Underwater Navigation System
AUVSI Sub Support Team
Chris Scherr (EE)        Gavin Lommatsch (EE)        Sam Hooson (EE)        Dr. Todd Kaiser (advisor)

    IMU - TI SensorTag
    IMU - Sparton GEDC-6
    Sensor Calibrations
    Euler Angles
    Body Frame to Navigation Frame

Kalman Filter
     Data Acquisition

Rigid Body Orientation Visualization (1st Method: Euler angles)

Rotation matrices involved with Euler angles

The team initially decided to use Euler angles to determine the rigid body orienation of the Sensortag, the main reason being the easy conceptualization of Euler angles. The roll, pitch, and yaw angles can be calculated  from the static accelerometer and magnetometer data. Roll and Pitch angles can be calculated from the static accelerometer data alone. The equations for the roll and pitch angles are shown below. Notice the difference between the same angles in the equations. This is because the rotation sequence that is used is crucial, and the sequence of rotations is not communitive.

XYZ rotation sequence               YXZ rotation sequence

A problem that can arise when using Euler angles and rotation matrices to obtain orientation is Gimbal Lock. This phenomena is the loss of a degree of freedom, in which an axis of rotation locks with another, and cannot be calcualted once this occurs. Two graphical examples of Gimbal lock are shown below. Since a main design goal was to create a robust navigation system no matter the orientation of the IMU, the team decided to look at other options for determining rigid body orientation.

                                                                                    Illustration of Gimbal lock