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

Project Description Review  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  Low power for a wireless/remote system  Zigbee/RF optimized  AD converter for input/output control  Code Composer development environment

Compass 3-Axis Compass HMC6343  Mounted on microcontroller PCB  I2C communication to microcontroller at pins 30 and 31  Outputs 3 bytes of data: heading, pitch, and roll  Typical 2° Heading Accuracy with 1° Pitch and Roll Accuracy  On breakout board due to size of chip

Compass Functionality

Wireless Communications  The Xbee will provide communications between our computer and the lawn mower  Initiation of lawn mower via computer  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  Sending to microcontroller through RS232 ASCII characters at a baud rate of 9600bps  The Xbee module will be hooked up on pins 32 and 33 of the microcontroller  For testing with the USB to Xbee we are using X-CTU software that came with the Xbee

XBee UART Data Flow

Microcontroller UART code

Demo of Microcontroller and Xbee Communication

Software  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  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  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  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  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  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  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)  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 PartVendorPrice (USD) MicrocontrollerTI samplesFree XbeeSparkfun.com$100 CompassSparkfun.com$150 ChassisRetrofit existing modelFree WheelsTBD$50 Wheel EncodersSparkfun.com$30 Drive MotorsPittman$100 Mower MotorPittman$50 Mower BatteriesDonationFree Base Station BatteryDonationFree Solar PanelSiliconsolar.com$130 Misc. ComponentsEE store / Sparkfun.com$100 PC BoardsTBD~$100 TOTAL$810

Updated 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

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?