Thanks for trying! Yes, it is not as difficult as it sounds 
There is initial drift. In fact there are 2 types of drifts:
- initial
- yaw
The MPU has an internal calibration mechanism that is triggered after 8 seconds of no motion. You can find more information in mpu.c and google DMP_FEATURE_SEND_CAL_GYRO.
The yaw drift is normal for this MPU and is very marginal.
Hope this clarifies.