team solbot preliminary design review martin carbajal mike mellman curtis porter erik zurinskas
TRANSCRIPT
TEAM SOLBOTPRELIMINARY DESIGN REVIEWMartin Carbajal Mike Mellman
Curtis Porter Erik Zurinskas
Project Description
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
Mower will have the ability to be controlled remotely It will be able to store the desired mowing path in
memory It will have wheels that control forward and backward
movement as well as turning Wireless interaction between mower, base station, and
control unit Solar power to large battery to mower batteries Automatic shut-off if it tips over Micro-controller to interact with and control other
components (motors for blades/wheels, wireless component, compass, and power management)
Possible Extra Features
• 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
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
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)
•Low power for a wireless/remote system
•Zigbee/RF optimized
• AD converter for input/output control
•Code Composer development environment
•Very versatile for future upgrades or additional accessory options
Wireless Communications
The Xbee will provide communications between our Base station and the Lawn mower
•Initiation of lawn mower via base station
• Current location in mower pattern to base station
•Send an alarm if tilt switch activated
•Controlled by micro controller through RS232
•300ft outdoor range
Navigational Equipment
3-Axis Compass HMC6343
•Mounted on mower
•Compass Heading
•Tilt Outputs to detect tip over
•3 axis Accelerometers
•I2C communication to Microcontroller
•Typical 2° Heading Accuracy with 1° Pitch and Roll Accuracy
•On breakout board due to size of chip
Chassis
• 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
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
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
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
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
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
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 CostPart 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 LaborTASK CURTI
SERIK 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 User’s Manual X X X X
Final Technical Manual X X X X
Final User’s Manual X X X X
Risks
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?