The Development of Neural Network Based System Identification ...

72 CHAPTER 3 AERIAL PLATFORM AND CUSTOM-BUILT FLIGHT TEST SYSTEM
operation and 256 MB of non-volatile memory for storing programs and data logging.
This device features a built-in 10/100 Mbit/s Ethernet port that can be use to conduct
communication over the network. For sbRIO-9605 variant, only a RS232 serial port is
provided to control peripheral devices.
The main tasks of the real-time processor in the NI sbRIO-9605 are to gather
sensory information from the IMU and to compute the necessary control update. On the
other hand, the FPGA in the on-board computer system is programmed with Labview R○
software to functions as a data logger in charge of collecting positioning data from
linear transducer, rotary encoders and servo inputs. It is also responsible for handling
switching between autonomous control and manual control as well as updating the
servo actuators according to the computed flight control laws. During manual flight
mode, the helicopter is controlled remotely using standard RC equipment by human
pilot. While in the autonomous flight mode, the helicopter movement will be directly
controlled and supervised by the on-board flight controller.
3.4.3 Inertial Measurement Unit
The IMU sensor is used to measure the orientation of the helicopter UAV in the
body frame reference system. Attitude determination of a UAV is critical in order to
ensure maintained flight for the autopilot system developed in this project. The Xsens
MTi IMU was selected for UAV attitude measurement. It produces measurements of
16 calibrated states consisting of Euler angle (φ, θ, ψ), in quaternion representation
(q 0 , q 1 , q 2 , q 3 ), angular rates in body coordinate frame (roll rate, p, pitch rate, q and
yaw rate, r), body accelerations (A x , A y , A z ) and magnetic fields (m x , m y , m z ). The
orientation of the MTi is computed by a Kalman filter algorithm for 3 DOF orientations.
The Kalman filter algorithm uses signals from the rate gyroscopes, accelerometers and
magnetometers to compute an optimal 3D orientation estimate of high accuracy with
no drift for both static and dynamic movements. Figure 3.11 shows the location of
this sensor on the helicopter. The MTi IMU outputs ASCII data at 100 Hz via RS232
protocol at 115 200 bit/s with no flow control.
The IMU provides Euler angles representation ranging from +π rad to −π rad.