Kauai Labs navX-MXP User Manual page 74

Guidance
Gyro/Accelerometer Calibration
performing this process before using your robot the first time it is used within a new environment
(e.g., when you arrive at a FTC competition event).
The value of re-running Factory Calibration at the same temperature navX-MXP will be operated
at is potentially increased yaw accuracy as well as faster Startup Calibration. If a significant
temperature shift has occurred since the last Factory Calibration, the Startup Calibration time
may take longer than normal, and it's possible that yaw accuracy will be diminished until the
next On-the-fly Gyro Calibration completes.
Startup Calibration
Startup Calibration occurs each time the navX-Micro is powered on, and requires that the
sensor be held still in order to complete successfully. Using the Factory Calibration as a starting
point, the sensor calibrates the accelerometers and adjusts the gyroscope calibration data as
well based upon current temperature conditions.
If the sensor continues to move during startup calibration, Startup Calibration will eventually
timeout – and as a result, the navX-Micro yaw angle may not be as accurate as expected.
Initial Yaw Offset Calibration
Immediately after Startup Calibration, an Initial Yaw Offset is automatically calculated. The
purpose of the Initial Yaw Offset is to ensure that whatever direction the "front" of the navX-
MXP circuit board is pointed to at startup (after initial calibration is applied) will be considered "0
degrees".
Yaw Offset Calibration requires that navX-MXP be still for approximately 2 seconds after Startup
Calibration completes. After approximately 2 seconds of no motion, navX-MXP will acquire the
current yaw angle, and will subtract it from future yaw measurements automatically. The navX-
MXP protocol and libraries provide a way to determine the yaw offset value it is currently using.
NOTE: If navX-MXP is moving during startup, this Yaw Offset Calibration may take much longer
than 2 seconds, and may not be calculated at all if the sensor continues moving long enough.
Therefore it is important to keep navX-Micro still until initial calibration and Initial Yaw Offset
calibration completes.
On-the-fly Gyro Calibration
In addition to Startup Calibration, during normal operation navX-MXP will automatically re-
calibrate the gyroscope (e.g., to account for ongoing temperature changes) during operation,
whenever it detects 8 seconds of no motion. This process completes after about 7-8 more
seconds, and is completely transparent to the user. Therefore each time navX-MXP is still for
approximately 15 seconds, the gyroscopes are re-calibrated "on-the-fly". The purpose of On-
the-fly Gyro re-calibration is to help maintain yaw accuracy when shifts in ambient temperature
occur during operation.
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