The sensors used to estimate the angular velocity of the body are gyroscopes,
one for each body axis. The gyro signals are low pass filtered before sent to the
control loop. To estimate the attitude of the hexarotor the gyroscopes are used
together with accelerometers. The estimation is made by a complementary filter.
The attitude is estimated by integrating the angular velocities from the gyroscope.
Since all gyros have a small drift the accelerometers are used to compensate for
that drift. The estimation of heading of the body is made in a similar manner, but
instead of accelerometer data a magnetometer is used.