-
DESIGN AND FABRICATION OF FLAPPING WING MAV
A Project Report
Submitted to
MATS UNIVERSITY AARANG, RAIPUR (C.G.), INDIA
in the partial fulfillment for the award of the Degree of
Bachelor of Engineering in
Aeronautical
by ANKIT CHAKRADHARI (MU11BEAE006) ANKIT CHANDRAKAR
(MU11BEAE007)
Under the Guidance of
Mr. KALPIT P. KAURASE ASSISTANT PROFESSOR
Department of Aeronautical Engineering School of Engineering
& I.T.
MATS University, Aarang, Raipur (C.G.), India June 2015
-
DECLARATION BY THE CANDIDATE
I the undersigned solemnly declare that the report of the
project work entitled DESIGN AND FABRICATION OF FLAPPING WING MAV
is based on my own work carried out during the course of my study
under the supervision of MR. KALPIT P. KAURASE, Assistant
Professor, Department of Aeronautical Engineering, School of
Engineering & I.T., Aarang, Raipur.
I assert that the statements made and conclusions drawn are an
outcome of my study of research work. I further declare that to the
best of my knowledge and belief the report does not contain any
part of any work which has been submitted for any award of any
other degree/diploma/certificate in this University or any other
University of India or abroad.
_________________ _________________
(Signature of the Candidate) (Signature of the Candidate) Ankit
Chakradhari Ankit Chandrakar
MU11BEAE006 MU11BEAE007 School of Engineering & I.T., School
of Engineering & I.T.,
Aarang, Raipur (C.G.) Aarang, Raipur (C.G.)
-
CERTIFICATE BY THE SUPERVISOR
This is to certify that the report of the project entitled
DESIGN AND FABRICATION OF FLAPPING WING MAV is a record of research
work carried out by ANKIT CHAKRADHARI bearing Roll No. MU11BEAE006
& Enrolment No. 111133 and ANKIT CHANDRAKAR, Roll No.
MU11BEAE007 & Enrolment No. 111134 under my guidance and
supervision for the submission of Project work of Bachelor of
Engineering in Aeronautical of MATS University, Raipur (C.G.),
India. To the best of my knowledge and belief the report i) Fulfils
the requirement of the Ordinance relating to the B.E. degree of
the
University and ii) Is up to the desired standard both in respect
of contents and language for being
referred to the examiners.
____________ __________________
(Signature of HoD) (Signature of the Supervisor) Mr. Brijesh
Patel, Mr. Kalpit P. Kaurase, School of Engineering & I.T.,
School of Engineering & I.T., MATS University, Raipur MATS
University, Raipur
Forwarded to MATS University, Raipur
_______________
(Signature of the Director) School of Engineering &
I.T.,
MATS University, Raipur
-
CERTIFICATE BY THE EXAMINERS
The project entitled DESIGN AND FABRICATION OF FLAPPING WING MAV
submitted by ANKIT CHAKRADHARI, Roll No. MU11BEAE006, Enrolment No.
111133, and ANKIT CHANDRAKAR, Roll No.MU11BEAE007, Enrolment No.
111134 has been examined by the undersigned as a part of the
examination and is hereby recommended for the completion of project
work of the degree of Bachelor of Engineering in Aeronautical,
School of Engineering & I.T., MATS University, Aarang, Raipur
(C.G.), India.
.. Internal Examiner External Examiner
Date: Date:
-
i
ABSTRACT
In recent years the subject of flying vehicles propelled by
flapping wings, also known as ornithopter, has been an area of
interest because of its application to micro aerial vehicles
(MAVs). These miniature vehicles seek to mimic small birds and
insects to achieve never before seen agility in flight. This
renewed interest has raised a host of new problems in vehicle
dynamics and control to explore.
In order to better study the control of flapping wing flight we
have developed a large scale ornithopter called the Phoenix. It is
capable of carrying a heavy (400 gram) computer and sensor package
and is designed especially for the application of controls
research. The design takes special care to optimize payload
capacity, crash survivability, and field repair abilities.
This project aims at the development of a bio-mimetic propulsion
mechanism for a Flapping Wing Micro Aerial Vehicle, without
considering the aerodynamics of the wings in the design. This
artificial bird will be the size of approximately 10-20cm.
Therefore the aerodynamic phenomena in flapping flight are studied
and summarized.
-
ii
ACKNOWLEDGEMENT
We welcome this opportunity to express our heartfelt gratitude
and regards to our project guide Mr.Kalpit P. Kaurase, Assistant
Professor, Department of Aeronautical Engineering, School of
Engineering & I.T. for his unconditional guidance. He always
bestowed parental care upon us and evinced keen interest in solving
our problems. An erudite teacher, a magnificent person and a strict
disciplinarian, we consider ourselves fortunate to have worked
under his supervision. I feel motivated and encouraged every time I
meet him. Without his encouragement and guidance this project would
not have been materialized.
We are highly grateful to Mr. Brijesh Patel, Head of Department,
Department of Aeronautical Engineering, School of Engineering &
I.T. for providing necessary facilities during the course of the
work. He has willingly provided the resources necessary in
completing this project and has dedicated his time to ensure my
success.
I would also like to acknowledge with much appreciation the
crucial role of the staff of Aeronautical Department, who gave the
permission to use all required machinery and the necessary material
to complete the Differential Simulation Rig.
We greatly appreciate & convey our heartfelt thanks to my
family and friends, flow of ideas, dear ones & all those who
helped us in completion of this work. A special thanks to our
parents, who taught us the value of hard work by their own example
and who instilled us the free thinking and the joy of making
researches.
-
iii
TABLE OF CONTENT
Title Page No. ABSTRACT i ACKNOWLEDGEMENT ii TABLE OF CONTENTS
iii LIST OF FIGURES v LIST OF SYMBOLS vi CHAPTER 1: Introduction
1-12
1.1 General
1.2 Ornithopter 1.3 Different from an airplane or helicopter
1.4 Flapping Wing Aerodynamics 1.5 Flapping Wing Worldwide 1.6
Different Layouts
1.7 Applications of Ornithopter CHAPTER 2: Literature Review
13-16 CHAPTER 3: Problem Identification 17-18 CHAPTER 4:
Methodology 19-23 4.1 Theoretical Model 4.2 Mechanical Modeling
CHAPTER 5: Selection of Design Parameter 24-29 5.1 Gear Arrangement
5.2 Wings 5.3 Overall Parameters CHAPTER 6: Design and Fabrication
30-38 6.1 Body
6.2 Wings and Tail 6.3 Drive Train 6.4 Battery 6.5 Motor
-
iv
6.6 Actuators and Receiver 6.7 Transmitter 6.8 Microcontroller
6.9 Final Assembly
CHAPTER 7: Experimental Section 39-40 7.1 Motor Testing
7.2 Drive Train Testing
7.3 Electrical Component Setup and Testing 7.4 Actuator
Testing
CHAPTER 8: Result and Discussion 41-43 8.1 Result 8.2
Discussion
CHAPTER 9: Conclusion and Future Work 44-46 9.1 Conclusion 9.2
Future Work
References 47
-
v
LIST OF FIGURES
S. NO. TITLE PAGE NO. FIG. NO. 1 Leading edge vortex 05 1 2 Clap
and Fling mechanism 06 2 3 Wing rotation over one flapping cycle 07
3
4 DelFly 08 4 5 Robotic insect 08 5 6 Flapping wing at ETH 09 6
7 Direct actuation 10 7 8 Actuation with mechanism 11 8
9 Mechanism combine with torsional spring 11 9 10 Process flow
diagram 23 10 11 Strut type gear 25 11 12 Plate type gear 26 12 13
Chain drive 26 13 14 Body design 32 14 15 Main wings design 33 15
16 Tail wing design 33 16 17 Originally intended flapping mechanism
34 17 18 Gear arrangement 34 18
19 150mAh 3-7V Li-Po battery 35 19 20 Solarbotics GM15A 35 20 21
Microstrain 3DM-GX1 IMU 36 21 22 Arduino microcontroller 37 22
23 Final assembly 38 23
-
vi
LIST OF SYMBOLS
Tm Number of teeth on the main gear Tp Number of teeth on the
pinion gear G Gear ratio Nn Nominal speed of the main motors Na
Actual speed of the motors V Voltage of the Li ion battery KV KV
rating of the main motors
Loss coefficient of the motor owing to frictional forces
Rotational speed of the rotor W Weight force on the ornithopter
body Mb Mass of body FL Lift force on the rotor blade CL
Coefficient of lift
h Rotational speed of rotor at hover condition vb Linear speed
of the blade A Area of rotor disk FL(t) Total lift force acting on
tail
FL(b) Lift force acting on body FD Drag force
CD Coefficient of drag FC Centripetal force
R Radius of rotor disk
-
1
CHAPTER ONE INTRODUCTION
-
2
CHAPTER 1 INTRODUCTION 1.1 General
The research on Micro Aerial Vehicles (MAV) is a comparably
young field, which has emerged over the past few years. The ongoing
miniaturization of electric components such as electric motors and
the improvements in microelectronics made it possible to build
miniature planes and helicopters at relatively low costs. This
development also made it possible to start imitating insect and
bird flight, which need a sophisticated miniaturized actuation
chain for their flapping wing motion. The goal of this research is
to come up with small aerial vehicles that can operate
independently from ground stations, performing certain operations
such as surveillance or measurement, especially in environments
that are hardly accessible or even dangerous for people. The United
States Air Force has been pursuing design projects for surveillance
vehicles that have the ability to disguise themselves in plain
sight. One of these avenues has been the research and development
of micro aerial vehicles, or MAVs. These vehicles often mimic the
flight characteristics of hummingbirds and dragonflies because of
their size and unique hovering capabilities (AeroVironment Inc.
Nano Hummingbird) MAVs will be used as miniature surveillance
instruments and will aid the soldiers and civilians of the
future.
The micro aircrafts are designed based on the three ways for
lift generations. They are fixed, rotary and flapping wings. Among
of these methods the flapping wing propulsion systems occupy a
special place because so many living species have developed them.
For comparison of man-made objective and flying creatures,
researchers use the relative speed parameter (Ratio of the speed of
flying to maximum length of an object). The birds and insects have
relative speed between 60 and 170, while this value for jet
airplanes is between 4 and 9. These notes demonstrate the
importance of flapping crafts to design of more efficient airplanes
to reach to higher relative speeds.
A successful design of flapping-wing crafts requires the
contribution of different disciplines including aerospace and
biology. It is known that flapping flight of birds is a coupled
pitching and plunging oscillation with a phase difference between
these two motions. This concept has led engineers to design the
next generation of flapping-wing
-
3
crafts. A typical flapping-wing craft which is preliminary
composed of a fixed body, two flapping-wings and a controlled tail.
The fixed body typically consists of battery, flapping mechanism
and motors, electrical controlling systems.
Many experimental, theoretical and computational works have been
conducted for understanding the flapping-wing aerodynamics. It is
still not clearly known how to distribute the pitching angle and
plunging velocity over the flapping cycle to achieve a desired mean
thrust and lift and at the same time to minimize the required power
for flapping the wings at realistic frequencies and amplitudes.
1.2 Ornithopter An ornithopter (from Greek ornithos "bird" and
pteron "wing") is an aircraft that
flies by flapping its wings. Those machines are driven by
rotating airfoils. In an ornithopter, the driving airfoils have an
oscillating motion instead. This imitates nature, because no
animals have any rotating parts.
The ornithopter works on the same principle as the airplane. The
forward motion through the air allows the wings to deflect air
downward, producing lift. The flapping motion of the wings takes
the place of a rotating propeller. The wing design is designed with
the spar as far forward of the airfoil but still having acceptable
dimensions of strength. Engineers and researchers have experimented
with wings that require carbon fiber, plywood, fabric, ribs, and
the trailing edge to be stiff, strong, and for the mass to be as
low as possible. Any mass located to the aft or empennage, reduce
the wings performance and hinder the design of the ornithopter. In
order to calculate the performance of the ornithopter, the wings
lift is determined by the lift of the wing versus weight, drag and
thrust. A smooth aerodynamic surface with a double-surface airfoil
is more efficient then a single-surface airfoil to produce more
lift.
1.3 Different from an airplane or helicopter Unlike airplanes
and helicopters, the driving airfoils of the ornithopter have a
flapping or oscillating motion, instead of rotary. As with
helicopters, the wings usually have a combined function of
providing both lift and thrust. Theoretically, the flapping wing
can be set to zero angle of attack on the upstroke, so it passes
easily through the air.
-
4
Since typically the flapping airfoils produce both lift and
thrust, drag-inducing structures are minimized. These two
advantages potentially allow a high degree of efficiency.
In propeller- or jet-driven aircraft, the propeller creates a
relatively narrow stream of relatively fast moving air. The energy
carried by the air is lost. The same amount of force can be
produced by accelerating a larger mass of air to a smaller
velocity, for example by using a larger propeller or adding a
bypass fan to a jet engine. Use of flapping wings offers even
larger displaced air mass, moved at lower velocity, thus improving
efficiency. In order to create an effective ornithopter, it had to
be able to flap its wings to generate enough power to get off the
ground and travel through the air. Efficient flapping of the wing
is characterized by pitching angles, lagging plunging displacements
by approximately 90 degrees. Flapping wings increase drag and are
not as efficient as propeller-powered aircraft. To increase
efficiency of the ornithopter, more power is required on the down
stroke than on the upstroke. If the wing on the ornithopter was not
flexible and flapped at the same angle while moving up and down, it
would act like a huge board moving in two dimensions, not producing
lift or thrust. The flexibility and move-ability of the wing let it
twist and bend to the reactions of the ornithopter while in
flight.
1.4 Flapping Wing Aerodynamics Lift is the force that utilizes
the fluid continuity and Newton's laws to create a
force perpendicular to the fluid flow. It is opposed by weight,
which is the force that pulls things towards the ground. Thrust is
the force that moves things through the air while drag is the force
of flight that is an aerodynamic force that reduces speed.
The ornithopter wing is attached to the body at sight angle,
which is called the angle of attack; the downward stroke of the
wing deflects air downward and backward
generating lift and thrust. Also the wing surface is flexible,
this causes the wing to flex to the correct angle of attack we need
in order to produce the forces that we want to achieve flight.
The mechanics of flapping flight are far more complicated than
that of fixed -wing flight. For an aircraft with fixed wings, only
forward motion is necessary to induce aerodynamic lift. But for
flapping flight wing not only has to have a forward motion, but
-
5
also must travel up and down. This additional dimension means
the wing constantly changes shape during flight.
The air flow field in flapping wings cannot be assumed as
steady. A large angle of attack would lead to flow separation and
turbulences too. Obviously, there must be phenomena producing extra
lift. This unsteady aerodynamics cant be explained by common
airfoil theory and are illustrated below.
1.4.1 Unsteady Aerodynamics The highly difficult fact is that
lift production of flapping wing mechanisms are
explained with unsteady aerodynamic effects is the reason for
the emerging and so far not yet fully explored field of FWMAVs. In
the following the most important effects are listed.
Leading edge vortex Clap and fling mechanism Rotational lift
Wing-wake interactions A leading edge vortex (LEV) is created at a
high angle of attack. A high angle of
attack would normally lead to flow separation. But the LEV is
responsible for the flow to stay attached to the wing. At the
beginning of the down stroke, a strong vortex flowing from the base
to the tip is formed at the leading edge and helps to generate high
lift force. This is best seen in the right part of the next
figure.
Fig.1 Leading edge vortex [10]
-
6
In the left part another effect of the LEV is shown. The vortex
generated in the down stroke is separated after it reaches the tip
of the wing. This vortex works as a support for the upstroke and
helps to produce even more lift force. In the clap and fling
mechanism the wings come together dorsally at the end of the
upstroke to perform a clap (A).
Fig.2 Clap and fling mechanism [10]
After the clap the wings fling apart (B). Air is sucked in (C)
as the wings start to move downwards creating a bound vortex on
each of the wings which produces an instantaneous lift force (D).
At the end of each half stroke, the wing performs a rotation around
a span wise axis which allows an insect to maintain a positive
angle of attack during both down stroke and upstroke.
-
7
Fig.3 Wing rotation over one flapping cycle [10] This rotation
guarantees continuous lift production over the whole flapping
cycle.
The wings operate with the surrounding flow in specific ways.
Used air interacts positively into the flapping process. This
phenomenon is also referred to as wake capture.
1.5 Flapping Wing Worldwide Birds inspired Leonardo da Vinci
when he designed his ornithopter in 1490.
Leonardo da Vinci was interested in flying during 14881514. He
never saw his dream of flight take place because his ornithopter
was too heavy and required too much energy to produce lift or
thrust. In 1929, the human-powered ornithopter constructed by
Alexander Lippisch was towed into the air and glided around. In
1959, in England, another ornithopter was towed into the air and
demonstrated the ornithopter being a birdlike machine. By the
1960s, there were powered unmanned ornithopter flights of various
sizes demonstrating how ornithopter flew. In 1991 Harris and
DeLaurier flew the first successful engine-powered remotely piloted
ornithopter in Toronto, Canada. By 1999, there was an ornithopter
design that was designed to take off from a level pavement.
1.5.1 DelFly DelFly is a MAV developed at TU Delft in the
Netherlands. It has four wings,
which are actuated by one electric motor. The wings are arranged
in pairs, with the right upper wing connected to the left lower
wing and vice versa. Via a small gear train the wing pairs are
connected to the electric motor so that the upper and the lower
wing flap
-
8
towards each other. In forward flight, the course can be
controlled with rudders installed at the tail of the vehicle.
DelFly also carries a camera onboard that sends images to a ground
computer from where the vehicle is controlled.
Fig.4 DelFly [6]
1.5.2 Robotic Insect Another interesting project is the so
called Robotic Insect, being developed at the
Harvard Microrobotics Laboratory. The underlying concept is the
flapping motion of small insects such as flies. For the actuation
of the wings of this very small scale MAV a
piezoelectric cantilever is used, inducing an oscillation of the
wings at their resonance frequency, in order to produce high
amplitude. The joints are integrated in the structure as flexible
parts. The power supply however is not included in this vehicle,
which means that despite of already producing remarkably high lift
it is not yet able to actually fly.
Fig.5 Robotic Insect [6]
-
9
1.5.3 Flapping Wings at ETH The autonomous system lab (ASL) at
ETH also aims to develop a MAV of bird
size that is based on the aerodynamic principles used in insect
flight and by small birds. Unlike other developments in this area,
the intended MAV at ETH shall be able to hover like insects or
Humming birds, and so it is supposed to become an interesting
alternative to helicopters as currently being developed at ASL.
Furthermore, such an aerial vehicle should be large enough to carry
some payload such as a camera, but still small enough to have high
agility. Hovering is closely connected to unsteady aerodynamic
effects at small Reynolds numbers used in nature by insects and
small birds. With a wingspan of 280mm and a weight of about 20g the
Giant Hummingbird is one of the largest species in nature that can
hover, and therefore had been selected as natural ante type. The
goal, hover, is not to copy nature but to adopt the basic
principles.
Fig.6 Flapping wing at ETH [6] In the last few years,
comprehensive researches have been conducted on the
kinematic optimization of flapping-wing vehicles and on its
influence on aerodynamics involved in propulsion.
The experimental and numerical analyses conducted by
Triantafyllou et al.
showed that a Strouhal number between 0.2 and 0.4 leads the
propulsive efficiency to be maximized. With respect to the
numerical study by Pedro et al. the appropriate pitch amplitude is
also around 3040.
Based on the observations from natures, observations by Taylor
et al. demonstrate the obtained results by experimental and
computational works.
-
10
For more descriptions, Amiralaei et al. developed the 2D
Navier-Stokes which is associated with Finite Volume Method
simulating the flapping-wing in low Reynolds Number flows. They
have demonstrated that the importance of pitch amplitude and phase
angle difference between plunging and pitching is more than
Reynolds and Strouhal numbers. They also announced that the best
aerodynamic performance occurs in symmetrical oscillations.
1.6 Different Layouts One of the most important criteria that
the mechanism should fulfill is simplicity.
Hence the number of components needs to be limited and the
entire design should be compact. In the following sections, three
possible layouts for the actuation mechanism are presented.
1.6.1 Direct Actuation Starting with an electric motor and a
wing, the mechanism to be found will define
how the movement from the motor is translated to the wing. The
simplest way to connect motor and wing is to attach the wing
directly to the motor (figure 7).
In order to obtain flapping of the wing, the motor can be fed by
an alternating input signal, which is intended to result in a
periodic oscillation of the wing within certain amplitude. This
design is quite simple, no additional parts and joints would be
needed which means that the weight can be kept low. Another
positive effect of direct actuation is that the possible flapping
amplitude of the wing is not predefined, but can be varied by the
input signal. The possibility to vary the flapping amplitude and to
set the frequency can be seen as two degrees of freedom. Over all
it can be said that this design brings very high flexibility.
Fig.7 Direct Actuation [10]
1.6.2 Actuation with Mechanism Another possibility for
transferring the motion from the motor to the wing is to
use a lever (figure 8). The wing is articulated at a fixed
joint, and a lever is attached directly to the motor's shaft, so
that the end of the shaft rotates around the motors center of
rotation on a circular path. A second lever connects the end of the
motor lever with the
-
11
wing, and translates the rotation from the motor to an
oscillatory motion at the wing. The wing now follows a clearly
defined motion with constant amplitude. The value of this amplitude
as well as the transfer characteristics between motor motion and
wing depend on the geometry of the levers. Compared to concept A,
this mechanism only has 1 degree of freedom, which is the
rotational speed of the motor
.
Fig.8 Actuation with Mechanism [10]
1.6.3 Mechanism combined with torsional spring The mechanism in
this concept is basically the same as in concept B, but with
the
addition of a torsional spring in series at the wing's center of
rotation (figure 9).The idea of the torsional spring is that the
flapping amplitude gets amplified if the wing is actuated at
resonance.
During one oscillation cycle, the motor has to accelerate the
wing into one
direction, then stop it and accelerate it into the opposite
direction. This needs energy because the motor is not operated at
constant conditions. The idea of the torsional spring is that it
supports the motor by storing energy when the wing is stopped and
releasing this energy in the acceleration phase. Therefore it
should have a positive effect on the flapping motion and make the
mechanism run smoother. Also, higher amplitudes than without spring
are possible.
Fig.9 Mechanism combined with torsional spring [10]
-
12
1.7 Applications of Ornithopter Practical applications
capitalize on the resemblance to birds or insects. The
Colorado Division of Wildlife has used these machines to help
save the endangered Gunnison Sage Grouse. An artificial hawk under
the control of an operator causes the grouse to remain on the
ground so they can be captured for study.
Because ornithopters can be made to resemble birds or insects,
they could be used for military applications such as aerial
reconnaissance without alerting the enemies that
they are under surveillance. Several ornithopters have been
flown with video cameras on board, some of which can hover and
maneuver in small spaces. In 2011, AeroVironment, Inc. demonstrated
a remotely piloted ornithopter resembling a large hummingbird for
possible spy missions and they can also used for-
Defense applications Wild life study and photography Traffic
monitoring Tracking criminal and illegal activities Inspection of
pipes Border surveillance Reconnaissance Surveillance Seismic
detection
-
13
CHAPTER TWO LITERATURE REVIEW
-
14
CHAPTER 2 LITERATURE REVIEW Baker, N. S., et al1
This paper describes the fabrication, development, and testing
results for a proof-of-concept bio-inspired flapping wing Micro Air
Vehicle (MAV) actuation system. This paper also discusses proposed
EAP configurations as well as the electrical power supply and
methods employed for controlling the actuation system.
Esfahani, M. A., et al2 In this paper the optimization of
kinematics, which has great influence in
performance of flapping foil propulsion, is investigated. The
purpose of optimization is to design a flapping-wing micro aircraft
with appropriate kinematics and aerodynamics features, making the
micro aircraft suitable for transportation over large distance with
minimum energy consumption. In this paper the optimization of
flapping-wing micro
aircraft based on the kinematics of flying is conducted using
the multi-objective genetic algorithm. A rectangular NACA0012
airfoil with high aspect ratio is specified and according to
manipulation of pitch amplitude, wing reduced frequency and phase
difference between plunging and pitching the optimization is done.
The optimization procedure is performed based on the both
propulsive efficiency and thrust. The aerodynamic model used for
simulation of flapping foil follows 2D quasi-steady
approximation.
Floreano, D., et al3
In this article they explained how flapping micro air vehicles
(MAVs) can be designed at different scales, from bird to insect
size. The common believe is that micro fixed wing airplanes and
helicopters outperform MAVs at bird scale, but become inferior to
flapping MAVs at the scale of insects as small as fruit flies. Here
they present our
experience with designing and building micro flapping air
vehicles that can fly both fast and slow, hover, and take-off and
land vertically, and they present the scaling laws and structural
wing designs to miniaturize these designs to insect size.
-
15
Hsu, C. K., et al4 In the paper, they discussed about an
approach they used to design flapping wing Micro Air Vehicles
(MAV). The approach makes use of the conventional precision
machining methods, such as Rapid Prototyping 3D printing,
Electrical Discharge Machining and Laser Micromachining techniques,
to manufacture the MAV parts.
Malik, M. A. and Ahmad, F.5 In this paper Modified Strip Theory
based on blade elemental analysis has been used to develop the
aerodynamic model for semi-elliptical wing form. Parametric study
has been carried out to show the effect of different parameters on
lift, thrust and drag forces for better understanding of
ornithopter flight.
Patil, R., et al6 The main objective of this paper is to
introduce one of the promising Rapid
Prototyping (RP) technology as a potential application for the
fabrication and development of a Flapping Wing Micro Air Vehicle (a
rubber band powered Ornithopter). The conventionally constructed
Ornithopter of Balsa Wood has been compared with an Ornithopter of
ABS-M30 constructed using RP technology (Fused Deposition
Modeling). An assessment of their flight time, cost and time
involved in the construction, demonstrated the significance of RP
technology in the development of MAVs. Further, it is concluded
that RP technology can be a right choice to make aerodynamic body
parts or airframe structures either hollow or porous which in turn
would help in weight reduction with enhanced strength and further
with improved flight characteristics.
Pornsin-Sirirak, T. N., et al7 This paper reports the successful
development of Microbat the first electrically
powered palm-sized ornithopter. This first prototype was flown
for 9 seconds in October 1998. It was powered by two 1-farad super
capacitors. Due to the rapid discharge of the capacitor power
source, the flight duration was limited. To achieve a longer
flight, a rechargeable battery as a power source is preferred. The
second prototype houses a small
-
16
3-gramrechargeable Ni-Cad battery. The best flight performance
for this prototype lasted 22 seconds. The latest and current
prototype is radio-controlled and is capable of turning left or
right, pitching up or down. It weighs approximately 12.5 grams. So
far, the best flight duration achieved is 42 seconds.
Tandon, A., et al8 In this paper to better study the control of
flapping wing flight they have researched
and modeled a large scale ornithopter called the Garuda. The
Garuda is capable of carrying a microcontroller, sensor package and
an on board surveillance camera to transmit live video feed to the
receiver in real time. The design takes special care to optimize
payload capacity, crash survivability, and field repair abilities.
This model has applications in the field of defense spy
surveillance over enemy territories without being detected or
arousing suspicion.
Wood, R.J.9 In this article an elegant manufacturing paradigm is
employed for the creation of a
biologically inspired flapping-wing micro air vehicle with
similar dimensions to insects. A novel wing transmission system is
presented which contains one actuated and two passive degrees of
freedom. The design and fabrication are detailed and the
performance of the resulting structure is clarified highlighting
two key metrics: the wing trajectory and the thrust generated.
-
17
CHAPTER THREE PROBLEM IDENTIFICATION
-
18
CHAPTER 3 PROBLEM IDENTIFICATION
Many studies have been able to model and simulate insect control
mechanisms and grasp an understanding of the aerodynamics behind
the flight mechanism but very few have designed methods of controls
in mechanical design. Therefore there is a need for mechanical
designs for control mechanisms in flapping wing micro aerial
vehicle. Practicality is also an issue, many prototypes that are
small in size but require an external power source, without the
ability to fly independently and without control they cannot fly
effectively and efficiently.
As mentioned earlier, the project was motivated by the work of
the DelFly. DelFly is a MAV developed at TU Delft in the
Netherlands. It has four wings, which are actuated by one electric
motor. The wings are arranged in pairs, with the right upper wing
connected to the left lower wing and vice versa. Via a small gear
train the wing pairs are connected to the electric motor so that
the upper and the lower wing flap towards each other. Due to the
lack of appropriate testing measures, it was determined that a
testing mechanism for flapping wing MAV prototypes would need to be
developed in addition to the creation of a framework for
ornithopter design. Upon consideration of these issues, the project
goal was established.
Based on the goal, the project called for the creation of two
separate components: a theoretical model and ornithopter prototype.
The theoretical model provides the framework for the development of
ornithopter designs and the physical prototype provides a device on
which to conduct test experiments.
-
19
CHAPTER FOUR METHODOLOGY
-
20
CHAPTER 4 METHODOLOGY The methodology which we used in our
project completion is divided into two sections that match the
goals set for the project. Section 4.1 outlines the theoretical
model, how it was modeled and considerations that were taken into
account for the mechanical design. Section 4.2 describes the steps
taken in manufacturing and creating the flapping wing MAV prototype
based upon considerations from the theoretical model and it shows
in detail the experiment used to analyze the physical prototype and
validate the theoretical model. It should be noted that hereafter,
the term airfoils will be referred to as wings.
Reject
Reject
Fig.10 Process flow diagram
Selection of Project Area
Literature Review
Literature Review on Selected Projected Title
Title Finalization
Problem Identification
Selection of Design Parameter
CAD Design
Material Selection
Result and Discussion
Experimental Section
Conclusion and Future Work
-
21
4.1 Theoretical Model A theoretical model is a description
technique which applies mathematical and
scientific concepts to engineering disciplines for the purpose
of explaining systems, studying the effects of different components
within the system, and predicting component behavior. Theoretical
modeling is a highly beneficial pre prototyping measure that allows
for a better understanding of the needs and capabilities of a
system physical model prior to construction. This concept was
utilized to aid in the creation of the flapping wing MAV prototype
component of the test platform.
This section comprises of Selection of project, Literature
review, Title finalization, Literature survey on selected topic,
problem identification and selection of design parameter. They are
further explained.
4.1.1 Selection of project Among the 5-8 project topics we
choose flapping wing micro aerial vehicle as our
final project. The first step of this process, identification,
requires a clearly defined and communicated strategy. The best
option would be to set up a strategy development process that
contains project identification and project selection as an
integral part. 4.1.2 Literature review
In the literature review we read about as possible as
literatures on different topics. After reading the entire papers,
we decided to make flapping wing micro aerial vehicle.
4.1.3 Title finalization After the literature survey we found
that this topic is under our criteria, we
decided to make this topic as our final year project. 4.1.4
Literature survey on selected topic
Then finally we read literatures on selected topic and problem
identification is carried out in the project. 4.1.5 Selection of
design parameter
In this section the required parameters like weight, size, shape
etc. are taken or calculated.
-
22
4.2 Mechanical Modeling The flapping wing MAV proposed design
utilized an electric motor to transfer
power to the wings and thus produce lift. For this reason, most
of the theoretical modeling focused on the mechanical system that
transfers that power. To simplify the model, the system was divided
into three subsections; the drive mechanism (slider crank and
motor), the double rocker mechanism, and the wing component. To
begin, the slider-crank two bar linkage converts the rotational
motion of the motor into linear motion that moves the wings. The
velocity and position of the slider can be determined through
knowing the motors speed. The next component is the double-rocker
two bar linkage. This linkage amplifies the angular displacement of
the wing relative to the slider-cranks linear movement from the
slider-crank.
This mechanism also serves as the pivot position and shoulder
joint for wing motion. Finally, the wings are modeled as flat
plates with a given attack angle during the forward and
backstroke.
The overall goal in creating a theoretical model to acquire an
understanding of the lift forces acting on the ornithopter.
Accordingly, known aerodynamic concepts for lift of a fixed plate
were incorporated within the model to assist in analyzing these
forces. By understanding the kinematics of actuation, the
transmission of force from the motor to the wing was tracked. An
understanding of the typical forces was developed using the
equations for lift.
This section comprises of CAD design, material selection and
experimental section.
4.2.1 CAD design On the basis of design parameters a CAD design
is made with the help of CATIA
or other design software.
4.2.2 Material selection Then the required materials are also
select for the fabrication of flapping wing
micro aerial vehicle.
4.2.3 Experimental section Finally the experimental section will
be carried out and results are taken, than the
conclusion of project report will be declared.
-
23
CHAPTER FIVE SELECTION OF DESIGN
PARAMETER
-
24
CHAPTER 5 SELECTION OF DESIGN PARAMETER
The design of the Flapping Wing MAV is carried out with a
thorough understanding of the working of the various mechanical
elements and parts used in the fabrication of the system. The
various mechanical elements of the system are:
Gear arrangement Wings The electrical components are of equally
vital significance in the fabrication the
flapping wing MAV. The different electrical components used
during the course of fabrication are as follows:
Power supply (LiPo Battery) Micro controller Electric motors
5.1 Gear Arrangement Unless we use an electric motor, we'll need
to gear down the motor speed, so that it
gives enough torque to flap the wings. In designing the flapping
wing aircraft, gearbox can be one of the most challenging parts of
the ornithopter to build. There are different types of gear
mechanisms; few of them are:
5.1.1 Strut Type Gearbox This type of gearbox is recommended for
micro-sized Ornithopters because it is
very simple. In a strut type gearbox, the gear axles are spaced
along a linear rail of strut as shown in figure 10. The strut type
gearbox has no bearings and since the large ornithopters require
bearings to support the loads, so this type of gearbox is not
suitable for large ornithopters.
Fig. 11 Strut type gear [11]
-
25
5.1.2 Plate Type Gearbox The plate type gearbox is recommended
for larger ornithopters, because of its
compatibility with bearings. It has dual crank mechanisms and is
a more complex design. Figure 12 shows a plate type gearbox that
consists of two or more plates with spacers between them, with
bearings to support the gear axles.
Fig. 12 Plate type gear [11]
5.1.3 Chain Drive This type of gearbox is also used for large
ornithopter because it reduces the
weight of the system by distributing load onto more of the gear
teeth.
Fig. 13 Chain drive [11]
5.2 Wings When fabricating ornithopter, an efficient wing design
can make the difference
between failure and success. This is where we talk about
aerodynamics to check where the lift comes from. The wings are the
main lifting body, which can make the flight success, so the wing
consideration is very important. An effective ornithopter must have
the wings, which are capable of generating thrust and the lift to
keep the aircraft airborne. Since, there will be drag and the
gravitational force (weight) pulling the aircraft backward and
downward respectively, so the thrust and lift must overcome the
drag and weight.
-
26
5.2.1 Geometric Similarities The concept of geometric similarity
can help relate different physical quantities
by means of the dimensional argument. If flyers are assumed to
be geometrically similar, the weight W, lift L, and mass m for
un-accelerated level flight, can be expressed with respect to a
characteristic length l as
W = L= mg .Eq. 1 Here, L=lift
The wing area S and weight are expressed as S = l2 .Eq. 2
W = l3 .Eq. 3 5.2.2 Wing Span
When we are studying the flapping birds or ornithopter,
parameters of interest are related to the body mass m of the bird
or ornithopter. We can relate the wingspan and mass by using
geometric similarity. Liu (2006) suggests that, over a large range
of the weight, birds and aircraft basically follow the power law as
given below:
l = 1. 654m1/3 (for aircraft) .Eq. 4 l = 1.704m1/3(for birds)
.Eq. 5
5.2.3 Wing Area The historical data shows that there is a large
variation in the wing area (Norberg,
1990). Greenewalt studied different species of the birds and
then categorized the birds into three categories (Greenewalt,
1975). He gave the relationship of the wing area and mass for big
birds as:
S = m0.78 .Eq. 6 5.2.4 Aspect Ratio
The AR is a relation between the wingspan b and the wing area S:
= 2 .Eq. 7 Generally, decreasing AR. increases the maneuverability
and induced drag tends to decrease with higher AR. Similarly; the
lift to drag L/D (glide ratio) increases with increasing AR.
-
27
5.2.5 Frequency The frequency by the birds or the ornithopter
flaps their wings depends on the size
of the ornithopter. The flapping frequency is an important
parameter in the ornithopter
design. There is an upper limit and lower limit of this
frequency. The upper and lower frequency limits means that the body
cannot flap the wings with the frequency higher or lower
(respectively) than the specified frequency due to structural and
power limitations. In an updated study, Pennycuick (1996) studied
different species of the birds and made a detailed analysis of the
frequency, leading to the following expression:
f = m3/8g1/2b23/24S1/3 3/8 .Eq. 8 Where
m = Mass of the bird (kg) g = Acceleration due to gravity (m/s2)
b = Wingspan (m) S = Wing area (m2) = Air density (kg/m3). The
above equation can be used to predict the wing-beat frequency of
species thats mass, wingspan, and wing area is known.
The following design parameters were used to guide project
development. 5.3 Overall Parameters 5.3.1 Cost
The total cost of the theoretical model and ornithopter
prototype may not exceed 5000/-. 5.3.2 Theoretical Model Parameters
1. Functionality:
The theoretical model must be input customizable and allow for
the performance prediction for any desired ornithopter weight,
dimension, or angle of attack.
The theoretical model must be able to predict expected
ornithopter prototype lift and airfoil flapping frequency for a
given set of input variables.
-
28
5.3.3 Ornithopter Prototype Parameters 1. Weight:
The prototype cannot exceed 500g in total weight 2.
Dimension:
The prototype chassis must be no larger than 20cm in either
width or length and cannot exceed 8cm in height.
The prototype airfoils may be no larger than 6cm in either
length or height. 3. Functionality:
The prototype must allow for synchronous flapping of the
airfoils. The prototype must allow for interchangeable airfoils.
The prototype must be powered by an electronic speed controller
(ESC), RC
Transmitter, and receiver.
-
29
CHAPTER SIX DESIGN AND FABRICATION
-
30
CHAPTER 6 DESIGN AND FABRICATION
Regarding the design of the mechanism it needs to be considered
that it is intended to actually fly, but only be used for further
studies and measurements. Hence the mechanism is not optimized for
lightweight but nevertheless kept as simple as possible, allowing
room for improvement towards a future mechanism that will be able
to fly.
The main purpose of this effort is to present an idea about how
to fabricate a flapping wing MAV. Here are few design
considerations, which are useful and necessary for designing and
fabrication of an ornithopter.
The course of action for this chapter included a detailed design
of the individual mechanical components of the flapping wing MAV
and then fabricating by assembling all the mechanical and
electrical components at the required places. The detailed design
of the mechanical components of the flapping wing MAV is carried
out using CATIA V5 software.
CATIA (Computer Aided Three-dimensional Interactive Application)
is a multi-platform CAD/CAM/CAE commercial software suite developed
by the French company Dassault System, in 1977 by French aircraft
manufacturer Avions Marcel Dassault. CATIA is PLM (Product
Lifecycle Management) software. CATIA enables the creation of 3D
parts, from 3D sketches, sheet metal, composites, molded, forged or
tooling parts up to the definition of mechanical assemblies. The
software provides advanced technologies for mechanical surfacing.
It provides tools to complete product definition, including
functional tolerances as well as kinematics definition. CATIA
provides a wide range of applications for tooling design, for both
generic tooling and mold.
CATIA can be applied to a wide variety of industries, from
aerospace and defense,
automotive, and industrial equipment, to high tech,
shipbuilding, consumer goods, plant design, consumer packaged
goods, life sciences, architecture and construction, process power
and petroleum, and services. CATIA V4, CATIA V5, Pro/ENGINEER and
Solid Works are the dominant systems.
-
31
6.1 Body Because weight is a significant design constraint, the
group eliminated metals as
an option for the body material and instead decided to research
composites and polymers. The group eventually narrowed the field to
two different materials. The first, balsa wood, had been used in
previous flapping wing MAVs. The group also found a polymer,
Polymethacrylimide foam that is often used in sandwich construction
and less dense than balsa wood. This foam is easy to shape, as it
can be sliced with a hot-wire foam cutter, and also adhesive to
epoxy, which would aid in the construction of the MAV. However,
this foam is less widely available than balsa wood, and thus more
expensive. Balsa wood would be easy to customize in-house, for it
can be easily cut and sanded to the desired size and shape.
Although balsa is denser than the polymer foam, the body is small
enough for this weight difference to be minimal. Because balsa wood
is cheap, customizable, and durable, the group selected it to build
the body of the MAV.
The shape of the body was designed to be simple and lightweight.
There is a solid piece running from the tail to the nose, where
there is another section designed to mount the drive train and
hinge. The length of the body was designed to match the wing span,
thus keeping the MAV as small as possible while making control
feasible as well. The body shape was finalized for ease of
manufacturing and for simplicity as well. The finalized drive train
was used to design the front part of the body, and a very
simplistic final design was chosen. Minimizing the frontal area
mitigates drag losses due to the frontal profile. To connect the
slim body structure to the front portion, a simple approach was
taken. Milling out a section on the front piece that the back
section could be slotted into and glued gave the body stability and
strength. The finalized body was rather simplistic, and its design
can be seen in Figure 14.
Fig. 14 Body design
-
32
6.2 Wings and Tail For a design involving two wings, it is
crucial for each wing to be as lightweight
as possible. For this purpose, the group decided to research
thin polyester films to comprise the wing, and lightweight spars to
provide support and allow for the flapping effect.
While researching different wing shapes, the group took previous
MAVs and manufacturing techniques into consideration. The design,
mostly rectangular in shape, was selected to mimic that of the
DelFly. This design will prevent the wing spars from being overly
complicated and flimsy, while still keeping much of the surface
area necessary for lift. The design is tapered at the outer edge of
the trailing edges, allowing for the support spar to bed closer to
the leading edge and preventing the backside corners of the wings
from being unstable during flapping.
Fig. 15 Main wings
The group also researched multiple designs for the tail
structure. The first option considered was an inverted V-tail. This
requires only two control surfaces; however the MAV would not be
highly maneuverable. This is demonstrated by the DelFly, where the
V-tail was abandoned due to inadequate control of longitudinal
motion in wake of the flapping wings.
-
33
Fig. 16 Tail wing
6.3 Drive Train The motion of the hinge will be created by a
drive train connected to the motor.
The group considered a single drive train options. The first
contained gears that would spin parallel to the axis of forward
movement (with their axels perpendicular). Although this design has
been successfully implemented onto previous MAVs, it was dismissed
due its complicated drive train and the effect that gyroscopic
forces would have on flight. Instead, the group chose a method
involving counter-rotating gears, spinning perpendicular to the
forward movement of the MAV (with their axels parallel).
Mechanically, this design is more simple and easier to construct,
and due to the counter-rotation, the gyroscopic forces would be
minimized.
Fig.17 Diagram of the originally intended flapping mechanism
From our motor tests we discovered that a drive train ratio of
70:7 would be desirable, and we ordered gears to match this design.
This would give us an acceptable drive train
-
34
assembly, and this drive train can be seen in Figure 17. This
drive train is simplistic and secure, so we are anticipating
minimal issues with its assembly.
Fig.18 Gear arrangement
For the design of the drive bar and the other design parameters,
we used CATIA V5R16 to create and test the kinematics of the drive
train.
6.4 Battery Lithium polymer batteries are commonly used in
remote controlled planes and
MAVs. These batteries are fairly cheap and lightweight, which
allows for longer and smoother flights. After researching many
lithium polymer batteries, the group settled on a one cell, 160
milliampere-hour, and 3.7 volt battery from the vendor DraganFly
(rctoys.com). The group researched both batteries and motors
together, for the battery must have the ability to run the motor.
The battery voltage is crucial, for if it is below the nominal
voltage of the motor, the motor will not start. The electrical
charge of 160 mAh is comparable to batteries used in other small
ornithopters. This battery was also selected for its small mass of
4.1 grams and slender profile that will allow it to fit nicely into
the
body of the MAV.
Fig.19 150mAh-3-7V-Li-PO-Battery [8]
-
35
6.5 Motor The group researched different types of motors and
decided that a brushless DC
motor would be most appropriate for this project. Brushless
motors have several advantages over brushed motors. They have more
torque per weight, and more torque per watt, making them more
efficient. Brushless motors have increased reliability, leading to
a longer lifetime. The group narrowed the motor selection down to
two: the Hobby King AP-02 Brushless Micro Motor and the Micromo
Series 1307 004 BH brushless geared motor, each of which weigh less
than 2.5 grams.
Fig.20 Solarbotics GM15A [8]
6.6 Actuators and Receiver Because the tail will have three
separate control surfaces, it will require three
actuators to control these movements. The group initially
settled on the Toki Biowire servos from HobbyKing. Weighing only 1
gram each, these servos are fairly light, and their slender shape
would allow for easy integration with the rear end of the fuselage.
These servos would be able to rotate the elevators and rudders 30
in both directions. However, after further research, the group
discovered PlantracoMicroflights 1.1 gram magnetic actuators. With
the same range of motion and weight, this became the groups primary
choice. These actuators also cost half as much as the Biowire
servos, which will
make an effective difference when purchasing three. Because
these actuators are magnetic, the original plan to use small metals
brads to fasten them to the body was replaced with the design of
three actuator mounts. These mounts, made from PEEK, could be cut
using the Washburn Shops laser cutter.
-
36
Fig.21 MicroStrain 3DM-GX1 IMU [8]
6.7 Transmitter The group encountered issues with finding a
transmitter suitable for this project.
The receiver is designed to operate on a 900 MHz frequency. The
group sought to find a 900 MHz transmitter on campus; however all
of the transmitters owned by WPI professors unfortunately operate
on either 2.4 GHz or 72 MHz. These are the most
common frequencies for RC aircraft in the US and 900 MHz is hard
to find. This is because in the USA, 900 MHz is right on the edge
of the cell phone band, so amateur radio applications like RC
planes stay away from that range. However, our receiver was
manufactured in Canada where the cell phone band ends at 850 MHz,
allowing RC applications to extend further.
Some older transmitters made for robotic applications have been
made to operate on the correct frequency. One such transmitter was
obtained by the group from the local FIRST robotics chapter. This
transmitter was designed to plug into a computer and simply serve
as a transmitter for a ground station. Finding documentation for
the controller, cable to attach to a computer, and programming a
ground station would have been very difficult for the limited time
available to our group. The group decided to pursue other
options.
The group decided to purchase a transmitter from plantraco, the
same vendor for the actuators and receiver. This circumnavigated
the problem entirely as this transmitter is 900 MHz and designed to
work specifically with Plantraco products. The transmitter has
controls for throttle, rudder, elevators, and ailerons. Since this
design calls for two separately moving elevons and a rudder the
aileron and elevator control will both be used to control the
flaps.
-
37
6.8 Microcontroller The group originally planned on programming
the MAV to run autonomously. If
this is the case, a microcontroller is necessary. However, the
group determined autopilot is not a primary objective of this
project, and using a transmitter to control the MAV remotely is a
much more practical option. In future developments and experiments
with autopilot, the group recommends a microcontroller such as the
Arduino Pro Mini, which has several analog and digital inputs and
has been widely used at WPI. This MAV, however, will not contain a
microcontroller as it is outside the scope of this project.
Fig.22 Arduino microcontroller [8]
6.9 Final Assembly After manufacturing the individual parts,
assembly was rather straightforward.
The hinge, gears, drive bars, and control discs could all be
fastened to the body with small metal brads. Super glue is very
effective in attaching the spars to the hinge, as well as the
actuators to the mounts and subsequently, the mounts to the body. A
photograph of this assembly is shown below in Figure 23.
Fig.23 Final assembly
-
38
CHAPTER SEVEN EXPERIMENTAL SECTION
-
39
CHAPTER 7 EXPERIMENTAL SECTION 7.1 Motor Testing
The group performed a test on the motor to verify that it
operated as intended and its power output was as stated by the
manufacturer. For ease of testing, the receiver/transmitter was
replaced with an Arduino Uno board. This allowed for far greater
throttle control over the motor. Based on documentation for the
motor controller, it was established that the correct duty cycle at
full throttle had pulse duration of 2ms and the low throttle was
1.1ms. This was programmed into the Arduino and an oscilloscope was
used to verify the signal clarity. Because the Arduino nominally
outputs 5V, a voltage divider was created to lower the voltage to
3.7V. A 4k and a 3k resistor were used to reduce this voltage while
still maintaining a clear signal to the motor. In order to start a
brushless motor, the throttle must first be set at full, then zero,
then some middle throttle. The board was programmed to output this
and then run at 80% throttle continuously. To test the total output
of the motor system, enough torque was applied to stall the motor
while the total current draw was measured, based on the formula
W=AV The group was able to determine at 3.7V and full throttle the
motor draws 0.3A, giving a total of 1.1W of power.
7.2 Drive Train Testing After assembling the drive train, a test
was performed to ensure that the gears and
drive bars would perform properly. Because the motor had not yet
been mounted to the body, this was done through the use of a drill.
The drill, with the smallest gear attached to the drill tip and
locked into one of the larger gears, was spun at increasing speeds.
The drive train functioned properly, moving the hinge so that the
wings flapped in a
symmetrical manner.
7.3 Electrical Component Setup and Testing The electrical
components operate in two basic control loops that are then
connected together. The first control loop is the actuators,
transmitter and receiver working together to provide stability and
control. The actuators are plug and play with
-
40
the receiver and respond well to controls from the transmitter.
The receiver has magnetic points where a power supply can be
attached. At rest the receiver draws 40 mA of current and when the
actuators are moving the current draw peaks at 200mA. The second
control loop involves the motor and electronic speed controller or
ESC. All brushless motors require an ESC to function. The ESC takes
signals from the receiver and coverts them into a pulse with
modulation signal (PWM). A PWM signal is an analog signal that
behaves similar to a digital signal. It fluctuates between high and
low voltages and the ratio between the time it is high and the time
it is low is known as the duty cycle. Our receiver outputs a signal
known as Pulse Position Modulation. This signal is very similar to
a PWM signal except it outputs a larger magnitude of voltage. The
ESC is capable of converting between the two automatically and the
motor will be directly connected to the receiver.
7.4 Actuator Testing Before mounting the actuators to the body
of the MAV, tests are conducted to
ensure that the actuators function properly and can be
controlled in tandem by the dual joystick transmitter. Each of the
three actuators is wired into the receiver so that the two
actuators corresponding to the left and right elevators could be
controlled with horizontal movements of the left and right
joystick, respectively, and so the rudders actuator could be
controlled with vertical movements of the right joystick. This
would leave the vertical axis of the left joystick to interact with
the motors speed controller. Because this test was successful, the
group attached the actuators to the body using the PEEK mounts.
Next, a test is performed to ensure that the actuators were
powerful enough to move the tail structure. Unfortunately, with the
current design, the actuators were unable to spin the control discs
and move the tail. A solution to this is to design control discs
with larger
moment arms, thus allowing for the same actuators to move the
tail.
-
41
CHAPTER EIGHT RESULT AND DISCUSSION
-
42
CHAPTER 8 RESULT AND DISCUSSION
Many test flights were conducted with the finished flapping wing
MAV, first with an equivalent weight and distribution payload under
manual control to determine whether the machine would actually be
able to fly. Initial tests showed that sustained flight was
possible but the robot was exceedingly difficult to control and
quickly crashed. Later tests with a PD control on the elevator to
stabilize pitch qualitatively showed promise but difficulties with
gearbox and wing spar reliability plagued the testing process.
This process of breaking things during testing is an essential
part of the design process and leaps of progress were made during
this time in tracking down problems and implementing design
solutions to them. Parts of the gearbox like the connection between
the final rocker link and the shoulder were a common point of
failure and received stopgap design revisions until enough changes
accumulated for a full design iteration of the machine. Changes
were incorporated into the gearbox design, the electronics package
switched over to the much lighter Gumstix based system, and the
frame was reconfigured to balance the new weight distribution
properly.
8.1 Result The design process detailed by this report began with
an examination of the
project objective. This is to build a flapping-wing micro air
vehicle capable of takeoff, hover, and forward horizontal flight.
After a thorough literary review, it was decided that the wing
movements of most birds and insects is very complex with twists and
other motions that are not yet fully understood by experts. This
allows for the design of a vehicle capable of flight with a
simplified wing motion. These wings are attached to a symmetric
hinge that is powered by a motor. A battery powers the motor,
allowing for
free flight with an onboard power source. Aside from the main
wings, the design also includes a tail structure. Allowing full
movement in each component of the tail structure simplifies both
the design and manufacturing processes.
8.2 Discussion The flapping wing MAV made using gear drive which
was rotated through the
DC motor and it was tested for its flying capability. The flight
time of the Ornithopter (the time between the hand launch and its
landing on the ground) was recorded for many
-
43
trials. For a 150 mAh LiPo battery rotations of gear train an
average flight time of 5 minutes was observed. Whereas, for the
same rotations the balsa wood Ornithopter gave an average flight
time of 5 minutes 10 seconds. This limitation of flight travel time
mainly is because of the change in the weight of body material.
However, considering the fabrication method, balsa wood Ornithopter
is significant since the total time taken for the fabrication
procedure is found very short. The total time to transform CAD
models to physical models took only a time of 30 minutes.
Special light-weight material like balsa wood which is generally
used for building the MAVs is rarely available in few places in the
world. Cost and time factor for building the MAV from these kinds
of wooden materials also is comparatively high. Other materials
like fiberglass epoxy composite also exhibits high strength and low
weight to suit the MAV construction. However, there have been
difficulties to hold the desired aerodynamic shapes with these
materials.
-
44
CHAPTER NINE CONCLUSION AND FUTURE
WORK
-
45
CHAPTER 9 CONCLUSION AND FUTURE WORK 9.1 Conclusion
The goal of this thesis was to develop a Flapping Wing MAV
capable of hovering flight. The focus was also in the improvement
in wing design and controllability. These goals were, except of the
controllability, fully reached.
The chosen mechanism for turning rotation of the DC-motors into
a flapping
movement of the wings is accurate and leads to error free
functioning. By decreasing the amplitude even smoother behavior of
the motor can be expected.
Through more than 20 tests the wings were optimized in angle and
chord length and yield to enough lift generation for hover flight.
The weight of the MAV is about 250g and therefore could be extended
by additional hardware such as electronic or batteries or
sensors.
The static behavior with respect to controllability was not
fully characterized. It was shown that by changing the inputs to
the motors the applied torques can be changed also but there was no
reduction of the torques to the center of gravity of the MAV. The
motor controller that allows independent inputs to each motor is
essential for control issues. These input scan easily be mapped to
the wished behavior through a coupled gamepad.
9.2 Future Work In order to achieve more lift generation the
search space for finding the optimal
wing and mechanical configuration can be extended by a smoother
discretization and including also the wing shape. There were no
improvements on the motors so far. Many suppliers have the same
size of DC-Motors but with different parameters, such as velocity
constant.
Also there should be betterment in the controllability by
calibrating the motors and reducing play in the structure.
Concluding it can be said that the flapping wing MAV designed
and developed in this thesis is capable of hovering flight. Yet it
is not controlled and yields to torque in the
-
46
pitch and roll axis. The gained knowledge can be used for
further improvements and opens the way toward an autonomous
flapping wing MAV.
-
47
REFERENCES
1. Baker N. S., Hayes M., Smith D., Damman R.,Design of a
Flapping Wing Micro Air Vehicle Actuation System, OhioNorthern
University, Ada, OH 45810,2010.
2. Esfahani, M.A.,karbasian, H.R.,Esfahani, J. A.,
EbrahimB,Optimization of flapping-wing micro aircrafts based on the
kinematic parameters using genetic algorithm method, Ferdowsi
University of Mashhad, Iran.,pp.43-51,2013.
3. Floreano, D. (eds.),Flying Insects and Robots,
Springer-Verlag Berlin Heidelberg ,pp.31-37,2009.
4. Hsu, C.K.,Evans J., VytlaS. and Huang P. G.,Development of
Flapping Wing Micro Air Vehicles -Design,CFD, Experiment and Actual
Flight, Wright State University, Dayton, Ohio, 45435-00001,pp.
67-72,2010.
5. Malik, M. A. and Ahmad Farooq,Effect of Different Design
Parameters on Lift, Thrust and Drag of an Ornithopter, World
Congress on Engineering 2010 Vol II, WCE 2010, London,
U.K.,2010.
6. Patil R., Kumar S.M., Abhilash E., Fabrication Of Flapping
Wing MAV using Rapid Prototyping Technology, International Journal
of Emerging Technology and Advanced Engineering, Volume 2, Issue 2,
pp. 56-60, February 2012.
7. Pornsin-Sirirak T. N., Tai Y. C., Ho C. M., Keennon M.,
Microbat: A Palm-Sized Electrically Powered Ornithopter, USA,pp.
86-91,2008.
8. Tandon A., Vajpai A., Mishra A. N., Design of an Autonomous
Ornithopter with Live Video Reception for Military Surveillance,
SRM University, Chennai, India, International Journal of Research
in Engineering and Technology, Volume: 02 Issue: 10, pp.489-492,
Oct-2013.
9. Wood, R.J.,design, fabrication and analysis of a 3DOF, 3cm
flapping wing MAV, School of engineering and applied sciences,
Harvard University, Cambridge, ma02138,pp.106-114,2010.
10. SANE S. P., The Aerodynamics of Insect Flight, The Journal
of Experimental Biology 206, 4191-4208, 2003.
11. Yousaf U., Khan N. S., Conceptual Design And Practical
Recourse Of A Flapping Wing Micro Air Vehicle,CAE, Nust,
Pakistan.