Page 78 - The Definitive Guide to Building Java Robots

Preston_5564C03.fm Page 59 Wednesday, October 5, 2005 7:21 AM

CHAPTER 3 ■ MOTION 59

// move from position 0 to 255, 5 per 100 ms
for (int pos = 0; pos < 255; pos = pos + 5) {
// move
ssc.move(0, pos);
// wait 100 milliseconds
Utils.pause(100);
}
// close serial port
sPort.close();
} catch (Exception e) {
// print stack trace and exit
e.printStackTrace();
System.exit(1);
}
}

}

Section Summary
In this section, we showed a difficult way and an easy way to model a servo controller. We also
added an interface to ensure communication for different controllers and added an implementa-
tion for the MiniSSC-II. The classes discussed were the following:

• SerialSsc.java: A serial version of servo control (an example of a hard way)
• SSCProtocol.java: An interface designed to standardize communication to a servo
controller

• SSC.java: Super-class used by the MiniSSC and other classes for servo communication
• MiniSSC.java: Implementation class for the Scott Edwards MiniSSC-II

Now that you know how to control servos with your PC, you’re ready to get a robot to move.
In the next section, I’ll talk about differential drive robots (with two wheels) and there I’ll use
the MiniSSC and your PC’s serial port to make it move.

3.2 Wheeled Motion

Using a servo controller connected to an electronic speed controller or a pair of “hacked” or
continuous rotation servos is an excellent way to facilitate wheeled motion. Figure 3-5 shows a
picture of the differential drive of a CubeBot connected to a MiniSSC-II. Notice that the servo
wires are to the rear of the platform. This means the motors are inverted, so I’ll have to account
for this in the classes in this section.

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