Question

Pre-Condition

An FOG IMU is mounted on a high speed Autonomous Vehicle to track linear acceleration and angular velocity of the vehicle under dynamic conditions, Here FOG Z axis (accelerometer + gyroscope) points towards the sky and X axis (accelerometer + gyroscope) points towards the front of the vehicle and Y axis (accelerometer + gyroscope) points towards the left side of the vehicle.

The IMU is fixed at the center of the vehicle

Question

I was trying to record centripetal acceleration captured by the accelerometers by moving the vehicle on a curved path wherein I observed a strange phenomenon,

During this motion I observed, Angular velocity measured in the Yaw or Z axis of gyroscope is similar to Angular Velocity Measured by the IMU when vehicle is moving on a straight path.

I am unable to understand as to why the gyroscope would pick up angular velocity while moving on a straight path whose magnitude is equivalent to when the same vehicle is moving on a curved path.

Kindly guide me through the principle as I think I am missing something basic.

Thanks for helping me out !!

Answer 1

Gyroscopes resist changes to their rotation axis due to the conservation of angular momentum, causing precession instead of direct movement in response to applied torques. This principle explains why the gyroscope in an IMU can show angular velocity when moving in a straight line, similar to what may be observed when taking a curved path.

Step-by-step explanation:

The phenomenon you are describing with the gyroscope in an Autonomous Vehicle's Inertial Measurement Unit (IMU) involves understanding gyroscopic precession and the conservation of angular momentum. Gyroscopes are designed to maintain their angular momentum, meaning they resist changes to their axis of rotation.

When your vehicle executes a turn, a centripetal force acts upon it, creating a torque. However, due to angular momentum conservation, instead of this torque causing the gyroscope to tilt or rotate out of its plane as might be intuitively expected, the gyroscope experiences precession—the gyroscope's axis of rotation shifts perpendicularly to the applied torque.

This is why you observe angular velocity measurements while moving in a straight path, which might be confused with those of a curved path. Small disturbances or forces can induce this precession. Moreover, the Earth itself behaves like a gigantic gyroscope, with its angular momentum along its axis pointing towards Polaris, the North Star—a fact which assures us that gyroscopes can maintain constant angular momentum even under the influence of other forces or motions.