> For the complete documentation index, see [llms.txt](https://docs.cb21829.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.cb21829.org/ftc-java-beginner-guide/autonomous-encoders-the-imu-and-heading-correction.md).

# Autonomous: encoders, the IMU, and heading correction

Autonomous means the robot must move known distances and turn to known angles without a driver.

### Encoders

Every FTC motor has a built-in encoder that reports tick counts.

To convert ticks to distance:

```
ticks per inch = (ticks per motor revolution × gear ratio) / (wheel circumference in inches)
```

Common encoder setup:

```java
motor.setMode(DcMotor.RunMode.STOP_AND_RESET_ENCODER);
motor.setMode(DcMotor.RunMode.RUN_USING_ENCODER);
```

Use `RUN_TO_POSITION` for simple position moves:

```java
int target = 1000;
motor.setTargetPosition(target);
motor.setMode(DcMotor.RunMode.RUN_TO_POSITION);
motor.setPower(0.5);

while (opModeIsActive() && motor.isBusy()) {
    telemetry.addData("pos", motor.getCurrentPosition());
    telemetry.update();
}
motor.setPower(0);
```

### The IMU

The IMU reports robot orientation. The heading value you use most is yaw.

```java
import com.qualcomm.robotcore.hardware.IMU;
import org.firstinspires.ftc.robotcore.external.navigation.AngleUnit;
import com.qualcomm.hardware.rev.RevHubOrientationOnRobot;

IMU imu = hardwareMap.get(IMU.class, "imu");

IMU.Parameters parameters = new IMU.Parameters(
    new RevHubOrientationOnRobot(
        RevHubOrientationOnRobot.LogoFacingDirection.UP,
        RevHubOrientationOnRobot.UsbFacingDirection.FORWARD
    )
);
imu.initialize(parameters);
imu.resetYaw();
```

Read heading like this:

```java
double heading = imu.getRobotYawPitchRollAngles().getYaw(AngleUnit.DEGREES);
```

The hub orientation must match the physical mounting.

### Angle wrapping

Headings wrap at `±180°`. Normalize the error so the robot turns the short way.

```java
public double angleWrap(double degrees) {
    while (degrees > 180)  degrees -= 360;
    while (degrees < -180) degrees += 360;
    return degrees;
}
```

### Heading correction with a P controller

```java
public void turnToHeading(double targetDeg) {
    double kP = 0.02;

    double error = angleWrap(targetDeg - getHeading());

    while (opModeIsActive() && Math.abs(error) > 1.0) {
        error = angleWrap(targetDeg - getHeading());

        double turnPower = kP * error;
        turnPower = Math.max(-0.5, Math.min(0.5, turnPower));

        frontLeft.setPower(-turnPower);
        backLeft.setPower(-turnPower);
        frontRight.setPower(turnPower);
        backRight.setPower(turnPower);

        telemetry.addData("target", targetDeg);
        telemetry.addData("current", getHeading());
        telemetry.addData("error", error);
        telemetry.update();
    }

    frontLeft.setPower(0);
    backLeft.setPower(0);
    frontRight.setPower(0);
    backRight.setPower(0);
}

private double getHeading() {
    return imu.getRobotYawPitchRollAngles().getYaw(AngleUnit.DEGREES);
}
```

Tune `kP` until the turn is crisp without oscillation.

### Driving straight while holding heading

```java
double targetHeading = getHeading();
double kP = 0.02;

double error = angleWrap(targetHeading - getHeading());
double correction = kP * error;

frontLeft.setPower(drivePower - correction);
backLeft.setPower(drivePower - correction);
frontRight.setPower(drivePower + correction);
backRight.setPower(drivePower + correction);
```

This combination gives you a strong first autonomous foundation.


---

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