Lesson 4.4: Shaping Joystick Sensitivity with squareInputWithSign()

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Technical Context

Standard linear joystick mapping makes it difficult to perform fine adjustments at low power because small physical movements of the stick result in large percentage changes in motor voltage. By implementing a squared sensitivity curve, the robot gains higher granularity at lower speeds, improving the precision of scoring maneuvers while maintaining the ability to reach full speed for field navigation.

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How Input Shaping Makes Driving Smoother

Squaring a joystick input (e.g., 0.5 * 0.5 = 0.25) reduces the output power for the majority of the stick's range. However, a standard square operation turns negative inputs positive (e.g., -0.5 * -0.5 = 0.25), which would destroy the driver's ability to reverse the robot. Professional FTC code uses a custom method called squareInputWithSign(). This method calculates the square but then uses a conditional if statement to check if the original input was negative; if so, it multiplies the result by -1 to preserve the direction of movement.

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Annotated Code

@TeleOp(name="Sensitivity_Tuning")
public class SensitivityTuning extends OpMode {

    @Override
    public void init() {}

    // Method designed to provide fine-grained control at low speeds
    double squareInputWithSign(double input) {
        double output = input * input;
        if (input < 0) {
            output = output * -1; // Preserve the 'backward' direction
        }
        return output;
    }

    @Override
    public void loop() {
        double rawInput = -gamepad1.left_stick_y;

        // Applying the custom method to the joystick data
        double precisionPower = squareInputWithSign(rawInput);

        telemetry.addData("Input",          rawInput);
        telemetry.addData("Squared Output", precisionPower);
    }
}

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Fill-in-the-Blank Practice

1. Squaring an input improves the robot's __________ when the joystick is near the center.
2. If you square a negative joystick value without a sign check, the robot will move __________ even when the stick is pushed down.
3. The keyword __________ is used in a method declaration to indicate it returns a decimal value.

Show answers

1. precision (granularity / sensitivity at low speeds)
2. forward (a negative squared becomes positive, reversing the intended direction)
3. double

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Template Challenge

Robot Scenario: You need to create a custom scaling method for the drive team. Implement a method that cubes the input (input * input * input) instead of squaring it to provide an even "softer" feel at low speeds. (Note: Cubing naturally preserves the sign!)

Unit 4 simulator

Supports buttons, joysticks, triggers, bumpers, and D-pad input.

Shows live input values, basic telemetry, deadzones, and curve visualization when relevant.

Best for simple control logic, variable math, and single-method practice code.

Show answer

double cubeInput(double input) {
    return input * input * input;
}

@Override
public void loop() {
    double result = cubeInput(gamepad1.right_stick_x);
    telemetry.addData("Cubed Output", result);
}

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