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Design, Fabrication and Working of a Wall Climbing Robot
Design, Fabrication and Working of a Wall Climbing Robot
Session 2006-08
Project Advisor
Mr. Yasir Mehmood
Submitted By
Muhammad Abdul Qadir
Muhammad Luqman Ali
The University of Azad Jammu & Kashmir
Department of Computer Science & Information Technology
Mirpur Campus
Design, Fabrication and Working of a Wall Climbing Robot
It is to certify that the following students have completed their project on
M. Abdul Qadir
M. Luqman Ali
It is to certify that following students have successfully completed their final year project as
prescribed by the CS&IT Department of AJK University for the course of Artificial Intelligence
Project Advisor
External Examiner
Department of CS&IT
Mirpur (A.K)
Project Coordinator
Design, Fabrication and Working of a Wall Climbing Robot
To our respected and affectionate parents, teachers and friends who sacrificed all the
comforts of their lives for our future and whose love and affections have always guided us to
face the challenges of life with patience and courage and their guidance inspired us throughout
our life to get our destination.
Design, Fabrication and Working of a Wall Climbing Robot
All praises to ALLAH, the source of all knowledge, wisdom within and beyond our
comprehension. In fact, we cannot repay even a single blessing conferred upon us by ALLAH.
So first of all we offer our thanks to “ALMIGHTY ALLAH”. Who gave us courage and interest
to complete our project, and without whose help and will, it was not possible for us to finish it.
We pay our sincere gratitude to our kind parents whose love affection and priceless prays
for us, let us do our work with devotion, which finally let us complete our project.
We are highly privileged in taking the opportunity to record a deep sense of gratitude and
indebtedness to our project coordinator “Mr. Yasir Mehmood”, Chairman CS&IT Department,
who kindly assigned us with such an interesting project and under whose sincere guidance and
scholarly approach, this important piece of work finally, achieved its goal. His consistent advice
and supervision generated the vigor for excellence in its pursuits, without which this would never
have been materialized.
Last, we consecrate our sincere thanks to all our friends and colleagues for their helps and
valuable suggestion during our project.
Team Members
Design, Fabrication and Working of a Wall Climbing Robot
Almost in all developed countries of the new age robotics is flourishing and help establish
technology and can be said as the back bone of industries.
In Pakistan robotics is just on the verge of global robotic competition and it is the need of new
age to introduce different and efficient working principles, phenomina and economical
fabrication techniques to enhance and optimize basic robot concept.
Wall climboing robots is basically based upon optimized fabrication techniques and working
phenomina that can solve tipical industrial problems, relating to inspection methods, live
observations and security system.
Different jobs and operations can also upgrade the purpose of WCR.
As for as research on WCR is concerned, this study will be helpful for robot making industries.
The material selection problems can be solved through this fresh and latest research. Uses and
ideas of material selection in any type of structural design in robotics and simplicity that has
been introduced here is brighter step towards robotics development.
Design, Fabrication and Working of a Wall Climbing Robot
1. INTRODUCTION ………………………………………………..……..9
1.1 Background ……………………………………………………………………..…9
1.2 Purpose and scope ………………………………………………………………..10
1.3 Project time line ……………………………………………………………….....10
2. LITERATURE REVIEW ……………………………………………..12
2.1 Development of semi-self contained wall climbing robot with scanning
Type suction cups ………………………………………………’’……………....12
2.2 Walking and running of the Quadruped Wall Climbing robot …………………..12
2.3 A wall climbing robot using propulsive force of propeller ……………………....13
2.4 Machine that can walk and climb on floors, walls and ceiling …………………..14
2.5 Development of small size window cleaning robot by wall
Climbing mechanism …………………………………………………………...…14
2.6 Vortex’s wall climbing robot ……………………………………………….…….15
2.7 Gecko inspired surface climbing robots …………………………………….…....15
2.8 Stanford’s skickybot wall climbing robot lizard …………………………...…….15
2.9 The BIGALLO wall climbing robot …………………………………………...…16
3. MECHANICAL SYSTEM ……………………………………………17
3.1 Overview …………………………………………………………………….......17
3.2 Different techniques to stick robot onto wall ……………………………………18
3.3 Mathematical calculations ……………………………………………………….19
3.4 Mechanical structure …………………………………………………………….24
3.4.1 Main column …………………………………………………………………….24
3.4.2 Legs ………………………………………………………………………….…..25
3.4.3 Slider housing ……………………………………………………………….….26
3.4.4 Slider ………………………………………………………………………….…27
3.4.5 Eccentric ………………………………………………………….….….……..28
3.4.6 Washer …………………………………………………………….…..……….28
3.4.7 Tee …………………………………………………………………….………...29
3.4.8 Screws …………………………………………………………….….……..….29
3.5 Suction cups ……………………………………………………….….……......31
3.5.1 Selecting a vacuum cup………………………………………….….…………32
3.5.2 Forces holding the cup on the wall …………………………….….………..35
Design, Fabrication and Working of a Wall Climbing Robot
3.5.3 Material used in vacuum cup…………………………………….….……….36
3.6 Vacuum pump……………………………………………………….….………37
3.6.1 Types ……………………………………………………………….…………..37
3.6.2 Performance measures …………………………………………..…………..38
3.6.3 Positive displacement…………………………………………….…….…….38
3.6.4 Techniques ……………………………………………………….…….……..40
3.6.5 Vacuum pump verses venture effect……………………………...........41
3.6.6 Vacuum pump used ……………………………………………………...42
3.6.7 Syringe …………………………………………………………….………42
3.7 Tubing ……………………………………………………………..………43
3.8 Sealant …………………………………………………………..………...45
3.8.1 Types of sealants ………………………………………………..……….45
3.8.2 Silicon sealants ………………………………………………..…………45
3.9 Gait of robot ……………………………………………………..………..49
4.1 DC motor ……………………………………………………….………...51
4.2 Power supply …………………………………………………….…… ...57
5.1 Suction cups ……………………………………………………….……..63
5.2 Vacuum pump ……………………………………………………….…...63
5.3 Materials …………………………………………………………….……64
5.4 Size of DC motor…………………………………………………………64
5.5 Limited direction of motion ………………………………………...……64
6. APPANDICES ………………………………………………..…65
6.1 Aluminium casting alloy LM6 ……………………………………….….65
6.2 Mild steel …………………………………………………………….…..67
6.3 Brass ……………………………………………………………………..69
6.4 Sand casting ……………………………………………………………...72
6.5 Cad diagrams ………………………………………………………...…..80
7. IMPLEMENTATIONS ……………………………………...…91
7.1 Future planes………………………………………………………..……91
7.2 Conclusions ………………………………………………….….……….93
7.3 References …………………………………………………….…………93
Design, Fabrication and Working of a Wall Climbing Robot
In our introduction to WALL CLIMBING ROBOT we have some background history of
all kinds of WALL CLIMBING ROBOTS, secondly the purpose and scope of the project, then
lastly the project timeline.
There are a variety of potential applications of robotics to wall climbing operations that
can increase efficiency and safety. These include inspection of concrete walls, to access of under
side of bridges, reactor pressure vessel inspection and cleaning tall buildings which are usually
performed by humans. Wall climbing robots have the potential to provide a revolutionary step in
doing dangerous tasks that are usually performed by humans. Thus increasing the rate of human
life .Recently, there have been many demands for automatic cleaning system on outside surface
of buildings such as window glass by increasing of modern architectures. Some customized
window cleaning machines have already been installed into the practical use in the field of
building maintenance. However, almost of them are mounted on the building from the beginning
and they needs very expensive costs. Therefore, requirements for small, lightweight and portable
window cleaning robot are also growing in the field of building maintenance. As the results of
surveying the requirements for the window cleaning robot, the following points are necessary for
providing the window cleaning robot for practical use:
It should be small size and lightweight for portability.
Design, Fabrication and Working of a Wall Climbing Robot
Automatic operation during moving.
The purpose of the project is to develop a robot that can climb wall. Keeping this in view,
our purpose was to build a machine that can stick on walls and climb upwards. After studying the
literature written by the previous searchers, suction cups technique was used to stick the robot to
the wall as all the required materials were available in the local market. In suction robot that are
used for wall climbing robot, they used onboard pump that created a pressure drop inside the
vacuum cups that are pressed against the wall or ceiling. As the vacuum cup are pressed against
the wall, the on board pump will start to pump the air in the vacuum cup out to the surrounding.
After some time, the pressure inside the vacuum cup is lower than that outside the vacuum cup
thus it is able to stick onto the wall.
The suction adhesion robots are normally used on valley bridges and the temperature
could be around 0 to 50 degree Celsius. As for the weight, this type of robot should not be more
than 35 kg. The centre of gravity of the robot must be kept as close as to the vertical surface as
possible, as the force required to hold the whole weight of the robot will be reduced. Although
this kind of robot is normally used to do the cleaning for high buildings and under high way
bridges, this will in turn replace human beings thus reducing the accident rate. This will further
increase the human being rate of living.
The time management was one of the crucial factors while undertaking this project. So,
the time had to be managed properly in order to meet the task in time. Following is an outline of
our program showing our targets achieved in last semester.
Design, Fabrication and Working of a Wall Climbing Robot
Design, Fabrication and Working of a Wall Climbing Robot
Many techniques were studied for sticking the robot to the wall. The list of the
papers studied with there abstract is given below.
2.1 Development of a Semi Self-contained Wall Climbing
Robot with Scanning Type Suction Cups
Tomoaki yano, tomohiro suwa, masato muraxami, takuji yamamotq
A semi self-contained Wall Climbing Robot with Scanning Type SucMon Cups is
developed and tested. This robot has two vacuum pumps on it. The robot is connected to the
equipment on the ground only through the electric power cables and information cables. From
the experimental results, the robot can walk wound on walls, clear steps, and stick on cracks and
gaps. I; he walking speed attains I38[cm/min] which is 59% faster than the wall climbing robot I
with tubes connected to the external vacuum pump on the ground. These experimental results
show higher possibility towards the development of a complete self-contained wall climbing
robot by putting a battery and a CPU on the robot.
2.2 Walking and Running Of the Quadruped Wall-Climbing
Akihiko Nagakubo and Shigeo Hirose
The development of a wall climbing robot which is able to move over the surface of "3Dimensional terrain", a terrain including floor, wall, and ceiling of any kinds of structures with
agility and terrain adaptability is strongly demanded in many industries. The conventional wall
climbing machines were far from fulfilling the demand, authors thus have been developing U
Design, Fabrication and Working of a Wall Climbing Robot
wall-climbing robot with four-terrain-adaptive legs and basic mobility were already
demonstrated by the manufactured prototype model NINJA-I. However, as there are almost no
examples of wall-climbing quadruped animals and conventional machines, the gait control
method specific for the quadruped wall-climbing is not at all known by now. As the first step to
consider a general gait problem of a quadruped wall-climbing robot, this paper investigates a gait
of the robot on a vertical and flat wall. The gait is analyzed with the criterion to maximize the
locomotion speed under the constraints of predetermined conditions of the supporting-legs
position, order and phases of swing legs to prevent turn over motion. As a result of the analysis,
the optimal standard gait, named "Wall Gait", is shown to maintain foot posture of A shape and
moves the leg in the order of leg1 - leg2 - leg4 - leg3 in static walk and the order of "pace" in
dynamic walk.
2.3 A Wall Climbing Robot Using Propulsive Force of a
Akira Nishi
A robot capable of moving on a vertical wall of high rise building s has been expected
for a long time to utilize it for rescuing, wall inspection, fire-fighting, etc. those hazardous tasks
are suitable missions for the robot. A wall climbing robot using thrust force of propellers has
been developed. The thrust force is inclined a little to the wall side to produce the frictional force
between the wheels and wall surface. As the strong wind is predicted on the wall surface of
buildings, the direction of thrust force is controlled to compensate the wind force acting on the
robot. A frictional force augmenter is also considered, which is an air foil to produce the lift
force directed to the wall side by the cross-wind. Its effect is tested in the wind tunnel. The
overall performance of the robot is examined by computer simulation and a model was
constructed and tested on the wall.
Design, Fabrication and Working of a Wall Climbing Robot
2.4 Machine That Can Walk and Climb on Floors, Walls and
Shigeo Hirose, Akihiko Nagakubo and Roysei Toyama
The configuration design for a wall-climbing robot which is capable of moving on
diversified surfaces of wall and has high payload capability is discussed and a developed
quadruped wall climbing robot, NINJA-1 is introduced. NINJA-1 is composed of
1. Legs based on a 3D parallel link mechanism capable of producing a powerful driving
force for moving on the surface of the wall.
2. 2. A CP (conduit-wire-driven parallelogram) mechanism to adjust the posture of the
3. A VM (Valve-regulated Multiple) sucker which can provide suction even if there are
grooves and small differences in level of the wall.
Finally the data of the trial manufactured NINJA-1 and the up-to-date status of the walking motion is
2.5 Development of Small-Size Window Cleaning Robot by
Wall Climbing Mechanism
Tohru Miyake, Hidenori Ishihara, Ryu Shoji and Shunichi Yoshida
The objective of this research is to develop the small-size and light weight window
cleaning robot. The prototype of window cleaning robot has been developed. The dimensions of
prototyped robot are approximately 300mm x 300mm x 100mm and its weight is approximately
3 kg. The prototyped robot consists of two independently driven wheels and an active suction
cup. The control system which includes traveling direction controller using accelerometer and
traveling distance controller using rotary encoder and edge sensors ware installed for
autonomous operation. This paper includes background and objectives of this research,
prototyped mechanical systems, moving control system, experimental result of basic traveling
control and window wiping motion by comparing to with or without of motioned control system,
some discussions in each experiment and a conclusion.
Design, Fabrication and Working of a Wall Climbing Robot
2.6 Vortex's Wall Climbing Robot
It utilizes a vortex vacuum to suction itself to vertical surfaces, and then relies on the
wheels to get it moving. The vortex climber is based on a so-called "tornado in a cup"
technology. Figure in Appendix D.
2.7 Gecko Inspired Surface Climbing Robots
Carlo Menon, Michael Murphy, and Metin Sitti, Member, IEEE
Many applications call for robots to perform tasks in workspaces where traditional
vehicles cannot reach. Using robots to perform these tasks can afford better human safety as well
as lower cost operations. This paper focuses on the development of gecko inspired synthetic dry
adhesives for wall climbing robots which can scale vertical walls. Many applications are of great
interest for this kind of robot such as inspection, repair, cleaning, and exploration. The
fabrication of synthetic dry adhesives inspired by nature is discussed as well as the design of
prototype wall climbing robots. Results are presented and discussed to show the feasibility of
novel Gecko inspired robots.
The gecko’s ability to stick to surfaces lies in its feet, specifically the very fine hairs on
its toes. There are billions of these tiny fibers which make contact with the surface and create a
significant collective surface area of contact. The hairs have physical properties which let them
bend and conform to a wide variety of surface roughness, meaning that the adhesion arises from
the structure of these hairs themselves.
2.8 Stanford's Stickybot Wall-Climbing Robot Lizard
The robot gecko has feet coated with a polymer designed to mimic the properties
of setae, the tiny hairs on gecko feet that enable the lizards to climb walls. That allows the bot to
clamber freely without the surface in question having to be doused with slime, as required by
MIT's bot. Figure in appendix D
Design, Fabrication and Working of a Wall Climbing Robot
2.9 The BIGGALO Wall Climbing Robot
The BIGGALO Wall Climbing Robot was an ELEC/CENG 499A Design Project Course
project at the University of Victoria. Figure in appendix D.
BIGGALO (BIG uGly And LOud robot) is a pneumatics based robot that is designed to
climb relatively smooth vertical surfaces. It was designed and built during the summer semester
(May-August) in 2003 by a team of engineering students at the University of Victoria.
The project itself was an exercise in mechanical design, control, and microcontroller
programming. It worked to combine the mechanical, electrical and computer engineering fields
together. It uses externally compressed air to generate suction at each of its suction cups, and
solenoids to move pneumatic cylinders. All of this is controlled by a central microcontroller. The
robot can climb walls through a series of motions, by turning off the suction to a few suction
cups, forcing the cylinders to extend, placing the suction cups down and reengaging suction, it
can move across vertical surfaces very easily.
Design, Fabrication and Working of a Wall Climbing Robot
The robot to its present form came through lots of changes. We started designing our
robot keeping in mind BIGGALO wall climbing robot. Many limitations due to the nonavailability or financial restraints came our way and we kept on changing our design so that we
could make a model from local resources.
Our wall climbing robot is two legged having two suction cups on each leg and uses
suction technique to stick on to the wall. Two legs of the robot are always in contact with the
wall while the other two are moving. It is designed to keeping in mind the lesser weight. A
single actuator moves the robot as well as provides necessary vacuum to keep it on to the wall.
Design, Fabrication and Working of a Wall Climbing Robot
One of the most challenging tasks in climbing robot design is to develop a proper adhesion
mechanism to ensure that the robot sticks to wall surfaces reliably without sacrificing mobility.
After review of the above mentioned literature and there developed prototypes we concluded that
So far, four types of adhesion techniques have been investigated
Magnetic devices for climbing ferrous surfaces
Attraction force generators based on aerodynamic principles;
Bio-mimetic approaches inspired by climbing animals
Vacuum suction techniques for smooth and nonporous surfaces.
Magnetic adhesion devices are most promising for robots moving around on steel
structures. Robots using permanent magnets or electromagnets can be found for climbing large
steel structures for internal inspection of iron pipes. However, their applications are limited to
steel walls due to the nature of magnets.
Choosing to create attraction force based on aerodynamic principles including the use of
propeller is a complex task. Robots which create attraction force based on aerodynamic
principles have demonstrated the capability moving on brick and concrete walls with
considerable success. However, the power consumption and noise are two issues need to be
addressed for some surveillance tasks. Keeping in view that all the materials are available in
market, using the technique of the propulsive force was not possible as there are no vendors to
make an exact propeller of required specification
Dry adhesive called geckos are synthetic polymers designed to mimic the properties of
setae. Setae are the naturally occurring adhesive in the feet of lizards which enable them to climb
almost all kind of surfaces. The ability of geckos to climb on sheer surfaces has been attributed
to van-der-Waals force. Van-der-Waals force refers to the attractive or repulsive forces between
molecules (or between parts of the same molecule) other than those due to covalent bonds or to
the electrostatic interaction of ions with one another or with neutral molecules. It is also
sometimes used loosely as a synonym for the totality of intermolecular forces. Van-der-Waals
Design, Fabrication and Working of a Wall Climbing Robot
forces are relatively weak compared to normal chemical bonds, but play a fundamental role in
many fields. A recent study suggests that water molecules of roughly monolayer thickness
(present on all surfaces) also play a role. Nevertheless, a gecko can hang on a glass surface using
only one toe. Efforts continue to create a synthetic "gecko tape" that exploits this knowledge. So
far, research has produced some promising results - early research yielded an adhesive tape
product, which only obtains a fraction of the forces measured from the natural material, and new
research are being developed with the goal of featuring 200 times the adhesive forces of the
natural material.
In applications for non-ferromagnetic wall surfaces, climbing robots most generally use
vacuum suctions to produce the adhesion force. We choose suction cups as the technique to stick
our robot to the wall as they were available in the local market.
The robot is supported on the wall with a vacuum cup .Their is a pressure
difference between inside of the cup and outside. This pressure difference produces
the force which holds the cup and as a result robot on the wall.
The force is given as
Atmospheric Pressure
Pressure inside Vacuum Cup
Area of Vacuum Cup
Design, Fabrication and Working of a Wall Climbing Robot
The force which does not let the cup slide on wall is frictional force.
Reaction Force
Frictional Force
Coefficient of Friction between Pad and Wall, it depends on the materials of
Wall and pad
The forces acting on the robot are shown in a free body diagram below
Design, Fabrication and Working of a Wall Climbing Robot
Where W
Weight of Robot
Angle of Inclination
The change in volume to create required pressure can be calculated from the following
Atmospheric Pressure
Pressure inside Vacuum Cup
Volume at t=max
Volume at t=0
Now the distance of centre of gravity from the cups varies .The cups below the centre of
gravity requires less force than the cups above the centre of gravity to keep the robot attached to
the wall.
vacuum cups.
Are the distance from centre of gravity to the centre of the respective
Design, Fabrication and Working of a Wall Climbing Robot
Suppose that the distance of cups from centre of gravity is same then the above equation
becomes the following equation.
The cups above the centre of gravity are at same height from centre of gravity so the
forces acting on these cups can be added. Similarly forces acting on the cups below the centre of
gravity can be added. Hence
As it can be seen from diagram that forces
the vacuum in the vacuum cup while
act opposite to the force created by
act along the force created by the vacuum in the
Design, Fabrication and Working of a Wall Climbing Robot
vacuum cups. For the selection of the cups of equal diameter the force acting on the cups above
the centre of gravity must be considered.
DC Motor Speed Control without Feedback (Open Loop Control):
It is desirable to have a variable speed electric motor that can provide an adjustable speed
to the process which is then maintained constant. This can be accomplished with the DC Electric
motor with the voltage controller
Torque of the motor is exactly proportional to the current and voltage is directly
proportional to the angular speed. As shown in following two equations.
Where K
constant of proportionality
Real amplifiers lose voltage as the output current increases due to output resistance
an overall amplifier gain
We can state the equation of the amplifier as
Since the torque driving the load is the motor torque and since the inertia, friction and the
disturbance torque oppose the motion the torque balance can be stated as
From this above equation we can eliminate
which gives us the speed of the motor.
Design, Fabrication and Working of a Wall Climbing Robot
linear viscous damping coefficient
amplifier gain
motor torque
control volume
Rotational speed
input speed (set-point speed)
natural frequency
motor speed
Output position
3.4.1 Main Column
It is the chassis of the whole robot. It keeps all the parts together. It is made of aluminum6061. It is also called LM6. The chemical composition of this alloy mainly consists of aluminum
and silicon. As it can been seen from the detailed drawing of the part, it was difficult to carve it
out from a block of metal. Hence this part was made by sand casting process. LM6 is widely
used for castings as it possesses exceptional casting characteristics and gave us the required
Design, Fabrication and Working of a Wall Climbing Robot
strength of 176.87 N/mm2. LM6 exhibits excellent resistance to corrosion under both ordinary
atmospheric and marine conditions. For the severest conditions this property can be further
enhanced by anodic treatment. LM6 can be anodized by any of the common processes, the
resulting protective film.
Main Column
Due to high silicon content this alloy is difficult to machine and causes rapid tool wear.
Hence after sand casting, to give finish to the part carbide tipped tools with large rake angles,
relatively low cutting speed, a cutting lubricant and coolant was employed. It cannot be heat
treated as its strength falls rapidly at elevated temperatures. A detailed drawing of the part is
given in Appendix D
3.4.2 Legs
The legs will hold the chassis with the suction cups. The leg is pivoted with the chassis or
main body. This part is also made by process of sand casting. Hence LM6 aluminum alloy is
Design, Fabrication and Working of a Wall Climbing Robot
used due to its exceptional casting characteristics. After casting the part was machined for
finishing. . A detailed drawing of the part is given in Appendix D
3.4.3 Slider Housing
This part is fixed in the center of the chassis as shown in the fig. this part is made up
of mild steel. As it is evident by the name given to this part, it will hold the slider which has to
slide in it. Hence the part has to be stiff and hard. That is why mild steel is chosen as its material.
As mild steel is easily machine able and the part is not of difficult make, hence part is machined
out of the mild steel block. It is also cheap but it has poor corrosion resistance i.e. it rusts. It will
also hold the syringes that create the vacuum. . A detailed drawing of the part is given in
Appendix D
Design, Fabrication and Working of a Wall Climbing Robot
Slider Housing
3.4.4 Slider
As it is evident from the name given to the part, it will slide. Sliding motion will take
place inside the slider housing. As low friction is required between the slider and its housing
hence slider is made of brass. Brass has chemical combination of copper and zinc. . A detailed
drawing of the part is given in Appendix D
Design, Fabrication and Working of a Wall Climbing Robot
3.4.5 Eccentric
This part connects the motor with the slider. This part is made of mild steel as it will
deliver the power from motor to the slider. A detailed drawing of the part is given in Appendix D
3.4.6 Washer
The main column and the legs of the structure are separated by washers. Washers are used
to reduce friction between the moving leg and the main column. As washer is employed to
reduce friction so the material used for washer is brass. Similarly washers are used between
slider and legs. . A detailed drawing of the part is given in Appendix D
Design, Fabrication and Working of a Wall Climbing Robot
3.4.7 Tee
The tee is made of mild steel. It is connected at the mouth of pump assembly. . A detailed
drawing of the part is given in Appendix D
3.4.8 Screws
Screws of different specifications are used as required. The details of the screws are
mentioned in the fig. A screw used as a threaded fastener consists of a shaft, which are usually
cylindrical and in many cases tapering to a point at one end and with a helical ridge or thread
formed on it, and a head at one end which can be rotated by some means. The thread is
essentially an inclined plane wrapped around the shaft. The thread mates with a complementary
Design, Fabrication and Working of a Wall Climbing Robot
helix in the material. The material may be manufactured with the mating helix using a tap, or the
screw may create it when first driven in (a self-tapping screw). The head is specially shaped to
allow a screwdriver or wrench (British English: spanner) to rotate the screw, driving it in or
releasing it. The head is of larger diameter than the body of the screw and has no thread so that
the screw can not be driven deeper than the length of the shaft, and to provide compression.
Screws can normally be removed and reinserted without reducing their effectiveness.
They have greater holding power than nails and permit disassembly and reuse.
The vast majority of screws are tightened by clockwise rotation; we speak of a right-hand
thread. Screws with left-hand threads are used in exceptional cases, when the screw is subject to
anticlockwise forces that might undo a right-hand thread. Left-hand screws are used on rotating
items such as the left-hand grinding wheel on a bench grinder or the left hand pedal on a bicycle
(both looking towards the equipment) or hub nuts on the left side of some automobiles.
Threaded fasteners were made by a cutting action such as dies provide, but recent
advances in tooling allow them to be made by rolling an unthreaded rod (the blank) between two
specially machined dies which squeeze the blank into the shape of the required fastener,
including the thread. This method has the advantages of work hardening the thread and saving
material. A rolled thread can be distinguished from a thread formed by a die as the outside
diameter of the thread is greater than the diameter of the unthreaded portion of the shaft. Bicycle
spokes, which are just bolts with long thin unthreaded portions, always use rolled threads for
Hexagonal (hex) socket head has a hexagonal hole and is driven by a Hex Wrench,
sometimes called an Allen key or Hex key, or by a power tool with a hexagonal bit. Tamperresistant versions with a pin in the recess are available. Hex sockets are increasingly used for
Design, Fabrication and Working of a Wall Climbing Robot
modern bicycle parts because hex wrenches are very light and easily carried tools. They are also
frequently used for self-assembled furniture
The screws used are of ISO metric standard. The details of this standard are given in
appendix. Screws used are recessed pan head screws. In figure shown below screw ‘a’ is a pan
head screw.
The list of part number used is
1. ISO 7045 – M5 x 12 – 4.8 – Z
2. ISO 7089 – 5 – 140 – HV
3. ISO 7045 – M3 x 8 – 4.8 – Z
4. ISO 7045 – M5 x 10 – 4.8 – Z
For nomenclature of screws consult Appendix B.
A suction cup is a device, usually made of rubber or plastic, that sticks to smooth,
nonporous surfaces. They are usually used to attach objects together with the use of suction.
Upon pressing the suction cup to a surface, the air pressure inside is drastically reduced. The
relatively higher atmospheric pressure outside prevents the cup from lifting off the surface;
friction does the rest of the work. Suction cups are believed to have first been used in the 3rd
century, B.C., and were made out of gourds. They were used to suction "bad blood" from
internal organs to the surface. Hippocrates is believed to have invented this procedure. Suction
cups are used on nerf darts and can also be found on plungers. The modern suction cup was
Design, Fabrication and Working of a Wall Climbing Robot
patented in 1882, and is based on the suction cup-like features on octopus arms. The patent has
3.5.1 Selecting a Vacuum Cup
a) The Load Or Lifting Capacity Of A Vacuum Cup
The load or lifting of capacity of a vacuum cup is determined by the
formula below
F = Weight of the object in pounds, multiplied by a safety factor
P = the expected vacuum level in bar.
A = the area of the vacuum cup in square millimeters.
b) Safety Factors For Vacuum Lifting:
Always include safety factors when calculating lifting capabilities.
Horizontal Lift = 2
Vertical Lift = 4
Safety factor of 2 is recommended
Safety factor of 4 is recommended
when cup face is in horizontal position.
when cup face is in a vertical position.
Design, Fabrication and Working of a Wall Climbing Robot
0.68 bar is maximum holding force. The goal is to lift a 5'x5' cardboard box
weighing 10 kg.
Load lifted in horizontal position (safety factor=2)
Using the formula, the area of the vacuum cups required can be calculated in the
following manner:
• F=20 kg. x 9.8 (weight x safety factor or 10 kg. x 2)
• P=0.68 bar
• A=2880mm2 (A=F/P)
Therefore, 2880mm2 is the total area of the cup or cups needed to lift this load
Load lifted in vertical position (safety factor=4)
• F=40 kg. X 9.8 (weight x safety factor or 10 kg. x 4)
• P=.68 bar
• A=5764mm2 (A=F/P)
Therefore, 5764mm2 is the total area of the cup or cups needed to lift this load
Again, for stability, we recommend using more than one cup. Therefore, for an
application to be lifted:
If you were to use 5 cups, you would look for cups with an Approx. Area in.2 of
4.… (20/5 = 4)
If you were to use 4 cups, you would look for cups with an Approx. Area in. 2 of
5…. (20/4 = 5)
c) Relationship between Cups Dia And Lifting Force
The chart below indicates the relationship between the cup diameter and lifting
force at various vacuum levels. Please note a vacuum cup adheres to a surface as
Design, Fabrication and Working of a Wall Climbing Robot
the surrounding or atmospheric pressure is greater than the pressure within the
vacuum cup. While selecting the cups consider a safety factor of 3 to 1.
Level (bar)
Cup Diameter
d) Three steps for selection of cup
From above we conclude that selection of cups is done in three steps
Step 1
Select the size by determining the best seal or picking area - ideally you
are seeking a smooth surface to achieve a good seal. The lifting capacities of the
different cups of varying sizes are given in the table above that is calculated. The
larger the cup the more lifting force will be available. If however, a single cup
cannot be used consider multiple mountings of smaller cups on a manifold block.
Step 2
Select preferred vacuum cup style. For example, if the sealing area is not
smooth, featheredge cups are used and if a pulling motion or immediate lift is
required a bellow style cup is used.
Design, Fabrication and Working of a Wall Climbing Robot
Step 3
Find the matching or corresponding diameter. The area of the cup
determines it's bonding capability and force between the cup and the picking area
surface. So larger the diameter, larger is its bonding capability.
3.5.2 Forces Holding the Cup on the Wall
There are two physics principles involved i.e. friction and air pressure. Friction keeps
the suction cup from sliding down the surface and air pressure keeps it against the surface. When
the suction cup is on the wall, gravity tries to pull it down. An upward force must oppose gravity
or the suction cup will fall. Friction opposes motion between two surfaces. The cup would slide
along the wall, so a frictional force opposes the fall.
In order to have a frictional force, a perpendicular force is required or the force should be
at right angles to the wall. This force is provided by air pressure. The suction cup is designed so
that when it is pressed against a smooth surface air is squeezed out of the cup. The suction cup is
smooth and can fill any microscopic holes with its squishy rubber. It prevents air from coming
back into the cup.
Design, Fabrication and Working of a Wall Climbing Robot
The cup is also springy. Once it has been pushed, it wants to return to its original shape.
Because air has been squeezed out of the cup, the cup makes a partial vacuum. The pressure in
the cup is less then the pressure of the air out side. Because the pressure is greater outside the cup
then inside, a force pushes on the cup to keep it against the wall. This is the force at right angles
to the wall, which is needed for friction. As the pressure difference inside and outside the cup
increases, the perpendicular force on the cup increases.
After a time, most suction cups fall of because air gets into them. This increases the
pressure inside. Eventually, the cup isn’t forced against the wall hard enough by the outside air,
so friction cannot hold it up. Better quality rubber in the suction cups tends to keep the air out
longer so the suction cups stick longer.
3.5.3 Materials Used In Vacuum Cup
Vacuum cups are manufactured from two main materials:
PVC Vinyl: This is primary material as it is found to be the softest yet hardest
wearing material - the soft, pliable nature of the product offers excellent sealing
capacity with wear resistance which is greater than rubber.
Silicone: This material is also soft but provides a greater temperature range (see
chart below). However it does not have the same wear resistant properties of vinyl.
Although we carry some silicone cups in stock most are available on a special order
Working temp
Wear resistance
Oil resistance
0°c to + 50°c
-45°c to + 200°c
For more details about the vacuum cup and its materials, consult Appendix C.
Design, Fabrication and Working of a Wall Climbing Robot
A vacuum pump is a device that removes gas molecules from a sealed volume in order to
leave behind a partial vacuum. The vacuum pump was invented in 1650 by Thomas Savery.
3.6.1 Types
Pumps can be broadly categorized according to three techniques:
Positive displacement pumps use a mechanism to repeatedly expand a cavity, allow
gases to flow in from the chamber, seal off the cavity, and exhaust it to the
Momentum transfer pumps, also called molecular pumps, use high speed jets of dense
fluid or high speed rotating blades to knock gaseous molecules out of the chamber.
Entrapment pumps capture gases in a solid or absorbed state. This includes
cryopumps, getters, and ion pumps.
Positive displacement pumps are the most effective for low vacuums. Momentum transfer
pumps in conjunction with one or two positive displacement pumps are the most common
configuration used to achieve high vacuums. In this configuration the positive displacement
pump serves two purposes. First it obtains a rough vacuum in the vessel being evacuated before
the momentum transfer pump can be used to obtain the high vacuum, as momentum transfer
pumps cannot start pumping at atmospheric pressures. Second the positive displacement pump
backs up the momentum transfer pump by evacuating to low vacuum the accumulation of
displaced molecules in the high vacuum pump. Entrapment pumps can be added to reach
ultrahigh vacuums, but they require periodic regeneration of the surfaces that trap air molecules
or ions. Due to this requirement their available operational time can be unacceptably short in low
and high vacuums, thus limiting their use to ultrahigh vacuums. Pumps also differ in details like
manufacturing tolerances, sealing material, pressure, flow, admission or no admission of oil
vapor, service intervals, reliability, tolerance to dust, tolerance to chemicals, tolerance to liquids
and vibration.
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3.6.2 Performance Measures
Pumping speed refers to the volume flow rate of a pump at its inlet, often measured in
volume per unit of time. Momentum transfer and entrapment pumps are more effective
on some gases than others, so the pumping rate can be different for each of the gases
being pumped, and the average volume flow rate of the pump will vary depending on the
chemical composition of the gases remaining in the chamber.
Throughput refers to the pumping speed multiplied by the gas pressure at the inlet, and is
measured in units of pressure-volume/unit time. At a constant temperature, throughput is
proportional to the number of molecules being pumped per unit time, and therefore to the
mass flow rate of the pump. When discussing a leak in the system or back streaming
through the pump, throughput refers to the volume leak rate multiplied by the pressure at
the vacuum side of the leak, so the leak throughput can be compared to the pump
Positive displacement and momentum transfer pumps have a constant volume flow rate,
(pumping speed,) but as the chamber's pressure drops, this volume contains less and less mass.
So although the pumping speed remains constant, the throughput and mass flow rate drop
sublimation and back streaming rates continue to produce a
constant throughput into the system.
3.6.3 Positive displacement
The manual water pump draws water up from a well
by creating a vacuum that water rushes in to fill. In a sense,
it acts to evacuate the well, although the high leakage rate
of dirt prevents a high quality vacuum from being
maintained for any length of time.
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Fluids cannot be pulled, so it is technically impossible to
create a vacuum by suction. Suction is the movement of fluids into a
vacuum under the effect of a higher external pressure, but the vacuum
has to be created first. The easiest way to create an artificial vacuum is
to expand the volume of a container. For example, the diaphragm
muscle expands the chest cavity, which causes the volume of the lungs to increase. This
expansion reduces the pressure and creates a partial vacuum, which is soon filled by air pushed
in by atmospheric pressure
To continue evacuating a chamber indefinitely without requiring infinite growth, a
compartment of the vacuum can be repeatedly closed off, exhausted, and expanded again. This is
the principle behind positive displacement pumps, like the manual water pump for example.
Inside the pump, a mechanism expands a small sealed cavity to create a deep vacuum. Because
of the pressure differential, some fluid from the chamber (or the well, in our example) is pushed
into the pump's small cavity. The pump's cavity is then sealed from the chamber, opened to the
atmosphere, and squeezed back to a minute size.
More sophisticated systems are used for most industrial applications, but the basic principle
of cyclic volume removal is the same
Rotary vane pump, the most common
Diaphragm pump, zero oil contamination
Liquid ring pump
Piston pump, cheapest
Scroll pump, highest speed dry pump
Screw pump (10 Pa)
Wankel pump
External vane pump
Roots blower, also called a booster pump, has highest pumping speeds but low
compression ratio
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Multistage Roots pump that combine several stages providing high pumping speed
with better compression ratio
Toepler pump
The base pressure of a rubber- and plastic-sealed piston pump system is typically 1 to 50 kPa,
while a scroll pump might reach 10 Pa (when new) and a rotary vane oil pump with a clean and
empty metallic chamber can easily achieve 0.1 Pa.
A positive displacement vacuum pump moves the same volume of gas with each cycle, so its
pumping speed is constant unless it is overcome by back streaming.
3.6.4 Techniques
Vacuum pumps are combined with chambers and operational procedures into a wide
variety of vacuum systems. Sometimes more than one pump will be used (in series or in parallel)
in a single application. A partial vacuum, or rough vacuum, can be created using a positive
displacement pump that transports a gas load from an inlet port to an outlet (exhaust) port.
Because of their mechanical limitations, such pumps can only achieve a low vacuum. To achieve
a higher vacuum, other techniques must then be used, typically in series (usually following an
initial fast pump down with a positive displacement pump). Some examples might be use of an
oil sealed rotary vane pump (the most common positive displacement pump) backing a diffusion
pump, or a dry scroll pump backing a turbomolecular pump. There are other combinations
depending on the level of vacuum being sought.
Achieving high vacuum is difficult because all of the materials exposed to the vacuum
must be carefully evaluated for their out gassing and vapor pressure properties. For example,
oils, and greases, and rubber, or plastic gaskets used as seals for the vacuum chamber must not
boil off when exposed to the vacuum, or the gases they produce would prevent the creation of the
desired degree of vacuum. Often, all of the surfaces exposed to the vacuum must be baked at
high temperature to drive off adsorbed gases.
Design, Fabrication and Working of a Wall Climbing Robot
3.6.5 Vacuum Pump versus Venturi Effect
Air or steam ejectors seem to offer a cheap and simple alternative to a vacuum pump.
What isn't appreciated is the substantial compressed air consumption required by vacuum
ejectors. A medium-capacity air ejector needs 4000 liter/min of compressed air at 7bar: an output
that requires 28.6kW of motive power.
A rotary vane vacuum pump of similar capacity only requires a 7.5kW motor. In other
words, it will use about one quarter of the power required by the vacuum air ejector. Vacuum air
or steam ejectors are simple venturi devices with no moving parts. Essentially, they comprise a
jet nozzle that is aligned with a diffuser. Compressed air is forced through the nozzle into the
diffuser, thus entraining the gas in the inlet chamber and creating a vacuum.
The sensible option from a power viewpoint, would be to opt for the vacuum pump in the
first place, Arguably, venturi devices are simple to maintain (compared with a rotary vane
design), but they are not maintenance-free, nor are the compressors that power them. However,
any marginal benefits in maintenance costs for vacuum ejectors are heavily outweighed by their
additional running costs.
Venturi Pump
Strong Vacuum without large hoses,
precise control of vacuum on/off, blowoff function an option, compressed air
hoses are more flexible and can be bent
without sacrificing vacuum strength
because of positive pressure inside the
Expensive component,
compressed air needs to be
vented somehow out of the
clean environment
Vacuum pump
Slightly less expensive component,
fewer tubes, no venting concerns,
simpler component, large volume
Less precise control with no
guaranteed precision on time
lag, less flexible hoses for
moving assemblies
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3.6.6 Vacuum Pump Used
In order to minimize the size of vacuum pump we used a technique. As we required low
vacuum so positive displacement pump was applied. We used a medical syringe to create
vacuum. The syringe works on positive displacement principle to create vacuum. The syringe is
driven by a four-bar mechanism. Two syringes are used, each provides vacuum to two vacuum
cups. Syringe is connected to the vacuum cups through a plastic pipe. The pipe used is same as
the pipe used to connect the medical drip to cannula in hospitals.
3.6.7 Syringe
A syringe nowadays nearly always means a medical syringe, but it can mean any of these:
A simple hand-powered piston pump consisting of a plunger that can be pulled and
pushed along inside a cylindrical tube (the barrel), which has a small hole on one end,
so it can suck liquid in and then squirt it out by the same hole. The word "syringe"
came from the Greek word meaning "tube" via extracting a new singular from its
Greek-type plural "syringes"
In former times the word "syringe" also meant big two-handed pumps of this type
used e.g. as early firefighting water pumps.
Nowadays the word "syringe" is restricted to smaller devices, used to transfer small
amounts of liquids or gases to or from otherwise inaccessible areas, including
particularly hypodermic syringes used with a needle for injection.
As a result, jet injectors are sometimes called syringes.
One medical survival of the word "syringe" for uses other than injection, is in "syringing an ear
out", i.e. washing unwanted matter out of the external ear canal.
Design, Fabrication and Working of a Wall Climbing Robot
When using mechanical vacuum pumps or vacuum generators that transport the vacuum
flow through tubing from the source to the suction cup. It is suggested that a few rules of thumb
be followed. First, do not let the total cross sectional area of the vacuum lines be smaller than the
vacuum port. ‘If [the pump] has a 3/4-inch vacuum port, don’t reduce that down to a 1/8-inch or
three 1/16-inch lines. The total area should equal the vacuum port.
It’s not scientific, but it’s a good rule of thumb,’ also, turn on the system with the vacuum
cups unencumbered. If the pump shows any vacuum level at all then the lines are restricted. Flow
is directly related to evacuation speed and also allows you to compensate for leakage caused by
porous materials like corrugated materials.
Design, Fabrication and Working of a Wall Climbing Robot
Design, Fabrication and Working of a Wall Climbing Robot
A sealant is a viscous material that changes state to become solid, once applied, and is
used to prevent the penetration of air, gas, noise, dust, fire, smoke or liquid from one location
through a barrier into another. Typically, sealants are used to close small openings that are
difficult to shut with other materials, such as concrete, drywall, etc. Desirable properties of
sealants include insolubility, corrosion resistance, and adhesion. Uses of sealants vary widely
and sealants are used in many industries, for example, construction automotive and aerospace
An example of a sealant is silicone.
3.8.1 Types of Sealants
Acryl sealants
Polysulfide sealants
Polyurethane sealants
Silicone sealants
WTK sealants
3.8.2 Silicone Sealants
Silicones are largely inert compounds with a wide variety of forms and uses. Typically
heat-resistant, nonstick and rubber-like, they are frequently used in cookware, medical
applications, sealants, lubricants and insulation.
Some of the most useful properties of silicone include:
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Thermal stability (constancy of properties over a wide operating range of
−100 to 250 °C).
Though not lipophilic, the ability to repel water and form watertight seals.
Excellent resistance to oxygen, ozone and sunlight.
Good electrical insulation.
Low chemical reactivity.
Low toxicity.
High gas permeability: at room temperature (25 °C) the permeability of
silicone rubber for gases like oxygen is approximately 400 times that of butyl
rubber, making silicone useful for medical applications (though precluding it
from applications where gas-tight seals are necessary).
a) Technical Details
More precisely called polymerized siloxanes or polysiloxanes, silicones
are mixed inorganic-organic polymers with the chemical formula [R2SiO]n, where
R = organic groups such as methyl, ethyl, and phenyl. These materials consist of
an inorganic silicon-oxygen backbone (…-Si-O-Si-O-Si-O-…) with organic side
groups attached to the silicon atoms, which are four-coordinate.
In some cases organic side groups can be used to link two or more of these
-Si-O- backbones together. By varying the -Si-O- chain lengths, side groups, and
crosslinking, silicones can be synthesized with a wide variety of properties and
compositions. They can vary in consistency from liquid to gel to rubber to hard
plastic. The most common siloxane is linear polydimethylsiloxane (PDMS), a
silicone oil. The second largest group of silicone materials is based on silicone
resins, which are formed by branched and cage-like oligosiloxanes.
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Polydimethylsiloxane (PDMS)
b) Synthesis
Silicones are synthesized from chlorosilanes, tetraethoxysilane, and
related compounds. In the case of PDMS, the starting material is
dimethylchlorosilane, which reacts with water as follows:
n [Si(CH3)2Cl2] + n [H2O] → [Si(CH3)2O]n + 2n HCl
During polymerization, this reaction evolves potentially hazardous
hydrogen chloride gas. For medical uses, a process was developed where the
chlorine atoms in the silane precursor were replaced with acetate groups, so that
the reaction product of the final curing process is nontoxic acetic acid (vinegar).
As a side effect, the curing process is also much slower in this case. This is the
chemistry used in many consumer applications, such as silicone caulk and
Silane precursors with more acid-forming groups and fewer methyl
groups, such as methyltrichlorosilane, can be used to introduce branches or crosslinks in the polymer chain. Ideally, each molecule of such a compound becomes a
branch point. This can be used to produce hard silicone resins. Similarly,
precursors with three methyl groups can be used to limit molecular weight, since
each such molecule has only one reactive site and so forms the end of a siloxane
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Modern silicone resins are made with tetraethoxysilane, which reacts in a
more mild and controllable manner than chlorosilanes.
c) Chemical Terminology
Silicone is often mistakenly referred to as "silicon." Although silicones
contain silicon atoms, they are not made up exclusively of silicon, and have
completely different physical characteristics from elemental silicon.
The word "silicone" is derived from ketone. Dimethylsilicone and
dimethyl ketone (a.k.a. acetone) have analogous formulas, thus it was surmised
(incorrectly) that they have analogous structures. The same terminology is used
for compounds such as silane (an analogue of methane).
A true silicone group with a double bond between oxygen and silicon (see
figure) does not exist in nature; chemists find that the silicon atom forms a single
bond with each of two oxygen atoms, rather than a double bond to a single atom.
Polysiloxanes are called "silicone" due to early mistaken assumptions about their
d) Uses:
Aquarium Joints
Aquarium manufacturers have used silicone sealant exclusively from its
inception in order to join glass plates, making aquariums of every size and shape.
Glass joints made with silicone sealant can withstand hundreds of metric tons of
pressure, making obsolete the original aquarium construction method using angleiron and putty.
Design, Fabrication and Working of a Wall Climbing Robot
The gait of this wall climbing robot is similar on both horizontal and vertical surfaces.
Assume that the suction pad is a vacuum sucker. A vacuum sucker requires a little bit of time in
order to pump out the air by a vacuum pump with a limited capacity (however, because the
return to atmospheric pressure is done much faster, the time for this phase is disregarded in the
primary considerations). When the vacuum pump is near its end position i.e. it is near its
maximum vacuum it slows down. Speed of the vacuum pump is a function of sine.
The robot is always held to the wall by two cups at a time. While the other to move
forward or backward. As shown from figure the cups in diagonal configuration are connected to
the one vacuum pump. So the diagonal cups alternatively hold the robot on the wall.
The vacuum generated by the both the pumps remains same throughout the robot
operation i.e. the amount of vacuum generated by both the pumps remains same.
Design, Fabrication and Working of a Wall Climbing Robot
The gait of the robot can further be explained with help of above mentioned figures. Let
us suppose that the robot is held on the wall by vacuum cups a & c in figure 1. The slider (shown
in brown color in the figures) moves from its left most position to the right most position. With
the movement of the slider, vacuum cups b & d moves ahead.
The vacuum cups a & c remain at the same position and robot moves ahead. Now the
posture of robot is as shown in figure 2. Now the slider is at its right most position and robot is
held to the wall by vacuum cups b & d. this cycle continues and robot moves forward.
Design, Fabrication and Working of a Wall Climbing Robot
In any electric motor, operation is based on simple electromagnetism. A currentcarrying conductor generates a magnetic field; when this is then placed in an external magnetic
field, it will experience a force proportional to the current in the conductor, and to the strength of
the external magnetic field. As you are well aware of from playing with magnets as a kid,
opposite (North and South) polarities attract, while like polarities (North and North, South and
South) repel. The internal configuration of a DC motor is designed to harness the magnetic
interaction between a current-carrying conductor and an external magnetic field to generate
rotational motion.
Let's start by looking at a simple 2-pole DC electric motor (here red represents a magnet
or winding with a "North" polarization, while green represents a magnet or winding with a
"South" polarization).
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The geometry of the brushes, commutator contacts, and rotor windings are such that
when power is applied, the polarities of the energized winding and the stator magnet(s) are
misaligned, and the rotor will rotate until it is almost aligned with the stator's field magnets. As
the rotor reaches alignment, the brushes move to the next commutator contacts, and energize the
next winding. Given our example two-pole motor, the rotation reverses the direction of current
through the rotor winding, leading to a "flip" of the rotor's magnetic field, driving it to continue
In real life, though, DC motors will always have more than two poles (three is a very
common number). In particular, this avoids "dead spots" in the commutator. You can imagine
how with our example two-pole motor, if the rotor is exactly at the middle of its rotation
(perfectly aligned with the field magnets), it will get "stuck" there. Meanwhile, with a two-pole
motor, there is a moment where the commutator shorts out the power supply (i.e., both brushes
touch both commutator contacts simultaneously). This would be bad for the power supply, waste
energy, and damage motor components as well. Yet another disadvantage of such a simple motor
is that it would exhibit a high amount of torque "ripple" (the amount of torque it could produce is
cyclic with the position of the rotor.
At a simplistic level, using DC motors is pretty straightforward -- you put power in, and
get rotary motion out. Life, of course, is never this simple -- there are a number of subtleties of
DC motor behavior that should be accounted for in BEAMbot design.
This is the simplest trait to understand and treat -- most DC motors run at very high output
speeds (generally thousands or tens of thousands of RPM). While this is fine for some
BEAMbots (say, photopoppers or solarrollers), many BEAMbots (walkers, heads) require lower
speeds -- you must put gears on your DC motor's output for these applications.
Design, Fabrication and Working of a Wall Climbing Robot
Just as putting voltage across a wire in a magnetic field can generate motion, moving a wire
through a magnetic field can generate voltage. This means that as a DC motor's rotor spins, it
generates voltage -- the output voltage is known as back EMF. Because of back EMF, a spark is
created at the commutator as a motor's brushes switch from contact to contact. Meanwhile, back
EMF can damage sensitive circuits when a motor is stopped suddenly.
A number of things will cause a DC motor to put noise on its power lines: commutation
noise (a function of brush / commutator design & construction), roughness in bearings (via back
EMF), and gearing roughness (via back EMF, if the motor is part of a gearmotor) are three big
Even without these avoidable factors, any electric motor will put noise on its power lines by
virtue of the fact that its current draw is not constant throughout its motion. Going back to our
example two-pole motor, its current draw will be a function of the angle between its rotor coil
and field magnets:
Every DC motor has six basic parts -- axle, rotor (a.k.a., armature), stator, commutator, field
magnet(s), and brushes. In most common DC motors (and all that beamers will see), the external
magnetic field is produced by high-strength permanent magnets1. The stator is the stationary part
of the motor -- this includes the motor casing, as well as two or more permanent magnet pole
pieces. The rotor (together with the axle and attached commutator) rotates with respect to the
stator. The rotor consists of windings (generally on a core), the windings being electrically
connected to the commutator. The above diagram shows a common motor layout -- with the
rotor inside the stator (field) magnets.
Design, Fabrication and Working of a Wall Climbing Robot
Since most small DC motors have 3 coils, the coils' current curves will overlay each other:
Added together, this ideal motor's current will then look something like this:
In this case, the peak-to-peak current ripple is approximately 0.29 mA, while the average
motor current is just under 31 mA. So under these conditions, the motor puts about less than 1%
of current ripple onto its power lines (and as you can see from the "clean" traces, it outputs
essentially no high-frequency current noise). Note that since this is a 3-pole motor, and each coil
is energized in both directions over the course of a rotor rotation, one revolution of the rotor will
correspond to six of the above curves (here, 6 x 2.4 ms = 0.0144 sec, corresponding to a motor
rotation rate of just under 4200 RPM).
Motor power ripple can wreak havoc in Nv nets by destabilizing them inadvertently.
Fortunately, this can be mitigated by putting a small capacitor across the motor's power lines
(you'll only be able to filter out "spikey" transients this way, though -- you'll always see curves
like the ones above being imposed on your power). On the flip side of this coin, motor power
ripple can be put to good use -- as was shown above, ripple frequency can be used to measure
motor speed, and its destabilizing tendencies can be used to reverse a motor without the need for
discrete "back-up" sensors.
Design, Fabrication and Working of a Wall Climbing Robot
As you tinker around with DC motors, you'll start to run across some interesting
relationship. Namely you'll discover that torque and current are linearly proportional to each
other, as are speed and voltage. Under a fixed load (torque), voltage and current will also be
proportional to each other.
Digging into the math (and I'll spare you this), it turns out that the current a motor draws is
ultimately determined by the torque the motor produces. The generated torque is dependent upon
the current I, and factors determined by the materials and internal geometry of the motor. Since
the construction of a finished motor will not (!) change during operation, a constant of
proportionality between the motor current and the materials / geometry dependent factors can be
calculated for a given motor. This constant, the torque constant Kt, describes the torque
generated by the motor for a specific motor current:
Kt = T / I
Or to put it another way,
Current through motor = torque produced / torque constant
I (Amps) = Torque (oz-in) / Kt (oz-in/A) in imperial units
I (Amps) = Torque (N-m) / Kt (N-m/A) in SI units
Because of the interrelationship of torque, speed, current, and voltage, the constant current
operation of a DC motor produces constant output torque regardless of speed. Given a constant
load (i.e. torque) the speed of a motor is solely dependent on the voltage applied to the motor.
For DC motors operated at a constant voltage, the speed and torque produced are inversely
related (the higher the torque, the lower the speed of the motor).
Design, Fabrication and Working of a Wall Climbing Robot
We earlier saw that an EMF will be developed across a motor's brushes when its coil is
rotated by an external torque -- the magnitude of this EMF is dependent upon materials /
geometry factors, and upon the speed at which the coil is rotated. Once again, there is a constant
of proportionality which describes the relationship between coil rotational speed and materials /
geometry factors, commonly known as the back EMF constant (Ke). The back EMF constant is
typically given in volts per unit of rotational speed (which in turn is generally expressed either in
RPM or radians / second).
If one takes the reciprocal of the back EMF constant, the result is a proportionality
constant which relates the voltage applied to the motor terminals to the rotational speed of the
coil. This version of the motor constant is commonly known as the velocity constant, Kv. The
velocity constant is given in units of rotational speed (again, either RPM or radians / second) per
Since the motor construction does not change, regardless of what we're measuring, it turns
out that these three constants (Kt, Ke, Kv) are all essentially the same number. The differences
between the torque constant and the back EMF constant are simply a matter of the units used,
while the velocity constant is simply a useful form of the back EMF constant.
If the torque constant is specified in N-m / A and the back EMF constant in V-sec / rad, then:
Kt = Ke = 1 / Kv
Those of us who live in the U.S., though, are stuck with using more colorful units.
Commonly used units for small motors are oz-in for torque and RPM for rotational speed. Using
these units of measure, torque constants are often given in oz-in / A, back EMF constants in mV /
RPM, and velocity constants in RPM / V. In imperial units, the relationships between motor
constants are then as follows:
Kt in units of oz-in / A
Ke in units of mV / RPM
Kv in units of RPM / volt
Design, Fabrication and Working of a Wall Climbing Robot
Kt = 1352.4 / Kv
Ke= Kt / 1.3524
Ke = 1000 / Kv
Kv = 1000 / Ke
So what good is all this? It means that given a source of known rotational speed (an
electric drill, or drill press if you have one), you can compute Ke for a given motor (clamp the
motor shaft in the drill's jaws, measure the resulting open-circuit voltage, then do the math).
Ke, along with the above information will then give you Kt (so you can compute your
motor's theoretical torque at any given current), and Kv (so you can compute your motor's
maximum speed at any given voltage). If you can measure stall torque, you can then compute
motor efficiency (measured torque expressed as a percentage of the theoretical torque).
In order to select the required power supply following term must be understood
Voltage is an electrical measure which describes the potential to do work. Higher the
voltage, more its risk to you and your health. Systems that use voltages below 50V are
considered low-voltage and are not governed by an as strict set of rules as high-voltage
Design, Fabrication and Working of a Wall Climbing Robot
Current is a measure of how many electrons are flowing through a conductor.
Current is usually measured in amperes (A). Current flow over time is defined as amperehours (a.k.a. amp-hours or Ah), a product of the average current and the amount of time it
Power is the product of voltage and current and is measured in Watts. Power over
time is usually defined in Watt-hours (Wh), the product of the average number of watts
and time. Your energy utility usually bills you per kilowatt-hour (kWh), which is 1,000
Battery manufacturers define the end-of-life of a battery when it can no longer hold a
proper charge (for example, a cell has shorted) or when the available battery capacity is
80% or less than what the battery was rated for.
The Depth of Discharge (DOD) is a measure of how deeply a battery is discharged.
When a battery is 100% full, then the DOD is 0%. Conversely, when a battery is 100%
empty, the DOD is 100%. The deeper batteries are discharged on average, the shorter
their so-called cycle life.
The Amp-hour (Ah) Capacity of a battery tries to quantify the amount of usable
energy it can store at a nominal voltage. All things equal, the greater the physical volume
of a battery, the larger its total storage capacity. Storage capacity is additive when
batteries are wired in parallel but not if they are wired in series.
Design, Fabrication and Working of a Wall Climbing Robot
Since batteries depend on a chemical reaction to produce electricity, their
Available Capacity depends in part on how quickly you attempt to charge or discharge
them relative to their Total Capacity. The Total Capacity is frequently abbreviated to C
and is a measure of how much energy the battery can store. Available Capacity is always
less than Total Capacity.
Typically, the amp-hour capacity of a battery is measured at a rate of discharge
that will leave it empty in 20 hours (a.k.a. the C/20 rate). If you attempt to discharge a
battery faster than the C/20 rate, you will have less available capacity and vice-versa. The
more extreme the deviation from the C/20 rate, the greater the available (as opposed to
total) capacity difference.
However, as you will discover in the next section, this effect is non-linear. The
available capacity at the C/100 rate (i.e. 100 hours to discharge) is typically only 10%
more than at the C/20 rate. Conversely, a 10% reduction in available capacity is achieved
just by going to a C/8 rate (on average). Thus, you are most likely to notice this effect
with engine starts and other high-current applications like inverters, windlasses,
desalination, or air conditioning systems.
The conversion efficiency denotes how well a battery converts an electrical charge
into chemical energy and back again. The higher this factor, the less energy is converted
into heat and the faster a battery can be charged without overheating (all other things
being equal). The lower the internal resistance of a battery, the better is its conversion
One of the main reasons why lead-acid batteries dominate the energy storage
markets is that the conversion efficiency of lead-acid cells at 85%-95% is much higher
than Nickel-Cadmium (a.k.a. NiCad) at 65%, Alkaline (a.k.a. NiFe) at 60%, or other
inexpensive battery technologies.
Design, Fabrication and Working of a Wall Climbing Robot
The self-discharge rate is a measure of how much batteries discharge on their own.
The Self-Discharge rate is governed by the construction of the battery and the metallurgy
of the lead used inside.
For instance, flooded cells typically use lead alloyed with Antimony to increase
their mechanical strength. However, the Antimony also increases the self-discharge rate to
8-40% per month. This is why flooded lead-acid batteries should be in use often or left on
a trickle-charger. As our motor draws 1.5 Amp current at no load, therefore a battery with
a current of 4.5 Ah is selected. The battery should be sealed and rechargeable. Hence a
lead acid battery is selected.
A lead-acid battery is an electrical storage device that uses a reversible chemical
reaction to store energy. It uses a combination of lead plates or grids and an electrolyte
consisting of a diluted sulphuric acid to convert electrical energy into potential chemical
energy and back again. The electrolyte of lead-acid batteries is hazardous to your health
and may produce burns and other permanent damage if you come into contact with it. Gel
batteries are used in back-up power supplies for alarm and smaller computer systems
(particularly in uninterruptible power supplies) and for electric scooters, electrified
bicycles and marine applications. Unlike wet cells, gel cells are sealed, with pressure
relief valves in case of overcharging. In normal use they cannot spill liquid electrolyte
The life of Lead Acid batteries is usually limited by several factors:
Cycle Life is a measure of how many charge and discharge cycles a battery can
take before its lead-plate grids/plates are expected to collapse and short out. The
greater the average depth-of-discharge, the shorter the cycle life.
Age also affects batteries as the chemistry inside them attacks the lead plates. The
healthier the "living conditions" of the batteries, the longer they will serve you.
Lead-Acid batteries like to be kept at a full charge in a cool place. Only buy
recently manufactured batteries, so learn to decipher the date code stamped on
Design, Fabrication and Working of a Wall Climbing Robot
every battery... (Inquire w/manufacturer). The longer the battery has sat in a store,
the less time it will serve you! Since lead-acid batteries will not freeze if fully
charged, you can store them in the cold during winter to maximize their life.
Construction has a big role in battery life too, some designs are better at
preserving batteries than others and the suitability of a design for a given
application plays a role also. For example, flooded lead-acid cells will typically
fare worse than their VRLA cousins in operations that involve a lot of jerky
motion - the immobilized plates in VRLA cells will be stressed less than
suspended plates in cheap flooded cells.
Plate Thickness helps - the thicker the plates, the more abuse, charge and
discharge cycles they can take. Thicker plates will also survive any equalization
treatments for sulphation better. The heavier the battery for a given group size, the
thicker the plates are, so you can use weight as one guide to buying lead-acid
Sulphation is a constant threat to batteries that are not fully re-charged. A layer of
lead sulphate can form in these cells and inhibit the electro-chemical reaction that
allows you to charge/discharge batteries. Many batteries can be saved from the
recycling heap if they are Equalized In closing, the design life of a battery
depends in part on its construction, its type, the thickness of the plates, its
charging profiles, etc. All these factors come together to determine just how long
your battery may ultimately serve you.
Batteries use a chemical reaction to do work on charge and produce a voltage between
their output terminals.
Design, Fabrication and Working of a Wall Climbing Robot
The discharge reaction can be reversed by applying a voltage from a charging source.
Design, Fabrication and Working of a Wall Climbing Robot
With aspect to mechanical system, there were certainly quite a lot of fabrications
involved in the system. It took a lot of time to complete the whole mechanical structure. During
this tenure there certainly have been quite a number of problems. Some rose due to ignored
aspects of the project and other due to lack of resources.
The proper calculations are very crucial for appropriate selection of vacuum pads. The
range of vacuum cups is very limited in the local market. The vacuum cups available in market
were either large or too small from our requirements. The vacuum cups available in market were
manual operated i.e. the vacuum cups available were operated by hand. In order to make the
vacuum cups connect with the vacuum pumps we have to drill holes in the cups. Nut bolt
configuration was applied to the cups to join them with the structure. Again bolts were extruded
from inside to give smooth passage to air. The vacuum pads available in market are of different
qualities so while purchasing cups it should be kept in mind that cups are of same material and
Vacuum pumps available in market were of huge size and weight. So we have to think
out-of-box. To get the pump on board, no miniature size pump was available. As described
earlier we used syringes to create vacuum. Syringes used were off-the-shelf products, to increase
the vacuum level it is recommended to use custom made syringe with a larger dia. as the vacuum
pump used doesn’t create vacuum continuously so the pipes and joints leading the vacuum to the
cups must be sealed properly. Similarly two vacuum cups are connected to the same pump
therefore if a leak occurs in one both the cups loose there hold on the wall.
Design, Fabrication and Working of a Wall Climbing Robot
To reduce weight we used aluminum to make most of the parts unless it was necessary
otherwise. It is recommended that to reduce weight the whole structure be made of plastics,
synthetic polymers. This will decrease the weight of the robot manifold hence motor could be
used of low torque and small size.
In order to keep the center of gravity as close to wall as possible we have to place the
motor under the robot i.e. its belly. Therefore we could not find a motor with such mechanical
dimensions that it could be fitted under its belly and still the center of gravity is close to the wall.
Hence we have to use such a heavy motor. This problem can be removed by using such a motor
that could fit the required dimensions. The size of motor will be further decreased if weight of
robot is decreased.
Our robot is limited in its motion. It can only move forward or backward. This is because
one vacuum pump is providing vacuum for two vacuum pads .Therefore, two vacuum pads have
to stick to the wall at any given time. To change the direction of motion instead of two only one
vacuum pad has to stick to the wall, as the motion continues the robot will turn in the required
Design, Fabrication and Working of a Wall Climbing Robot
(i) Alumnium casting alloy LM6
Mechanical Properties of aluminium (sand & die-casting) alloy LM6
Mechanical properties
Sand Casting
Chill Cast
0.2% Proof Stress (N/mm2)
Tensile Strength (N/mm2)
Elongation (%)
Impact resistance Load (Nm)
Brinell Hardness
(x103 71
Shear Strength (N/mm2)
Strength at Elevated Temperatures:
Tensile strength and hardness of this aluminium casting alloy decreases fairly regularly
with increasing temperature and become relatively poor at 250°C.
Design, Fabrication and Working of a Wall Climbing Robot
Physical Properties of Aluminium (Sand & Die casting) Alloy LM6:
Physical properties
Coefficient of Thermal Expansion (per °C @ 0.000020
@ 0.34
Electrical conductivity (% copper standard @ 37
Density (g/cm3)
Freezing range (°C) approx.
Aluminium alloys of this and similar compositions are rather difficult to machine, due to
their tendency to drag and to the rapid tool wear caused by their high Silicon content. Carbidetipped tools with large rake angles and low cutting speeds give comparatively good results when
cutting lubricant and coolant are employed.
Corrosion resistance:
Aluminium LM6 exhibits excellent resistance to corrosion under both ordinary
atmospheric and marine conditions. For the severest conditions, this property can be further
enhanced by anodic treatment.
LM6 can be anodized by any of the common processes, the resulting film ranging in
colour from grey to dark brown.
Application and general notes:
Having high resistance to corrosion and excellent castability, aluminium LM6 is suitable
for most marine 'on deck' castings, water-cooled manifolds and jackets, motor car and road
transport fittings, thin section and intricate castings such as motor housings, meter cases and
Design, Fabrication and Working of a Wall Climbing Robot
switch boxes, for a very large aluminium casting, e.g. cast doors and panels where ease of
casting is essential, for chemical and dye industry castings, e.g. pump parts, and for paint
industry and food and domestic castings. It is especially suitable for castings that are to be
welded. The ductility of LM6 enables castings to be rectified easily or even modified in shape,
e.g. simple components may be cast straight and later bent to the required contour.
LM6 is equally adaptable for sand casting and aluminium diecasting (gravity diecasting
and pressure die casting). It has excellent resistance to corrosion in marine environments,
possesses excellent ductility, but is of medium strength and is not heat treated. Its strength falls
off rapidly at high temperatures. Its elastic limit is low and there is difficulty with machining.
(ii) Mild steel
Carbon steel is sometimes referred to as 'mild steel' or 'plain carbon steel'. The
American Iron and Steel Institute defines a carbon steel as having no more than 2 % carbon and
no other appreciable alloying element. Carbon steel makes up the largest part of steel production
and is used in a vast range of applications.
Typically carbon steels are stiff and strong. They also exhibit ferromagnetism (i.e. they are
magnetic). This means they are extensively used in motors and electrical appliances. Welding
carbon steels with carbon content greater than 0.3 % requires that special precautions be taken.
However, welding carbon steel presents far fewer problems than welding stainless steels. The
corrosion resistance of carbon steels is poor (i.e. they rust) and so they should not be used in a
corrosive environment unless some form of protective coating is used.
Design, Fabrication and Working of a Wall Climbing Robot
Composition Units
Aluminum, Al
Chromium, Cr
Silicon, Si
Manganese, Mn
Nickel, Ni
Iron, Fe
Physical Properties
7.80 - 8.00 g/cc
0.282 - 0.289 lb/in³
Hardness, Brinell
Hardness, Knoop
Hardness, Vickers
Tensile Strength, Ultimate
420 MPa
60900 psi
Tensile Strength, Yield
350 MPa
50800 psi
Elongation at Break
15.0 %
15.0 %
Modulus of Elasticity
200 GPa
29000 kpsi
Bulk Modulus
140 GPa
20300 ksi
Poisson’s Ratio
65.0 %
65.0 %
Mechanical Properties
Design, Fabrication and Working of a Wall Climbing Robot
Shear Modulus
80.0 GPa
11600 ksi
0.0000170 ohm-cm
0.0000170 ohm-cm
CTE, linear 20°C
9.50 - 12.6 µm/m-°C
5.28 - 7.00 µin/in-°F
CTE, linear 250°C
11.7 µm/m-°C
6.50 µin/in-°F
CTE, linear 500°C
12.8 µm/m-°C
7.11 µin/in-°F
CTE, linear 1000°C
13.9 µm/m-°C
7.72 µin/in-°F
Specific Heat Capacity
0.470 J/g-°C
0.112 BTU/lb-°F
Thermal Conductivity
44.0 - 52.0 W/m-K
305 - 361 BTU-in/hr-ft²-°F
Electrical Properties
Electrical Resistivity
Thermal Properties
Wide variety available with different properties
High stiffness
Most carbon steels are easy machine and weld
Poor corrosion resistance (i.e. rusts)
(iii) BRASS
Brass is any alloy of copper and zinc; the proportions of zinc and copper can be varied
to create a range of brasses with varying properties. In comparison, bronze is principally an alloy
of copper and tin. Despite this distinction, some types of brasses are called bronzes. Brass is a
substitutional alloy. It is used for decoration for its bright gold-like appearance; for applications
where low friction is required such as locks, gears, bearings, ammunition, and valves; for
Design, Fabrication and Working of a Wall Climbing Robot
plumbing and electrical applications; and extensively in musical instruments such as horns and
bells for its acoustic properties.
Brass has a muted yellow color, somewhat similar to gold. It is relatively resistant to
tarnishing, and is often used as decoration and for coins.
Brass has likely been known to humans since prehistoric times, even before zinc itself
was discovered. It was produced by melting copper together with calamine, a zinc ore. In the
German village of Breinigerberg an ancient Roman settlement was discovered where a calamine
ore mine existed. During the melting process, the zinc is extracted from the calamine and mixes
with the copper. Pure zinc, on the other hand, has too low a boiling point to have been produced
by ancient metalworking techniques. The many references to ‘brass’ appearing throughout the
King James Bible are thought to signify another bronze alloy, or copper, rather than the strict
modern definition of ‘brass’.
The malleability and acoustic properties of brass have made it the metal of choice for
brass musical instruments such as the trombone, tuba, trumpet, euphonium, and the French horn.
Even though the saxophone is classified as a woodwind instrument and the harmonica is a free
reed aero phone, both are also often made from brass. In organ pipes designed as "reed" pipes,
brass strips are used as the "reeds".
Brass has higher malleability than copper or zinc. The relatively low melting point of
brass (900 to 940°C, depending on composition) and its flow characteristics make it a relatively
easy material to cast. By varying the proportions of copper and zinc, the properties of the brass
can be changed, allowing hard and soft brasses.
Today almost 90% of all brass alloys are recycled. Because most brass is nonmagnetic, it
can be separated from ferrous scrap by passing the scrap near a powerful magnet. Brass scrap is
collected and transported to the foundry where it is melted and recast into billets. Billets are later
heated and extruded into the desired form and size.
Design, Fabrication and Working of a Wall Climbing Robot
Aluminum makes brass stronger and more corrosion resistant. Aluminum also causes a
highly beneficial hard layer of aluminium oxide (Al2O3) to be formed on the surface that is thin,
transparent and self healing. Tin has a similar effect and finds its use especially in sea water
applications (naval brasses). Combinations of iron, aluminum, silicon and manganese make brass
wear and tear resistant. A well known alloy used in the automotive industry is 'LDM C673',
where the combination of manganese and silicon leads to a strong and resistant brass.
The so called dezincification resistant (DZR) brasses, like alloy 'LDM G563' (known for
its brand name 'Enkotal'), are used where there is a large corrosion risk and where normal brasses
do not meet the standards. Applications with high water temperatures, chlorides present or
deviating water qualities (soft water) play a role. DZR-brass is excellent in water boiler systems.
This brass alloy must be produced with great care, with special attention placed on a balanced
composition and proper production temperatures and parameters to avoid long-term failures.
Drunen, Netherlands, has the only active production facility which makes these high grade brass
The copper in brass makes brass germicidal, via the oligodynamic effect. For example,
brass doorknobs disinfect themselves of many bacteria within eight hours. This effect is
important in hospitals, but useful in many contexts.
Brass door hardware is generally lacquered when new, which prevents tarnishing of the
metal for a few years when located outside (and indefinitely when located indoors). After this
most manufacturers recommend that the lacquer is removed (e.g. with paint stripper) and the
items regularly polished to maintain a bright finish. Unlacquered brass weathers more
attractively than brass with deteriorated lacquer, even if polishing is not carried out. Freshly
polished brass is similar to gold in appearance, but becomes more reddish within days of
exposure to the elements. A traditional polish is Brasso.
Brass was used to make fan blades, fan cages and motor bearings in many antique fans
that date before the 1930s. Brass can be used for fixings for use in cryogenic systems; however
its use is not limited to this.
Design, Fabrication and Working of a Wall Climbing Robot
The density of brass is approximately 8.4 g/cm3.
(iv) Sand Casting
Sand casting is used to make large parts (typically Iron, but also Bronze, Brass,
Aluminum). Molten metal is poured into a mold cavity formed out of sand (natural or synthetic).
The processes of sand casting are discussed in this section, include patterns, sprues and runners,
design considerations, and casting allowance.
The cavity in the sand is formed by using a pattern (an approximate duplicate of the real
part), which are typically made out of wood, sometimes metal. The cavity is contained in an
aggregate housed in a box called the flask. Core is a sand shape inserted into the mold to produce
the internal features of the part such as holes or internal passages. Cores are placed in the cavity
to form holes of the desired shapes. Core print is the region added to the pattern, core, or mold
that is used to locate and support the core within the mold. A riser is an extra void created in the
mold to contain excessive molten material.
Typical Components of a Two-Part Sand Casting Mold.
Design, Fabrication and Working of a Wall Climbing Robot
In a two-part mold, which is typical of sand castings, the upper half, including the top half
of the pattern, flask, and core is called cope and the lower half is called drag. The parting line or
the parting surface is line or surface that separates the cope and drag. The drag is first filled
partially with sand, and the core print, the cores, and the gating system are placed near the
parting line. The cope is then assembled to the drag, and the sand is poured on the cope half,
covering the pattern, core and the gating system. The sand is compacted by vibration and
mechanical means. Next, the cope is removed from the drag, and the pattern is carefully
removed. The object is to remove the pattern without breaking the mold cavity. This is facilitated
by designing a draft, a slight angular offset from the vertical to the vertical surfaces of the
pattern. This is usually a minimum of 1° or 1.5 mm (0.060 in), whichever is greater. The rougher
the surface of the pattern, the more the draft to be provided.
The molten material is poured in the pouring cup, which is part of the gating system that supplies
the molten material to the mold cavity. The vertical part of the gating system connected to the
pouring cup is the sprue, and the horizontal portion is called the runners and finally to the
multiple points where it is introduced to the mold cavity called the gates. Additionally there are
extensions to the gating system called vents that provide the path for the built up gases and the
displaced air to vent to the atmosphere.
The cavity is usually made oversize to allow for the metal contraction as it cools down to
room temperature. This is achieved by making the pattern oversize. To account for shrinking, the
pattern must be made oversize by these factors, on the average. These are linear factors and
apply in each direction. These shrinkage allowance are only approximate, because the exact
allowance is determined the shape and size of the casting. In addition, different parts of the
casting might require a different shrinkage allowance. See the casting allowance table for the
approximate shrinkage allowance expressed as the Pattern Oversize Factor.
Design, Fabrication and Working of a Wall Climbing Robot
Sand castings generally have a rough surface sometimes with surface impurities, and
surface variations. A machining (finish) allowance is made for this type of defect. See casting
allowance table for the finish allowance.
ISO metric screw thread
The basic principles of the ISO metric screw thread are defined in international standard
ISO 68-1 and preferred combinations of diameter and pitch are listed in ISO 261. The smaller
subset of diameter and pitch combinations commonly used in screws, nuts and bolts is given in
ISO 262. The most commonly used pitch value for each diameter is known as the "coarse pitch".
For some diameters, one or two additional "fine pitch" variants are also specified, for special
applications such as threads in thin-walled pipes. ISO metric screw threads are designated by the
letter M followed by the major diameter of the thread in millimeters, e.g. "M8". If the thread
does not use the normal "coarse pitch" (e.g., 1.25 mm in the case of M8), then the pitch in
millimeters is also appended with a multiplication sign, e.g. "M8×1" if the screw thread has an
outer diameter of 8 mm and advances by 1 mm per 360° rotation.
The nominal diameter of a metric screw is the outer diameter of the thread. The tapped
hole (or nut) into which the screw fits has an internal diameter which is the size of the screw
minus the pitch of the thread. Thus, an M6 screw, which has a pitch of 1 mm, is made by
threading a 6 mm shaft and the nut or threaded hole is made by tapping threads in a 5 mm hole.
Metric hexagon bolts, screws and nuts are specified, for example, in British Standard BS
4190 (general purpose screws) and BS 3692 (precision screws). The following table lists the
relationship given in these standards between the thread size and the maximal width across the
hexagonal flats (wrench size):
Design, Fabrication and Working of a Wall Climbing Robot
1.6 2 2.5 3
3.2 4
5 5.5 7
8 10 12 16 20 24 30 36 42 48 56 64
8 10 13 17 19 24 30 36 46 55 65 75 85 95
In addition, the following non-preferred intermediate sizes are specified:
ISO metric
size (mm)
M14 M18 M22 M27 M33 M39 M45 M52 M60 M68
Vacuum cups
Bellows Cups with Convolutions
Bellows cups have a pliable outer rim that will conform to curved or uneven surfaces
while the bellows sections compensate for inconsistent stack heights. Under vacuum the
accordion-style bellows cup will collapse on contact. The collapsing action simulates a short
cylinder stroke lifting the product for a short distance, possibly saving the need for a separate
lifting mechanism.
Design, Fabrication and Working of a Wall Climbing Robot
Flat Cups with and without Cleats
Flat cups without cleats are flexible and work well in applications that do not require
lifting heavy loads. Flat cups only achieve the holding force of the area of the thru-hole. In food
packaging for example, a flat cup can be used to apply a label to an uneven surface such as a
package of chicken.
Flat cups with cleats are strong with a rigid, low profile that will lift heavy loads. The low
profile allows heavy loads to be lifted vertically without the cup “peeling” away from the
product surface or deforming the object being lifted. These cups perform well when gripping
smooth, flat heavy objects such as steel sheet, glass (television picture tubes) and coated
Oval Cups
Like cleated cups, oval cups have heavy load handling capabilities due to their rigid
design and large vacuum work area. Oval cups have the largest lifting force because they provide
the most surface area for a given cup footprint.
Deep Cups
Deep cups are used for curved and irregular surfaces, not for flat surfaces. They can lift
over corners and edges.
Universal Cups
Universal cups can handle flat or slightly curved surfaces.
Severe Cups
The severe duty cup line was originally developed to satisfy the harsh physical demands
that a cup experiences in the high volume, automotive, sheet metal stamping processes. These
cups are available in several styles, and have proven to be very reliable. Their design evolved
from the knowledge gained by supplying vacuum cups to the Automotive OEMs for more than15
Design, Fabrication and Working of a Wall Climbing Robot
Cups are available in various durometers, colors and materials. Below is a general
description of the various materials available and their characteristics.
material for
most applications
+32 to +125˚F
[0°C to +52°C]
+32 to +125˚F
[0°C to +52°C]
+32 to +150˚F
[0°C to +66°C]
-40 to +230˚F
to Excellent
+32 to +194˚F
[0°C to +90°C]
-50 to +400˚F
to Good
-94 to +392˚F
to Good
material with good oil
resistance and low
material with good oil
and abrasion resistance
good for applications
temperatures, food or
non-marking situation
Good for applications
temperatures, food or
non-marking situation
*Standard durometer for vinyl cups is A50 ±5 points — may vary with color.
Other Materials Available - please consult factory: FDA Vinyl, Anti-Static Vinyl, FDA Silicone
Design, Fabrication and Working of a Wall Climbing Robot
Vacuum Terms and Definitions:
Bellows: The fold or collapsible area that allows the cup to compress like an accordion.
Convolution: The folded area of a bellows cup that makes up 1 external “V”.
Cleats: Bottom protrusions used for maintaining a larger vacuum area.
Durometer: Method by which the hardness of a material is gauged.
Insert/Fitting: Metal piece bonded or inserted into the material to allow fastening by
threads or bolts.
Vacuum Cup: Cup that requires the use of an external vacuum source to
adhere to a
Vacuum Level: The magnitude of suction created by a vacuum pump typically measured in
inches of mercury (”Hg) or mm Hg
Vacuum Flow: The volume of free air induced by the vacuum pump per unit of time,
typically measured in SCFM
Permeability: Cardboard vs. steel — sometimes referred to as porosity
Standard Atmospheric Pressure Measured at Sea Level:
1 ATM = 14.7 psi = 29.92”Hg = 760mm Hg = 1 Bar
Conversion Chart - Vacuum vs. Pressure
In. Hg
mm Hg
Design, Fabrication and Working of a Wall Climbing Robot
Facts to Remember:
50 mm Hg = 1 PSI
1mm Hg = 1 torr (vacuum)
1”Hg = 25.4mm Hg
2”Hg = 1 PSI
29.92”Hg = 100 Kpa
14.7 PSI = 100 Kpa
14.7 PSI = 29.92” Hg
14.7 PSI = 760mm Hg
Design, Fabrication and Working of a Wall Climbing Robot
(v) Cad diagrams
Design, Fabrication and Working of a Wall Climbing Robot
Design, Fabrication and Working of a Wall Climbing Robot
Design, Fabrication and Working of a Wall Climbing Robot
Design, Fabrication and Working of a Wall Climbing Robot
Design, Fabrication and Working of a Wall Climbing Robot
Design, Fabrication and Working of a Wall Climbing Robot
Design, Fabrication and Working of a Wall Climbing Robot
Design, Fabrication and Working of a Wall Climbing Robot
Design, Fabrication and Working of a Wall Climbing Robot
Design, Fabrication and Working of a Wall Climbing Robot
Design, Fabrication and Working of a Wall Climbing Robot
Place the power supply on the robot.
Add sensors onto the robot to look for obstacles.
Create logic for the robot to be able to wander and not fall of or crash into things.
Pressure sensors on the suction cups to determine if a cup is attached or not.
Adding application devices (such as window washing apparatus).
Modify the robot to move faster.
Acquire better control over the exact position of the legs.
Find ways to arrange equipment to allow a greater range of motion.
DC motor position control can be applied as follows
The motor equations are same as used in section 3.3
The amplifier equation is given as
We have placed the position sensor and h is the gain of the sensor, θ is the angular position of
the output shaft
The motor speed
is reduced to a lower speed of the output shaft
with a speed ratio
. Attendant upon the reduction in speed is an increase in torque from
the motor torque to the output shaft
by a gear train
Design, Fabrication and Working of a Wall Climbing Robot
As we know angular speed is a derivative of angular position.
Torque balance equation is given as under
From above equation we can eliminate θ .Now we can see that position is a second order
function of input and disturbance.
Design, Fabrication and Working of a Wall Climbing Robot
This compact and lightweight robotic platform provides a safe and effective means to
deal with hazardous duty operations. With in the mechanical area our robust platform weighing
approximately 3 Kgs is developed to climb on relatively smooth surfaces .From test runs, the
vacuum cups are enough to stick the root on the wall but the vacuum pump is of less capacity.
Although the vacuum pump is of less capacity but we have achieved a wall climbing of 40
4QD Motor Current Calculator, 4QD Information section ,2004,
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Design, Fabrication and Working of a Wall Climbing Robot
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MRT CASTING LIMITED Founders, Machinists & Finishers Of Quality Non-Ferrous
Cast Components
Engineering Designer, V 30, N 3, May-June 2004
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EFUNDA ENGINEERING FUNDAMENTALS , sand casting ,www.efunda .com
Design, Fabrication and Working of a Wall Climbing Robot