The Development of Neural Network Based System Identification ...

3.4 FLIGHT INSTRUMENTATION SETUP FOR AUTOMATIC FLIGHT CONTROL TEST 69
Figure 3.11
Helicopter avionics and sensors on the test stand.
rotary encoders instead of vision based localisation system was to avoid high development
cost incurred from the use of high cost cameras [Vitzilaios and Tsourveloudis, 2009,
Valenti et al., 2006, 2007].
Figure 3.11 shows the arrangement of positioning and
rotational sensors in the test stand. Two rotary encoders are attached at each joint of
arm 1 and 2 in the test stand. These encoders are set to zero during the initialisation
phase and produce signed numbers that indicate the current position relative to the
initial position. A positive number gives a rotation reading that indicates movement to
the left, and vice versa, a negative reading indicates movement to the right.
Measuring the rotational displacement of the joints between the centre pivot and
the first arm (θ 1 ), and the first and second arm (θ 2 ), gives the location of the helicopter
in the XY plane. To calculate the XY coordinate of the helicopter relative to the base
and initial position, the following equation is used:
x = L 1 cos (θ 1 ) + L 2 cos (θ 1 + θ 2 ) (3.1)
y = L 1 sin (θ 1 ) + L 2 sin (θ 1 + θ 2 ) (3.2)