Of course, I’m using a four-motor quadcopter as a generic term
for electronically controlled, direct
drive flying platforms. There are
copters with three or six motors
arranged in a ‘Y’ configuration; with
four or eight motors arranged in an
‘X’ configuration; with six or 12
motors arranged in a “✭”
configuration; and so on. When a
configuration has double the motor
count, motors are paired vertically
with one pushing and one pulling.
If you’re itching to work with a
quadcopter, then consider the AR
Drone as a gentle introduction to
the platform. The quadcopter is
relatively inexpensive — I paid $299
at Amazon. However, the price
doesn’t include a controller – a
compatible IOS or Android device.
I use an iPad.
FIGURE 2. One of the AR
Drone's four integrated
ESC and brushless motor
The AR (Augmented Reality)
Drone is first and foremost a video
game peripheral. It’s not intended to
serve as a robotics platform, and
Parrot doesn’t support hacking their
copter. It’s a closed software
platform, unless you happen to be a
Many design features reflect
concern for the safety of young
video game players versus
performance or ease of modification
for robotics enthusiasts. There’s the
ample expanded foam padding to
protect the electronics from the
environment and to protect pets
and humans from flying electronics.
There’s a 1,000 mAh lithium-ion
battery encased in heavy, hard
plastic (see Figure 4), and a geared,
relatively inefficient propulsion
system. The advantage of this focus
on safety — besides international
access to toy stores — is that you
can use the AR Drone just about
anywhere without concern for
inflicting (much) harm on
bystanders. You certainly can’t say
that about the larger quadcopter
Brushless motors are essentially high speed, high efficiency stepper motors.
Compared with traditional brushed DC motors, brushless motors produce higher
torque by weight, operate at higher efficiency, produce less acoustic and electrical
noise, and have a greater mean time before failure. Of particular importance to flying
vehicles is torque/weight and efficiency which relate directly to thrust and battery life.
Brushless motors are rated in kV, the rpm constant, or number of revolutions per
minute that the motor will turn when 1V is applied to the motor with no load.
FIGURE 3. Underside of the AR Drone
showing the 720p camera, ultrasonic sensor,
and low res camera.
The hardware inventory of the
SERVO 08.2012 47