The Development of Neural Network Based System Identification ...

212 CHAPTER 8 CONCLUSIONS AND FUTURE WORKS
implementation of a full MIMO based controller. One of the primary causes of
the computational restriction was due to the Labview R○ plug and play driver for
MTi Xsens IMU which was executed together with other time critical processes
such as the NN training and NNAPC controller processes. For example, if the
user increases the number of prediction or control horizon steps too high, it
would significantly impact the IMU measurement loop rate. More computational
resources are used to maintain the loop timing of these time critical processes and
this significantly reduces the IMU measurement loop rate, thus making the IMU
produce chaotic results with measurement error. It is advisable to switch the data
handling of the IMU measurement from the sbRIO’s real-time processor to FPGA,
in order to reduce the total computation burden of the sbRIO real-time processor.
2. Since the NN model is linearised continuously, the system dynamics can change
rapidly at every time instance. For systems with non smooth non-linearity, there
will be problems since the extracted linear models are generally valid near the
operating point. To counter this problem and to gain a more stable system model,
a low-pass filter can be implemented to the A-matrix in the State Space Model as
recommended in Witt et al. [2007].
3. The translational controllers can be designed for the unmanned helicopter system,
thus establishing a full six degrees-of-freedom controller. A recommendation for
the design of translational control is to use several PID controllers, which will
construct set-points for the inner loop roll-pitch MPC controller to drive the
helicopter to the required translational positions.
4. To make the unmanned helicopter system ready for free flight, the altitude sensor
needs to be replaced. It is recommended to combine two different positional
measurement systems such as GPS for tracking translational motion or by using
pressure sensor such as a barometer for accurate altitude measurement.