At the start of the runOpMode method, the op mode uses an object named hardwareMap to get references to the hardware devices that are listed in the Robot Controller’s configuration file:

 imu = hardwareMap.get(Gyroscope.class, "imu"); motorTest = hardwareMap.get(DcMotor.class, "motorTest"); digitalTouch = hardwareMap.get(DigitalChannel.class, "digitalTouch"); sensorColorRange = hardwareMap.get(DistanceSensor.class, "sensorColorRange"); servoTest = hardwareMap.get(Servo.class, "servoTest"); 

The hardwareMap object is available to use in the runOpMode method. It is an object of type HardwareMap class.

Note that when you attempt to retrieve a reference to a specific device in your op mode, the name that you specify as the second argument of the HardwareMap.get method must match the name used to define the device in your configuration file. For example, if you created a configuration file that had a DC motor named “motorTest”, then you must use this same name (it is case sensitive) to retrieve this motor from the hardwareMap object. If the names do not match, the op mode will throw an exception indicating that it cannot find the device.

In the next few statements of the example, the op mode prompts the user to push the start button to continue. It uses another object that is available in the runOpMode method. This object is called telemetry and the op mode uses the addData method to add a message to be sent to the Driver Station. The op mode then calls the update method to send the message to the Driver Station. Then it calls the waitForStart method, to wait until the user pushes the start button on the driver station to begin the op mode run.

 telemetry.addData("Status", "Initialized"); telemetry.update(); // Wait for the game to start (driver presses PLAY) waitForStart(); 

Note that all linear op modes should have a waitForStart statement to ensure that the robot will not begin executing the op mode until the driver pushes the start button.

After a start command has been received, the op mode enters a while loop and keeps iterating in this loop until the op mode is no longer active (i.e., until the user pushes the stop button on the Driver Station):

 // run until the end of the match (driver presses STOP) while (opModeIsActive())

As the op mode iterates in the while loop, it will continue to send telemetry messages with the index of “Status” and the message of “Running” to be displayed on the Driver Station.

Building Your Op Mode

When you create or edit an op mode the OnBot Java editor will auto-save the .java file to the file system of the Robot Controller. However, before you can execute your changes on the Robot Controller, you must first build the op mode and convert it from a Java text file to a binary that can be loaded dynamically into the FTC Robot Controller app.

If you are satisfied with your op mode and are ready to build, press the Build button (which is the button with the wrench symbol, see image below) to start the build process. Note that the build process will build all of the .java files on your Robot Controller.

You should see messages appear in the message pane, which is located in the lower right hand side of the window. If your build was successful, you should see a “Build succeeded!” message in the message pane.

Once you have built the binary files with your updated op modes, they are ready to run on the Robot Controller. Before we run our example op mode, let’s see what happens if a problem occurs during the build process.

Troubleshooting Build Messages

In the previous section, the build process went smoothly. Let’s modify your op mode slightly to cause an error in the build process.

In the editing pane of the OnBot Java window, look for the line that reads “private Servo servoTest;”. This should appear somewhere near the beginning of your op mode class definition. Change the word “Servo” to the word “Zervo”:

private Zervo servoTest; 

Also, let’s modify the telemetry statement that informs the user that the op mode has been initialized, and let’s remove one of the two arguments so that the statement looks like this:

telemetry.addData("Status",); 

Note that when you eliminate the second argument, a little “x” should appear next to the line with the modified addData statement. This “x” indicates that there is a syntax error in the statement.

After you have modified your op mode, you can press the build button and see what error messages appear.

When you first attempt to build the op mode, you should get an “illegal start of expression error”. This is because the addData method is missing its second argument. The OnBot Java system also directs you to the file that has the error, and the location within the file where the error occurs.

In this example, the problem file is called “org/firstinspires/ftc/teamcode/MyFIRSTJavaOpMode.java” and the error occurs at line 62, column 37. It is important to note that the build process builds all of the .java files on the Robot Controller. If there is an error in a different file (one that you are not currently editing) you will need to look at the file name to determine which file is causing the problem.

Let’s restore this statement back to its original, correct form:

telemetry.addData("Status", "Initialized"); 

After you have corrected the addData statement, push the build button again to see what happens. The OnBot Java system should complain that it cannot find the symbol “Zervo” in a source file called “org/firstinspires/ftc/teamcode/MyFIRSTJavaOpMode.java” at line 51, column 13.

You should restore the statement back to its original form and then push the build button and verify that the op mode gets built properly.

private Servo servoTest; 

Running Your Op Mode

If you successfully rebuilt your op mode, you are ready to run the op mode. Verify that the Driver Station is still connected to the Robot Controller. Since you designated that your example op mode is a tele-operated op mode, it will be listed as a “TeleOp” op mode.
On the Driver Station, use the “TeleOp” dropdown list control to display the list of available op modes. Select your op mode (“MyFIRSTJavaOpMode”) from the list.

Press the INIT button to initialize the op mode.

The op mode will execute the statements in the runOpMode method up to the waitForStart statement. It will then wait until you press the start button (which is represented by the triangular shaped symbol) to continue.

Once you press the start button, the op mode will continue to iterate and send the “Status: Running” message to the Driver Station. To stop the op mode, press the square-shaped stop button.

Congratulations! You ran your first java op mode!

Modifying Your Op Mode to Control a Motor

Let’s modify your op mode to control the DC motor that you connected and configured for your REV Expansion Hub. Modify the code for the program loop so that it looks like the following:

// run until the end of the match (driver presses STOP) double tgtPower = 0; while (opModeIsActive())

If you look at the code that was added, you will see that we defined a new variable called target power before we enter the while loop.

double tgtPower = 0; 

At the start of the while loop we set the variable tgtPower equal to the negative value of the gamepad1’s left joystick:

tgtPower = -this.gamepad1.left_stick_y; 

The object gamepad1 is available for you to access in the runOpMode method. It represents the state of gamepad #1 on your Driver Station. Note that for the F310 gamepads that are used during the competition, the Y value of a joystick ranges from -1, when a joystick is in its topmost position, to +1, when a joystick is in its bottommost position. In the example code above, you negate the left_stick_y value so that pushing the left joystick forward will result in a positive power being applied to the motor. Note that in this example, the notion of forwards and backwards for the motor is arbitrary. However, the concept of negating the joystick y value can be very useful in practice.

The next set of statements sets the power of motorTest to the value represented by the variable tgtPower. The values for target power and actual motor power are then added to the set of data that will be sent via the telemetry mechanism to the Driver Station.

 tgtPower = -this.gamepad1.left_stick_y; motorTest.setPower(tgtPower); telemetry.addData("Target Power", tgtPower); telemetry.addData("Motor Power", motorTest.getPower()); 

After you have modified your op mode to include these new statements, press the build button and verify that the op mode was built successfully.

Running Your Op Mode with a Gamepad Connected

Your op mode takes input from a gamepad and uses this input to control a DC motor. To run your op mode, you will need to connect a Logitech F310 gamepad to the Driver Station.
Before you connect your gamepad to the phone, verify that the switch on the bottom of the gamepad is set to the “X” position.

Connect the gamepad to the Driver Station using the Micro USB OTG adapter cable.

Your example op mode is looking for input from the gamepad designated as the user or driver #1. Press the Start button and the A button simultaneously on the Logictech F310 controller to designate your gamepad as user #1. Note that pushing the Start button and the B button simultaneously would designate the gamepad as user #2.

If you successfully designated the gamepad to be user #1, you should see a little gamepad icon above the text “User 1” in the upper right hand corner of the Driver Station Screen. Whenever there is activity on gamepad #1, the little icon should be highlighted in green. If the icon is missing or if it does not highlight in green when you use your gamepad, then there is a problem with the connection to the gamepad.

Select, initialize and run your “MyFIRSTJavaOpMode” op mode. It is important to note that whenever you rebuild an op mode, you must stop the current op mode run and then restart it before the changes that you just built take effect.

If you configured your gamepad properly, then the left joystick should control the motion of the motor. As you run your op mode, be careful and make sure you do not get anything caught in the turning motor. Note that the User #1 gamepad icon should highlight green each time you move the joystick. Also note that the target power and actual motor power values should be displayed in the telemetry area on the Driver Station.