Intelligent Control and Automation, 2011, 2, 57-68
doi:10.4236/ica.2011.22007 Published Online May 2011 (http://www.SciRP.org/journal/ica)
Fabrication of Dual-Axis Solar Tracking Controller Project
Nader Barsoum
Curtin University, Sarawak, Malaysia
Received January 28, 2011; revised March 21, 2011; acce p te d Ma rch 24, 2011
Abstract
The recent decades have seen the increase in demand for reliable and clean form of electricity derived from
renewable energy sources. One such example is solar power. The challenge remains to maximize the capture
of the rays from the sun for conversion into electricity. This paper presents fabrication and installation of a
solar panel mount with a dual-axis solar tracking controller. This is done so that rays from the sun fall per-
pendicularly unto the solar panels to maximize the capture of the rays by pointing the solar panels towards
the sun and following its path across the sky. Thus electricity and efficiency increased.
Keywords: Controller, Tracker, Sensor, Battery, Inverter, Timer, Switches, Program, Installation
1. Introduction
Electrical energy from solar panels is derived by con-
verting energy from the rays of the sun into electrical
current in the solar cells. The main challenge is to maxi-
mize the capture of the rays of the sun upon the solar
panels, which in turn maximizes the output of electricity.
A practical way of achieving this is by positioning the
panels such that the rays of the sun fall perpendicularly
on the solar panels by tracking the movement of the sun
[1]. This can be achieved by means of using a solar panel
mount which tracks the movement of the sun throughout
the day. Energy conversion is most efficient when the
rays fall perpendicularly onto the solar panels. Thus, the
work is divided into three main parts namely the mount-
ing system, the tracking controller system and the elec-
trical power system.
In solar tracking systems, solar panels are mounted on
a structure which moves to track the movement of the
sun throughout the day. There are three methods of
tracking: active, passive and chronological tracking.
These methods can then be configured either as sin-
gle-axis or dual-axis solar trackers. In active tracking, the
position of the sun in the sky during the day is continu-
ously determined by sensors. The sensors will trigger the
motor or actuator to move the mounting system so that
the solar panels will always face the sun throughout the
day. This method of sun-tracking is reasonably accurate
except on very cloudy days when it is hard for the sensor
to determine the position of the sun in the sky thus mak-
ing it hard to reorient the structure [2].
Passive Tracking unlike active tracking which deter-
mines the position of the sun in the sky, a passive tracker
moves in response to an imbalance in pressure between
two points at both ends of the tracker. The imbalance is
caused by solar heat creating gas pressure on a “low boil-
ing point compressed gas fluid that is driven to one side
or the other” [2] which then moves the structure. How-
ever, this method of sun-tracking is not accurate. A
chronological tracker is a timer-based tracking system
whereby the structure is moved at a fixed rate throughout
the day. The theory behind this is that the sun moves
across the sky at a fixed rate. Thus the motor or actuator
is programmed to continuously rotate at a “slow average
rate of one revolution per day (15 degrees per hour)” [2].
This method of sun-tracking is very accurate. However,
the continuous rotation of the motor or actuator means
more power consumption and tracking the sun on a very
cloudy day is unnecessary.
A single-axis solar tracker follows the movement of
the sun from east to west by rotating the structure along
the vertical axis. The solar panels are usually tilted at a
fixed angle corresponding to the latitude of the location.
According to [3], the use of single-axis tracking can in-
crease the electricity yield by as much as 27 to 32 per-
cent. On the other hand, a dual-axis solar tracker follows
the angular height position of the sun in the sky in addi-
tion to following the sun’s east-west movement [3] re-
ports that dual-axis tracking increases the electricity
output as much as 35 to 40 percent.

N. BARSOUM 58
2. Description
The primary task of this pilot project is to build an actual
solar panel mount with a sun-tracking system to be in-
stalled outdoors in Miri (location: 4˚23′35″N 113˚58′49″E)
in Sarawak, Malaysia. Based on the background infor-
mation of the various types of solar trackers, it has been
decided that active tracking with a dual-axis set-up will
be used. The reason for this choice is active tracking is a
fairly effective method to track the sun and a dual-axis
tracking system has the capability of increasing the yield
of electrical energy output from the solar panels.
For the purpose of clarity, the east-west of the tracker
will be called the “horizontal tracking” while the angular
height tracker will be referred to as “vertical tracking”.
An active, dual-axis tracking system prototype has al-
ready been designed and built by [4], which consists of
the sensor system to determine the position of the sun
and a control system which reads data from the sensors
to command the movement of the tracker. A program to
control the tracking system has been also developed [4].
The sensor system consists of two sensors: one to deter-
mine the position of the sun in the sky and another to
determine the position of the sun’s movement from east
to west. Each sensor consists of two Cadmium Sulphate
(CdS) light dependant resistors (LDRs).
The LDRs were placed as shown in Figure 1, a
shadow will fall on one of the LDRs when the sensor is
not pointing directly toward the sun resulting in differ-
ence of the level of resistance between the two LDRs.
This difference will be detected by the microchip in the
control system and will move the tracker accordingly so
that both LDRs are pointing towards the sun.
To decide how the tracker would move, it is important
to consider the movement of the sun in the sky through-
out the year. The sun path diagram of Figure 2 shows
the annual variation of the path of the sun in Miri.
From the sun path diagram, the movement of the sun
Figure 1. Sensor response once a shadow is cast on one LDR.
Figure 2. Sun path diagram for M iri, Sarawak, Malaysia.

N. BARSOUM 59
in the sky throughout the year in Miri can be divided into
three different scenarios. As the sun rises from the East
to sets to the West, the sun path may move in the South-
ern or Northern region, or it may move almost directly
overhead.
If the path of the sun is in the Northern region, the
structure must be able to track the sun from East to West
in anti-clockwise direction. If the path of the sun is in the
Southern region, the structure must be able to track the
sun from East to West in clockwise direction. If the sun
is moving overhead, only the axis which tracks the an-
gular height of the sun will move. In all three situations,
there must be a way to turn back the tracker to its origi-
nal position after it has followed the movement of the
sun from morning to dusk. To achieve this, limit
switches are added to the system. When the limit switch
is triggered at the end of the day, the tracker will move
back to its original position.
While the prototype has been done and tested in the
lab, this paper focuses on the design, fabrication and in-
stallation of a solar panel mounting system with
dual-axis solar tracking controller to be tested and in-
stalled outdoors. The system is then connected to a bat-
tery bank via a charge controller and DC voltage from
the solar panels is converted to AC voltage through an
inverter. Improvements were made to the design of the
sensor, the controller program and limit switches were
added to the system.
3. Mounting System
The mounting system refers to the structure which holds
the solar panels; the structure consists of movable and
fixed parts based on a set of criteria.
Firstly, the structure must be able to support the
weight of the solar panels which are mounted on it. In
this work, two solar panels are used. The total weight is
31 kg, 15.5 kg each. Besides that, the column and the
base of the structure should also be able to support the
weight of the frame, which is estimated to be about 70 kg
[5]. That gives a total weight of slightly more than 100
kg.
Secondly, since the structure will be erected outdoors,
the structure must be able to withstand the elements of
nature, most notably the effects from the sun (heat), rain
(water) and the wind (air). Of utmost concern will be
effect of wind load on the structure when wind load is
acting upon the solar panels. Based on the recorded
maximum wind speed data of Miri which is 78 km/h [6],
and assuming the wind flow is acting perpendicularly
upon the maximum area of the solar panels, the wind
load is calculated using the generic formula [7] as fol-
lows:
Wind load: Force, F = A × P × Cd
A = projected area of the item = (1.58 m × 0.808 m × 2)
= 2.553 m2
P = Wind pressure (Psf), = 0.00256 × V2 (V = wind speed
74.5652 Mph) = 0.00256 × 74.5652 = 14.233 Psf =
0.0988 Psi = 69.492 Kg/m2
Cd = Drag coefficient, = 2.0 for flat plates.
 Wind load force = A × P × Cd = 2.553 m2 × 69.492
kg/m2 × 2.0 = 354.826 kg ≈ 3548.26 N
The calculation shows that the material chosen to
make the structure would need to be able to withstand a
perpendicular acting force of 3548.26 N.
Thirdly, the movable parts of the structure must be
able to rotate to follow the movement of the sun
throughout the day. A double-axis solar tracker means
the tracker must be able to rotate along the vertical axis
to follow the movement of the sun from East to West,
and also rotate along the horizontal axis to follow the
position of the sun’s angular height in the sky. In that
manner, the structure would be able to point the solar
panels towards the position of the sun in the sky.
The motor used for this pilot project is a 12 V DC
motor which has a torque of about 13.5 pound-feet (18.3
Nm) to 17.5 pound-feet (23.73 Nm) [8]. To justify the
use of this motor, the following calculation was done to
ensure that it has enough power to rotate the mass of 100
kg; the radius of the sprocket r = 0.1 m, and taking val-
ues of coefficient of friction of the bearing = 0.001 [9]
and the coefficient of friction between the chain and the
sprocket (steel and steel) = 0.42 [9], the torque needed is
calculated as:
Torque = F × r, where F = mgcf (Serway 2000, 132)
= (mgcf) × r = (100 kg × 10 m·s–2 × 0.001
× 0.42) × 0.1 m = 0.042 Nm
The ultimate tensile strength is about 50,000 psi while
the yield strength is about 30,000 psi. [10]. Based on the
strength of steel, the structure would be able to withstand
the effect of wind load as well as the other weight loads
placed on it. Thus, the optimum design is as shown in
Figure 3. It is important that there are no shadows cast
upon the solar panel. Any shadows can greatly affect the
output of electric current [11]. It is therefore important to
ensure that during day-time at the site for the installation
of the system, no shadows from trees, buildings or other
tall objects such as poles are cast onto the solar panels.
Thus, the site selection for this pilot project took into
consideration this particular issue.
4. Fabrication and Installation
The first part to be fabricated was the frame of the struc-
ture. At each end of the frame, a pillow block bearing is
used to enable the frame to rotate along the horizontal

N. BARSOUM 60
Figure 3. Finalised design of the structure.
axis. A metal shaft which goes through the centre of the
frame connects the two bearings. Also, the DC motor
controlling the vertical movement is placed on one side
of the frame. Figure 4 illustrate the fabrication parts.
Once the frame was completed, the column of the
structure was made. The upper part of the column is de-
signed to hold the other DC motor which controls the
horizontal movement the lower part of the frame was
then attached to the upper part of the column using two
flange bearings which are connected by a shaft. The
bearings are used to enable the structure to turn about the
vertical axis.
A sprocket is affixed unto the shaft of the motor, unto
one end of the shaft, besides the pillow block bearing and
at the end of the shaft on top the flange bearing. A chain
is then put in place so that when the motors are powered,
the structure can rotate. The gear ratio used is 10:40 (1:4),
10 on the motor and 40 on the shaft. After installing the
solar panels unto the frame, it was found that the rotation
was not stable due to imbalance in weight. Therefore, a
counter-weight was added to the back of the frame to
balance the torque action on the shaft, as given in Figure
5.
The base of the column was concreted with a tube pipe
and welded unto the galvanised pipe before bolting the
column unto the base. Then, the frame was secured unto
the column also using nuts and bolts. An extra layer of
concrete was then added to cover the lower part of the
base of the column. Figures 6 illustrate the installation
process.
5. Tracking Co ntroller System
The program for the tracking controller was written by
PICBasic which is then converted to binary or machine
language before being loaded into the microcontroller.
Pillow
block
bearing
Steel
frame
DC motor placed at the
side of the frame
Flange bearing
The column
DC motor affixed
at the top
Frame and column
attached
From left to right: Sprocket attached to motor, sprocket attached to
frame, chain connecting the two sprockets
Figure 4. Fabrication parts.
Figure 5. The solar panel affixed to the frame (left). The
counter-weigh t ( circled, right).

N. BARSOUM61
Base of the column is welded and the column being set up
The frame being attached to the column
Applying an extra layer of concrete to the base
Figure 6. Installation process.
The microcontroller together with the controller circuit
and the sensor will control the movement of the structure
to track the sun. [4] Has chosen to use Microchip’s
PIC16F84A microcontroller, given in Figures 7 and 8.
The program and circuit has been developed by [4].
Each tracking axis has its own control circuit. To control
the rotational direction of the motor, [4] used an
H-Bridge. The works and writings of [2,12] have been
referred to when making the following modifications to
[4] program:
Renaming symbols
Reassigning ports
Including limit switches
Changing values of scales and time
The algorithm is based on the classical basic language
to detect the voltage signal from the light sensors and
compare between 2 signals and calculate the different.
This different is converted to set a certain position angle
and send the signal to the motor to rotate precisely to an
accurate position so that facing the sun.
The program is too long and is not typed in this paper,
but small part of the program is given below:
Include "bs1defs.bas"
Start:
Symbol CDS1 = B0
Symbol CDS2 = B1
Symbol Diff = B6
TRISB.0 = 1 'set pin RB0 as input (sensor1)
TRISB.1 = 1 'set pin RB1 as input (sensor2)
TRISB.2 = 0 'set pin RB2 as output
TRISB.3 = 0 'set pin RB3 as output
Low PORTB.2 'pin RB2 set to low
Low PORTB.3 'pin RB3 set to low
Low PORTB.4 'pin RB4 set to low
(limit-switch1)
Low PORTB.5 'pin RB5 set to low
(limit-switch2)
The above description is: Symbols are declared and
the input/output and variables are initialised. The code
was written in PICBasic (saved as a .bas file) using Mi-
croCode Studio. Within this software, the program code
is then compiled and the .hex file is obtained. Figure 9
shows the MicroCode Studio.
To load the program into the microcontroller, Micro-
chip’s MPLAB IDE was used together with PICSTART
Plus.
Following the steps taken to set-up the PICSTART
Plus programmer, Figures 10 and 11:
 Ensure that PICSTART Plus is powered and con-
nected to the RS232 port of the computer.
 Open MPLAB IDE.
 Go to “configure > select device” and the corre-
sponding microcontroller model was chosen. Click
“ok”.
 Go to “programmer > select programmer” and “PIC-
START Plus” was chosen.
Figure 7. Pin setup for the PIC16F84A microcontroller.

N. BARSOUM 62
Pin No. Name Function
1 RA2 – PORTA bit 2 Second pin on port A. Has no additional function.
2 RA3 – PORTA bit 3 Third pin on port A. Has no additional function.
3 RA4/T0CK1 Fourth pin on port A. T0CK1 which functions as a times is also found on this pin.
4 MCLR – master clear Reset input and Vss programming voltage of PIC.
5 Vss – Gnd Ground of power supply.
6 RB0/INT – PORTB bit 0 Zero pin on port B. Interrupt input is an extra function.
7 RB1 – PORTB bit 1 First pin on port B. No additional function.
8 RB2 – PORTB bit 2 Second pin on port B. No additional function.
9 RB3 – PORTB bit 3 Third pin on port B. No additional function.
10 RB4 – PORTB bit 4 Fourth pin on port B. No additional function.
11 RB5 – PORTB bit 5 Fifth pin on port B. No additional function.
12 RB6 – PORTB bit 6 Sixth pin on port B. ‘Clock’ line in program mode.
13 RB7 – PORTB bit 7 Seventh pin on port B. ‘Data’ line in program mode.
14 Vdd + V supply Positive power supply of +2.0 V to +5.5 V
15 OSC2 Pin assigned for connecting with an oscillator.
16 OSC1 Pin assigned for connecting with an oscillator.
17 RA0 – PORTA bit 0 Second pin on port A. No additional function.
18 RA1 – PORTA bit 1 First pin on port A. No additional function.
Figure 8. Pin function for the PIC16F84A microcontroller.
Figure 9. Screenshot of Microcode studio.

N. BARSOUM63
Figure 10. Screenshot of MPLAB IDE.
Figure 11. PICSTART Plus programmer.
 Go to “programmer > enable programmer”.
 Go to “programmer > settings” and choose the “com-
munications” tab. The port which the PICSTART
Plus programmer is connected to was selected. Click
“ok”.
Once the programmer has been properly set-up, fol-
lowing were the steps taken to program the microcon-
troller using PICSTART Plus:
 The microcontroller was inserted into the corre-
sponding pinholes of the programmer.
 Go to “file > import” and from the targeted directory,
the “.hex” file which is to be programmed into the
microcontroller was selected.
 Go to “programmer > erase flash device” to erase any
data stored in the microcontroller.
 Go to “programmer > program” to program the mi-
crocontroller.
 If the programming was unsuccessful, the settings of
the programmer were re-checked. If the settings are
correct, the microcontroller might be spoilt. Another
way to check if the microcontroller is spoilt is by
verifying the microcontroller. Go to “programmer >
verify” and if the verification is unsuccessful, it is
possible that the microcontroller is faulty.

N. BARSOUM 64
5.1. Printed Circuit Board (PCB)
The PCBs in this pilot project were made by means of
chemical etching, it was noted that the PCB making pro-
cedure can be divided into six main processes. These are:
 Design the PCB by EAGLE software, the schematic
circuit was drawn in the program, by wiring up the
corresponding electronic components
 Develop the image of the board by placing the trans-
parency facedown unto the UV exposure unit, and
then place the board into the solution
 Etching by 250 g of Ferric Chloride Hexahydrate
granules was mixed with 500 ml boiling water and in
another plastic container
 Spray the board with a photoresist strip solution
 For tin-plating, Four teaspoons of tin crystals were
dissolved in 300ml boiling water and the board was
immersed into the solution to coat the copper part of
the circuit with thin layer of tin to prevent oxidation
and acts as solder flux. Once coated, the board is
given a rinse
 Drilling holes and soldering the electronic compo-
nents and testing the circuit board
Figure 12 shows the completed PCB.
5.2. Sensor
The sensors will trigger the motor to move the mounting
system so that the solar panels will always face the sun.
Some Improvements were made to the design of the
sensor holder to make the sensor more sensitive. This
was done by increasing the length of the sensor holder.
For the front sensor, the sensor holder was redesigned to
suit the angular movement of the sun so that shadow can
Figure 12. A completed PCB with electronic components
soldered on.
be cast onto the LDR from any angular height of the sun
in the sky. Figure 13 shows the new design of the hold-
ers
The sensor holder was then painted. After the paint
was dry, the LDRs were inserted into the holder and a
plastic cover was placed on top of the sensor and silicone
applied around the cover of the sensor holder to prevent
water ingress into the LDRs. This is shown in Figure 14.
6. System Connection
The overall electrical connection for the system is given
by Figure 15. As seen, the solar panels are connected to
Vertical tracking Horizontal tracking
Figure 13. Sensor holders.
Figure 14. Placement of the sensors on the structure.

N. BARSOUM 65
from the solar panels is higher than the voltage of the
battery bank, which is 48 V to enable charging the bat-
teries.
6.1. Charge Controller
The wire from the solar panel is connected to the charge
controller. The charge controller, Figure 20, is used to
maintain proper charging voltage on the batteries. It pre-
vents overcharging of the batteries should the input
voltage from the solar panels rises.
Figure 15. System connection.
the charge controller, which is then connected to the bat-
tery bank. The battery bank is then connected to the in-
verter and also another wire is connected from the bat-
tery to power the controller circuit and the motors (rep-
resented by the orange coloured wire in the Figure 15).
The controller box houses the controller circuits and
serves as a junction box for the various electrical con-
nections is as shown in Figure 16.
Figure 17 explains the various wire connections in the
junction box. For the wiring of the sensor, the wiring
configuration of Figure 18 was used:
Two solar panels, Figure 19, are connected in series to
give a total output voltage of 72 V. The reason they are
connected in series is to ensure that the output voltage Figure 16. Inside the controller box.
Figure 17. Explanation of the wiring connection inside the junction box.

N. BARSOUM 66
Figure 18. Connection of the coloured wires for the sensor.
Figure 19. The solar panels.
Figure 20. The charge controller.
6.2. Battery Bank
Four 12 V batteries are connected in series to create a
total output voltage of 48 V, shown in Figure 21. The
wire from the charge controller is then connected to the
battery bank which enables the batteries to be charged.
From the battery bank, a wire is connected to the inverter.
Then another wire is place on one of the 12 V batteries to
power the 12 V DC loads such as the motors as well as
the controller circuit.
6.3. Inverter, Isolator and Cut-off Timer
The inverter, Figure 22, converts the 48 DC voltage of
the battery to 230 AC single phase voltage to power AC
loads. An isolator is put in place to make maintenance
work on the system easier.
Figure 21. The battery bank.
Figure 22. The inverter.
The cut-off timer, Figure 23, is a 24-hour based timer
which allows electric current to pass through at pre-set
times. The timer is powered using AC voltage from the
inverter. The purpose of the timer is because the frame
holding the solar panel has made more than one full rota-
tion to the point that the cables were all twisted. Upon
inspection, it was discovered that the sensor responded to
the street lightings along lakeside which were lit after
sunset. To overcome the problem, a cut-off timer was
placed to cut-off the electricity supply to the controller
circuit between just before sunset (around 6 p.m.) until 8
a.m. the next morning. This timer is adjustable.
It was discovered that the structure did not rotate back
to its original position just before sunset because the
magnet never triggered the limit switch because they
never came in contact. The position of the limit switch
and the magnet was determined by noting the time and
position when the horizontal tracking has reached its
maximum for the day. However, due to the varying de-
gree of movement of the sun in the sky throughout the
year, the position of the limit switch and magnet for to-
day is not the same as the position in three weeks time.
To deal with this problem, the position of the limit
switch was manually adjusted to correspond with the
path of the setting sun.
Another problem which occurred was rain water
started to sip into the LDRs although the sensor holder
has been covered with silicone. This was most probably
due to inadequate silicone application. Hence, the sensor

N. BARSOUM67
Figure 23. 24-hour based timer switch.
was taken apart and the LDRs replaced. This time, sili-
cone was again applied to the sensor holder and an extra
plastic sheet was put over the sensor.
6.4. Output and Loads
The electricity output from the inverter is a single-phase
sinusoidal 230 V AC voltage at 50 Hz. This was con-
firmed and verified by connecting the output of the in-
verter to an oscilloscope. Figure 24 shows the AC volt-
age waveform.
While the aim of this work was to create a dual-axis
solar-tracking solar panel mount, nevertheless the elec-
tricity output derived was tested on a few AC loads such
as light bulbs, computer monitor and CPU, and a spot-
light. Meanwhile, the AC voltage is also used to power
the cut-off timer. The DC voltage derived from one of
the 12 V batteries is used to power the controller circuit
as well as the motors.
7. Suggestions
It is suggested to:
 Apply grease to the gears and chains.
 Paint structure.
 Inspect for water ingress into controller box and sen-
sor.
 Change plastic sheet over the sensor from time to
time.
 Position of limit switches and magnet needs to be
adjusted from time to time
It is recommended to make this maintenance every 2
months or after every session of heavy rain, to check
light sensors, timer sensors, all junctions, iron and cable
connections
8. Conclusions
The objective of this pilot project to design, fabricate and
Figure 24. The voltage waveform of the output AC voltage
form the inverter.
install a solar panel mount with dual-axis sun tracking
capability has been achieved. The work was made possi-
ble through the cooperation and involvement of many
different parties. Planning and communication skills
were essential to ensure that the project went smoothly.
There is still room for improvement for this system and it
is hoped that further study can be carried out to further
develop the system. Improvements can be done to the
design of the structure, for example by adding covers for
the motors and also improving the design of the sensor
holder by making it waterproof. Besides that, improve-
ments can be made to the current method of turning back
the frame to its original position, removing the need to
manually adjust the limit switches. Also, a detailed study
should be carried out to ascertain the percentage increase
of electricity yield by using this system to establish
whether or not the system is viable.
9. References
[1] M. R. Patel, “Wind and Solar Power Systems Design,
Analysis and Operations,” 2nd Edition, CRC Press Taylor
& Francis Group Producing a PCB. n.d., Boca Raton,
2006.
http://uk.farnell.com/images/en_UK/design_findings8pt2.
pdf
[2] Solar Tracker, “Sun Path Diagram Image,” 2010.
http://www.gaisma.com/en/location/miri.html,
http://en.wikipedia.org/wiki/Solar_tracker
[3] D. Appleyard, “Solar Trackers: Facing the Sun,” Renew-
able Energy World, Vol. 12, No. 3, 2009.
http://www.renewableenergyworld.com/rea/ne ws/article/
2009/06/solar-trackers-facing-the-sun
[4] N. Barsoum and P. Vasant, “Simplified Solar Tracking
Prototype,” Global Journal of Technology and Optimiza-
tion GJTO, Vol. 1, 2010, pp. 38-45.
[5] J. Mak, “Personal Communication Messenger,” In: R. A.

N. BARSOUM 68
Messenger and J. Ventre, Photovoltaic Systems Engi-
neering, 2nd Edition, CRC Press, Boca Raton, 2004.
[6] Yearly Trends: Weather Averages and Extremes, 2010.
http://www.myweather2.com/City-Town/Malaysia/Miri/c
limate-profile.aspx?month=4
[7] K. Andreas, “Wind Load,” 2002.http://k7nv.com/notebo
ok/=topics/windload.html
[8] S. Terry, “Using a Wiper Motor in Your Halloween Pro-
jects,” 2010. http://www.scary-terry.com/wipmtr/wipmtr.
htm
[9] R. Beardmore, “Rolling, Bearing, Friction,” 2010a; “Co-
efficient of Friction,” 2010b.
http://www.roymech.co.uk/Useful_Tables/Tribology /Bea
ring%20Friction.html
http://www.roymech.co.uk/Useful_Tables/Tribology /co_
of_frict.htm# coefficients
[10] E. A. Avallone and T. Baumeister, Eds., “Standard Hand-
book for Mechanical Engineers,” 10th Edition, Mc-
Graw-Hill, New York, 1996.
[11] R. A. Messenger and J. Ventre, “Photovoltaic Systems
Engineering,” 2nd Edition, CRC Press, Boca Raton,
2004.
[12] J. Iovine, “PIC Microcontroller Project Book,” McGraw
Hill, New York, 2000.