheel Encoders
Sparkfun.com
$30
Drive Motors
TBD
~$100
Mower Motor
TBD
~$50
Mower Batteries
Batteryjunction.com
$14 * 10 = $140
Base Station Battery
Donation
Free
Solar Panel
Siliconsolar.com
$129.95
Misc. Components
EE store / Sparkfun.com
$100
PC Boards
TBD
~$100
TOTAL
$902.40
Division of Labor
TASK
CURTIS
ERIK
MARTIN
MIKE
Hardware
Frame retrofit
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Motor Control
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Power system design
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RF Communication design
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PCB Layout
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Electronics mounting/soldering
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X
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Microcontroller path control
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X
Communication coding
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X
Memory management
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System testing
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X
Preliminary User’s Manual
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X
X
X
Final Technical Manual
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X
X
X
Final User’s Manual
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Software
Documentation
Risks
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Mechanical issues (motor mounting, frame retrofit) –
enlist mechanical major’s help
Motor issues (possible magnetic interference,
excessive power consumption) – might need to shield
motors, use smaller motors and lighter frame
Path reproduction – additional path reproduction
sensors to aid primary path control
Schedule
Questions?