TEAM SOLBOT PRELIMINARY DESIGN REVIEW Martin Carbajal Mike Mellman Curtis Porter Erik Zurinskas.

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?