Lesson 5: Keeping Track of Variables

As we get into more complicated topics and learn new things, our robot code is going to become larger and larger. Many things will be going on at once, and in order to keep our code clean and understandable, we need to have some organization. The focus of this lesson is going to be organizing all of your static number values (such as motor ports, calibration data, etc.).

Oftentimes, you will come back to a piece of code after not reading it for a while. If this code was written poorly, you may not understand how it works or what it does. In Lesson 3, you created a motor controller that took an integer value that represented the port on the roboRIO for that motor controller. It is not a good idea to simply put that number directly into the constructor because it decreases the overall quality of your code.

We can solve this problem by putting all of these values in one place. That way, we know where they are if we ever need to change them and it also makes our code cleaner. I recommend making two classes for this purpose: a Wiring class and a Calibration class. In the wiring class, we can store PWM ports, digital input ports, analog input ports, relays, etc. In the calibration class, we can store values that never change but we need to know nonetheless. (An example could be how many encoder ticks it takes to move a lift all the way from bottom to top.) You may be thinking that this sounds like ridiculous overkill, but as your code becomes larger you will lose track of where all these numbers are coming from if you don't keep them organized.

Here are the Wiring and Calibration classes from Code Red's 2015 robot code:

Wiring.java:

public class Wiring {

    /*
     * MOTOR CONTROLLERS
     */
    public static final int REAR_RIGHT_MOTOR = 0;
    public static final int FRONT_RIGHT_MOTOR = 1;
    public static final int FRONT_LEFT_MOTOR = 2;
    public static final int REAR_LEFT_MOTOR = 3;
    public static final int LIFT_MOTOR = 4;
    public static final int EXTENDER_MOTOR = 5;

    /*
     * DIO
     */
    public static final int REAR_RIGHT_ENCODER_A = 0;
    public static final int REAR_RIGHT_ENCODER_B = 1;
    public static final int FRONT_RIGHT_ENCODER_A = 2;
    public static final int FRONT_RIGHT_ENCODER_B = 3;
    public static final int FRONT_LEFT_ENCODER_A = 5;
    public static final int FRONT_LEFT_ENCODER_B = 4;
    public static final int REAR_LEFT_ENCODER_A = 7;
    public static final int REAR_LEFT_ENCODER_B = 6;
    public static final int LIFT_ENCODER_A = 8;
    public static final int LIFT_ENCODER_B = 9;

    /*
     * ANALOG INPUTS
     */
    public static final int GYRO = 0;
    public static final int EXTENDER_STRING_POT = 1;
    public static final int LIFT_LIMIT_SWITCH = 2;

    /*
     * RELAYS
     */
    public static final int RED_AND_GREEN_LEDS = 0;
    public static final int BLUE_LEDS = 1;
}

Calibration.java:

public class Calibration {

    // LIFT
    public static final double LIFT_MAX_DISTANCE = 8100;
    public static final double LIFT_MIN_DISTANCE = 200;
    public static final double LIFT_P = 0.8;
    public static final double LIFT_I = 0.0;
    public static final double LIFT_D = 0.0;

    // DRIVE
    public static final double X_DRIVE_P = -10;//-10;
    public static final double X_DRIVE_I = 0;
    public static final double X_DRIVE_D = 0;
    public static final double Y_DRIVE_P = -10;//-10;
    public static final double Y_DRIVE_I = 0;
    public static final double Y_DRIVE_D = 0;
    public static final double ROT_DRIVE_P = 0;//3;
    public static final double ROT_DRIVE_I = 0;
    public static final double ROT_DRIVE_D = 0;

    public static final double X_SCALE = 0.007854536;
    public static final double Y_SCALE = 0.01078828;
    public static final double ROT_SCALE = 0.022538738;
    public static final double X_TOP_SPEED = 0.12 * 8.064516129; // 0.35?
    public static final double Y_TOP_SPEED = 0.12;
    public static final double ROT_TOP_SPEED = 0.2;

    // EXTENDER
    public static final double EXTENDER_P = 0.12;
    public static final double EXTENDER_I = 0;
    public static final double EXTENDER_D = 0;
    public static final double EXTENDER_MOVE_SPEED = 1;

    public static final double EXTENDER_POT_MAX = 3.3;
    public static final double EXTENDER_POT_MIN = 0.3;
}

Hopefully now you realize why it can be useful to store all these values in one place. If we ever needed to change one of them, we don't need to hunt it down: we know exactly where it is. Remember if these variables have the public static modifiers on them, that means we can access them from anywhere without having to create any instances. For example, here is how the Lesson 3 motor controller constructors should look now:

left = new Talon(Wiring.LEFT_MOTOR);
right = new Talon(Wiring.RIGHT_MOTOR);

Take some time to convert your current code to use Wiring and Calibration classes. You shouldn't have any arbitrary numbers going into constructors if you don't have to. It is worth it to note however: don't go overboard. There are some instances where using an arbitrary number is OK. For now you can leave your Joystick constructor alone, as there isn't a very good place to put that number.

In the next lesson we are going to learn one more organization tactic, then we will move on to sensors!

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