SSP ROBOT DESIGN A. DEAN 11/29/05 LAB: ROBOT OBJECTS IN LEJOS

Transcription

1 SSP ROBOT DESIGN A. DEAN 11/29/05 LAB: ROBOT OBJECTS IN LEJOS As we saw in class last Tuesday (well, as at least a few of us saw the rest should check the web for the slides), everything in Java is based on objects. A quick review before you start the lab: An object has both data and methods (functions), sometimes one but not the other. An object must first be defined. This is what the class structure does. So each program we write is actually considered an object. Some objects have been predefined in a Java or lejos library that we import at the beginning of our program. For us the most important library is josx.platform.rcx, which contains all the robot object classes, but there are two others we may also use, java.lang (for math functions and other stuff) and java.util (for random numbers and other stuff). The predefined robot objects include the motors, the various sensors, the buttons on the RCX (except for the on/off button), and the LCD display on the RCX. In this lab you ll focus on the motor and sensor objects. PART 0 STARTING UP For this lab you will need your TankBot, and you ll be using both JCreator and the web, so please start up JCreator and Internet Explorer. You should also open a browser window, in which you should open your folder on Datastor. Create a new folder in there named lejos_programs. PART 1 THE Motor OBJECT 1. In Internet Explorer, open the website (From the SourceForge website: SourceForge.net is the world's largest Open Source software development web site, hosting more than 100,000 projects and over 1,000,000 registered users. ). 2. The website you ve opened is the home page for lejos. On the left are nine yellow buttons click the one named API (an acronym for Application Programming Interface). This brings you to a page where you can find all the predefined objects in lejos, and descriptions of their data and methods. 3. In the lower left window, scroll down and click on Motor. The large right-hand window now displays information and examples about the Motor class. As you scroll down this window, you see a short table named Field Summary, which gives the names of the three specific motor objects, A, B, and C. Below that is the table Method Summary, which lists all the methods (functions) that can be used by the Motor object. Finally, beneath these two tables are detailed descriptions of both the fields and each of the methods. 4. We want to create a new Java program, to try out using the Motor object, but here s a simpler way than creating (or finding) a workspace and project, as we did in the last Page 1 of 5

2 lejos lab. Check that the File View window on the upper left says No workspace loaded. If a workspace is loaded, then go to the File menu and select Close All Workspaces. 5. Now select File-New File, and a window will come up. For the name, enter MotorFunctions. For the location, click on the button at the right and find the folder you created in Part 0, named lejos_programs. Click Finish, and JCreator will set up a default workspace and open an editing window for your program. 6. Recall that every Java program must contain a class with the same name as the file. Type in the following code, remembering that when you type a left curly bracket, JCreator automatically types the right for you. After you type it in, use tool number 1 to compile it so you know there are no errors. Don t use tool #2 to download it yet: import josx.platform.rcx.*; public class MotorFunctions public static void main(string[] args) 7. We are going to add some void functions to make the robot move in different directions, as a way of seeing how to use some of the Motor class methods. Underneath the main function, but still inside the class MotorFunctions, add the following void function. Again, compile using tool #1: public static void goforward(int msecs) Motor.A.forward(); Motor.C.forward(); Thread.sleep(msecs); Note: The Thread.sleep() method requires any function that uses it, directly or indirectly, to throw and interrupted exception. Page 2 of 5

3 8. Finally, add the following single line to main: goforward(2500); Then compile and download the function. Your robot should go forward for 2.5 seconds, because the units for the Thread.sleep() method are in milliseconds. 9. Add a function gobackward(), similar to goforward() (feel free to copy and paste!), and modify the main function so that the robot goes forward for 3.2 seconds and backwards for 2.3 seconds. Look in the API for the Motor methods that you need to do this. By the way, you can use motors without using void functions by simply typing commands such as Motor.A.forward() directly into the main function. I wanted you to see the use of void functions in Java, as well as trying out the Motor class. PART 2 The Sensor Object: using a touch sensor 1. In Internet Explorer, scroll down the left window to Sensor, and then look over the information that comes up in the main window. The first thing you may notice is that, just as Motor has fields A, B, and C, the object Sensor has fields S1, S2, and S3. Using sensors is more complicated than using motors, and using sensors in lejos is more complicated than using sensors in NQC, so we ll learn about them in stages. Now look at the class SensorConstants, which contains the constants we ll need to set type and mode. 2. Without closing your MotorFunctions program, create a new program named TouchSensor, typing in the basic shell much as in step 6 of Part 1. Feel free to copy and paste from the other program, by clicking its tab at the top of the editing screen, but be sure to change the name. 3. As in NQC, we must set the type and mode of a sensor before we can use it. In order to use the SensorConstant names, you must modify the name of your program as follows: public class TouchSensor implements SensorConstants Inside the main function type the following lines, which configure sensor 1 as a touch sensor in bool mode (i.e., 0 or 1). Compile and run it to test it: Page 3 of 5

4 Sensor.S1.setTypeAndMode (SENSOR_TYPE_TOUCH, SENSOR_MODE_BOOL); while (true) int val = Sensor.S1.readValue(); if (val == 1) Sound.beepSequence(); else if (val == 0) Sound.buzz(); else Sound.twoBeeps(); //Wait a second before checking sensor again Thread.sleep(1000); 4. Now change the sensor mode to RAW. Recall that the range of raw mode is 0 to 1023 with lower numbers corresponding to harder press than higher numbers. See if you can modify the program so it can use the sounds to distinguish between no touch, medium touch, and hard touch. (For me, using 50 for hard, between 50 and 300 for medium, and above 300 for no touch, worked pretty well.) PART 3 The Sensor Object: using a light sensor 1. Now create another new file named LightSensor, and type in the following code, which is quite similar to the code in TouchSensor, but with at least one important difference. If you cut and paste, be sure to make all the appropriate changes: Page 4 of 5

5 import josx.platform.rcx.*; public class LightSensor implements SensorConstants public static void main(string[] args) Sensor.S2.setTypeAndMode (SENSOR_TYPE_LIGHT, SENSOR_MODE_PCT); Sensor.S2.activate(); while (true) int val = Sensor.S2.readValue(); if (val >= 40) Sound.beepSequence(); else Sound.buzz(); //Wait a second before checking sensor again Thread.sleep(1000); 2. This program uses a touch sensor on port 2, in percent mode (values from 0 to 100, with 0 dark and 100 bright). Note the extra line: Sensor.S2.activate(); Unlike the touch sensor, the light sensor requires electricity to operate, since it emits light and measures the reflected light to detect bright and dark. Compile and run this program. PART 4 PUTTING IT ALL TOGETHER If time permits, do the following exercises, which use both the sensors and the motors. 1. Write a program LineFollower, that does just that, using a light sensor. 2. Write a program that goes forward unless the robot runs into a wall, in which case it backs up, makes a left turn and goes forward again. That s plenty for today! Page 5 of 5