Page 122 - The Definitive Guide to Building Java Robots

Preston_5564C03.fm Page 103 Wednesday, October 5, 2005 7:21 AM

CHAPTER 3 ■ MOTION 103

// move leg backward
public String backward() {
return LM32.createCmd(horzServo.pin,horzServo.min,LM32.DEFAULT_SPEED);
}
// reset horz servo
public String neutralHorz() {
return LM32.createCmd(horzServo.pin,horzServo.neutral,LM32.DEFAULT_SPEED);
}

// reset vert servo
public String neutralVert(){
return LM32.createCmd(vertServo.pin,vertServo.neutral,LM32.DEFAULT_SPEED);
}

// reset both servos
public String neutral() {
return neutralVert() + neutralHorz();
}

}
The Hexapod class has as fields the LM32 as the worker class and six legs defined as
BasicLegs. I also defined two leg groups as ArrayList. Because of the gait I chose, I’ll move three
legs simultaneously. By placing them in a list, I can move all legs in this group with a single
command.
The fields UP, DOWN, and so on are enumerations. The int speed is the speed variable,
and MAX_SPEED represents what the minimum time should be for the group move of three legs.
The constructor takes, you guessed it, the JSerialPort and calls two methods init() and
setLegGroups(). The init method creates all leg positions for the six BasicLegs. The setLegGroups
method adds these to legGroup1 and legGroup2.
The forward() gait is a combination of eight separate commands. The gait commands are
created via the getTotalMove() method which comprises a StringBuffer. The method operates
by iterating through all the legs and (depending on the command) returns the string from the
BasicLeg.motion() method. This is repeated until all the legs are done. Then the group move is
executed in the time specified via the getSpeedInMs() method.
The getSpeedInMs() method uses an inverse relationship between the time of the leg
move and the speed. This is so that 10 is still fast and 1 is still slow. For example: the speed of
the robot at speed 10 is 2500 – 2500 + 250 milliseconds per move of a leg group, and at a speed
of 1 the speed of the robot is 2500 – 250 + 250 = 2500 milliseconds per leg.
In the forward() method with a millisecond parameter, it loops through calling forward
until the time is up. This is all a function of the speed of the robot and it even throws an exception
if the requested move time is less than the minimum time. (See Example 3-20.)