dlife.robot
Class Controller

java.lang.Object
  dlife.robot.Controller

Direct Known Subclasses:

FiniteStateController, SimpleWorldRobotController, SubsumptionController

public abstract class Controller
extends Object

Base class for controlling robots within the ControlCenter.

To control a robot (physical or simulated) you will create a sub-class of Controller. The Controller class is an abstract class that specifies three methods:

• startUp(Robot): The startUp method is invoked when the "Start Up" button in the ControlCenter is clicked and performs all of the initialization for the Robot. This method's main job is to create instances of the sensors and effectors that will be used to control the robot.
• step(): The step method is invoked over and over again by the ControlCenter after the "Run" button is clicked. Clicking the "Step" button will invoke the step method exactly once for each click. The step method will typically check the robot's sensors, decide on an action to take and issue commands to the robot's effectors.
• shutDown(): The shutDown method is invoked when the "Shut Down" button is clicked in the ControlCenter. The abstract Controller class provides an empty definition of this method which is sufficient for most sub-classes.

In addition, Controller sub-classes are required to have a no-arg (default) constructor in order to be used with the ControlCenter. Very typically this is accomplished by not defining any constructors in a Controller sub-class. Note: if you do not define any constructors in a class, Java automatically provides an empty default constructor. Controller sub-classes usually do not require the explicit definition of a constructor because all initialization can (and should) be done in the startUp(Robot) method.

Below is an example of a very simple Controller that moves a Hemisson robot forward until it detects an obstacle, at which point it simply stops.

 public class SimpleController extends Controller {
 
     private HemissonProximitySensor hps;
     private HemissonDifferentialDrive hdd;
 
     public void startUp(Robot robot) {
         // Create and add a ProximitySensor to the robot.
         hps = new HemissonProximitySensor();
         robot.addSensor(hps);
 
         // Create and add a DifferentialDrive to the robot.
         hdd = new HemissonDifferentialDrive();
         robot.addEffector(hdd);
     }
 
     public void step() {
         // Find the largest of the front 3 proximity sensor readings.
         // Larger readings indicate closer obstacles.
         int maxFront = hps.getMaximum(HemissonProximitySensor.FRONT_GROUP);
 
         // If there is no obstacle move forward, else stop.
         if (maxFront < 15) {
             hdd.translate(0.5); // forward at half speed.
         }
         else {
             hdd.translate(0); // stop.
         }
     }
 }
 

Additional sample controllers can be found in the robot sub-packages of the examples package. Studying a few of these examples is a good way to get started. A few that make particularly good starting points are:

• HemissonApproach
• HemiWander

Version:

Apr 24, 2007

Author:

Grant Braught, Dickinson College

Constructor Summary

Controller()

Method Summary

void	shutDown() This method is invoked when the Shut Down button in the ControlCenter is clicked.
abstract void	startUp(Robot robot) This method is invoked automatically when the Start Up button in the ContolCenter is clicked.
abstract void	step() This method is invoked either once when the Step button is clicked or periodically when the Run button is clicked.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Controller

public Controller()

Method Detail

startUp

public abstract void startUp(Robot robot)

This method is invoked automatically when the Start Up button in the ContolCenter is clicked. This is typically where Sensors and Effectors are created and added to the Robot.

Parameters:

robot - the Robot that this Controller will be controlling.

step

public abstract void step()

This method is invoked either once when the Step button is clicked or periodically when the Run button is clicked. The rate at which step is invoked varies from Robot to Robot and is dependent on the computer being used as well as the amount of processing done in step, the number and type of sensors attached to the Robot and the robot's communication latency.

shutDown

public void shutDown()

This method is invoked when the Shut Down button in the ControlCenter is clicked. The default implementation of this method is empty.