Your First TeleOp from Scratch

In this lesson you will build a complete Driver-Controlled (TeleOp) program step by step. By the end, one driver with one gamepad will be able to drive your robot forward, sideways and in turns. The code is written for a four-motor mecanum drivetrain, and a short tank drive alternative is included if your robot has normal wheels.

Step 1: Name your motors in the robot configuration

Your code never talks to a motor port directly. Instead, the Control Hub stores a robot configuration: a list that says which device is plugged into which port and what its name is. Your code asks for a device by that name. If the names do not match exactly, the program stops with an error, so set this up carefully first.

1. 1
   Open the configuration screen

   Power on the robot and connect the Driver Station. Open the menu (three dots) and choose Configure Robot, then New (or Edit an existing configuration).
2. 2
   Add the four drive motors

   Open the Control Hub, then Motors. For ports 0 to 3, pick the motor type that matches your hardware and type the names front_left, front_right, back_left and back_right. Names are exact: front_left and Front_Left are different, so use lowercase with underscores and write down which port each motor is plugged into.
3. 3
   Check the IMU

   On a Control Hub the built-in IMU usually already appears on I2C bus 0 with the name imu. Leave it there; you will use it in the next lesson.
4. 4
   Save and activate

   Press Done until you are asked to save, give the configuration a name such as training_bot, and make sure it is the active configuration shown on the main screen.

Step 2: Understand the OpMode lifecycle

An OpMode is one program the drivers can pick on the Driver Station. A LinearOpMode runs from top to bottom: the code before waitForStart() runs when the driver presses INIT, the code after it runs when they press START, and a while (opModeIsActive()) loop keeps repeating until STOP is pressed or the match ends.

Step 3: Write the TeleOp

Create a new Java file called FirstTeleOp in the teamcode folder. In OnBot Java, connect your laptop to the Control Hub's Wi-Fi, open the OnBot Java page in a browser and add the file inside org.firstinspires.ftc.teamcode. In Android Studio, add it to the TeamCode module in the same package. Then type in this complete program.

1package org.firstinspires.ftc.teamcode;
2
3import com.qualcomm.robotcore.eventloop.opmode.LinearOpMode;
4import com.qualcomm.robotcore.eventloop.opmode.TeleOp;
5import com.qualcomm.robotcore.hardware.DcMotor;
6
7@TeleOp(name = "First TeleOp", group = "Training")
8public class FirstTeleOp extends LinearOpMode {
9    @Override
10    public void runOpMode() {
11        // INIT: names must match the robot configuration exactly
12        DcMotor frontLeft = hardwareMap.get(DcMotor.class, "front_left");
13        DcMotor backLeft = hardwareMap.get(DcMotor.class, "back_left");
14        DcMotor frontRight = hardwareMap.get(DcMotor.class, "front_right");
15        DcMotor backRight = hardwareMap.get(DcMotor.class, "back_right");
16
17        // Motors on one side are mirrored, so reverse that side
18        frontLeft.setDirection(DcMotor.Direction.REVERSE);
19        backLeft.setDirection(DcMotor.Direction.REVERSE);
20
21        telemetry.addData("Status", "Ready - press START");
22        telemetry.update();
23        waitForStart();
24
25        while (opModeIsActive()) {
26            double y = -gamepad1.left_stick_y; // pushing forward gives a negative value
27            double x = gamepad1.left_stick_x;  // strafe left/right
28            double rx = gamepad1.right_stick_x; // turn
29
30            // Keep every power between -1 and 1 without changing the ratios
31            double max = Math.max(Math.abs(y) + Math.abs(x) + Math.abs(rx), 1.0);
32            double fl = (y + x + rx) / max;
33            double bl = (y - x + rx) / max;
34            double fr = (y - x - rx) / max;
35            double br = (y + x - rx) / max;
36
37            frontLeft.setPower(fl);
38            backLeft.setPower(bl);
39            frontRight.setPower(fr);
40            backRight.setPower(br);
41
42            telemetry.addData("Sticks", "y %.2f  x %.2f  rx %.2f", y, x, rx);
43            telemetry.addData("Front L/R", "%.2f / %.2f", fl, fr);
44            telemetry.addData("Back  L/R", "%.2f / %.2f", bl, br);
45            telemetry.update();
46        }
47    }
48}

• The @TeleOp(name = ...) annotation puts the OpMode in the TeleOp list on the Driver Station. Without it, the OpMode never appears.
• The call hardwareMap.get(DcMotor.class, "front_left") looks up the motor by its configuration name.
• Motor directions: motors on the left and right are mounted facing opposite ways, so the same power would spin them in opposite directions. Reversing one side means positive power drives every wheel forward. Which side to reverse depends on your motors and gearing, so you will test it.
• Forward is negative: on FTC gamepads, pushing a stick up gives a negative left_stick_y. The minus sign in -gamepad1.left_stick_y turns forward into a positive number.
• Normalisation: adding forward, strafe and turn can give values like 1.8, but setPower() only accepts -1 to 1. Dividing all four by the largest possible sum keeps them in range and keeps the wheel speeds in the right proportion, so the robot still moves in the direction you asked.
• Telemetry: telemetry.addData() queues a line and telemetry.update() sends it to the Driver Station screen. Use it to see what your code is thinking.

1// Each stick controls one side of the robot
2double left = -gamepad1.left_stick_y;
3double right = -gamepad1.right_stick_y;
4
5frontLeft.setPower(left);
6backLeft.setPower(left);
7frontRight.setPower(right);
8backRight.setPower(right);
9
10telemetry.addData("Left / Right", "%.2f / %.2f", left, right);
11telemetry.update();

Step 4: Upload, run and fix common errors

In OnBot Java, press Build Everything and wait for a successful build. In Android Studio, press Run with the Control Hub connected. On the Driver Station, assign the gamepad to user 1 by holding Start and pressing A. Choose First TeleOp from the TeleOp list, press INIT, then START. Test with the wheels off the ground first, then on the floor at low speed.