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Fig. 19.2
X.R.B with four
black balls. The positions of
the black balls in the image
planes are used as image
features
The two computers connected to cameras are called client computers. The computer
connected to the DA converter is called server computer.
Client computers extract image features and update the vectors of the image fea-
tures in the image planes every 8.5 ms. This follows from the use of fast IEEE
1394 cameras, Dragonfly Express
1
,
2
. The vectors of the extracted image features
are transferred to server computer.
Server computer determines a set of correctly extracted image features, or equiv-
alently visible image features, at each time step by using the algorithm proposed in
[2]. It also derives a required control signals in a manner presented in Section 19.7.
The control signals are supplied from server computer to the helicopter through the
DA converter and the transmitter. The clocks of the computers are not synchronized
with each other. Server computer uses the latest data transferred from client com-
puters. It takes 3 ms to update the control signals.
The unmanned helicopter used in experiments is X. R. B SR SKY ROBO Shuttle
(see Figure 19.2). It has a coaxial rotor configuration. The two rotors share the same
axis, and they rotate in opposite directions. The tail is a dummy. A stabilizer is
installed on the upper rotor head. It mechanically keeps the posture horizontal.
Table 19.1 summarizes specifications of the system.
Table 19.1
Specifications of the system
Length of the helicopter
0.40 m
Height of the helicopter
0.21 m
Rotor length of the helicopter
0.34 m
Weight of the helicopter
0.21 kg
Focal length of the lens
0.004 m
Camera resolution
640
×
480 pixels
Pixel size
7.4 μm
×
7.4 μm
1
Dragonfly Express is a trademark of Point Grey Research Inc.
Point Grey Research
TM
and Dragonfly Express
TM
2
are trademarks owned by Point Grey
Research, Inc. www.ptgrey.com
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