The Development of Neural Network Based System Identification ...

184 CHAPTER 7 FLIGHT CONTROL SYSTEM DESIGN: RESULTS AND DISCUSSION
separately since both dynamic motions are quite slow compared with the yaw dynamic.
This is due to the effect of stabiliser bar that introduces an increased damping effect to
the rotor [Mettler, 2003]. The yaw dynamics is tested in a separate test because of the
fast dynamic response while the altitude control is tested in the final part of the tuning
refinement stages. Similar to the yaw control test, the altitude control is also done in a
separate test since the involvement of chaotic movement induced by the sudden throttle
change can severely damage the helicopter if not properly executed. This leads to the
following experimental options:
1. Test the pitch rotation under automatic control while locking roll and yaw rotations
and keeping zero altitude.
2. Test the pitch and roll rotation under automatic control while locking yaw rotation
and keeping zero altitude.
3. Test the pitch and roll controller while manually controlling yaw rotation and
varying altitude levels.
4. Test the pitch, roll and yaw controller while keeping zero altitude.
5. Test the altitude controller while locking pitch, roll and yaw rotations.
6. Complete 4 DOF controller test.
7.2.1 Computation Time Improvement
The core of the UAS control hardware is the NI sbRIO-9605 flight computer which
provides a 400 MHz real-time processor with reconfigurable FPGA. The real-time sbRIO-
9605 flight controller handles the sampling of the IMU measurement, NN training (or
prediction), data logging and the MPC controller calculation. The data logging module
is set at the lowest priority and sampling rate, while the NN and NNAPC module are
run at a higher rate. Experience shows that setting the sampling rate of the NN training
and NNAPC module at 30 Hz are sufficient for hover (4 DOF) control. However, in the
early development phase of the flight controllers, the 4 DOF NNAPC controllers with