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Lesson 3.2: Using double for Motor Power and Precise Math

Technical Context​

Motor voltage control requires high-precision values to achieve smooth acceleration. Using the double datatype allows the robot to handle the fractional values (-1.0 to 1.0) required by the setPower() method, preventing the jerky movement or rounding errors associated with lower-precision types.

Why FTC Code Uses double So Often​

The double is a 64-bit primitive datatype used for floating-point numbers (decimals). In the FTC SDK, the setPower() method specifically expects a double parameter. While a float also handles decimals, it is only 32-bit; the JVM on the Control Hub defaults to double for maximum accuracy when calculating velocity or interpreting analog joystick data. Assigning a power level to a double variable allows you to perform math — such as halving the speed for a "Slow Mode" — without losing the decimal remainder.

Annotated Code​

@TeleOp(name="Precision_Power")
public class PrecisionPower extends OpMode {

    DcMotor drive;

    // Initializing a double variable for fine-grained speed control
    double targetSpeed = 0.35;

    @Override
    public void init() {
        drive = hardwareMap.get(DcMotor.class, "motor");
    }

    @Override
    public void loop() {
        // The SDK setPower method receives the double variable
        drive.setPower(targetSpeed);
        telemetry.addData("Current Power", targetSpeed);
    }
}

Fill-in-the-Blank Practice​

  1. To store a number with a decimal point for motor power, you should use the __________ datatype.
  2. The double datatype occupies __________ bits of memory, making it more accurate than a float.
  3. The valid range of values for a motor's setPower() method is from __________ to 1.0.
Show answers
  1. double
  2. 64
  3. -1.0

Template Challenge​

Robot Scenario: Your driver wants a specific "Auton Speed" of 0.45. Create a double variable to store this and apply it to a motor.

Unit 3 simulator
Tracks `String`, `double`, `boolean`, and `int` variables as you edit.
Supports telemetry, `gamepad1`, simple `if` blocks, and basic `setPower()` math.
Does not simulate full hardware behavior or complex Java control flow.
Show answer
@Override
public void loop() {
    double autonSpeed = 0.45;
    motor.setPower(autonSpeed);
}

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