Design and Fabrication of Stair Climbing Trolley

1. i
DESIGN AND FABRICATION OF STAIR CLIMBER
TROLLEY
A PROJECT REPORT
Submitted by
SUNIL KUMAR K R 310111114091
SUNITHA V S 310111114092
SURESH K 310111114094
UDAYA KUMAR S 310111114098
in partial fulfillment for the award of the degree
Of
BACHELOR OF ENGINEERING
in
MECHANICAL ENGINEERING
ANAND INSTITUTE OF HIGHER TECHNOLOGY
CHENNAI-603 103
ANNA UNIVERSITY :: CHENNAI-600 025
APRIL 2014

2. ii
Abstract
This project aims at developing a mechanism for easy transportation of
heavy loads over stairs. The need for such a system arises from day-to-day
requirements in our society. Devices such as hand trolleys are used to relieve
the stress of lifting while on flat ground; however, these devices usually fail
when it comes to carrying the load over short fleet of stairs. In the light of this,
the project attempts to design a stair climbing hand cart which can carry heavy
objects up the stairs with less effort compared to carrying them manually. It also
endeavors to study the commercial viability and importance of such a product.
Several designs were conceived that would allow a non-industrial hand trolley
to travel over stairs, curbs, or uneven terrain while reducing the strain on the
user.
In our project, the trolley is equipped with Tri-Star wheels which enable
us to carry load up and down the stairs. It also eases the movement of trolley in
irregular surfaces like holes, bumps, etc.

3. iii
TABLE OF CONTENTS
CHAPTER NO TITLE PAGENO
ABSTRACT ii
LIST OF TABLES vii
LIST OF FIGURES viii
LIST OF SYMBOLS ix
1. INTRODUCTION 1
1.1 HAND TROLLEY 1
1.1.2 DESCRIPTION 1
1.2 TYPES OF TROLLLEY 2
1.2.1 WHEELED TROLLEY 2
1.2.2 FOLDING TROLLEY 2
1.2.3 GARDEN TROLLEY 3
1.2.4 KITCHEN TROLLEY 3
1.2.5 STACK TROLLEY 3
1.3 NEED FOR STAIRCLIMBER TROLLEY 3
2 STAIR CLIMBER TROLLEY 4
2.1 NEW CONCEPT 4

4. iv
3. TRI-STAR WHEEL 5
3.1 TRI-STAR WHEEL DESIGN 5
3.2 APPLICATION OF TRI-STAR
WHEEL IN OUR PROJECT 6
4. SELECTION AND FABRICATION
OF STAIR CLIMBER TROLLEY 7
4.1 MATERIAL SELECTION 7
4.1.1 TROLLEY BODY 7
4.1.2 TRI-STAR WHEEL WEB 7
4.2 BEARING SELECTION 8
4.3 WHEEL SELECTION 9
4.3.1 TYPES OF WHEEL MATERIAL 9
4.3.1.1 FILLED RUBBER 9
4.3.1.2 POLYURETHANE 9
4.3.1.3 STEEL 10
4.3.2 STATIC FRICTION 10
4.3.3 VARIOUS WHEEL MATERIALS

5. v
AND CO-EFFICIENT OF FRICTION 10
4.4 WHEEL FRAME 11
4.4.1 TYPES OF WHEEL FRAMES 12
4.5 CAD MODEL OF TROLLEY 13
4.6 PROCESS INVOLVED IN FABRICATION 14
4.6.1 GAS CUTTING 14
4.6.2 PIPE BENDING 15
4.6.3 PLASMA ARC CUTTING 15
4.6.3.1 COMPONENTS OF
THE SYSTEM 16
4.6.3.2 PROBLEMS FACED
BY THE EQUIPMENTS 17
4.6.4 WELDING 17
4.6.4.1 ARC WELDING 18
4.7 PROTOTYPE OF STAIR CLIMBER TROLLEY 19
5. DESIGN ANALYSIS OF TROLLEY 20
5.1 LOAD CALCULATION FOR AXLE 20
5.2 FORCE NECESSARY TO PULL THE
TROLLEY 22

6. vi
5.3 FORCE ANALYSIS ON WHEEL FRAME 23
6. COST ESTIMATION OF THE PROJECT 25
7. DISCUSSION AND CONCLUSION 26
7.1 INFERENCE 26
7.2 CONCLUSION 27
REFERENCES 28
LIST OF TABLES

7. vii
TABLE NO. TABLE PAGE NO.
4.1 Various wheel materials
and co-efficient of friction 10
6.1 Account statement 25

8. viii
LIST OF FIGURES
FIGURE NO. FIGURE PAGE NO.
3.1 Tri-Star wheel in motion 5
4.1 Close-up showing surface roughness 10
4.2 Co-efficient of kinetic friction of
various tyre materials and surface 11
4.3 Straight Wheel Frame 12
4.4 Curved Wheel Frame 12
4.5 Quasi-Planetary Wheel Frame 13
4.6 CAD model of trolley Side View 13
4.7 CAD model of trolley Front View 13
4.8 CAD model of trolley Isometric View 14
4.9 Plasma Arc Cut Tri-Star Wheel Web 16
4.10 Prototype of Stair Climber Trolley Side View 19
4.11 Prototype of Stair Climber Trolley Front View 19
7.1 Modified Wheel Frame Setup 26

9. ix
LIST OF SYMBOLS
SYMBOL DEFINITION
F Force
M Bending Moment
R1, R2 Reaction Forces
I Moment of inertia
ߪ Bending Stress
y Distance between neutral axis and
centroidal axis
E Young’s Modulus
R Radius of Curvature
x Height of the trolley
y Distance between mid-point of the weight
and trolley wheel axis
W Weight acting on the trolley
W1 Weight of object to be carried
W2 Weight of the trolley
Re Reaction force on one side

10. - 0 -

11. - 0 -

12. - 1 -
Chapter 1
INTRODUCTION
1.1 HAND TROLLEY
A hand trolley is a small transport device used to move heavy loads from
one place to another. It is a very common tool used by a large number of
industries that transport physical products. Also called a hand truck or a dolly,
the hand trolley is often used by stock persons who arrange and restock
merchandise in retail stores. When used properly, trolleys can protect people
from back injuries and other health problems that can result from lifting heavy
loads.
1.1.2 Description
A typical hand trolley consists of two small wheels located beneath a
load-bearing platform, the hand trolley usually has two handles on its support
frame. These handles are used to push, pull and maneuver the device. The
handles may extend from the top rear of the frame, or one handle may curve
from the back. An empty hand trolley usually stands upright in an L-shape, and
products are usually stacked on top of the platform. When the goods are in
place, it is tilted backward so that the load is balanced between the platform and
the support frame. Especially if heavy or fragile materials are moved, the person
operating the trolley should return it to an upright position carefully, to insure
nothing falls off the platform. The front of the frame may be squared off for
boxes or curved for drums and barrels. Sometimes, a hand truck also has straps
for securing loose freight during transport.
Professional material handlers prefer to use a hand truck when moving
stackable items such as boxes, crates or packages. Heavier items are usually
stacked on the bottom of the hand truck, with lighter objects saved for the top.

13. - 2 -
Hand truck users must be careful not to stack it so high that their vision is
blocked or the load becomes unstable. Generally, it is safe to load a hand truck
to the level of its handles or the top of the frame. The load is then shifted onto
the wheels with a backwards lifting motion. The user can maneuver
the cargo by steering it left, right or forward.
1.2 TYPES OF TROLLEY
Different types of these trolleys exist, and the type used is often chosen
based on what type of material it will move. Hand trolleys are made of various
types of hard materials, including steel, aluminium and high-impact plastic.
Most hand trolleys come in standard sizes and are used for general loads, but
there are some that are specifically designed for very small or large products.
1.2.1 Wheeled trolley
Wheeled trolleys made from stainless steel are the most common type of
hand trucks used. These are used in places with heavy loads to move, like retail
stores and factories, and typically have wheels made out of stainless steel as
well. Welded steel and metal wheel trolleys are typically much more
lightweight and are often used to carry lighter materials.
Those with a frame and wheels made of a metal alloy are heavier and sturdily
made. Trolleys of this type usually have a wider platform for oversized loads.
Metal alloy hand trucks are typically used to transport heavy products, such as
items made of steel.
1.2.2 Folding Trolley
A folding trolley is another type of hand tool, and is often made of rust-
proof aluminium. It is also lightweight but is usually able to carry heavy loads,
and can fold to take up less space when not in use. This feature also allows it to
be easily transported to places where it is needed.

14. - 3 -
1.2.3 Garden Trolley
The garden trolley is a maneuverer with the use of a pull
handle. Garden trolleys tend to have narrow profiles so that they will fit easily
on paths and walks without damaging plants. These are designed so that they
are capable of lifting both dry and marshy loads which are most commonly
found in gardens.
1.2.4 Kitchen Trolley
A kitchen trolley is a serving cart that can also be used for storage. It is
designed that it has more than one section in it which enables people to carry
various utensils and for various purposes.
1.2.5 Sack Trolley
Sack trolley or Sack barrow is a fairly generic term describing a range of
light, single operator hand trucks or trolleys used to move cartons, feed and
grain sacks, and other light, stackable goods. Lots of different materials are used
to make sack trucks. This includes high impact plastics, tube steel, aluminium
steel, and aluminium excursion.
1.3 NEED FOR STAIR CLIMBER TROLLEY
Lifting heavy objects to upper stories or lifting patients to upper levels
from the ground are not painless jobs, especially where there are no lifting
facilities (elevator, conveyer, etc.). Moreover, most of the buildings are
structurally congested and do not have elevators or escalators. This project can
introduce a new option for the transportation of loads over the stairs. The stair
climbing hand trolley can play an important role in those areas to lift loads over
a short height.

15. - 4 -
CHAPTER 2
STAIR CLIMBER TROLLEY
2.1 NEW CONCEPT
The stair-climbing hand truck is designed to reduce liability rather than
increase it. Conventional hand trucks work well on flat ground, but their
usefulness decreases when it becomes necessary to move an object over an
irregular surface. Package deliverymen, for example, often find it necessary to
drag loaded hand trucks up short flights of stairs just to reach the front door of a
building. The entire purpose of using a conventional hand truck is to avoid
having to lift and carry heavy objects around.
Lifting a hand truck up the stairs defeats the purpose of the device, since
the user must provide enough upward force to lift the entire weight of the cart
and its contents. Furthermore, the geometry of a hand truck makes it nearly
impossible to lift with one's legs, as is the proper form. Considerable strain is
placed on the back muscles and the risk of operator injury is sharply increased.
The pulling up of a standard hand truck up the stairs results in a bumpy and
jarring motion. This motion may damage the items loaded on the hand truck or
cause them to fall off entirely. A hand truck that could climb stairs without
requiring the user to lift would improve the safety of moving heavy objects over
irregular surfaces.
In our project, we are designing and fabricating normal hand trolleys with
Tri-Star wheel in order to enable the trolley to move up or down the stairs.

16. - 5 -
CHAPTER 3
TRI-STAR WHEEL
3.1 TRI-STAR WHEEL DESIGN
The Tri-Star wheel was designed in 1967 by Robert and John Forsyth of
the Lockheed Aircraft Corporation. They were first developed as a module of
the Lockheed Terrastar, a commercially unsuccessful amphibious military
vehicle. A Tri-Star wheel functions as an ordinary wheel on flat ground, but has
the ability to climb automatically when an impediment to rolling is encountered.
This wheel design consists of three tires, each mounted to a separate shaft.
These shafts are located at the vertices of an equilateral triangle. The three
shafts are geared to a fourth, central shaft (to which a motor may be attached).
When geared in this quasi-planetary fashion, these triangular sets of wheels can
negotiate many types of terrain, including sand and mud; they can also allow a
vehicle to climb over small obstructions such as rocks, holes, and stairs. The
wheel assembly may be gear-driven, with two wheels in rolling contact with the
ground. The third wheel idles at the top until the lower front wheel hits an
obstruction. The obstruction prevents the lower front wheel from moving
forward but does not affect the motion of the driving axle. This causes the top
wheel to roll forward into position as the new front wheel. This wheel usually
lands on top of the obstruction and allows the rest of the assembly to vault over
the obstruction. Tri-Star wheel in motion is shown in figure 3.1.
Fig3.1 Tri-Star wheel in motion

17. - 6 -
3.2 APPLICATION OF TRI-STAR WHEEL IN OUR PROJECT
In our project, we are using this Tri-Star wheel arrangement in a hand
trolley in the place of normal wheels setup to enable the trolley to climb up and
down the stair cases and also to up come small obstacles like holes and bumps
on its path.

18. - 7 -
CHAPTER 4
SELECTION AND FABRICATION OF STAIR CLIMBER TROLLEY
4.1 MATERIAL SELECTION
Material selection is a step in the process of designing any physical
object. In the context of product design, the main goal of material selection is to
minimize cost while meeting product performance goals. Systematic selection
of the best material for a given application begins with properties and costs of
candidate materials.
4.1.1 Trolley body
Material Used- Mild Steel
Mild Steel
Mild steel, also called as plain-carbon steel, is the most common form of
steel because its price is relatively low while it provides material properties that
are acceptable for many applications, more so than iron. Low-carbon steel
contains approximately 0.05–0.3% carbon making it malleable and ductile. Mild
steel has a relatively low tensile strength, but it is cheap and malleable; surface
hardness can be increased through carburizing. It is often used when large
quantities of steel are needed, for example as structural steel. The density of
mild steel is approximately 7850 kg/cm3
and the Young's modulus is 210 GPa
(30,000,000 psi).
4.1.2 Tri-Star wheel web
Material Used- Stainless Steel Grade 304
Stainless Steel Grade 304:
Steel Type 304 is a variation of the basic 18-8 grade, Type 302, with a
higher chromium and lower carbon content. Lower carbon minimizes chromium

19. - 8 -
carbide precipitation due to welding and its susceptibility to inter-granular
corrosion. In many instances, it can be used in the “as-welded” condition, while
Type 302 must be annealed in order to retain adequate corrosion resistance.
Type 304L is an extra low-carbon variation of Type 304 with a 0.03%
maximum carbon content that eliminates carbide precipitation due to welding.
As a result, this alloy can be used in the ”as-welded“ condition, even in severe
corrosive conditions. It often eliminates the necessity of annealing weldments
except for applications specifying stress relief. It has slightly lower mechanical
properties than Type 304.
4.2 BEARING SELECTION
Ball bearing
A ball bearing is a type of rolling-element bearing that uses balls to
maintain the separation between the bearing races. The purpose of a ball bearing
is to reduce rotational friction and support radial and axial loads. It achieves this
by using at least two races to contain the balls and transmit the loads through
the balls. In most applications, one race is stationary and the other is attached to
the rotating assembly. As one of the bearing races rotates it causes the balls to
rotate as well. Because the balls are rolling they have a much lower coefficient
of friction than if two flat surfaces were sliding against each other.
Selecting a ball bearing with minimum inner diameter of 30mm,
minimum load carrying capacity of 50kg radially and speed greater than
100rpm
Bearing Selected - SKF 6006 Open Deep Groove Ball Bearing
30x55x13mm
Inside Diameter: 30mm
Outside Diameter: 55mm
Width: 13mm

20. - 9 -
This 6006-2RS 30x55x13-millimeter sealed ball bearing has deep groove
geometry for high speeds and supporting both radial and axial loads. This
bearing has rubber seals on both sides of the bearing to keep lubricant in and
contaminants out, and comes pre-lubricated from the manufacturer so that no
additional lubrication is required. This deep groove sealed ball bearing is for use
in applications that involve combined radial and axial loads, and a need for high
running accuracy at high rotational speeds. Such applications include clutches,
drives, gearboxes, compressors, pumps, turbines, and printing and textile
machines, among others.
4.3 WHEEL SELECTION
Wheel material selected – Filled rubber
4.3.1 Types of Wheel Material
4.3.1.1 Filled rubbers
In tyres rubbers are usually filled with particles like carbon black or
silica. They consist of a tread and a body. The tread is the part of the tire that
comes in contact with the road surface. The portion that is in contact with the
road at a given instant in time is the contact. Treads are often designed to meet
specific product marketing positions.
4.3.1.2 Polyurethane
Polyurethane (PUR and PU) is a polymer composed of a chain
of organic units joined by carbamate (urethane) links. While most polyurethanes
are thermosetting polymers that do not melt when heated, thermoplastic
polyurethanes are also available. The main ingredients to make a polyurethane
are isocyanates and polyols. Other materials are added to help processing the
polymer or to change the properties of the polymer.

21. - 10 -
4.3.1.3 Steel
Steel is an alloy of iron, with carbon being the primary alloying element,
up to 2.1% by weight. Carbon, other elements, and inclusions within iron act as
hardening agents that prevent the movement of dislocations that naturally exist
in the iron atom crystal lattices.
4.3.2 Static friction
The surface of the wheel and what it is rolling on are not perfectly
smooth. They have irregularities shown in figure 4.1.
Fig4.1 Close-up showing surface roughness
In sliding friction, this surface roughness is the reason for the static and kinetic
resistance to motion. Although the wheel is not sliding, the surface roughness
causes a "jiggle" when the wheel is rolling.
4.3.3 Various Wheel Materials and their Co-efficient of Frictions
Various Wheel materials and their co-efficient of frictions are tabulated in
table 4.1 and shown graphically in figure 4.2.
Table4.1 Various Wheel Materials and their Coefficient of friction
S.no Material Coefficient of friction
1 Rubber/concrete .85
2 Polyurethane/Concrete .5
3 Steel/Concrete .45

22. - 11 -
Fig 4.2 Coefficient of kinetic friction of various tyre materials and concrete
surface
4.4 WHEEL FRAME
A specially designed wheel frame is required to hold the three wheels
together on each side of the shaft. In the existing design, the power transmission
to the single or double wheel trolley is useless to climb the stairs due to height
factor of stairs. The design of the straight wheel frame became more
complicated and was needed to be modified with its curved- spherical shape to
give proper drive, which creates more frictional force. For these reason, three
wheel set on each side of vehicle attached with frame was introduced to provide
smooth power transmission in order to climb stairs without much difficulty.
Frame arrangement is suitable to transmit exact velocity ratio also. It provided
higher efficiency and compact layout with reliable service. Easier maintenance
was possible in case of replacing any defective parts such as nut, bolt, washer,
etc.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Coefficient of
Kinetic Friction
Rubber Vs. Concrete
Polyurethane Vs. Concrete
Steel Vs. Concrete

23. - 12 -
4.4.1 Types of wheel frames
A few types of wheel frames are shown in the figure4.3, 4.4 and 4.5.
Fig 4.3 Straight Wheel Frame
Fig 4.4 Curved Wheel Frame
Fig 4.5 Quasi Planetary Wheel Frame
Wheel Frame Selected – Quasi planetary Model made of stainless
steel grade 304.

24. - 13 -
4.5 CAD MODEL OF TROLLEY
The cad diagrams of trolley is shown in the figure4.6, 4.7 and 4.8.
Fig 4.6 Side View
Fig 4.7 Front view

25. - 14 -
Fig 4.8 Isometric View
4.6 PROCESSES INVOLVED IN FABRICATION
4.6.1 Gas cutting(Oxy-Fuel cutting)
Oxy-fuel cutting is a cost-effective method of plate edge preparation for
bevel and groove welding. It can be used to easily cut rusty and scaled plates
and only requires moderate skill to produce successful results. The oxy-fuel gas
cutting process creates a chemical reaction of oxygen with the base metal at
elevated temperatures to sever the metal.
We have used this cutting to cut the measured lengths of hollow mild
steel pipes and flat bottom plate as per our design.

26. - 15 -
4.6.2 Pipe bending
Tube bending as a process starts with loading a tube into a pipe bender
and clamping it into place between two dies, the clamping block and the
forming die. The tube is also loosely held by two other dies, the wiper die and
the pressure die. The process of tube bending involves using mechanical force
to push stock material pipe or tubing against a die, forcing the pipe or tube to
conform to the shape of the die. Often, stock tubing is held firmly in place while
the end is rotated and rolled around the die. For some tube bending processing,
a mandrel is placed inside the tube to prevent collapsing. Much of the tooling is
made of hardened steel or tooled steel to maintain and prolong the tools life.
However wherever there is a concern of scratching or gouging the work piece, a
softer material such as aluminium or bronze is utilized. Pipe bending machines
are typically human powered, pneumatic powered, hydraulic assisted, hydraulic
driven, or electric servomotor.
We have employed human powered-tube bending process to bend two
mild steel hollow pipes to make 60௢
bent handles.
4.6.3 Plasma arc cutting
Plasma cutting is a process that is used to cut steel and other metals of
different thickness and sometimes other materials, using a plasma torch. In this
process, an inert gas is blown at high speed out of a nozzle; at the same time an
electrical arc is formed through that gas from the nozzle to the surface being
cut, turning some of that gas to plasma. The plasma is sufficiently hot to melt
the metal being cut and moves sufficiently fast to blow molten metal away from
the cut. Through the application of CNC technology in industrial production,
the technology cut a wide range of high accuracy, low-cost and high efficiency.
It gradually achieves its purpose of high- tech computer numerical control
cutting, with both computer- controlled and plasma arc characteristics.

27. - 16 -
We have used plasma arc cutting for cutting four stainless steel webs for
the Tri-Star wheel arrangement which is shown in figure 4.9.
Fig 4.9 Plasma Arc cut Tri-Star wheel web
4.6.3.1 Components of the system
CNC system CNC system is an important part of the cutting machine,
which consists of a computer system, servo system, the control unit, and the
executive agencies. The computer system is made up of a keyboard, a monitor,
and the unit. Servo system exploits a computer to implement a closed-loop
control of the motor and to achieve its variable speed. Now it usually adopts
communicate servo system. The control unit is central of sending a control
signal to realize the control of the computer, the motor and the solenoid valve.
The executive agencies include the electric motor and the solenoid valves and
so on
Programming system Programming system is parts of auxiliary
programming and nesting system for developing CNC cutting machine. It can
make the entire production process to form a whole, and to organize
systematically. After the programmed machine compiles the program on the
floppy disk, enter the cutting machine and start cutting, it can also be

28. - 17 -
programmed in a simple cutter. Gas system Gas system include the gas pipeline,
pressure gauge, regulator, etc., which can be controlled by the control system to
realize the automatic on-off road of the gas. Mechanical operation system
Mechanical operation system consists of the beam, gear box, chassis, lifting
mechanism and other components.
4.6.3.2 Problems faced by the equipment
Due to the high frequency of CPU and large power and high heat of hard
drive, the internal parts of the system is subjected to overheating, making the
CNC system and cutting machine unable to work normally and increases the
requirement of industrial fans for cooling. When each part is not used
efficiently during cutting edges, taking sides, linking bridge etc., it results in
thermal deformation of the various parts and consequently results in low
efficiency. Automatic cutting cannot be achieved. There are no automatic
cutting on CNC system and parameter libraries, workers can only speak of their
own experience and observation of the eye, manually adjusting and controlling,
thus it cannot effectively play productivity of the CNC cutting machine
4.6.4 WELDING
Welding is a fabrication process that joins materials,
usually metals or thermoplastics, by causing coalescence. This is often done by
melting the work pieces and adding a filler material to form a pool of molten
material (the weld pool) that cools to become a strong joint, with pressure
sometimes used in conjunction with heat, or by itself, to produce the weld. This
is in contrast with soldering and brazing, which involve melting a lower-
melting-point material between the work pieces to form a bond between them,
without melting the work pieces.
Many different energy sources can be used for welding, including a
gas flame, an electric arc, a laser, an electron beam, friction, and ultrasound.

29. - 18 -
While often an industrial process, welding may be performed in many different
environments, including open air, under water and in outer space. Welding is a
potentially hazardous undertaking and precautions are required to
avoid burns, electric shock, vision damage, inhalation of poisonous gases and
fumes, and exposure to radiation. The main Types of welding used in industry and
by home engineers are commonly referred to as MIG welding, Arc welding,
Gas welding and TIG welding.
4.6.4.1 Arc welding
These processes use a welding power supply to create and maintain an
electric arc between an electrode and the base material to melt metals at the
welding point. They can use either direct (DC) or alternating (AC) current, and
consumable or non-consumable electrodes. The welding region is sometimes
protected by some type of inert or semi-inert gas, known as a shielding gas, and
filler material is sometimes used as well.
We have used Arc-Welding to join trolley parts together. The completed
prototype of the trolley is shown in figure 4.10 and 4.11.

30. - 19 -
4.7 PROTOTYPE OF STAIR CLIMBER TROLLEY
Fig 4.10 Side View
Fig 4.11 Front View
The modified hand truck was able to climb stairs while bearing a moderate load.

31. - 20 -
CHAPTER 5
DESIGN ANALYSIS OF TROLLEY
5.1 LOAD CALCULATION FOR AXLE
Length of the axle =0.44m
Distance between welds = 0.40m
Load applied/ carried = 30 kg (distributed equally by the welds to the axle)
=15 kg through each weld = 147.15N
Weight of the trolley = 20kg (uniformly distributed throughout the axle)
=196.2 N
Neglect the overhang beyond welded points since the wheel provides only
negligible reaction
From equilibrium equation∑ ‫ܨ‬ = 0
And ∑ ‫ܯ‬ = 0
Find reaction at the supports,
R1= 190.314N ; R2= 190.314N
Calculate the maximum bending moment for the beam,
M(max) =6.7155 N-m
Considering FOS =1.5,
M(max) =10.07N –m

32. - 21 -
Bending equation,
‫ܯ‬
‫ܫ‬
=
ߪ
‫ݕ‬
=
‫ܧ‬
ܴ
Substituting M(max) =10.07 N-m
I =
గ௥^ସ
ସ
Y =
஽
ଶ
ߪ = 3.8
ܰ
݉݉ଶ
Bending stress for the given material can be assumed to be 0.66×yeild strength
Thus, the allowable bending stress for the given material is 165 N/mm^2
The calculated bending stress for the material is within the allowable bending
stress for the material,
Thus the design is safe.

33. - 22 -
5.2 FORCE NECESSARY TO PULL THE TROLLEY
‫.ܨ‬ ‫ݔ‬ = ܹ . ‫ݕ‬
‫ܨ‬ =
‫ݕ‬
‫ݔ‬
. ܹ
F
y
x
W
Maximum load determination

34. - 23 -
5.3 FORCE ANALYSIS ON WHEEL FRAME
Where,
W1= weight of object to be carried
W2= weight of the trolley
Re = reaction force on one side
F = force applied (on one lever)
ܴ௢ = distance of centroid from centre of wheel
Forces acting on the system
(W1+W2)/2
F
F cosθ
Fsinθ
Re
Recosφ
Resinφ
K
R
(ܴ௢
2
-K2
)1/2

35. - 24 -
K = distance between centre of wheel and line of action of weight
൬
ܹ1 + ܹ2
2
− ‫ߠ݊݅ݏܨ‬൰ . ݇ = ‫.ߠݏ݋ܿܨ‬ ඥܴଶ − ݇ଶ
ܴ௘ܿ‫߮ݏ݋‬ = ‫ߠݏ݋ܿܨ‬
ܴ௘‫߮݊݅ݏ‬ + ‫ߠ݊݅ݏܨ‬ =
ܹ1 + ܹ2
2
ܴ௘ = ඨ(‫)ߠݏ݋ܿܨ‬ଶ + (
ܹ1 + ܹ2
2
− ‫)ߠ݊݅ݏܨ‬ଶ
‫߮݊ܽݐ‬ =
ܹ1 + ܹ2 − 2‫ߠ݊݅ݏܨ‬
2‫ߠݏ݋ܿܨ‬

36. - 25 -
CHAPTER 6
COST ESTIMATION OF THE PROJECT
The total cost of the project is tabulated in table 6.1.
Table 6.1 Account Statement
ACCOUNT STATEMENT
S.No Item Description Rate Quantity Price
₹
1 Rubber Wheels OD=150mm 250 each 6 pcs 1500
2 Ball Bearing Deep groove,
SKF6006
60 each 4 pcs 240
3 S.S. grade304 250mmx900mm 200/kg 3.5kg 700
4 M.S. hollow pipe OD=30,ID=26 - 4m long 200
5 Pipe Bending Costs Handle Pipes 20 each 2 40
6 M.S. plate 300mmx400mm 55/kg 1.7kg 90
7 Pipe and plate cutting costs - 10 per
cut
15 150
8 Plasma arc Cutting - 50 each 4 200
9 M.S. L angle 1inch - 1 120
10 Material for Shaft & Bearing
housings
- - - 170
11 Turning & Facing for Bearings
housings & shaft
- - - 350
12 Washer and Cotter pin - - - 20
13 Welding and Finishing costs - - - 1120
Total
4900

37. - 26 -
CHAPTER 7
INFERENCE AND CONCLUSION
7.1 INFERENCE
After its fabrication, we inferred few limitations like large noise
production while moving the trolley up and down the stairs. In order to reduce
the noise production the design of the wheel frame is to be modified such that
line passing through the mid-point of the trolley wheel should pass through the
mid-point of the step. The modified wheel CAD model is shown in figure 7.1.
Fig 7.1 Modified Wheel Frame Setup

38. - 27 -
7.2 CONCLUSION
Though this project had some limitations regarding the strength and built
of the structure, it can be considered to be a small step forward, as far as Stair
Climbing Vehicles are concerned. During the test run of this project, it was
realized that it wouldn’t be a bad idea to consider this design for carrying heavy
loads up the stairs. This product will be well acclaimed if it can be
commercialized to suit the needs. Though the initial cost of the project seemed
to be higher but more accurate manufacturing would shorten this.
As far the commercial aspects of this product are concerned, if this
product can be fully automated and produced at a lower cost the acceptance will
be unimaginable. Presently, there are no competitors for such a kind of product
in our market.

39. - 28 -
REFERENCES
1. Dr. R.K. Bansal, A text book of Strength of Materials, Laxmi Publications (P) Ltd.
2. R.S. Khurmi, J.K. Gupta, A textbook of Machine Design, S.Chand Publishing House
(P) Ltd.
3. www.wikipedia.com
4. www.mit.edu