IMU

What is an IMU?

An Inertial Measurement Unit (IMU) is a sensor that measures your robot's orientation and movement. In FTC, the IMU is most commonly used to determine the robot's heading, allowing your code to know which direction the robot is facing.

Modern REV Control Hubs include a built-in IMU, so no additional hardware is required.

What Does It Measure?

An IMU combines multiple sensors into one package.

• Gyroscope measures rotational velocity.
• Accelerometer measures linear acceleration.
• Some IMUs also include a magnetometer, although the FTC SDK primarily uses the gyroscope and accelerometer.

For most FTC applications, you'll mainly work with the robot's yaw, which represents its heading on the field.

Common Uses

• Field-centric driving
• Maintaining a heading during autonomous
• Turning to a specific angle
• Detecting robot tilt
• Correcting drift while driving

Coordinate Axes

The IMU reports rotation around three axes.

Most FTC programs only need the yaw value.

Reading the IMU

The FTC SDK allows you to read the robot's orientation at any time.

YawPitchRollAngles orientation = imu.getRobotYawPitchRollAngles();

double heading = orientation.getYaw(AngleUnit.DEGREES);

The heading can also be requested in radians if needed.

Initializing the IMU

Before using the IMU, initialize it in your OpMode.

IMU.Parameters parameters = new IMU.Parameters(
        new RevHubOrientationOnRobot(
                RevHubOrientationOnRobot.LogoFacingDirection.UP,
                RevHubOrientationOnRobot.UsbFacingDirection.FORWARD
        )
);

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

The orientation values must match how your Control Hub is mounted on the robot.

Resetting the Heading

Sometimes you'll want the robot's current direction to become zero.

imu.resetYaw();

This is commonly done at the start of TeleOp.

Best Practices

• Initialize the IMU once.
• Reset yaw when appropriate.
• Use degrees unless your math requires radians.
• Verify the Control Hub orientation settings match your robot.