FIGURE 4. Stock lithium-ion battery
mounted in main fuselage. The USB
connector is for storing video files.
AR Drone reads just like that of a smartphone: 1 GHz,
32-bit ARM processor, 1 GB RAM, 720p 30 fps HD camera
with video streaming, and Wi-Fi, all running under
embedded Linux. The onboard sensor complement includes
an ultrasonic range finder, an atmospheric pressure sensor
and ultrasonic range finder to determine altitude, a three-axis gyroscope, magnetometer, and three-axis
accelerometer. In addition to the forward-facing 720p video
and still camera, there is the equivalent of an optical mouse
– a downward facing, low resolution camera for tracking
ground speed and for hovering motionless.
The large indoor hull protects
the props from hitting walls,
curtains, and fingers. The outdoor
hull is an expanded foam top that
fits on the fuselage. Either hull
essentially creates a lightweight,
flying marshmallow that is best
suited for indoors or outdoors on a
dead calm day.
The electronic speed
controllers are matched and tuned
to the four brushless motors,
pulsing at 200-300 Hz. Whereas
most quadcopters on the market
use direct drive, the AR Drone uses
a step-down gear system to drive
the specially-designed slow speed
props. As a result, I can stop the
AR Drone dead in flight by
brushing a prop with the back of
my hand – all without injury.
Touch one of the AR Drone
blades and you’ll feel a modest bite before it immediately
shuts down and falls to the ground. I’ve tried this several
times – it’s not pleasant, but it doesn’t leave a mark. Of
course, a prop to the eye can cause blindness. Perhaps
that’s why the AR Drone is rated for children 14+.
The 2.0 version of the AR Drone is less teardown
friendly than the original. The bottom plate — which is
made of thin plastic — is glued to the expanded foam with
a super-tacky adhesive that takes
some of the foam with it. The same
goes for the stamped aluminum
supports on the sides and top of
the fuselage (see Figure 5). If you
have strong fingernails, you can
remove the supports, but don’t
expect a clean extraction. In other
words, once you take it apart, you’ll
never get it back to the original
state. Getting to the 720P camera
requires that you peel off the top
aluminum plate as in Figure 5.
Once inside, you’ll find the
circuit board with sensors and CPU
are tucked away in a cozy bed of
expanded polypropylene (see
Figure 6). The board is held in
place by four screws attached to
the plastic battery compartment.
Remove the four plastic adhesive
patches from where the beams
enter the expanded polypropylene
hull and peel open the sides to
extract the board and crossbeam
FIGURE 5. Extracting the 720p
forward-facing camera requires
removal of the top aluminum plate.
Note the foam pieces adhering to
the removed plate.
48 SERVO 08.2012