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

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.

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

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

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

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

vii

TABLE NO. TABLE PAGE NO.

4.1 Various wheel materials

and co-efficient of friction 10

6.1 Account statement 25

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

ix

LIST OF SYMBOLS

SYMBOL DEFINITION

F Force

M Bending Moment

R1, R2 Reaction Forces

I Moment of inertia

� 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

- 0 -

- 0 -

- 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.

- 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.

- 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.

- 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.

- 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

- 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.

- 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

- 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

- 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.

- 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

- 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

- 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.

- 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

- 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.

- 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.

- 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

- 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.

- 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.

- 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.

- 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∑ � = 0

And ∑ � = 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

- 21 -

Bending equation,

� = � � = �

Substituting M(max) =10.07 N-m

I = ��^��

Y = ��

� = 3.8 ����

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.

- 22 -

5.2 FORCE NECESSARY TO PULL THE TROLLEY

�. � = � . �

� = �� . �

F

y

x

W

Maximum load determination

- 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

- 24 -

K = distance between centre of wheel and line of action of weight

��1 + �22 − �!"#$% . & = �'(!$. ) � − &�

*'(!+ = �'(!$

*!"#+ + �!"#$ = �1 + �22

* = ,(�'(!$)� + (�1 + �22 − �!"#$)�

/0#+ = �1 + �2 − 2�!"#$2�'(!$

- 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

- 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

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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.

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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