Como Hacer Un Micromouse

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    AbstractThe IEEE micromouse competition has been apopular event among engineering students and engineers. A

    micromouse is an autonomous vehicle whose objective is tofind the center of a 16 by 16 cell maze within 10 minutes.After exploring the maze for some time, the micromouse willattempt to make its fastest run from the starting point to thedestination cells. This report summarizes the design and

    implementation of the MightyMouse project for the spring andfall semesters of 2005. The design method of theMightyMouse project consisted of two stages. The first stage

    was to design and construct individual components. Thesecond stage of the design process was to interface thecomponents to form the final prototype. The individualcomponents of micromouse system consist of the motorcontrol system, navigation sensor array, digital compass fordetecting orientation, and a mapping system for navigating the

    maze intelligently. A test plan was developed in order tovalidate the overall performance of the micromouse. A lifeproduct life cycle and reliability reports have also been writtenin hopes to encourage and aid future micromouse teams.

    Index Termsmicromouse, autonomous, maze, IEEE

    competition

    I. INTRODUCTION

    HE micromouse is an autonomous vehicle whose goal is

    to find the center of a maze. The official IEEE

    Micromouse Competitions began in 1987 at the World

    Micromouse Competition, where David Otten of MIT

    captured first and second place with his MITEE Mouse. This

    competition used a new scoring system design to reward

    intelligence, efficiency, and self reliance. Micromouse

    competitions have become a popular event among engineering

    students and engineers.

    II. PROJECT DESCRIPTION

    A. Problem StatementDesign and construction of a micromouse requires a broad

    range of engineering skills. This combined with an open

    design process makes the micromouse project a very practical

    Manuscript received December 12, 2005. This senior design project was

    sponsored by Dr. Herb Hess of the Electrical Engineering Department,

    University of Idaho.

    and challenging senior design project.

    1) Objectives: The primary objective of this project is to

    build an autonomous vehicle, a micromouse, according to

    IEEE specifications which is able to navigate to the center of a

    maze. A secondary objective is to design a full size maze also

    in accordance to IEEE specifications.

    2) Constraints: Constraints for the micromouse come fromregulatory competition rules. The mouse size, time allowedto solve the maze, methods for solving the maze, and amonetary limit placed on the final prototype are all constraints

    imposed by IEEE competition rules.a) Size: The mouse is can be no larger than 25cm

    square.b) Time Limit to solve maze: During a IEEE

    competition the micromouse has 10 minutes to solve

    the maze and complete the run.c) Battery life: The batteries must supply power to the

    micromouse for at least 10 minutes.d) Micromouse expenses: The total cost for Micromouse

    must not exceed $500.e) Maze: The maze consists of 16 x 16 cells; each cell is

    18 cm square. The southwest corner is the startingcell. The four center cells are the destination.

    B. Solution Method1) Brief Description: There are two fundamental phases to

    our design process. The first phase was to design individual

    components of the micromouse and get them to operate

    according to individual specifications independent of one

    another. The second phase was to interface the individual

    components and have the micromouse operate as one

    autonomous unit. The first semester of the Senior Design

    course was dedicated to working on the individual

    components. The goal of the second semester was to integrate

    the individual components. The individual working

    components include the navigation sensor array, mappingalgorithm, distance and bearing devices, motor control, and

    chassis design

    An effective micromouse design must perform the

    following functions in order to find the center of a maze

    a) Recognize walls and openingsb) Stay centered within each cellc) Know position and bearing within the mazed) Control the distance needed to travele) Make precise 45 and 90 turns

    MightyMouse: An Autonomous Maze SolvingRobot

    Kelly Ridge, Sanjeev Giri, Peter Shaw, Jason Flynn

    T

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    f) Perform mechanicallyg) Navigate the maze intelligently

    2) Overview of Micromouse functions: The mouse mustrecognize walls and openings in order to navigate the mazeand prevent crashes. The navigation sensor array provides the

    mouse with this information. The navigation sensor arrayconsists of a combination of four short-range and two long-

    range infrared sensors.The mouse must stay centered within the maze to prevent

    compounding errors in distance and position calculations. Adigital compass determines if the deviates from its desiredbearing. This information is sent to the motor control systemto make proper corrections, either speeding up or slowingdown one wheel.

    The motor control portion of the project is responsible forsafely moving the micromouse through the maze. There aretwo maximum speeds, one for the mapping portion of thecompetition and one for the racing portion of the competition.

    The motor control code is given a distance to travel as input.It is then the responsibility of the motor control to accelerate

    and decelerate the mouse during travel. The rate ofacceleration is fixed based upon the traction of the wheels onthe maze surface.

    In order to ensure that the mouse is not slipping, the motorsare controlled with PI feedback. The shaft encoders (built intothe motors) read in the speed of the wheels and send this datato the motor control code that adjusts the speed of each wheel

    accordingly.The mouse must keep track of position and bearing during

    each run to provide navigation information to the mappingsystem. The shaft encoders that are built in to the motorsmonitor the distance the micromouse travels. The electronic

    compass determines which direction the micromouse is facing.

    The combination of these two systems provides the dataneeded by the mapping and navigation systems.To move efficiently through the maze the micromouse must

    be able to make precise 90 turns. The digital compass ispolled during turns to provide control feedback to the motorsand navigation systems.

    The mechanical soundness of the micromouse design is animportant factor. The chassis needs to keep the systems stable

    during operation so accurate data is recorded. The chassisalso keeps the drive train in line in order to reduce the numberof path corrections made.

    To successfully and efficiently solve the maze the mouse

    must make intelligent navigation decisions based on its

    current position. The mapping system utilizes a modifiedflood-fill algorithm to determine the best solution as the mazeis discovered.

    C. Component Descriptions1) Sharp GP2D Sensor Array: The short-range sensor array

    consisting of two Sharp GP2D120 infrared sensors is

    interfaced to the microcontroller and can determine whenthere is an opening to the left or the right of the mouse.

    These sensors are positioned so that the angle of incidencewith a sidewall is 90 degrees. The side sensors crossfire

    across the body of the mouse thus keeping the sensors outside

    the minimum firing range of 4cm. The side sensors aremounted directly to main circuit board of the mouse.

    The long-range sensor array, consisting of two SharpGP2D12 infrared sensors, determines walls in front of or

    behind the mouse and outputs their approximate distances.The long-range sensors cross-fired across the length of themicromouse preventing the sensors from exceeding the

    minimum sensing range of 10cm.

    Fig.1 Navigation Sensor Array

    2) Devantech Digital Compass: The Devantech electroniccompass is interfaced to the microcontroller via an I2Cinterface. It returns values between 0 and 255 indicating itsrotational orientation. A one-time calibration is performed

    that improves accuracy when the compass is moved to newlatitude.

    The compass experiences strong electromagneticinterference when it is in close proximity to the DC motors.

    The minimum distance required to yield accurate readings isapproximately three inches. The compass is also most

    accurate when it is positioned horizontal to the ground. Theseconstraints forced the compass to be mounted on a pole wellabove the rest of the micromouse.

    3) Mapping System: The mapping system solves a full

    16x16 maze using input from the sensor array, shaft encoders,

    and digital compass. The modified flood filled algorithm used

    to solve the maze is explained in detail in the method of

    solution section for the Mapping System.

    4) Motor Drive System: The motor drive system consists oftwo DC motors with built in shaft encoders that are poweredby two monolithic H-bridge ICs. The ICs contains all of the

    free-wheel diodes and power transistors necessary for drivingthe motors. Also, the input to the ICs is CMOS and TTL

    compatible. These properties allow us to minimize the size ofthe circuitry necessary to power the mouse.

    The Zilog project for controlling the H-bridge also

    incorporates the shaft encoders, I2C compass, and the serialHyperTerminal output. This integration was done to helpensure that the code for controlling the motors will notinterfere with these other functions.

    The built in shaft encoders are 16 count and output a square

    wave. These magnetic encoders rely on hall-effect sensorsand are used for indication and control of both, shaft velocity

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    and direction of rotation as well as for positioning. The

    encoders provide the feedback for the motor drive system.

    6) Chassis: The final prototype chassis was made out ofcarbon fiber. This allowed the chassis to be strong and rigidbut also lightweight. The chassis has a skid-plate design withmotor mounts incorporated into the carbon fiber.

    7) Maze: The final maze design involved creating a mazethat was transportable as well as one that would last, thus

    providing a solid testing and competition platform for futuremicromouse projects. The maze base consists of 4-5x5 ft

    interlocking pieces of inch ACX plywood. The walls werecut into 18cm long by 3cm high strips from 12mm thickplywood. The walls come in four different configurations:perimeter, double-post, single-post, and no-post. The wallsides were painted white and the tops red. The base was

    painted flat black. Paint colors are specified by IEEEmicromouse competition rules.

    D. Method of Solution

    Fig.2 MightyMouse

    1) Sharp GP2D Sensor Array: The Sharp GP2D InfraredSensors consist of an LED emitter and receiver and can be

    used to determine the distance to an object based on the angleof reflected light. The sensors are insensitive to ambient lightand are reliable in detecting the reflected LED beam on anumber of different surfaces varying in both color and sheen.The sensors have an analog voltage output that corresponds to

    the measured distance. These analog outputs are sampled bythe onboard Analog to Digital Converters of the Zilogmicrocontroller, providing a digital value that can be used forrange calculations. Drawbacks of the GP2D sensors are that

    the relationship between the actual ranges and the A/Dconverted values is nonlinear and there are also slightdifferences in the outputs between sensors.

    The Sharp GP2D120 short-range sensors had to benormalized in order to ensure accurate and repeatable readings

    from all four sensors. To normalize the short-range sensors,20 readings were taken at each centimeter within themanufacturer specified range (4-30 cm) and then the readingsfrom each sensor at each range were averaged. A plot of these

    A/D readings vs. the range produces a nonlinear curve (dataand graph available in Appendix C). This means that a largechange in the A/D value did not necessarily correspond to a

    large change in range. For the micromouse to make decisions

    based on sensor input there must be a direct correlationbetween the A/D value and the actual range. To find thiscorrelation a linear regression was performed on the averagedshort-range sensor data producing an equation relating the

    A/D value to actual range.The function of the short-range sensors is to determine side

    openings. The short-range sensors are continuously sampled

    by the A/D converter to determine side openings. Taking intoaccount that the side sensors crossfire across the body of the

    mouse: to still be able to determine an opening, the mousewould have to read a range value greater than approximately18 cm (corresponding to an A/D value of 323).

    The function of the long-range sensors is to determine the

    mouses proximity to front and rear walls. This information isuseful in mapping the maze as well as providing the motorcontrol algorithm with information on deceleration to avoidfront and rear crashes.

    Regression data from the manufacturers website was used

    for the purposes of testing the Sharp GP2D12 long-rangesensors. Data was taken to find linearization equations for

    each long-range sensor in order to increase the absoluteaccuracy of their readings.

    The navigation sensors act as the eyes of the mouse. Theyprovide the mouse with topographical information of themaze. The mapping algorithm relies on the sensors todetermine openings and walls in order to map the maze andmake decisions on the best path to the center. The long-range

    sensors also provide the motor control algorithm withinformation on front and rear walls in order to avoid crashes.

    2) Devantech Digital Compass: The electronic compasshelps the micromouse keep its bearings while navigating the

    maze. Our micromouse design will use the compass moduleto make accurate 45 and 90 degree turns as well as to ensure

    that the micromouse travels in a straight lineThe compass uses two Philips KMZ51 magnetic fieldsensors to detect the earths magnetic field. The sensors are

    sampled by a PIC microcontroller and supporting circuitrywhich compute the compass direction and provides aninterface to the host Zilog system. The compass modulerequires a 5V supply at a nominal 15mA and provides data via

    two output methods, I2C and a PWM signal.

    Fig.3 Devantech Digital Compass Pin Out

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    Pin 9 must be connected to the ground bus of the host

    microcontroller

    Pin 1 must be connected to a 5V supply

    Pin 7is an input to select either a 50Hz (low) or a 60Hz(high) operating environment. This is used to reduce outputjitter caused by the mains power supply frequency. The

    compass module has an onboard pull-up resistor and pin 7 canbe left floating for a 60Hz (U.S.) operating environment.

    Pin 4 is the PWM output, which is not used in ourimplementation. It has in onboard pull-up resistor and can be

    left floating.

    Pin 6enables a calibration mode, which is also available viathe I2C bus. It has in onboard pull-up resistor and can be leftfloating.

    Pin 2 & 3 provide an I2C bus capable of communication at

    up to 1 MHz. Pull-up resistors of approximately 2 K arerequired on both...