Universal IMU Guide

The Inertial Measurement Unit (IMU) is one of the most important sensors on your robot. It combines a Gyroscope (measuring rotation) and an Accelerometer (measuring acceleration) to help your robot understand its orientation in 3D space.

In modern FTC (SDK 8.0+), we use the universal IMU interface, which works across all REV Control Hub and Expansion Hub versions.

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1. Defining Orientation

Before initializing the IMU, you must tell the software how the Control Hub is mounted on your robot. This is done using RevHubOrientationOnRobot.

You need to specify:

1. Logo Direction: Which way the REV logo on the hub is facing (UP, DOWN, FORWARD, etc.)
2. USB Direction: Which way the USB ports on the hub are facing.

import com.qualcomm.hardware.rev.RevHubOrientationOnRobot;
import com.qualcomm.robotcore.hardware.IMU;

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

// Adjust these to match your robot's actual mounting!
IMU.Parameters parameters = new IMU.Parameters(new RevHubOrientationOnRobot(
    RevHubOrientationOnRobot.LogoFacingDirection.UP,
    RevHubOrientationOnRobot.UsbFacingDirection.FORWARD
));

imu.initialize(parameters);

2. Reading Angles (Yaw, Pitch, Roll)

The IMU provides three primary angles:

• Yaw: The direction the robot is facing (Heading). This is the most used angle for driving straight or turning.
• Pitch: The “tilt” of the robot (front-to-back).
• Roll: The “side-to-side” tilt.

import org.firstinspires.ftc.robotcore.external.navigation.AngleUnit;
import org.firstinspires.ftc.robotcore.external.navigation.YawPitchRollAngles;

YawPitchRollAngles angles = imu.getRobotYawPitchRollAngles();

double yaw = angles.getYaw(AngleUnit.DEGREES);
double pitch = angles.getPitch(AngleUnit.DEGREES);
double roll = angles.getRoll(AngleUnit.DEGREES);

telemetry.addData("Yaw (Heading)", "%.2f", yaw);

3. Resetting the Heading

When your OpMode starts, the IMU’s Yaw is set to 0 based on the robot’s current position. If you want to “re-zero” the robot (e.g., in a field-centric drive system), use:

imu.resetYaw();

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Full Example: Field-Centric Heading

This example shows how to initialize the IMU and read the Yaw for use in a basic heading-display OpMode.

package org.firstinspires.ftc.teamcode;

import com.qualcomm.hardware.rev.RevHubOrientationOnRobot;
import com.qualcomm.robotcore.eventloop.opmode.LinearOpMode;
import com.qualcomm.robotcore.eventloop.opmode.TeleOp;
import com.qualcomm.robotcore.hardware.IMU;
import org.firstinspires.ftc.robotcore.external.navigation.AngleUnit;

@TeleOp(name = "Universal IMU Example", group = "Sensor")
public class IMUExample extends LinearOpMode {

    private IMU imu;

    @Override
    public void runOpMode() {
        // 1. Initialize IMU
        imu = hardwareMap.get(IMU.class, "imu");

        // 2. Configure Orientation
        // Change these to match your hub's mounting!
        IMU.Parameters parameters = new IMU.Parameters(new RevHubOrientationOnRobot(
                RevHubOrientationOnRobot.LogoFacingDirection.UP,
                RevHubOrientationOnRobot.UsbFacingDirection.FORWARD
        ));

        imu.initialize(parameters);

        telemetry.addData("Status", "Initialized");
        telemetry.update();

        waitForStart();

        while (opModeIsActive()) {
            // 3. Reset Yaw if 'A' is pressed
            if (gamepad1.a) {
                imu.resetYaw();
            }

            // 4. Read Heading
            double yaw = imu.getRobotYawPitchRollAngles().getYaw(AngleUnit.DEGREES);

            telemetry.addData("Heading", "%.2f degrees", yaw);
            telemetry.addData("Tip", "Press 'A' to reset Yaw");
            telemetry.update();
        }
    }
}

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[!CAUTION] Initialization Time: It is best to initialize the IMU in the init section of your OpMode (before waitForStart). Moving the robot during IMU initialization can cause drift or incorrect readings. Ensure the robot is stationary while the code is initializing!