Page 87 - The Definitive Guide to Building Java Robots

Preston_5564C03.fm Page 68 Wednesday, October 5, 2005 7:21 AM

68 CHAPTER 3 ■ MOTION

// stop
public void stop() throws Exception;
// forward
public void forward(int ms) throws Exception;
// reverse
public void reverse(int ms) throws Exception;
// pivot right
public void pivotRight(int ms) throws Exception;
// picot left
public void pivotLeft(int ms) throws Exception;
// setting speed of robot
public void setSpeed(int speed)throws Exception ;
// get speed of robot
public int getSpeed();

}

■Note The speed will not work in a hacked servo because it’s either full on or full off. There you will have
to delay the on-off cycles of your servo to something very fast. It might be difficult getting this to work and be
smooth given our baud rate. However, it will work well for an electronic speed control (ECS), but you might
want to adjust the speed to a higher resolution than 10.

In the SpeedDiffDrive class, I implement the JMotion interface and have a single field
speed which I defaulted to 5.
The setSpeed() method is the heart of the method as it sets the high values for the servo
controller as well as the low values. So, at a speed of 10, the high value would be 255, while at a
speed of 9 it would be 255 – 13 (12.7) = 242, and so on.
At the bottom of the class, I have to implement the methods from the interface that already
exist in the super-class. Why do we need to just create pass-through? Java does not support
multiple inheritance, so the compiler only sees the BasicDiffDrive’s method for the interface
and not the TimedDiffDrive class. (See Example 3-9.)

Example 3-9. SpeedDiffDrive.java
package com.scottpreston.javarobot.chapter3;

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

public class SpeedDiffDrive extends TimedDiffDrive implements JMotion{

// set initial speed
private int speed = 5;