TEAM SOLBOT PRELIMINARY DESIGN REVIEW Martin 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 RS ft 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 = µ k x N  µ k 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 Cost PartVendorPrice (USD) MicrocontrollerDigikey.com$6.60 XbeeSparkfun.com$45.90 CompassSparkfun.com$ ChassisRetrofit existing modelFree WheelsTBD$50 Wheel EncodersSparkfun.com$30 Drive MotorsTBD~$100 Mower MotorTBD~$50 Mower BatteriesBatteryjunction.com$14 * 10 = $140 Base Station BatteryDonationFree Solar PanelSiliconsolar.com$ Misc. ComponentsEE store / Sparkfun.com$100 PC BoardsTBD~$100 TOTAL$902.40

Division of Labor TASKCURTISERIKMARTINMIKE Hardware Frame retrofitXX Motor ControlXX Power system designXX RF Communication designXX PCB LayoutXXXX Electronics mounting/solderingXXXX Software Microcontroller path controlXX Communication codingXX Memory managementXX System testingXXXX Documentation Preliminary User’s ManualXXXX Final Technical ManualXXXX Final User’s ManualXXXX

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

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