Lesson 12.4: Monitoring Pitch and Roll for Robot Tip Detection

When Tipping Becomes a Real Risk

Tall robots, high center-of-mass designs, and fast directional changes are all common in competitive FTC. A robot that tips over during a match cannot score and may receive a penalty if a referee must right it, or worse, it may damage itself or a field element. Physical countermeasures like a wide wheelbase and low ballast weight help, but software can add a second layer of protection by detecting dangerous tilt angles and responding before the tip actually occurs.

The IMU's pitch and roll channels provide exactly this data. Because the IMU detects acceleration along its axes, and gravity is a constant downward acceleration, the sensor can determine how much the robot is leaning in any direction even when the robot is stationary. This is the same principle used in smartphones to detect landscape versus portrait orientation.

Pitch, Roll, and Their Axes

Pitch measures rotation around the robot's side-to-side axis. Visually, this is the robot nodding forward or backward like a car accelerating or braking hard. Roll measures rotation around the robot's front-to-back axis. This is the robot leaning left or right, like a car taking a sharp corner.

Both values are retrieved from the same YawPitchRollAngles object used for Yaw in Lesson 12.2. The methods are getPitch(AngleUnit) and getRoll(AngleUnit), and they accept the same AngleUnit.DEGREES or AngleUnit.RADIANS parameter.

When checking for tipping, you almost always want to use Math.abs() on the result. A robot that is tilting 25 degrees to the left and a robot that is tilting 25 degrees to the right are both in danger, but one produces a positive roll value and the other produces a negative roll value. Taking the absolute value collapses both cases into a single threshold check.

Designing a Tip Safety Response

The appropriate response to a detected tip depends on the robot's design. Common strategies include:

Setting all drive motor power to zero to stop the motion causing the tip.
Retracting a tall scoring mechanism to lower the center of gravity automatically.
Sending a telemetry warning to the Driver Station so the drive team can intervene.

A production implementation would combine two or three of these simultaneously. The code pattern is an if statement that checks whether either pitch or roll exceeds a threshold, using a logical OR (||) to trigger on tipping in any direction.

boolean isTipping = Math.abs(pitch) > 20.0 || Math.abs(roll) > 20.0;

The threshold value of 20 degrees is a starting point. Each robot's actual tip angle depends on its geometry, and the team should measure and calibrate this number during practice sessions.

Annotated Code

package org.firstinspires.ftc.teamcode;

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

@TeleOp(name="Tip_Detection_Demo")
public class TipDetectionDemo extends OpMode {

    private DcMotor leftDrive, rightDrive;
    private IMU     imu;

    private static final double TIP_THRESHOLD_DEG = 20.0;

    @Override
    public void init() {
        leftDrive  = hardwareMap.get(DcMotor.class, "left_drive");
        rightDrive = hardwareMap.get(DcMotor.class, "right_drive");
        rightDrive.setDirection(DcMotor.Direction.REVERSE);

        imu = hardwareMap.get(IMU.class, "imu");
        imu.initialize(new IMU.Parameters(new RevHubOrientationOnRobot(
            RevHubOrientationOnRobot.LogoFacingDirection.UP,
            RevHubOrientationOnRobot.UsbFacingDirection.FORWARD
        )));
    }

    @Override
    public void loop() {
        YawPitchRollAngles angles = imu.getRobotYawPitchRollAngles();

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

        // Check both axes simultaneously -- tipping in any direction is dangerous
        boolean isTipping = Math.abs(pitch) > TIP_THRESHOLD_DEG
                         || Math.abs(roll)  > TIP_THRESHOLD_DEG;

        if (isTipping) {
            // Emergency stop: cut all drive power immediately
            leftDrive.setPower(0.0);
            rightDrive.setPower(0.0);
            telemetry.addData("WARNING", "TIP DETECTED -- MOTORS STOPPED");
        } else {
            leftDrive.setPower(-gamepad1.left_stick_y);
            rightDrive.setPower(-gamepad1.right_stick_y);
        }

        telemetry.addData("Pitch (deg)", "%.1f", pitch);
        telemetry.addData("Roll  (deg)", "%.1f", roll);
        telemetry.addData("Tipping",     isTipping);
        telemetry.update();
    }
}

Fill-in-the-Blank Practice

Rotation around the robot's side-to-side axis, describing a forward or backward lean, is called __________.
Rotation around the robot's front-to-back axis, describing a left or right lean, is called __________.
When checking a tilt angle for a danger threshold, Math.__________() should be applied to the angle value so that leaning in either direction triggers the same check.

Show answers

Pitch
Roll
abs

Template Challenge

Robot Scenario: Write a helper method called isTipping() for a mechanism class. It should return true if either the pitch or the roll of the robot exceeds 15 degrees in magnitude. Assume imu is a class member that has already been initialized.

package org.firstinspires.ftc.teamcode.mechanisms;

import com.qualcomm.robotcore.hardware.IMU;
import org.firstinspires.ftc.robotcore.external.navigation.AngleUnit;
import org.firstinspires.ftc.robotcore.external.navigation.YawPitchRollAngles;

public class SafetyMonitor {

    private IMU imu;
    private static final double TIP_LIMIT = 15.0;

    public SafetyMonitor(IMU imu) {
        this.imu = imu;
    }

    // INSERT CODE HERE: Write the isTipping() method.
    // It should read pitch and roll in DEGREES and return true if either
    // exceeds TIP_LIMIT in absolute value.

}

Show answer

public boolean isTipping() {
    YawPitchRollAngles angles = imu.getRobotYawPitchRollAngles();
    double pitch = angles.getPitch(AngleUnit.DEGREES);
    double roll  = angles.getRoll(AngleUnit.DEGREES);
    return Math.abs(pitch) > TIP_LIMIT || Math.abs(roll) > TIP_LIMIT;
}

Ready to move on?

When Tipping Becomes a Real Risk​

Pitch, Roll, and Their Axes​

Designing a Tip Safety Response​

Annotated Code​

Fill-in-the-Blank Practice​

Template Challenge​