LEGO NXT Robot Programming Introduction to Programming a Lego NXT robot in Java

Objectives Software requirements Java Libraries Creating a Java forms application Running Java applications Creating objects and initialisation Robot navigation Using a timer The touch sensor Displaying a message box Pausing the program to enable the robot to respond The ultrasonic sensor

Software Required NetBeans Java development software – SE version is sufficient LeJOS Java robot API – PC installer – Download special firmware to the robot – Programs can run on the PC (controlling the robot) – Programs can be downloaded and run on the robot

NetBeans

Libraries required Copy libraries to folder within project: – C:\Program Files\leJOS NXJ\lib\pccomm.jar – C:\Program Files\leJOS NXJ\lib\pctools.jar – C:\Program Files\leJOS NXJ\3rdparty\lib\bluecove.jar Link to project within NetBeans – Right click project – Select Libraries category – Add Jar/Folder button

Forms Development Select controls from palette Set properties Rename variable (right click control) Attach an event handler – Double click control – Select “Create new action” – Choose a name for your event-handler – Code will be created for the method

Running a NetBeans App To run from within NetBeans – Make sure the required project is the currently highlighted one Right click project and select “Set as Main project” – Use the Green arrow on the toolbar – Or right click the project name and select “Run” – Interrupt if necessary using Run/Stop build/run from the menu To run from outside NetBeans – Use the hammer icon on the toolbar or right click project and select “Build” – This will create an executable JAR in the dist folder of the project – Double click the JAR file to run

Java Coding (General) Import external Java classes (similar to Using statements in C#) import lejos.nxt.*; import lejos.robotics.navigation.*; Instance variables – Placed at the bottom of form code: private TachoPilot pilot; DO NOT Modify auto-generated code

Initialisation and creating objects This will normally be done in the constructor The constructor already contains a lot of auto- generated code Add your code at the end Suggestion: – Write your own initialisation method – Call this from the bottom of the constructor – This means only one line needs to be added to the constructor and keeps your code separate

Auto-generated code Custom initialization method Call custom initialisation

Robot Navigation import lejos.robotics.navigation.*; Create pilot object (in initialisation method) private TachoPilot pilot; pilot = new TachoPilot(2.1f, 4.4f, Motor.A, Motor.C, true); Set speed of motion pilot.setMoveSpeed(3); pilot.setTurnSpeed(20); Move and rotate pilot.travel(-12); pilot.rotate(90); 11 The Tribot has the motors on backwards so needs negative number for distance

More Navigation Methods Methods exist to move the robot continuously: pilot.backward(); pilot.forward(); pilot.stop(); Remember if your robot has the motors on backwards then backwards will move forwards etc! It is also possible to obtain the maximum available speeds: float fMaxMoveSpeed = pilot.getMoveMaxSpeed(); float fMaxTurnSpeed = pilot.getTurnMaxSpeed();

Creating a Timer Create an instance variable private Timer touchTimer; Create a timer object, which includes the interval and an “action listener” method which is called for each timer tick touchTimer = new Timer(50, new ActionListener() { public void actionPerformed(ActionEvent e) { touchTimerTick(); } }); Start or stop the timer touchTimer.start(); touchTimer.stop();

The Touch Sensor Create an instance variable private TouchSensor touchSensor; Create the object and attach to the port touchSensor = new TouchSensor(SensorPort.S1); Check if the sensor is pressed if (touchSensor.isPressed()) …………

Simple Message Box Uses a class from the Java “Swing” library import javax.swing.JOptionPane; A simple message box JOptionPane.showMessageDialog(null, "Message"); A message box with a title and message type JOptionPane.showMessageDialog(null, "Message", "Title", JOptionPane.ERROR_MESSAGE); A variety of other message types are available

Adding a Pause Use the Thread.sleep command but requires exception handling to be added //include a 25ms delay to pick up values try { Thread.sleep(25); } catch(Exception e) { JOptionPane.showMessageDialog(null, "Error in pause"); return; }

The Ultrasonic Sensor Created in the same way as the touch sensor To obtain the value should first “ping” the sensor ultrasonicSensor.ping(); Then pause for at least a 25ms delay (see previous slide) Distance value can then be obtained iDist = ultrasonicSensor.getDistance();