Building Robots with NXT and LEJOS. Introduc<on. What is the NXT Robot Michael Wooldridge liv.ac.uk)

Transcription

1 Building Robots with NXT and LEJOS Introduc<on Michael Wooldridge liv.ac.uk) What is the NXT Robot Pla@orm? A simple, cheap, well supported pla6orm for experimental robo;cs, manufactured by LEGO Comes with a collec;on of LEGO- manufactured sensors and actuators, and has a number of third party sensors & actuators available The brain is the NXT brick 1

2 The NXT Brick The NXT Brick 2

3 The NXT Brick 3 ports for actuators (named A to C) Mainly used for motors 4 ports for sensors (named 1 to 4) connected via RJ12 (phone- like) connector Touch sensors, colour sensors, LCD display panel (monochrome, 100x64 resolu;on) Programs can write to this panel at pixel level 4 Input buwons (lex, right, enter, escape) USB port Mainly used for downloading programs to the brick Bluetooth connec;on Allows robots to communicate with each other The NXT Brick The brick is a bawery- powered computer, specifically intended for robot control 32- bit ARM7 processor, running at 48MHz 256 Kbytes non- vola;le flash storage mainly used for storing programs 64 Kbytes RAM run;me memory 3

4 Ultrasonic Sensors Essen;ally sonars Used to find the distance to obstacles Work by transmidng ultrasonic signal, and ;ming how long it takes for the signal to get back Works up to about 255cm, precision of ±3 cen;meters!!caution!! Ultrasonic sensors interfere with each other, if others are using ultrasonics nearby, your robot might get confused Colour Sensors Can be used to iden;fy the colour of objects immediately in front of them Simplest use is to detect colour patches (eg tracks) immediately underneath the robot Mainly good for red, green, blue, white, black 4

5 Touch Sensors Detect sensor being pressed Usually used to make bumpers for forward colision detec;on, and on other sides to detect other vehicles driving into us Return a boolean value, True = depressed False = not depressed If we want many touch sensors, we can use a mul-plexer Servomotors The basic actuators we will use Not simply on/off motors, but servo motors Allow precise posi;oning of motors, fine degree of control of rota;on Surprisingly powerful, with sophis;cated gear mechanism Simplest use is to connect to wheels and use for locomo;on More sophis;cated uses include: Building robot arms Controlling ultrasonic sensor to give 360 coverage 5

6 Standard Configura<on Robot For most of the course, we will use robots in a standard configura;on Sensors Port 1 ultrasonic (facing forward) Port 2 colour sensor (at rear) Port 3 - empty Port 4 touch sensor (front bumper) Standard Robot Configura<on Robot with caterpillar tracks Output port A right motor (i.e., right from robot s perspec;ve) Output port B lex motor Output ports C,D - - empty 6

7 21/10/2011 Standard Configua<on Robot Standard Configura<on Robot Front-facing Ultrasonic sensor Front bumper Touch sensor motors on left and right 7

8 21/10/2011 Standard Configura<on Robot ground facing colour sensor at rear Programming NXT Robots: The Default Programming Environments Our of the box, NXT bricks come with a LEGO- provided opera;ng system Programs are developed on a PC with a graphical development environment, and downloaded to the robot via USB This development approach is good for small children, wimps, and wusses 8

9 LEJOS LEJOS provides an alterna;ve opera;ng system for NXT robots An implementa;on of the JAVA virtual machine for NXT Not all Java language features supported! Not all Java classes supported! The LEJOS environment provides a much richer, object- oriented development environment Special classes provide interface for sensors and actuators Main drawbacks: limited onboard RAM, limited onboard flash memory for storing programs (JAVA not renowned for being compact) LEJOS Development Cycle 1. Develop code on your PC (using eg Eclipse) 2. Compile & link 3. Download linked binary (.nxj) to robot via USB 4. Run Main problem: debugging problem code on robots is hard very limited UI, oxen no feedback on what problem is. 9

10 HelloWorld.java import lejos.nxt.*; public class HelloWorld { public static void main (String[] args) { System.out.println("Hello World"); Button.waitForPress(); import lejos.nxt.*; Makes all the LEJOS classes available by default 10

11 public class HelloWorld Just as in regular Java, LEJOS development is based on OO principles So, the program is built from a set of classes public static void main (String[] args) Just like regular Java, LEJOS needs a class that contains a method called main This method must be declared public static void With arguments as indicated 11

12 System.out.println("Hello World"); Button.waitForPress(); If our main( ) method just contained the println( ) statement, then the text would print, but then the program would terminate and the LCD panel would revert to the default text would disappear Button.waitForPress() causes the program to suspend un;l a buwon (any buwon) is pressed. Using Motors: The NXTMotor Class import lejos.nxt.*; import java.lang.*; // for Thread public class ProgOne { public static void main (String[] args) throws Exception { NXTMotor MA = new NXTMotor(MotorPort.A); NXTMotor MB = new NXTMotor(MotorPort.B); MA.setPower(100); //power to 100% MB.setPower(100); Thread.sleep(2000); // suspend for 2 seconds MA.stop(); // stop MB.stop(); 12

13 Variables No;ce that we have completely standard Java variable declara;ons: NXTMotor MA = new NXTMotor(MotorPort.A); NXTMotor MB = new NXTMotor(MotorPort.B); Here, MA and MB are just standard (object) variables Can use int, float, etc The NXTMotor Class Class constructor takes a single argument, which must be one of the constants A, B, or C defined in the MotorPort class Other methods (actually from BaseMotor interface, which NXTMotor implements): forward() backward() flt() stop() ismoving() setpower(int p) int getpower() motor forward motor backwards cuts power to motor, which floats to a halt stops the motor (not the same as flt!) returns true if motor is in mo;on set power of motor (0 <= p <= 100) get power of motor (returns value in range ) 13

14 Using Sensors: The TouchSensor Class import lejos.nxt.*; Import java.lang.*; public class ProgTwo { public static void main (String[] args) throws Exception { NXTMotor MA = new NXTMotor(MotorPort.A); NXTMotor MB = new NXTMotor(MotorPort.B); TouchSensor T = new TouchSensor(SensorPort.S4); MA.setPower(100); // go! MB.setPower(100); while(! T.isPressed()) { Thread.sleep(200); MA.stop(); MB.stop(); // motors will keep running! Using Sensors: The TouchSensor Class The TouchSensor class has a very simple interface! Provides one method: boolean ispressed() 14

15 Using Sensors: The UltrasonicSensor Class import lejos.nxt.*; Import java.lang.*; public class ProgThree { public static void main (String[] args) throws Exception { NXTMotor MA = new NXTMotor(MotorPort.A); NXTMotor MB = new NXTMotor(MotorPort.B); UltrasonicSensor us = new UltrasonicSensor(SensorPort.S1); MA.setPower(100); MB.setPower(100); while(!(us.getrange() < 20) ) { // 20cm threshold Thread.sleep(200); MA.stop(); MB.stop(); Using Sensors: The ColorSensorHT Class import lejos.nxt.*; import lejos.nxt.addon.colorsensorht; public class ProgFour { public static void main(string[] args) throws Exception{ ColorSensorHT cs = new ColorSensorHT(SensorPort.S2); while(!button.escape.ispressed() ) { LCD.clear(); LCD.drawString("ID = "+cs.getcolorid(),0,2); Thread.sleep(500); 15

16 WARNING: you ll have to do your own calibration! 0 = black 1 = violet 2 = purple 3 = blue 4 = green 5 = lime getcolorid() 6 = yellow 7 = orange 8 = red 9 = crimson 10 = magenta 11 to 16 = pastels 17 = white WARNING: you ll have to do your own calibration! LEJOS at the Command Line Three main tools: nxjc the LEJOS Java compiler nxjlink the LEJOS linker nxjupload uploads files to NXT brick 16

17 nxjc The LEJOS Java Compiler The LEJOS replacement for javac Takes as input a.java file Produces as output a.class file nxjc ProgFour.java nxjlink The LEJOS Linker Normally in JAVA, linking is done dynamically, when you run the JAVA interpreter/virtual machine over your.class file (Standard JAVA is dynamically linked: referenced classes are loaded, as needed at run -me. This doesn t work on NXT because of lack of memory on the brick. Classes are sta-cally linked, i.e., linked at compile ;me.) [mjw@mjw-imac]$ nxjlink ProgFour -o ProgFour.nxj [mjw@mjw-imac]$ 17

18 nxjupload Uploading Files to the NXT Brick Will try USB and Bluetooth Make sure brick is switched on and showing main menu nxjupload ProgFour.nxj Found NXT: NXT lejos NXJ> Connected to NXT lejos NXJ> Upload successful in 997 milliseconds 18