Page 81 - The Definitive Guide to Building Java Robots

Preston_5564C03.fm Page 62 Wednesday, October 5, 2005 7:21 AM

62 CHAPTER 3 ■ MOTION

The constructor for this class takes a JSerialPort, which builds the MiniSSC. The setMotors()
method sets parameters regarding the position and movement of the SSC. This method is
followed by move(), which calls the MiniSSC method of the same name.
The four directional methods—forward(), reverse(), pivotLeft(), and pivotRight()—have
two functions: first, to check to see if the motors are connected in an inverted fashion (like the
CubeBot), and then to set the values of the motors, and secondly, to call the move method.
While I could have just called the ssc.move(), allowing me to extend and add a speed control
later, I could not have reused the method for later subclasses. However, if you don’t want speed
control, you can simplify this by just inserting the move positions directly in each of the four
directional methods.
The setters and accessor methods are included so classes can access the state variables of
right and left for the subclass TimedDiffDrive. Finally, in main() I test the class by sending the
robot forward for 2 seconds, and then stopping. (See Example 3-6.)

Example 3-6. BasicDiffDrive.java
package com.scottpreston.javarobot.chapter3;

import com.scottpreston.javarobot.chapter2.JSerialPort;
import com.scottpreston.javarobot.chapter2.SingleSerialPort;
import com.scottpreston.javarobot.chapter2.Utils;

public class BasicDiffDrive {

// drive will use MiniSSC
private MiniSsc ssc;

// left wheel hooked to pin 0
public static final int LEFT_WHEEL = 0;
// right wheel hooked to pin 1
public static final int RIGHT_WHEEL = 1;
// set all to neutral values
private int right = SSCProtocol.NEUTRAL;;
private int left = SSCProtocol.NEUTRAL;
private int rightHigh = SSCProtocol.MAX;
private int rightLow = SSCProtocol.MIN;
private int leftHigh = SSCProtocol.MAX;
private int leftLow = SSCProtocol.MIN;

// right will always be the one inverted can change this
private boolean motorsInverted = false;

// constructor takes JSerialPort
public BasicDiffDrive(JSerialPort serialPort) throws Exception {
// create MiniSSC
ssc = new MiniSsc(serialPort);
}