Usas filtro de Kalman?
Yo se que no se pueden usar asi como estan. Tengo muchos enlaces que lo demuestran
Lee esto
The use of accelerometer and gyroscope to build little robots, such as the self-balancing, requires a math filter in order to merge the signals returned by the sensors.
The gyroscope has a drift and in a few time the values returned are completely wrong. The accelerometer, from the other side, returns a true value when the acceleration is progressive but it suffers much the vibrations, returning values of the angle wrong.