Aerospace and Electronic Systems Magazine July 2018 - 15

By Peter van der Sluijs, shared under GFDL (http://www.gnu.org/copyleft/fdl.html) from Wikimedia Commons.

in [22]. In order to respond to mission requirements, full models
with complex dynamics that take into consideration aerodynamic
forces and moments are needed. Several studies on the rotor model
have been developed based on results obtained for conventional
helicopters [23]-[30].
Numerous studies treat the stabilization problem and control algorithms used for quadrotors. In [31], a survey on control algorithms
for quadrotors has been presented, and similar work has been presented in [32], in the review of control algorithms for autonomous
quadrotors. In [33], a comparative study of some linear and nonlinear
controllers applied to quadrotor helicopters has been presented. In
the area of identification of the quadrotor, we can find the survey
[34], which treats the problem of identification of small, low-cost
unmanned aerial vehicle systems, and explains that the system has
unstable dynamics which makes open loop identification unpractical.
Several studies treat the research axis of fault tolerant control
and its applications on the UAV. In [7], Sadeghzadeh presents a
brief review of fault tolerant control (FTC) strategies applied to
the UAV. This study reviews various control architectures in order
to provide a potential solution for tolerance to faults, failures, and
damages relevant to UAV components during flight. Among different types of UAV test-bed structures, a sample of every class of
UAVs, including single-rotor, quadrotor, and fixed-wing types, are
selected and briefly illustrated.
Several papers on the development of different collision avoidance systems have been published. Reference [35] presents an important survey of collision avoidance strategies and approaches, describing and summarizing their important characteristics. More recent
collision avoidance techniques are presented and analyzed in [36].
It is important to note that most of aforementioned documents
and studies focus on certain subsets or specific areas of the UAV.
It is indeed very rare to find a compact document that can provide
a fairly comprehensive review on a chained data base of the UAV
from the system configuration to the fault tolerant control. The absolute necessity for this type of study has ignited our motivation
and driven us to complete this survey work. Each topic presented
in this article constitutes a necessary point that should be treated
and analyzed before prototyping. The logical flow of the discussion proceeds from understanding the customer constraints, then
choosing the configuration of the quadrotor based on those conJULY 2018

straints. Then, a mathematical model should be developed based
on the chosen configuration. From there, modeling and model
identification help to analyze the system, develop control strategies, diagnose faults, and develop fault tolerant control algorithms.
Obstacle avoidance analysis is needed to ensure that in the case of
autonomous flight, the mission is accomplished.

CONFIGURATIONS
Several configurations can be found for quadrotors, starting from
the first flight demonstration as presented in [37], and then in the
design of six-bladed rotors placed at each end of an X-shaped truss
structure in [22], [38].
UAVs are subdivided into three general categories: fixed wing
UAVs, rotary wing UAVs, and flapping wings (Figure 1). Rotary
winged crafts are superior to their fixed wing counterparts in terms
of achieving higher degrees of freedom, lower flying speeds, stationary flight ability, and suitability for indoor usage. A quadrotor
is a rotary wing UAV, consisting of four rotors located at the end
of a cross structure. The control of this system is achieved by varying the speed of each rotor. Quadrotors possess certain essential
characteristics, which highlight their potential for use in search and
rescue applications. A comparison among the three categories can
be summarized in Table 1 (see [39]).
In recent literature, many research teams focused on designing
and modeling their own quadrotor. For that reason, we can find
in the literature several types of quadrotors. We see for example
quadrotor type OS4 in [40], DraganFlyer presented with detailed
model in [41], Aviator described and modeled in [42], X4yer modeled in [26], Starmac described in [43], and Pixhawk presented and
described in [44]. For specific tasks and more powerful operations,
several new types of quadrotors with tilting propellers have been
designed and constructed [45] ̶ [52] in order to treat and to propose
solutions for some difficulties due to the under actuated system.
Modeling and performance assessment of hybrid terrestrial/aerial
quadrotors has been presented in [53]. Moreover, a number of
open-source projects for quadrotors are shown in [54].
In most of the selected configurations, each pair of blades spins
in the same direction and is implemented on one of the axes of the
body frame coordinate system, such as seen in the assembly of the

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Table of Contents for the Digital Edition of Aerospace and Electronic Systems Magazine July 2018