Aerospace and Electronic Systems Magazine March 2017 - 59

AUAV PROTOTYPE DESIGN AND ASSEMBLY
A prototype was built using four brushless motors, resulting in an
aircraft commonly known as quadrotor. The quadrotor is a rotarywing UAV with several advantages in comparison with fixed-wing
aircraft such as better stability in control actions, possibility of loitering, i.e., remaining in a stable position facilitating image acquisition by cameras embedded to the aircraft for example.
As for the frame architecture, an X-type structure was chosen, with flight dynamics as described in the previous section.
The reasons for choosing the X configuration were higher maneuverability, because all four propellers take part in the pitch
and roll motion dynamics. In addition, the X configuration
avoids the propellers blocking the front of the aircraft, allowing
a better image for flights with FPV (first person viewing). Figure
2 shows the design, in the software SolidWorks, of the quadrotor
used in the first tests.
During the design stage of the prototype, the software provided
the calculation of the center of gravity (CG) for the structure, located at the center of the prototype to ensure stability and precision, as well as the estimation of the prototype's weight, which
was approximately 1.4 kg. This information was important for dimensioning the motors and calculating the payload that the prototype would carry. In addition, the landing gear was designed with
enough height to reduce the probability of damage to the aircraft's
peripherals as well as its propellers during landing.

The chosen power supply was composed by a three-cell battery, whose capacity is 8400 mAh and continuous 40 C discharge
rate, connected by a power board to four 30 A electronic speed
controllers (ESCs). The prototype, with all the peripherals and the
battery, weighs 2.08 kg, therefore, the load requirement in each
motor is approximately 520 g, yielding 6.7 A per motor. The consumption of the controller unit and the peripherals is around 600
mA, totaling an in-flight consumption of 27.4 A. The battery has
8400 mAh and can provide a maximum power of approximately
3700 W; thus, the autonomy of the prototype is approximately 18
min and the power-to-weight ratio is about 5.78 W/g.
In order to make it possible for the flying robot to successfully follow its mission and to coordinate the power system, the
Pixhawk was chosen due to being a well-documented and reliable
solution, which integrates as its on-board features sensors like accelerometer, barometer, gyroscope, and magnetometer. Also, Pixhawk is widely accepted by the UAV research and development
community; it is an open source architecture that allows developing specific solutions for each application. The other reason is the
capability to process real-time multithreading due to the UNIX
embedded system, making it compatible with ROS multinode system and the ODROID companion computer.
The workgroup developed C++ routines for automatic control
of the UAV using the MAVlink communication protocol in high
level supported by ROS package called MAVROS. This package
allows sending velocity or pose setpoints.

Figure 2.

Mechanical project design for the initial prototype.

MARCH 2017

IEEE A&E SYSTEMS MAGAZINE

59



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