Lesson 2.3: Running Real-Time Robot Logic Inside loop()

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Technical Context

The loop() method controls the robot's performance during the match. Because it runs at a high frequency (approximately 50 times per second), it allows for smooth movement and rapid sensor polling. Efficiency in this method is critical, any "blocking" code (like a sleep command) will freeze the robot and could cause a communication timeout with the Driver Station.

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The loop() Lifecycle

In an OpMode, the loop() method is executed repeatedly after the driver presses the "Play" button and until they press "Stop". It usually follows a sensing → thinking → acting cycle: it reads the latest values from the Gamepads or sensors, calculates the necessary power adjustments, and commands the Control Hub's motor controllers to update voltage outputs.

Since loop() is non-blocking, it is ideal for TeleOp where driver inputs are changing in real-time.

OpMode Lifecycle Flow

1

Init pressedinit() runs once for setup and hardware mapping.

2

Waitinginit_loop() may repeat while the robot is not started.

3

Start pressedstart() runs once for timers or one-time transitions.

4

Active matchloop() repeats: read inputs, decide, command hardware, update telemetry.

5

Stop pressedstop() runs once for cleanup and safe shutdown.

Official reference

Use the FTC SDK Javadocs when you want to confirm the exact method names and inheritance chain for OpModes: FTC RobotCore Javadocs.

Mentor note: debugging lifecycle bugs

If telemetry says the OpMode is "Initialized" but robot controls do nothing, ask which lifecycle method owns the code. Hardware mapping belongs in init(), live driver logic belongs in loop(), and one-time cleanup belongs in stop().

Do not make match autonomous depend on gamepad input

The SDK exposes gamepad objects to either OpMode style, but an Autonomous routine is expected to run from its programmed logic after Start. Use sensors, timers, and state transitions for match autonomous behavior rather than requiring driver input.

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Annotated Code

@TeleOp(name="Loop_Demo")
public class LoopDemo extends OpMode {

    @Override
    public void init() {
        telemetry.addData("Status", "Ready to Play");
    }

    @Override
    public void loop() {
        // This logic runs ~50x a second to check for driver input
        double drivePower = -gamepad1.left_stick_y;

        // Streaming hardware data back to the DS for real-time monitoring
        telemetry.addData("Motor Command", drivePower);
        telemetry.addData("Cycle Time", getRuntime());
    }
}

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Fill-in-the-Blank Practice

1. The loop() method runs repeatedly at a frequency of approximately __________ times per second.
2. If you put a long delay inside loop(), you risk losing connection to the __________ Station.
3. The robot stops executing the loop() method once the driver presses the __________ button.

Show answers

1. 50
2. Driver Station
3. Stop

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Simulator Challenge

You need to create a simple diagnostic that shows the status of the "A" button on gamepad1 during the entire match.

1.Complete the codeWork in fullscreen when you need more room for the editor and visualizer. Where file tabs are available, hover over the tab strip and choose + to create a file or reuse saved code.

2.Run the lifecyclePress Init, then Start. Use the available gamepad or scene controls.

3.Debug the behaviorCheck telemetry, motion, requirements, and hints before opening the answer.

Telemark Unit 2 Simulator

Supports `init()`, `init_loop()`, `start()`, `loop()`, and `stop()`.

Reads `@TeleOp`, `@Autonomous`, `@Disabled`, telemetry, and `gamepad1`.

Handles local variables, simple math, `resetRuntime()`, and `getRuntime()`.

Does not execute hardware, `gamepad2`, `else` blocks, or loop structures.

Show answer

@Override
public void loop() {
    telemetry.addData("Button A", gamepad1.a);
    telemetry.update();
}

A Team Loop Keeps Coordination Short

Titan Robotics Club's TeleOp passes driver input to its robot layer during each periodic call. Here is that pattern renamed to match this lesson:

public void loop() {
    robot.driveWith(gamepad1);
    robot.updateStatus();
}

The framework callback and dashboard details were removed. The two remaining calls show the lesson's point: read controls and update the robot once per loop. Adapted from Team 3543 Titan Robotics Club's FtcTeleOp.java at a pinned commit under the MIT License.

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