Development of Flexible Wings and Flapping Mechanism With Integrated Electronic Control System, For Micro Air Vehicle Research

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T E C H N I C A L A R T I C L E

Development of Flexible Wings and Flapping Mechanismwith Integrated Electronic Control System, for Micro AirVehicle Research

H. Yusoff1, M.Z. Abdullah1, M.A. Mujeebu1, and K.A. Ahmad2

1 School of Mechanical Engineering, Universiti Sains Malaysia, Nibong Tebal, Penang, Malaysia

2 School of Aerospace Engineering, Universiti Sains Malaysia, Nibong Tebal, Penang, Malaysia

Keywords

Micro Air Vehicle, Bat Wing, Four-bar Linkage

Mechanism, Electronic Control System, Lift

and Drag, Flapping Angle

Correspondence

H. Yusoff,

School of Mechanical Engineering,

Universiti Sains Malaysia,

Engineering Campus,

14300 Nibong Tebal,

Penang, Malaysia

Email: [email protected]

Received: September 22, 2010; accepted:

January 6, 2011

doi:10.1111/j.1747-1567.2011.00729.x

Abstract

This paper presents the development of flexible wings, flapping mechanism,

and integrated electronic control system (ECS) to emulate the bat wing flapping

for the ongoing micro air vehicle (MAV) research. Three bat species having

dimensions close to the design requirement of MAV, namely, Mormopterus

Planiceps, Nytophilus Geoffroyi, and Scotorepens Balstoni were selected, and theaverage of their physical dimensions was chosen. The commercially available

titanium alloy, Ti 6Al 4V, was used for the wing frame, and the membrane

was made of latex. A four-bar slider-crank mechanism was designed and

fabricated to facilitate the wing flapping; ECS controlled the flapping frequency

in the real-time mode. The system was tested in open air wind tunnel at

frequency6 Hz, angle of attack(AOA)0 50

, and velocityrange 2 7 ms1. The

experimental flapping angle which is compared with the theoretical flapping

angle was obtained from the analytical kinematic model. The mean lift and drag

coefficients were also measured and the results were found to be excellent.

Compared to the manual control and measurement of flapping frequency,

the proposed ECS demonstrates efficient control and accurate measurement.

Moreover, the tedious procedure involved in the repeated calibrations for the

manual system is totally eliminated by ECS.

Introduction

Micro air vehicles (MAVs) are a class of unmanned

aircraft with a maximum size limited to 15 cm,

capable of operating speeds of 15 m/s or less. They

are used in military and defense tasks such as

over-the-hill battlefield supervision, bomb damage

assessment, chemical weapon detection, etc. They

have also applications in environmental, agriculture,

wildlife, and traffic-monitoring. Fixed, flapping, and

rotary wing MAVs are all viable candidates for these

missions. An excellent review on this topic was

provided by Shyy et al.1 The rapid advancement

in MAV design has driven the researches on flight

of insects, birds, and bats. Wings of thin and very

flexible membranes are unique to flying and gliding

mammals, such as bats, flying squirrels, and sugar

gliders, and these animals exhibit extraordinary

flight capabilities with respect to maneuvering and

agility that are not observed in other species of

comparable size. Bat wings are characterized by their

sufficiently flexible bones supporting very compliant

and anisotropic wing membranes; the unique features

of bat wing as a promising candidate for MAV has been

well established, as outlined by Swartz et al.2 The

founding researches on bat flight were summarized by

Norberg3 who studied the kinematics, aerodynamics,

and energetics of the long-eared bat Plecotus auritusin

slow horizontal flight.

Proper mimicking of the biological wing and

its flapping is a challenging task in the study

of aerodynamics of flexible skin flapping wings.

Moreover, an integrated electronic system to control

and monitor the flapping frequency is desirable as

Experimental Techniques37 (2013) 25 37 2011, Society for Experimental Mechanics 25


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Bat Wing Flapping Mechanism H. Yusoff et al.

it will provide more flexibility in measurements.

Many researchers have developed different types of

wings and flapping systems for diverse applications.

An outline of the previous works on wing design,

flapping mechanism, and control system is presented

as follows.

Pornsin-sirirak et al.4 developed MEMS-based

wing technology using titanium-alloy metal as

wing frame and poly-monochloro-para-xylylene

(Parylene-C) as membrane. They studied the

unsteady-state aerodynamics of various types of

MEMS-based and other wings. Finally, they

built a lightweight, palm-sized flapping-wing MAV

(FWMAV) which was demonstrated successfully. Kim

and Han5 proposed a smart flapping wing with a

macro-fiber composites (MFC) actuator to investigate

the aerodynamic characteristics related to the birds

and ornithopters. The membrane was made of PVC.

The camber of the wing could be changed by using

the MFC actuator to enhance the aerodynamic perfor-mance of the wing. It was shown that the deformation

of the wing surface generated by the MFC was suffi-

cient to control the lift and thrust, and the lift could

be increased by 20% when the MFC was actuated. In

a series of investigations to mimic the mammalian

flight, Galvao et al.6 and Song et al.7 studied the

aerodynamic performance of thin compliant wings.

They found that, in comparison with rigid wings,

compliant wings have higher lift slope, maximum

lift coefficients, and delayed stall to higher angles of

attack. The wings were fabricated with stainless-steel

frame and latex membrane. Lin et al.8 developed flex-

ible wings with carbon fiber frame and PVC plasticfilm membrane to simulate the flapping motion of

birds by means of four-bar linkage mechanism. The

wing motion of hummingbird and hovering insects

was mimicked by McIntosh et al.9 who devised a

novel mechanism to actuate the wings of a hover-

ing MAV. The mechanism used a single actuator, but

each wing could rotate about two orthogonal axes.

The wings were made of carbon fiber frame and

nylon fabric membrane. Nguyen et al.10,11 presented

the design of a motor-driven flapping-wing system

emulated the beetle (Allomyrina dichotoma), in terms

of dimension, flapping frequency, and wing kinemat-

ics. Carbon fiber was used as wing frame and kapton

film as membrane. Hu et al.12,13 studied the aerody-

namic benefits of flexible membrane wings for the

development of FWMAV. The time-averaged lift and

drag generation of two flexible membrane wings with

different skin flexibility (i.e., a flexible nylon wing

and a more flexible latex wing) were compared with

those of a rigidwing. The rigidwing was found to have

better lift production performance for flapping flight

in general. The latex wing was found to have the best

thrust generation performance for flapping flight. The

less flexible nylon wing, which has the best aerody-

namic performance for soaring flight applications, was

found to be the worst for flapping flight applications.

The success of a flapping mechanism lies in its abil-

ity to facilitate maximum degrees of freedom while

emulating the actual biological wing; maintaining

symmetry and wide angle of flapping are some of

the challenging tasks. With a basic four-bar linkage

mechanism, researchers have tackled this issue in a

variety of fashions. Baskar and Muniappan14 com-

pared three flapping mechanisms namely sliding link,

movable hinge, and fixed hinge, and found that the

fixed hinge mechanism was free from unsymmet-

rical flapping and strut movement. In a study on

the energetics of FWMAV, Madangopal et al.15 used

single-crank mechanism with springs to duplicate the

flying of insects; similar mechanism without springswas used by Lin et al.8 Use of lightweight piezo com-

posite actuator (LIPCA) with the four-bar linkage was

reported by Syaifuddin et al.16 The limited displace-

ment with a natural frequency of 9 Hz produced by

the LIPCA was transformed into large flapping angle

by the four-bar linkage system.

The lack of flapping symmetry encountered in the

single-crank four-bar system was rectified by the use

of double crank in series, as proposed by McIntosh

et al.9 However, Conn et al.17 demonstrated that the

flapping angle could be improved further by using

double crank in parallel. Employing a slider with

single crank was another way of maintaining flappingsymmetry, and this technique was simpler compared

to the use of double crank. Recently, Fenelon and

Furukawa18 have proposed a modified slider-crank

mechanism, in which a rotary actuator was employed

for the spherical joint, in order to enhance the

degrees of freedom. As remarkable contribution to

MAV research, Wood and coworkers1923 and Sitti24

developed and analyzed four-bar linkage flapping-

wing system inspired by the thoracic mechanism of

dipteran insects. A deviation from the basic four-

bar linkage was the use of Scotch Yoke linkage

mechanism, as proposed by Galinski and Zbikowski25

and Nguyen et al.10,11

As far as the control and monitoring of flapping

frequency is concerned, almost all researchers have

relied on external means such as oscilloscope, optical

sensor, and high-speed camera, which could measure

the frequency for a given setting. It would be more

convenient and effective to have an in-built electronic

system to measure as well as control the flapping

26 Experimental Techniques 37 (2013) 25 37 2011, Society for Experimental Mechanics


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H. Yusoff et al. Bat Wing Flapping Mechanism

frequency. In the present study which is focused

on the aerodynamics of flexible flapping wings for

FWMAV, the flapping of bat wing is emulated

by the use of motor-driven four-bar single-crank

slider mechanism. A microcontroller-based frequency

measuring and controlling system is also developed

and incorporated into the flapping mechanism. In

order to compare the aerodynamic performance,

thick and thin flexible wings are fabricated with

titanium alloy frame and latex membrane. The

ultimate objective of this study was to analyze the

effect of membrane flexibility on the aerodynamic

performance of flapping wings for MAVs. However,

this paper covers the details of development of

wings, flapping mechanism, and the electronic control

system (ECS); the analysis part will be presented in

our future article.

Materials and Methods

Wing development

Obtaining the wing specifications

While emulating the bat wing, especially for FWMAV

applications, scaling analysis is very important to

obtain the proper wing dimensions and aerodynamic

features. With reference to the data provided by

Bullen et al.,26 for the present study, only three bat

species having dimensions close to the design require-

ment of FWMAV were selected, namely,Mormopterus

Planiceps, Nytophilus Geoffroyi, and Scotorepens Balstoni,

whose physical and kinematic features are summa-

rized in Tables 1 and 2, respectively. Considering theaverage of the three wings, the values for physical

Table 1 Wing bat parameters of three species and present study

Bat species

Wing

span

(mm)

Wing

area

(m2)

Aspect

ratio

Wing

loading

(N/m2)

Wing

mass

(g)

Mormopterus planiceps 263.5 0.010 7.3 8.7 8.3

Nyctophilus geoffroyi 263.1 0.012 5.7 4.7 5.8

Scotorepens balstoni 266.0 0.011 6.3 7.0 7.9

Present study 270 0.013 4.95 4.61 6.0

Table 2 Flight parameters of three species and present study

Bat species

Speed range

(m s1)

Frequency

(Hz)

Flapping angle

()

Mormopterus planiceps 2.1 9.4 9.34 1.38 40.68 10.15

Nyctophilus geoffroyi 0.8 7.2 10.94 0.96 43.92 16.44

Scotorepens balstoni 3.3 5.0 11.31 0.67 35.00 8.29

Present study 2 7 6 9 60

parameters such as wing span, aspect ratio, wing area,

wing loading, and wing mass have been approximated

as 270 mm, 0.013 m2, 4.95, 4.61 N m2, and 6 g,

respectively. Similarly, the kinematic characteristics

such as wind speed, flapping frequency, and flapping

angle are chosen as 2 7 m s1, 69 Hz, and 60 3

.

Wing frame and membrane

The wing frame materials previously used include

titanium alloy,3 and composites such as epoxy

reinforced carbon,8 graphite epoxy,5 carbon rod,17

carbon fiber,10,11 and glass fiber.13 Titanium alloy

is widely used for aircraft gas turbine disks and

blades as well as airframe structural components that

require strength and high temperature tolerance. It

is light and strong, and can be easily tapered to

vary the thickness of wingspars. Being ductile, it

can also be bent to create wing camber to improve

performance. In addition, the etching process of

titanium alloy can be conducted at room temperatureand yields a reasonable etching rate.3 In the present

study, the commercially available titanium alloy,3

Ti 6Al 4V, is used. Wing layouts are developed

from photographs of bat with their wings extended

that are scaled to have a length (R) of 120 mm per

wing. The wing frame has two battens in the cordwise

direction to strengthen the stiffness of the wing and

control the wing deformation during flapping. The

thickness of the entire frame is 0.35 mm, and gradual

tapering in width is provided for the frame and

battens, from leading edge to trailing edge, and from

root to tip as shown in Fig. 1.

Next attempt is to develop the flexible wing

membrane. Generally, polymers3,8,5,10,11,16,17 and

elastomers13 have been used for flexible wing mem-

brane. It is well established that, when compared

with the polymers, elastomers exhibit low Youngs

Figure 1 Schematic of the wing frame.



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Figure 2 The latex membrane glued on the wing frame.

modulus while maintaining the same range of density

(http://www.grantadesign.com/ashbycharts.htm);

this makes them a better choice for flexible wing

membrane. Therefore, latex, a typical elastomer, is

used in the present study, which is glued onto the

frame as shown in Fig. 2. Membranes with thick-

nesses 0.37 mm, 0.28 mm, and 0.13 mm are chosen,

which are named as least flexible, flexible, and most

flexible, respectively.

Flapping mechanism

Four-bar linkage mechanism

A four-bar slider-crank mechanism is designed and

tested to facilitate the sinusoidal flapping motion,

with the amplitude adjustable from 40 to 60.

The design considerations of the mechanism are

light weight, simplicity, rigidity, minimum joints,

harmonic motion, and minimum phase difference

between the wings. Before fabrication, a complete set

of CAD models are developed using SOLIDWORKS-

2007 to ensure an accurate fit between parts; all the

views are shown in Fig. 3. The flapper is 56 mm high

and 25 mm long. For the selected flapping angle of

60 the lengths of rockers are 10 mm for the output

link, 16.34 mm for the connecting rod, and 5 mm for

the crank.

The linkages and supporting frame of the flapper

are made from brass, by means of CNC machine.

The flapper is driven by a single DC-micromotor

(Type: 1224A015SR, speed: 901 rpm, manufacturer:

Dr. Fritz Faulhaber GmbH & Co. KG, Germany)

which is attached to the reduction gear and mag-

netic encoder to control the flapping frequency. The

output flapping frequency (f) in relation to the input

voltage can be simply calculated by Eq. 1, where Scis the motor speed constant, Vis the applied voltage,

and Rg is the reduction gear ratio. Accordingly, with

the reduction gear ratio of 1:3 and voltage of 15 V,

we can expect a flapping frequency of about 75 Hz

without any wing attachment.

f=Sc

60RgV. (1)

Kinematic model

A mathematical model has been developed to study

the kinematics of the mechanism, thereby ensuring

that the flapping was symmetric. The governing

equations of the mechanism are as follows:From Fig. 4, we have the following:

f= a cos 1 + b cos 2, (2)

c= a sin 1 + b sin 2. (3)

From Eq. 3,

2 = sin1

a sin 1

b

. (4)

The effective distance between B and C (or D) is as

follows:

g = f e. (5)

From symmetry of triangles BMC and BMD, we get

the following:

f = sin1g

d

. (6)

(a) (b)

Figure 3 (a) Different views of the flapping mechanism. (b) Zoomed view at A.



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Figure 4 The kinematic model of the flapping mechanism.

Substituting Eqs. 2 and 5 in 6, we obtain the

following:

f = sin1

a cos 1+ b cos

sin1

a sin 1

b

e

d

.

(7)

Using the chain rule, angular velocity can beexpressed as follows:

d

dt=a1

g cos

sin 1 + cos 1 tan

sin1

a sin 1

b

.

(8)

Hence the angular acceleration is

d2

dt2 =

a

21

g

cos 1 sin 1 tan

sin1

a sin 1

b

+

a

b

cos2 1

cos2

sin1

a sin 1

b

+ sin

d

dt

2

cos

. (9)

Electronic control system

System architecture overview

The ECS consists of a microcontroller, motor driver,

DC minimotor with encoder, variable resistor, power

supply, and a personal computer with graphical user

interface (GUI) software. The PIC16F876 microcon-

troller acts as a brain to the system and controls every

input and output. One of the main functions is to

control the speed of the DC minimotor through the

motor driver. A DC power supply is used to provide

15 V which is then converted to 5 V by an LM7805

voltage regulator. The communication to the motor

driver from the microcontroller is accomplished usingpulse width modulation (PWM); the data are then

used by the motor driver (MCP 1404) to control

motor speed detected by the built-in encoder (series

30B20). The encoder helps to measure the actual

speed of the motor, and acts as a feedback to the

system to synchronize the required speed and actual

speed. The output of the encoder is in the form of

pulses (05 V) with a resolution of 10 lines per rev-

olution. Figures 5 and 6 show the block diagram and

prototype, respectively, of the ECS.



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Figure 5 ECS block diagram.

Figure 6 ECS prototype board.

PIC16F876 is a 28-pin 8-bit CMOS Flash micro-

controller which contains 256 bytes of EEPROM data

memory, ICSP (In-Circuit Serial Programming), an

ICD, 5 channels of 10-bit analog-to-digital con-

verter (ADC), 2 additional timers, and 2 cap-

ture/compare/PWM functions with 10-bit maximum

resolution. The synchronous serial port can be con-

figured as either three-wire serial peripheral interface

(SPI) or the two-wire inter-integrated circuit (I2C)

bus and a universal asynchronous receiver transmit-

ter (USART). The PIC16F876A can be driven at a

maximum clock speed of 20 MHz. In this experiment,

the ADC is set to 8-bit, so that the detectable range is

between 0 and 255 (28 = 256). The conversion from

analog voltage to digital bits is shown in

Table 3 Analog voltage to 8-bit of PIC microcontrollers ADC

Analog voltage (V) PIC 8-bit (bit)

0 0

1 51

2 102

3 153

4 2045 255

Table 3. Since 8-bit is used for ADC, the same

resolution is applied toward the PWM modules. The

frequency of 10 kHz is chosen to match with the

motor driver, hence make the time for 1 cycle equal

to 100s. Figure 7 shows two different values of

PWM, for 50 and 10% duty cycle. Next, RS232 UART

is used for the serial communication with the personal

computer. The microcontroller can support the baud

rates from 300 up to 57,600 bps. However, at higher

speed, it is more prone to higher percentage of data

transfer error. A 9600 bps baud rate is chosen for this

experiment with driven inverted state. The RS232 is

configured as 8N1, which means eight data bits, no

parity bit, and one stop bit as shown in Fig. 8.

ECS functioning and testing

The operation of the ECS in this flapping model is

shown in Fig. 9. The system starts after the power

source has turned on to enable PC serial com-

munication using Windows HyperTerminal (WHT)

software. Before getting connected, the software has

to be configured as a serial RS232 COM terminal,

by setting the port as follows: baud rate = 9600 bps,data bits = 8, parity = none, stop bits = 1, flow con-

trol = hardware. A modification value ranging from

0.1 to 9.9 needs to be entered into the WHT write-

display space to ensure that connection is established

and there is a handshaking link between system

board and PC. The speed of the motor is adjusted

to the desired value by the potentiometer. The ADC

50% duty cycle

(50 s)

1 cycle

(100 s)

10% duty cycle

(10 s)

1 cycle

(100 s)

Figure 7 PWM waveforms of two different duty cycles.

Figure 8 8N1 configuration; eight data bits, no parity bit, and one

stop bit.



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Figure 9 Flow chart of the ECS functioning.

digital values are then calculated and converted into

PWM values to drive the MCP1404 PWM driver chip,

which runs the motor at variable speeds. The signalsent to the MCP1404 driver is programmed at a fre-

quency of 10 kHz, with variable PWM duty cycles to

get variable motor speeds. Then the microcontroller

calculates RPS (revolutions per second) value pro-

duced by the magnetic encoder (pulse signal). The

calculated RPS value is then sent and displayed on

the PC via serial COM port in real-time mode. The

process will repeat until the modification values and

potentiometer trim are being changed.

In the open air test section, the pitch angle ofthe flapping axis, w, with respect to the free stream

velocity Vcan be changed by adjusting the test mount

which supports the driving part. The analog signal

from strain gauge (load cell) is amplified, digitized,

and conditioned via PCD-300A sensor interface and

linked to the data acquisition board to collect the

frequency signal (x) and transmit the raw data into



8/13


computer by using GUI software data acquisition.

The data collection frequency is set at 5000 Hz and

15,000 data points are collected at each test run.

The raw data are smoothed using digital Butterworth

low-pass filter with cut-off frequencies set at 5 Hz and

second order.

The frequency signal from the load cell is matched

with the frequency value obtained by the ECS,

and if any difference is noticed, the ECS facilitates

further adjustments until the difference becomes zero,

ensuring calibration at the required frequency. The

testing of ECS is performed with velocity ranging from

2 to 8 m s1 and AOA from 0 up to 50, at 6 Hz. The

schematic and photograph of the experiment setup

are shown in Fig. 10.

Results and Discussion

Flapping angle, angular velocity, and acceleration

Figure 11 shows the sequel images of the wing for one

cycle of flapping, captured by high-speed camera, and

Fig. 12 shows the flapping angle. The flapping angle

obtained from Eq. 7 is compared with the experi-

mental results as shown in Fig. 13. Since the stroke

plane is coplanar with the image, the flapping angle

can be measured directly from the image. From

the high-speed camera images, the flapping angle is

calculated to be 33, whereas the theoretical value

is 30

; the difference is attributed to the flexibility

of the wing and the small assembly clearance. This

flapping angle suits quite well with the bats flapping

angle, 35 43

as in Table 2.Equations 29 are solved using Matlab tool,

SIMULINK. Figure 14 shows the angular velocity

and angular acceleration for one cycle of rotation

at 1 Hz. The rotational speed of the motor is

assumed to be constant in the analysis and it

is ensured that the mechanism operates smoothly

without obvious jumps or jerks. The results show a

sinusoidal flapping motion. Figure 14(a) shows that

the angular velocity corresponding to the maximum

flapping amplitude (30) is 3.189 rad/s, and the

corresponding angular acceleration is 18.94 rad/s2

as shown in Fig. 14(b).

Flapping frequency

ECS versus manual control of flapping frequency

Manual control of flapping wing has disadvantages

of repeatability and need of more time to balance

and calibrate for each experiment, especially for large

AOA and velocity. ECS could tackle this problem

and facilitate accurate measurement and control

of frequency. The comparison of relative errors

with respect to the required frequency value (6 Hz)

estimated without ECS and with ECS is presented

in Fig. 15. The relative error is defined by Eq. 10 as

follows:

Ec = sSmain

100%, (10)

where Ec is the relative error, s is the difference

between the measured frequency and the required

frequency (Smain). As shown in Fig. 15(a), in the

absence of ECS, Ec is within 5%, for velocities 2 to

4 m s1, and it shoots up to 2535 % above 4 m s1.

The cause of larger Ec for the load cell is attributed

to the increased air resistance at high AOA resulting

in the reduction of frequency. To minimize this error,

the calibration procedure must be repeated many

times for each experiment; this is time consuming

and tedious. As already mentioned, this problem is

effectively solved by the use of ECS, as is evident

from Fig. 15(b) which shows that Ec with ECS falls

within the acceptable range of 0.41.8%. Thus, it

is demonstrated that, besides facilitating the control,

the proposed ECS can significantly contribute to the

accuracy and speed of frequency measurement.

Aerodynamic tests

The aerodynamic force is measured in open air wind

tunnel setup at the free stream velocity of 47 m s1.

The Kyowa data acquisition system (PCD 300A

model) and Deltalab sensor cell are used to measure

lift and drag with high precision. The precision of theforce sensor is 0.3% of the full scale (5 N). The data

breeding rate of the load cell is set as 5000 points

per second. About 40,000 points of data are selected

for every flapping condition, and integrated them

into time-averaged values of lift and drag coefficients,

CL mean (Eq. 11) and CD mean (Eq. 12), respectively.

C(Lmean) = L mean/[(1/2)(V)2S], (11)

C(Dmean) = D mean/[(1/2)(V)2S], (12)

where L is the the mean lift force, D the mean drag

force,S the wing platform area,Vthe forward flight

speed, and the air density.

Figure 16 shows the variations of CL mean and

CD mean for frequencies 69 Hz, at AOA 20. As

expected, CL mean and CD mean increase dramatically

with increase of frequency and decrease of velocity.

Figure 17 shows the corresponding histories of

flapping angle lift and drag coefficients (CL and

CD, respectively). It is seen that the lift has almost



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(a)

(b)

Figure 10 (a) Schematic of experiment setup of flapping mechanism using ECS and load cell for calibration. (b) The experimental apparatus.



10/13


Figure 11 Sequel images of the wing for one cycle of flapping.

Figure 12 Flapping angle observed by high-speed camera.

Crank angle, Degree (One cycle)

0 50 100 150 200 250 300 350

Angulardisplacem

ent,Degree

-40

-30

-20

-10

0

10

20

30

40

Theoretical

Experiment

Figure 13 Comparison of experimental and theoretical flapping angle.

same frequency as the flapping angle and drag signalis twice the flapping frequency. At the beginning

of the downstroke (1), the lift force is maximum,

and decreases to the minimum near the end of the

downstroke (2). In general, the lift during downstroke

is higher than that during upstroke. The values of

CL and CD are in reasonable agreement with those

obtained by Norberg3 for the low-speed flier P. auritus.


0 50 100 150 200 250 300 350

0 50 100 150 200 250 300 350

Angularvelocity(rads-1)

-4

-3

-2

-1

0

1

2

3

4(a)

(b)

Theoretical


Angulara

ccleration,(rads-2)

-30

-20

-10

0

10

20

30

Theoretical

Figure 14 Variation of angular velocity and angular acceleration with

crankangle. (a) Flappingangular velocity versuscrank angle.(b) Flapping

angular acceleration versus crank angle.

Conclusion

As part of the ongoing research on aerodynamics of

MAV, an efficient and accurate flexible flapping wing

mechanism is developed and tested. The introduction

of integrated ECS to control and measure the flapping

frequency is the major contribution in the present

work. Three bat species having dimensions close to

the design requirement of MAV, namely,M. Planiceps,



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0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

23

45

67

8

010

2030

40 XData

3D Graph 7

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0

5

1015

20

25

30

35

XData

3D Graph 5

0

5

10

15

20

25

30

35

-20

-10

0

10

20

30

40

(a) (b)

23

45

67

8

010

2030

40

Percenta

geoferror(%)

Velo

city

,ms-1

AoA,Degree

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

23

45

67

8

010

2030

40

Percentage

oferror(%)

Velo

city

,ms-1

AoA,Degree

Figure 15 Percentage of error in frequency distribution (a) without ECS and (b) with ECS.

0.2

0.4

0.6

0.8

1.0

1.2

1.4

(a) (b)

4.55.0

5.56.0

6.57.0

6.06.5

7.07.5

8.08.5

9.0

CLmean

Velocity, ms-1 Fre

quen

cy,Hz

0.40.61.01.21.4

0.1

0.2

0.3

0.4

0.5

0.6

0.7

4.55.0

5.56.0

6.57.0

6.06.5

7.07.5

8.08.5

9.0

CDmean

Velocity,ms-1 Frequen

cy,Hz

0.20.30.40.50.6

Figure 16 The variations ofCL meanand CD meanfor frequencies 69 Hz, at AOA 20.

0.00 0.05 0.10 0 .15 0 .20-60

-40

-20

0

20

40

60

2

3

5

4

Time (sec)

Flappingangle,

Degree

Flapping angle

Instantaneous Lift

Instantaneous Drag

1

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

CLand

CD

V=6ms-1, F=9Hz,AoA=20

0

Figure 17 Instantaneous flapping angle, lift and drag coefficients.

N. Geoffroyi, and S. Balstoni, are selected, and their

average physical and kinematic features are chosen.

The titanium alloy, Ti 6Al 4V, is used for the

wing frame, and latex for the membrane. A four-bar

slider-crank mechanism is designed and fabricated

to facilitate the wing flapping. The major issues

associated with the traditional means of controlling

and measuring the flapping frequency, such as

repeated calibration, large time consumption, and

measurement inaccuracy at higher AOA and velocity

are successfully rectified by the proposed ECS; the

relative error is reduced from 2535% to 0.41.8%.

The experimental flapping angles are well matched

with those obtained from the theoretical kinematic

model. This system would be highly efficient for the

study of aerodynamic characteristics of FWMAVs.

Future work may be done to improve the ECS by

introducing wireless communication for the ECSto the flapping mechanism, and to reduce it to

a microchip.

Acknowledgments

The authors would like to thank the Ministry of

Technology and Innovation, Malaysia, and Universiti



12/13


Sains Malaysia for the financial support for this

research work. Thanks are also due to Mr. Mohd

Fairuz Zakaria and Mr. M. Khalil Abdullah, for their

valuable assistance in the experiments.

References

1. Shyy, W., Berg, M., and Ljungqvist, D., Flapping

and Flexible Wings for Biological and Micro Air

Vehicles,Progress in Aerospace Sciences 35:455505

(1999).

2. Swartz, S.M., Iriarte-Diaz, J., Riskin, D.K., et al.,

Wing Structure and the Aerodynamic Basis of

Flight in Bats,Proceedings of 45th AIAA Aerospace

Sciences Meeting and Exhibit, Reno, NV; January 811,

2007.

3. Norberg, U.M., Aerodynamics, Kinematics, and

Energetics of Horizontal Flapping Flight in the

Long-eared Bat Plecotus auritus,Journal of

Experimental Biology65:179212 (1976).

4. Pornsin-sirirak, T.N., Tai, Y.C., Nassef, H., and

Ho, C.M., Titanium-alloy MEMS Wing Technology

for a Micro Aerial Vehicle Application,Sensors and

Actuators A 89:95103 (2001).

5. Kim, D.-K., and Han, J.-H., Smart Flapping Wing

Using Macro-fiber Composite Actuators, SPIE 13th

Annual Symposium Smart Structures and Materials, San

Diego, CA, USA; Volume 6173-16, February

26March 2, 2006.

6. Galvao, R., Israeli, E., Song, A., et al., The

Aerodynamics of Compliant Membrane Wings

Modeled on Mammalian Flight Mechanics, 36th

AIAA Fluid Dynamics Conference and Exhibit, San

Francisco, CA; AIAA 2006-2866; June 5 8, 2006.7. Song, A., Tian, X., Israeli, E., et al., Aeromechan-

ics of Membrane Wings with Implications for

Animal Flight,AIAA Journal46(8):20962106

(2008).

8. Lin, C.S., Hwu, C., and Young, W.-B., The Thrust

and Lift of an Ornithopters Membrane Wings With

Simple Flapping Motion,Aerospace Science and

Technology10:111119 (2006).

9. McIntosh, S.H., Agrawal, S.K., and Khan, Z.,

Design of a Mechanism for Biaxial Rotation

of a Wing for a Hovering Vehicle,IEEE/ASME

Transactions on Mechatronics11(2):145153

(2006).10. Nguyen, Q.V., Truong, Q.T., Park, H.C., Goo, N.S.,

and Byun, D., A Motor-driven Flapping-wing

System Mimicking Beetle Flight, Proceedings of the

2009 IEEE,International Conference on Robotics and

Biomimetics, Guilin, China, pp. 10871092,

December 1923, 2009.

11. Nguyen, Q.V., Park, H.C, Goo, N.S., and Byun, D.,

Characteristics of a Beetles Free Flight and a

Flapping-wing System That Mimics Beetle Flight,

Journal of Bionic Engineering7:7786 (2010).

12. Hu, H., Kumar, A.G., Abate, G., and Albertani, R.,

An Experimental Study of Flexible Membrane

Wings in Flapping Flight, 46th AIAA Aerospace

Sciences Meeting and Exhibit AIAA-2009-0876, Reno,

NV; January 710, 2008.

13. Hu, H., Kumar, A.G., Abate, G., and Albertani, R.,

An Experimental Investigation on the

Aerodynamic Performances of Flexible Membrane

Wings in Flapping Flight, Aerospace Science and

Technology14(8):575 586 (2010).

14. Baskar, V., and Muniappan, A., Development of

Flapping Mechanism for Micro Air Vehicle (MAV),

Proceedings of the International Conference on Mechanical

Engineering2003 (ICME2003), Dhaka, Bangladesh,

December 2628, 2003.

15. Madangopal, R., Khan, Z.A., and Agrawal, S.K.,

Biologically Inspired Design of Small Flapping

Wing Air Vehicles Using Four-bar Mechanisms and

Quasi-steady Aerodynamics,Journal of Mechanical

Design, Transactions of the ASME127:809816 (2005).

16. Syaifuddin, M., Park, H.C., and Goo, N.S., Design

and Evaluation of a LIPCA-actuated Flapping

Device,Smart Materials and Structures15:12251230

(2006).

17. Conn, A.T., Burgess, S.C., and Ling, C.S., The

Parallel Crank-rocker Flapping Mechanism: An

Insect-inspired Design for Micro Air Vehicles,

International Journal of Humanoid Robotics

4(4):625 643 (2007).

18. Fenelon, M.A.A., and Furukawa, T., Design of an

Active Flapping Wing Mechanism and a Micro

Aerial Vehicle Using a Rotary Actuator, Mechanism

and Machine Theory45:137146 (2010).

19. Wood, R.J., Liftoff of a 60 mg Flapping-wing

MAV,Proceedings of the 2007 IEEE/RSJ International

Conference on Intelligent Robots and Systems, San Diego,

CA, USA, pp. 18891894, October 29November 2,

2007.

20. Wood, R.J., Design, Fabrication, and Analysis of a

3DOF, 3cm Flapping-wing MAV, Proceedings of the

2007 IEEE/RSJ International Conference on Intelligent

Robots and Systems, San Diego, CA, USA,

pp. 15761581, October 29November 2, 2007.

21. Wood, R.J., The First Take-off of a Biologically

Inspired At-scale Robotic Insect, IEEE Transactions

on Robotics24(2):341 347 (2008).

22. Finio, B.M., and Wood, R.J., Distributed Power and

Control Actuation in the Thoracic Mechanics of a

Robotic Insect,Bioinspiration and Biomimetics

5:045006045017(2010).

23. Sreetharan, P.S., and Wood, R.J., Passive

Aerodynamic Drag Balancing in a Flapping-wing



13/13


Robotic Insect,Journal of Mechanical Design

132:051006-1-11 (2010).

24. Sitti, M., Piezoelectrically Actuated Four-bar

Mechanism With Two Flexible Links for

Micromechanical Flying Insect Thorax,IEEE/ASME

Transactions on Mechatronics8(1):26 36 (2003).

25. Galinski, C., and Zbikowski, R., Insect-like Flapping

Wing Mechanism Based on a Double Spherical

Scotch Yoke,Journal of the Royal Society Interface

2:223235 (2005).

26. Bullen, R.D., and McKenzie, N.L., Scaling Bat Wing

Beat Frequency and Amplitude, The Journal of

Experimental Biology205:26152626 (2002).


Documents

Development of Flexible Wings and Flapping Mechanism With Integrated Electronic Control System, For Micro Air Vehicle Research