final report (7 copies)

Design and Fabrication of Motorized Stairs Climbing Vehicle Model

Department of Mechanical Engineering (TOCE)

CHAPTER 1

INTRODUCTION

The wheel chair is a device providing wheeled mobility and seating support for a person

with difficulty in walking or moving around. It is one of the most commonly used assistive

devices for enhancing personal mobility, which is a precondition for enjoying human rights

and living in dignity and assists people with disabilities to become more productive

members of their communities.

Stairs are frequently encountered obstacles in daily living. Although healthy persons climb

stairs quite easily, this movement task is quite demanding when motor functions are

reduced, for example: elderly or obese subjects, women during pregnancy, people with

different neuromusculoskeletal impairments, subjects with joint or limb replacements.

A model in 3:1 scale of a stair climbing system for a wheelchair was created and tested in

this project work. This project describes the modified design of the traditionally existing

wheel chair introducing to it, the versatility of climbing the stairs in addition to running on

the ground. The planetary wheel mechanism is main concept used to enable the vehicle to

climb the stairs in this project work. It is constituted by several small wheels that are

equally distributed on a tie bar with shapes like “Y” or “+”. The small wheels can revolve

on its axis, and it can also make a revolution around the central shaft. Every small wheel

revolves on its own axis, when the wheelchair moves on the ground; and every small wheel

revolves round the central axis, when the wheelchair goes up or down stairs. This type of

stair- climbing wheelchair can fulfill overloading and move smoothly but has low

automation.

The outline of the vehicle including the front wheels was drawn on a chart paper. The scale

of 3:1 was taken to make this model for taking all the measurements. For the dimensions of

the stairs (linear dimensions), the public areas like temple, hospital, colleges were surveyed

so as to design the front and the rear wheel. Anthropometric data were used to determine

the lengths and size of the body parts of human being as well as the body weight.



CHAPTER 2

PROBLEM ANALYSIS

2.1 PROBLEM DESCRIPTION:

Many times, the disabled people encounter difficulties when they have to ascend or

descend the stairs. For example, enter or exit buildings that have no ramps, go up or down

in buildings that have no elevators or cross pedestrian bridges. For these situations, many

assistants are required to carry a lower limb disabled person and a wheelchair. However,

this leads to a risk of injury for both the disabled person and the assistants. As a result,

there are a number of researches about a stair-climbing wheelchair to help the disabled

people. For example, Watkins designed a customized stair-climbing wheelchair which used

a sensor to detect a stair and a caterpillar track to climb the stair. Lawn et al developed a

dual section caterpillar track stair-climbing wheelchair. It could climb the twisting and

irregular stairs. Wellman et al designed a wheelchair equipped with two legs. The leg was

used to walk like a human to climb the stair. Lawn and Ishimatsu developed a stair-

climbing wheelchair mechanism with high single step capability. The mechanism consisted

of front and rear wheel clusters attached to powered linkages. Johnson & Johnson

Company produced the powered wheelchair iBOT which equipped with many sensors and

could climb the stair using four wheels.

Although these systems could help the disabled people when climbing the stairs.

Nevertheless, these systems were very complex and difficult to maintain. Therefore, this

project was aimed to provide an alternative and enhance the quality of life for the disabled

people by enabling the wheelchair to climb the stairs using a simple system. A model in

3:1 scale of a stair climbing system for a wheelchair was created and tested in this project

work.

2.2 DEMOGRAPHIC STUDIES:

About 10% of the global population, i.e. about 650 million people, have disabilities.

Studies indicate that, of these, some 10% require a wheelchair. It is thus estimated that

about 1% of a total population – or 10% of a disabled population – need wheelchairs, i.e.

about 65 million people worldwide. In 2003, it was estimated that 20 million of those

requiring a wheelchair for mobility did not have one. There are indications that only a



minority of those in need of wheelchairs have access to them, and of these very few have

access to an appropriate wheelchair.

Figure below shows that the sick or disabled people among working age of 15 to 64 are

13.2% of the population in EU, and Sweden have the highest number which is 36.5%.

Therefore the situation in Sweden is very serious and nursing care for the elderly and

disabled people will become a big burden in the near future.

Figure 2.1: Percentage of disabled population in various countries in EU

The demographic results show that 2.3% of the total population of India falls under the

category of disabled. In the country like India where alone the population has surged above

1.3 billion, the total population of the disabled is quite remarkable. Also 15% of the total

population of world suffers disability which is again surprisingly high.

The following tables illustrate a comparative analysis of Guidelines and Standards for

accessible design used in India, UK and USA. Also comparison has been done with the

standard „ISO 7913: Wheelchairs-Maximum overall dimensions‟ and „ISO/TR 9527:

Building Construction- Needs of disabled people in buildings- Design guidelines. For USA

„Americans with Disabilities Act Accessibility Guidelines‟ (ADAAG) were reviewed

whereas for UK, “BS 8300: Design of buildings and their approaches to meet the needs of

disabled people- Code of practice” and “Inclusive Mobility” which are accessibility



guidelines produced by DETR. The tables include wheelchair dimensions, clear floor area

provisions, space requirements for maneuvering, knee and toe clearances and reach limits.

The columns in light green background represent the Indian anthropometric

recommendations and the columns in lavender background represent the international

ones. Figures in red indicate exact matches and figures in blue indicate close similarity

between the Indian and international access standards and guidelines. The various exact

matches and several close similarities for the dimensional data clearly hint that the Indian

recommendations may be a negotiated settlement of international minimum guidelines and

requirements.

Table 1: Comparison of structural anthropometry of wheel chair users (in mm)



Table 2: Comparison of functional anthropometry of wheel chair user (in mm)

Figure 2.2: Static anthropometry of occupied and unoccupied wheel chair



CHAPTER 3

LITERATURE SURVEY

3.1 TYPES OF WHEEL CHAIRS:

3.1.1 MANUALLY PROPELLED:

Manual wheelchairs are those that require human power to move them. Many manual

wheelchairs can be folded for storage or placement into a vehicle, although modern

wheelchairs are just as likely to be rigid framed.

Manual or self-propelled wheelchairs are propelled by the occupant, usually by turning the

large rear wheels, from 20-24 inches (51–61) cm in average diameter, and resembling

bicycle wheels. The user moves the chair by pushing on the hand rims, which are made of

circular tubing attached to the outside of the large wheels. The hand rims have a diameter

that is slightly less than that of the rear wheels. Attendant-propelled chairs (or transport

wheelchairs) are designed to be propelled by an attendant using the handles, and thus the

back wheels are rimless and often smaller.

Foot propulsion of the wheelchair by the occupant is also common for patients who have

limited hand movement capabilities or simply do not wish to use their hands for

propulsion. Foot propulsion also allows patients to exercise their legs to increase blood

flow and limit further disability.

Figure 3.1: Manually propelled wheel chair



3.1.2 ELECTRIC POWERED:

An electric-powered wheelchair is a wheelchair that is moved via the means of an electric

motor and navigational controls, usually a small joystick mounted on the armrest, rather

than manual power. A power-assisted wheelchair is a recent development that uses the

frame & seating of a typical manual chair while replacing the standard rear wheels with

wheels that have small battery-powered motors in the hubs. For users who cannot manage

a manual joystick, head switches, chin-operated joysticks, sip-and-puff or other specialist

controls may allow independent operation of the wheelchair.

Figure 3.2: Electric powered wheel chair

3.1.3 OTHER VARIANTS:

Bariatric wheelchair is one designed to support larger weights; most standard chairs are

designed to support no more than 250 lbs. (113 kg) on average.

Pediatric wheelchairs are another available subset of wheelchairs. Hemi wheelchairs have

lower seats which are designed for easy foot propulsion. The decreased seat height also

allows them to be used by children and shorter individuals.

Smart wheelchair is any motorized platform with a chair designed to assist a user with

a physical disability, where an artificial control system augments or replaces user control

controlled by a computer, has a suite of sensors and applies techniques in mobile robotics.

http://en.wikipedia.org/wiki/File:Pride_Jazzy_Select_power_chair_001.JPG



Sports variants is the one which athletes with a disability use for disabled sports that

require speed and agility, such as basketball, rugby, tennis, racing and dancing.

3.2 TYPES OF MOTORS:

3.2.1 AC MOTORS:

An AC motor is an electric motor driven by an alternating current (AC). It commonly

consists of two basic parts, an outside stationary stator having coils supplied with

alternating current to produce a rotating magnetic field, and an inside rotor attached to the

output shaft that is given a torque by the rotating field. There are two main types of AC

motors, depending on the type of rotor used.

The first type is the Induction motor or asynchronous motor; this type relies on a small

difference in speed between the rotating magnetic field and the rotor to induction current.

The second type is the Synchronous motor, which does not rely on induction and as a result

can rotate exactly at the supply frequency or a sub-multiple of the supply frequency. The

magnetic field on the rotor is either generated by current delivered through slip rings or by

a permanent magnet. Other types of motors include eddy current motors, and also AC/DC

mechanically commutated machines in which speed is dependent on voltage and winding

connection.

Figure 3.3: AC motor



3.2.2 DC MOTORS:

A DC motor relies on the fact that like magnet poles repels and unlike magnetic poles

attracts each other. A coil of wire with a current running through it generates an

electromagnetic field aligned with the center of the coil. By switching the current on or off

in a coil its magnet field can be switched on or off or by switching the direction of the

current in the coil the direction of the generated magnetic field can be switched 180°.

A simple DC motor typically has a stationary set of magnets in the stator and an armature

with a series of two or more windings of wire wrapped in insulated stack slots around iron

pole pieces (called stack teeth) with the ends of the wires terminating on a commutator.

The armature includes the mounting bearings that keep it in the center of the motor and the

power shaft of the motor and the commutator connections. The winding in the armature

continues to loop all the way around the armature and uses either single or parallel

conductors (wires), and can circle several times around the stack teeth. Types of DC

motors includes: With brush, Brushless, Un-commutated, Permanent magnet stators,

Wound stators.

Figure 3.4: DC motor

3.2.3 GEARED MOTORS:

Gear motors are complete motive force systems consisting of an electric motor and a

reduction gear train integrated into one easy-to-mount and -configure package. This greatly

reduces the complexity and cost of designing and constructing power tools, machines and

appliances calling for high torque at relatively low shaft speed or RPM. Gear motors allow

the use of economical low-horsepower motors to provide great motive force at low speed

such as in lifts, winches, medical tables, jacks and robotics. They can be large enough to

lift a building or small enough to drive a tiny clock.

http://en.wikipedia.org/wiki/Dc_motor#Brushless

http://en.wikipedia.org/wiki/Dc_motor#Uncommutated

http://en.wikipedia.org/wiki/Dc_motor#Permanent_magnet_stators

http://en.wikipedia.org/wiki/Dc_motor#Permanent_magnet_stators

http://en.wikipedia.org/wiki/Dc_motor#Wound_stators



Figure 3.5: Inside the geared motor

Figure 3.6: Geared motors

3.2.4 SERVO MOTORS:

A servomotor is a rotary actuator that allows for precise control of angular position,

velocity and acceleration. It consists of a suitable motor coupled to a sensor for position

feedback. It also requires a relatively sophisticated controller, often a dedicated module

designed specifically for use with servomotors. Servomotors are not a specific class of

motor although the term servomotor is often used to refer to a motor suitable for use in a

closed-loop control system.



Servomotors are used in position and speed controlled applications such as in

robotics, CNC machinery or automated manufacturing.

Figure 3.7: Servo motors

3.2.5 STEPPER MOTORS:

A stepper motor (or step motor) is a brushless DC electric motor that divides a full rotation

into a number of equal steps. The motor's position can then be commanded to move and

hold at one of these steps without any feedback sensor (an open-loop controller, as long as

the motor is carefully sized to the application.

Figure 3.8: Stepper motor



3.3 DRIVE SYSTEMS:

3.3.1 BELT DRIVE SYSTEM:

It is a mechanical system in which the motion/power is transferred from one shaft to the

other by a flexible element called belt. A belt is a loop of flexible material used to

mechanically link two or more rotating shafts, most often parallel. Belts may be used as a

source of motion, to transmit power efficiently, or to track relative movement. Belts are

looped over pulleys and may have a twist between the pulleys, and the shafts need not be

parallel. In a two pulley system, the belt can either drive the pulleys normally in one

direction (the same if on parallel shafts), or the belt may be crossed,

Figure 3.9: Belt drive system

3.3.2 GEAR DRIVE SYSTEM:

The system of transmission of rotation between the shafts by contacting toothed wheels

keyed to the shafts is gear drive system. A gear train is formed by mounting gears on a

frame so that the teeth of the gears engage. Gear teeth are designed to ensure the pitch

circles of engaging gears roll on each other without slipping, providing a smooth

transmission of rotation from one gear to the next.



Figure 3.10: Gear drive system

3.3.3 CHAIN DRIVE SYSTEM:

Chain drive is a way of transmitting mechanical power from one place to another by

a roller chain, known as the drive chain or transmission chain, passing overa sprocket gear,

with the teeth of the gear meshing with the holes in the links of the chain. The gear is

turned, and this pulls the chain putting mechanical force into the system. It is often used to

convey power to the wheels of a vehicle, particularly bicycles and motorcycles. It is also

used in a wide variety of machines besides vehicles.

Figure 3.11: Chain drive system



3.4 FRAME:

A frame is the main structure of the chassis of a motor vehicle. All other components

fasten to it; a term for this design is body-on-frame construction. The main functions of a

frame in motor vehicles are:

1. To support the vehicle's chassis components and body

2. To deal with static and dynamic loads, without undue deflection or distortion. This

includes: weight of the body, passengers, and cargo loads, vertical and torsional

twisting transmitted by going over uneven surfaces, transverse lateral forces caused

by road conditions, side wind, and steering the vehicle,

Types of frames

Ladder frame

Diamond

Backbone tube

Cantilever

X-frame

Recumbent

Perimeter frame

Truss

Unibody Monocoque

Figure 3.12: Frame

3.5 BEARINGS:

A bearing is a machine element that constrains relative motion and reduces friction

between moving parts to only the desired motion. The design of the bearing may, for

example, provide for free linear movement of the moving part or for free rotation around a



fixed axis; or, it may prevent a motion by controlling the vectors of normal forces that bear

on the moving parts. Many bearings also facilitate the desired motion as much as possible,

such as by minimizing friction. Bearings are classified broadly according to the type of

operation, the motions allowed, or to the directions of the loads (forces) applied to the

parts. Common motions permitted by bearings are:

axial rotation e.g. shaft rotation

linear motion e.g. drawer

spherical rotation e.g. ball and socket joint

hinge motion e.g. door, elbow, knee

There are at least 6 common principles of operation:

Plain bearing: bushing, journal bearing, sleeve bearing, rifle bearing

Roller bearings: rolling-element bearing such as ball bearings and

Jewel bearing: in which the load is carried by rolling the axle slightly off-center

Fluid bearing: in which the load is carried by a gas or liquid

Magnetic bearing: in which the load is carried by a magnetic field

Flexure bearing: in which the motion is supported by a load element which bends.

Figure 3.13: Journal and Thrust Bearings

http://en.wikipedia.org/wiki/Plain_bearing

http://en.wikipedia.org/wiki/Journal_bearing

http://en.wikipedia.org/wiki/Rolling-element_bearing

http://en.wikipedia.org/wiki/Jewel_bearing

http://en.wikipedia.org/wiki/Fluid_bearing

http://en.wikipedia.org/wiki/Magnetic_bearing

http://en.wikipedia.org/wiki/Magnetic_field

http://en.wikipedia.org/wiki/Flexure_bearing



3.6 BATTERY:

An electric battery is a device consisting of one or more electrochemical cells that convert

stored chemical energy into electrical energy. Each cell contains a positive terminal,

or cathode, and a negative terminal, or anode. Electrolytes allow ions to move between the

electrodes and terminals, which allows current to flow out of the battery to perform work.

Primary (single-use or "disposable") batteries are used once and discarded; the electrode

materials are irreversibly changed during discharge. Common examples are the alkaline

battery used for flashlights and a multitude of portable devices.

Secondary (rechargeable batteries) can be discharged and recharged multiple times; the

original composition of the electrodes can be restored by reverse current. Examples include

the lead-acid batteries used in vehicles and lithium ion batteries used for portable

electronics.

Batteries come in many shapes and sizes, from miniature cells used to power hearing

aids and wristwatches to battery banks the size of rooms that provide standby power

for telephone exchanges and computer data centres.

Figure 3.14: Lead-acid Battery

http://en.wikipedia.org/wiki/Electrochemical_cell

http://en.wikipedia.org/wiki/Cathode

http://en.wikipedia.org/wiki/Anode

http://en.wikipedia.org/wiki/Electrolyte

http://en.wikipedia.org/wiki/Primary_battery

http://en.wikipedia.org/wiki/Flashlight

http://en.wikipedia.org/wiki/Secondary_battery

http://en.wikipedia.org/wiki/Rechargeable_batteries

http://en.wikipedia.org/wiki/Hearing_aid

http://en.wikipedia.org/wiki/Hearing_aid

http://en.wikipedia.org/wiki/Telephone_exchange

http://en.wikipedia.org/wiki/Data_center



CHAPTER 4

DESIGN AND FABRICATION

4.1 BODY FRAME

4.1.1 DESIGN OF FRAME:

A complete new design is proposed for frame which sums up to various advantages. The

frame has been designed in such a way that it enables the smooth climbing of the entire

vehicle on encountering the stairs. The side view of the vehicle looks like a Human shoe

with a curve at the front end. The arrangement for the placement of the rear and front axles

including the seat is carefully done.

Figure 4.1: Body frame

As the vehicle starts climbing the stairs, the whole body rotates and hence the line shown

in the figure tends to become vertical. If so happens since the load continues to act



vertically downwards there is the probability of reverse torque generation due to weight

being offset backwards from the rear axle.

Figure 4.2 Analysis of the direction of action of load on the frame while climbing

To take care of this the frame has been designed in such a way that the angle of inclination

of the line passing through the rear axle and the point of application of main load should be

more than the angle of ascent of the stairs. This confirms that at all the times, the line of

action of load stays in front of the rear axle which avoids reverse torque due to self-weight.

Analysis of frame on ANSYS:

Analysis of frame was done for two different configurations to check the best condition to

support the load which is as shown in the figure. One configuration was having vertical

element connecting the chair fulcrum to the horizontal base element. The other

configuration involved use of inclined element. The modeling was done using pipe

element. Heavy load can be carried in the straight position. If the pipe is kept in the slanted

manner then the bending and deformation of pipe will be more and the vehicle can‟t

withstand the more load.

PARTICULARS CONFIGURATION 1 CONFIGURATION 2

Load applied 100 N 100 N

Maximum

displacement

0.255E-07 m 0.115E-06 m

Table 3: Analysis of frame in ANSYS

Angle more than 30 degrees

Load acts here

30 cm

15 cm 28.07 degrees



Figure 4.3: Deformation analysis of frame in ANSYS

It was found that the load bearing capacity of first configuration was more as the analysis

shown comparatively less displacement for the same load applied at the top as shown. Since

the results were favourable for the first configuration the design was finalized to be based on

it.

MODIFIED ASCENT ASSISTIVE ANTERIOR:

One of the most important feature of the frame design is that it has a very simple but very

important modification of the anterior which is very favorable regarding the placement of the

front axles. It was decided to modify the anterior part of the vehicle to be curved which on

one hand prevent any possible collision with the stairs and on the other hand helps in

favourably palcing the front axles.

The major benefit of placing the front axle at this region is that the reaction force acting on

the front axle is directed incliningly upwards. Thus this force of reaction can be resolved into

two components such that the vertical component helps in raising the vehicle upwards. This

also reduces the backward resistance on the front wheels which makes the vehicle easier to

climb up.

Another main advantage is that the vehicle is inclined forwards by about 10 degrees under

normal conditions which helps the C.G. to shift towards front hence ensuring the equal

distribution of loads on both the front and the rear axles. Also while climbing, the line of



action of weight should not pass through or behind the rear axle as explained in section 4.1.1.

Although the line of action of weight passes through between the axles under normal

conditions, while climbing, the vehicle assumes inclined position which shifts the C.G. of the

vehicle backwards. This increases the chances of somersaulting of vehicle due to backward

rolling caused by the moment due to the weight. This forward inclination of the vehicle takes

very good care of this problem and ensures that all the time, the line of action of weight falls

between the axles.

Figure 4.4: Modified ascent assistive anterior



4.1.2 FABRICATION OF FRAME:

The entire outer frame was prepared using hollow metal pipe made of cast steel with the

dimensions of 2 cm outer diameter and 2.5 mm thickness. Frame was made by cutting the

pipe into required length. The structure of frame was drawn on the chart paper, so with the

reference of dimensions from that drawing the metal pipe was cut into required

dimensions.

Cutting was followed by bending of pipe. Bending of pipe was done by placing the pipe in

the bench vice. After bending, the pipe was welded and the structure of the frame was

made. Electric arc welding was carried out using 2.5 mm consumable electrodes. The

frame was drilled with the drill bit of diameter 3mm so that the cover plates could be

fastened to it using nut and bolts of 2.5 mm diameter.

Figure 4.5: Fabrication of frame



4.2 FRONT WHEELS

4.2.1 DESIGN OF FRONT WHEELS:

There are different wheel proposed to be used in the wheel chair and they are as follows: -

1. Triangular

2. Rectangular

3. Pentagonal

4. Hexagonal

Figure 4.6: Proposed front wheel types

Although all the configurations seem convincing that they are able to make the ascent over

the stairs, different configurations come with various inbuilt drawbacks.

In case of triangular and rectangular arms the following shortcomings were observed:

The axle is below/very near the edge of the obstacle

This makes it very difficult to rotate the axle at obstacles since torque will be

negative/less.

The path traversed by the end of the arm is very large because the angle of

separation between two consecutive arms is 120 degrees.

The rotating arm accelerates for longer time and hence impact is very high due to

high velocity at the instant of hitting on the surface of the stair.



Figure 4.7: Analysis for different front wheel arrangement

Using the pentagonal arrangement when compared with the hexagonal one, it came with

the following common advantages:

The axle is at the sufficient distance from the edge of the obstacle; hence it will be

easier to turn the wheel across the edge since this offset causes the moment to be

produced will be enough to rotate the wheel forwards.

The path traversed by the arm is almost equal in both cases

The arm accelerates for very less time since the gap is not very large compared to

the former case, hence impact will be less.

Going for hexagonal arrangement will simply incur extra cost while the results are

equivalent to that of pentagonal arrangement.

After various modifications on the former wheel design, an improved design was proposed

to the front wheel which looks like an incomplete wheel with 5-arms projecting outward.

The front wheel is of 16 cm pitch diameter made up of 6 cm long arms projecting out

from side of 5 cm circular disc made of mild steel material.



Figure 4.8: Solid Edge model of front axle

4.2.2 FABRICATION OF FRONT AXLE:

The arms, each of length 6 cm were welded on the circular disc and a hole was made was

drilled near the tip of each arm at a distance of 8 cm from the center of the wheel falling on

the pitch circle to accommodate the front sub-wheels. Each sub-wheel is 3.25 cm in

diameter and 1.25 cm in width.

The front wheel is designed in such a way that it can ascend and descend the stairs without

any problem. First, we bought the wheel of 5cm diameter, washer and the arms of required

length. We made the arms by cutting the metal pieces into required length and then

grinding at the edge of the arms is done and made semicircular. In the drawing which we

have drawn, the washer and arms are kept so as to check the measurement. With the same

fixing, the arms are welded in the washer. Another washer and arms is brought and kept in

the same drawing for the measurement and welding is done. In the middle of both washer

arms attachment circular wood of required diameter is kept and it is drilled in the middle

with the same diameter of the washer. Hence, front wheel is made and attached in the

shaft.



Such two fabricated parts, one on the left and other on the right with smaller sub-wheels

freely rotating in the middle make up a complete wheel as shown in the fig.

Figure 4.9: Steps involved in fabrication of front axle

S.N. ITEM USED PARTICULARS

1. Shaft Cast steel, O.D.=18mm I.D.=14mm (1)

2. Bearings I.D.=19mm O.D.=40mm (2)

3. Central disk I.D.=14mm O.D.=50mm (4)

4. Arms L=60mm B=18mm T=2.5mm (20)

5. Sub-wheels Hole=6mm O.D.=32.5mm Thickness=12.5mm

(10)

6. Hexagonal bolts M5 shank length 20mm with no thread upto

15mm (10)

7. Cir-clip I.D. 16mm (2)

Table 4: Details of the materials used in making of front axle



4.3 REAR AXLE:

4.3.1 DESIGN OF REAR AXLE

Rear wheels used on the prototype are circular in shape with the friction material on the

circumference of the wheel. The wheel is of 20 cm diameter. The wheel is supported on the

axle using bolts welded in a small solid shaft using washer which is again inserted and

welded to the axle. The wheel is easily removable from the axle using bolt and nut

arrangement as shown in the figure. The wheel of the model is of plastic material with

metal fitted in the center through which the bolts pass which in turn is tightened using

washer and nut. This makes wheel to fix on the axle.

Figure 4.10: Solid Edge model of rear axle

4.3.2 FABRICATION OF REAR AXLE:

The axle is a hollow shaft made of cast steel material which is cut to required dimensions.

A Sprocket of 4 cm diameter and is fixed on the axle which gives drive to the rear wheel

taking power from the motor shaft. The axle is 2 cm in diameter with bearings and is fixed

to the frame by the help of clamps “C” Clamps. At the end of axle a 1.5 cm diameter and 4

cm length of solid shaft is fixed such that the solid shaft inserts into the hollow shaft and is

welded, which supports the rear wheels.



Figure 4.11: Fabrication of rear axle

S.N. ITEMS USED PARTICULARS NUMBER

1. Shaft Cast steel, O.D.=18mm I.D.=13mm (1)

2. Bearings I.D.=19mm O.D.=40mm (2)

3. Cir-clips I.D.= 16mm (4)

4. Sprocket Cast iron, no. of teeth=26 thickness=3mm

5. Circular disc I.D.=14mm O.D.=50mm (2)

6. Bolts and nuts M8 , shank length=80mm (8)

7. Wheels Diameter=200mm (2)

Table 5: Details of the materials used in making of rear axle



4.3.3 OPTIMIZATION OF REAR WHEEL DIAMETER:

Whenever a round object encounters rectangular obstacle like stair step, to climb over the

obstacle, it should rotate about the point of contact between the wheel and the stairs. This

point of rotation about which the wheel rotates is called “Instantaneous center of rotation”.

When it does so, the maximum amount of displacement of the center of the wheel can be

found out by finding the point of intersection between the arc and the normal to the stair‟s

inclination as shown in the figure.

Following were the proposed rear wheel diameters:

1. 30 centimetres 4. 60 centimetres





Figure 4.12: Finding the amount of vibration for various sizes wheels

The amplitude of the vibration normal to stairs surface was found for different sized

wheels and tabulated and the graph was drawn as shown below:

Table 6: Amplitude of vibration for different sized wheels



Figure 4.13: Plot of amplitude of vibration against rear wheel diameter

The selection of wheel diameter to be used in rear axles has to be done in such a way that

the vibration should be minimum since vibration invites a lot of problem. To reduce

vibration to minimum, the optimum wheel diameters have to be used.

The wheel with 30 centimeters diameter cannot be used at all because of the following

reasons:

The amplitude of vibration is excessive

The point of contact about which the wheel rotates i.e. “instantaneous center” lies

above/same level to the center of wheel

The reaction given by the edge of the stairs is dominant which prevents further

climbing of the wheel over it

0

1

2

3

4

5

6

7

8

0 20 40 60 80 100

Axi

s Ti

tle

Axis Title

AMPLITUDE OF VIBRATIONNORMAL TO STAIRS SURFACE(IN CMS)



Figure 4.14: Force analysis for 30 cm rear wheel diameter

Although the amplitude of vibration goes on decreasing as the diameter of rear wheel is

increased, the other prominent factors make the use of 70cm and 80cm wheel obsolete.

The center of the wheel lies at the edge or outside the edge of the stair

Very much chances of falling back because of the reverse torque due to the vertical

load on the rear axle



Figure 4.15: Effect of vehicles self-weight on 70 and 80 cm rear wheels

4.4 DRIVE SYSTEM:

Since the vehicle undergoes a lot of vibration during climbing the stairs, use of belt drives

is not very recommendable. The belt may shift from the pulley due to the vibration and

hence may disengage suddenly causing the vehicle to roll backwards. On the other hand,

the belt drive is always susceptible to slipping problem which may be disastrous while

climbing the stairs. This risk can be avoided by use of gear or chain drive.

For using the gear drive following things need to be taken into considerations:-

Perfect alignment of shafts

Close dimensional tolerances

Perfect pressure angles

Perfect shaft center distances

Arrangement of proper lubrication system

Use of gears comes with many disadvantages. Use of gear drive system requires number of

different types of bearings to be used. The large scale speed reduction is difficult since it

causes increase in the overall weight of the vehicle as many gears have to be used. Also the



proper lubrication system has to be incorporated for smooth functioning of gears which is

another problem.

Solution to all these problems was deciding to use the chain drive system. It just requires

one driving sprocket, one driven sprocket and the chain of required length for given center

distance. Thus it does not add much load on the vehicle for same power transmission

compared to gear drives. On one hand this requires very little lubrication and maintenance

compared to gears and on the other hand if chain used is of proper size there is no chance

of slip unlike in belt drive system. Power transmission efficiency for chain drive system is

also very good and is more suitable for the center distances we are going to have.

Figure 4.16: Chain drive system being employed in rear axle

4.5 SEAT:

4.5.1 DESIGN FOR SELF ALIGNMENT:

In most of the available stair climbing wheelchairs, it was found that the horizontal

alignment of the chair while climbing the stairs was done by employing the

pneumatic/hydraulic lifters coupled with the sensors and the microprocessors. A very

simple solution to this was found out by using the self-aligning property of every hanging

body. Any hanging body‟s weight through C.G. always is directed downwards. Using this

principle the self-aligning chair was designed by providing it the rotatory joint to the chair

with the frame.



When the vehicle is normally running on plain ground, the chair obviously by virtue of

gravity is horizontal as shown in figure. Even when the vehicle is in the middle of the

ascent, the weight of the chair along with anything kept on it, tries to continue to be

directed vertically downwards which brings the chair back to its original horizontal

alignment. This completely eliminates the use of the sophisticated devices like

microprocessors and sensors.

To prevent the sudden swinging of the chair during movement of the vehicle, and also

during the ascent/decent, the damping can be done by employing eyed dashpots. One eye

of the dashpot is to be connected to the frame and the other to the chair with rotary joint.

Figure 4.17: Gravity aligned self-adjusting seating arrangement

4.5.2 DESIGN OF SEAT:

The self-aligning chair although seemed to be very simple, since it has to be virtually

hanged with the rotary joint, the chair in the first place aligns itself to gain equilibrium.

For the chair to be in equilibrium in the first place, the line of action of weight through

C.G. should pass through the point of pivot. On doing this the chair reclines in such a way

that it faces downwards making it not suitable for sitting purpose.

Specially designed chair was fabricated such that whatever position the entire vehicle

assumes, the chair comes to its original horizontal position using the counterweight as

shown in figure. Nevertheless inverted “T” shaped chair is obsolete and hence cannot be

used. To take care of this, the frame of the chair itself was modified into a curve such that



some portion of it goes backwards from the point of pivot which itself acts as the

counterweight and hence eliminates the necessity of using visible counterweight.

Figure 4.18: Problem analysis of equilibrium of seat with rotatable support at the top

Figure 4.19: Solid Edge model of the seat



4.6 STAIRS:

4.6.1 DESIGN OF STAIRS:

The entire design of the vehicle is based on the average value of the readings obtained

from a mini survey conducted by project members over various public places like hostels,

temples, hospitals and malls.

Places Height (cms) Width (cms) Length (cms)

Gopalan Mall 15 30 200

Prashanth Hospital 16 29 90

Ganesh Temple 17 40 285

Hostel Building 13 29 187

Oxford Dental Building 15 30 130

Average value 15 32 180

Table 7: Readings for the dimensions of the stairs conducted by the project group

The average values thus obtained were converted by the scale of 3:1 and hence the model

stairs was made of the height 5 centimeters, width of 10 centimeters and length of 60

centimeters. These values when used gave the inclination of the stairs to be roughly around

30 degrees. The values obtained from the survey were cross verified with the civil and

architecture departments.



4.6.2 CONSTRUCTION OF STAIRS:

Simple wood works of sawing, filing, chiseling and nailing was involved in making the

model stairs. The plywood of 1 cm width was used to make the supports on which the

pattern of the stairs was cut using wood saw in workshop lab and flakes of thickness 5 mm

were glued and nailed on the patterns consecutively to get the stairs.

Thus obtained wooden staircase was used as the mold cavity for making the concrete

stairs.

Figure 4.20: Construction of model stairs



4.7 MOTOR:

4.7.1DESCRIPTION OF THE MOTOR

Figure 4.21: Solid edge modeling of motor

The motor used in the vehicle is a 12 volts DC flange mounting geared motor. It is high

torque motor used for medium load applications. The side shaft is given to reduce power



losses and to make the size compact. The rotation of shaft of the motor is coupled with

worm gear arrangement and taken out sideways.

A worm gear combines a motor and a worm gear in a pre-assembled, ready to use package.

The gearing consists of a pinion meshed with a helical screw, a worm-and-wheel

arrangement. This results in right-angle transmission unless an angle gear is added.

The weight of the motor is proportional to the windings of the coil and more the winding

more is the power output.

It is a Dynaflux company based D63 series product which is to be operated using a 12 volt

DC battery similar to which we use in car and motor bikes. It is mounted at the base of the

vehicle. Flange mounting at the front and is clamped using a „C‟ clamp at the back, so that

the motor is rigid in its position.

4.7.2 SPECIFICATIONS OF THE MOTOR:

Manufacturer : DYNAFLUX

Power in: 75 W (0.1 HP)

Speed: 1700 RPM

Voltage in DC: 12 V

Current in: 7.4 A

Output speed: 30 RPM

Speed ratio: 56.667

Torque: 80 kg-cm /784 N-cm



CHAPTER 5

CALCULATIONS

Figure 5.1: Calculation of power required for climbing stairs

We know that when any object is taken from lower altitude to higher altitude, some

definite amount of work has to be done on the object. This work done is stored in the form

of potential energy of the body after reaching at the height.

Amount of work done on the object = Potential Energy gained by the object

(Joules)

Where,

“m” is the mass of object being raised in Kilograms

“g” is the acceleration due to gravity in N/m2

“h” is the height through which object is to be raised in Meters

“E” is the energy gained by the object in Joules

This is the amount of work done “E” without considering any frictional losses.

Considering the frictional losses and the overload case, let us take the amount of work to

be done for lifting the object through height „h‟ be three times the normal work done.

Hence the amount of work to be done

Eact = 3 E

If total time of ascent for the height “h” = t seconds

Then power required,

P = Eact / t (Watts)

Height (h)

Mass (m)

g



CALCULATIONS FOR THE FORCE OF PULL:

Figure 5.2: Calculation of circumferential force required to roll over the step

When the wheel is about to turn over the curb/step, the contact with the floor is lost and

hence there is no reaction from the floor C. The body is in equilibrium under the action of

three forces, namely

1. Applied force F ( in Newton)

2. Self-weight W (in Newton), which is vertically downwards acting through the

center of roller and

3. Reaction R ( in Newton) from the edge of the step.

Since the body is in equilibrium under the action of only three forces, they must be

concurrent. It means the reaction at edge “A” of step passes through the point B as shown

in figure.

Referring to the figure above,

Since the wheel radius is double the step height,

Considering equilibrium of vertical forces,

∑

………………………..5.1

Considering equilibrium of horizontal forces,



∑

……………………………....5.2

This gives the required amount of force to pull the wheel over the obstacle which tells us

that amount of force depends on the point of application of force which in turn determines

the value of ɵ. As the value of ɵ increased, so does the value of force to be applied.

If applied on the circumference as shown in above figure, ɵ =30° which gives

………………………..5.3

This equation suggests us that force equal to almost 60% of the total weight has to be

applied at the circumference (generally manually propelled wheelchairs) to overcome the

obstacle.

Using the sprocket on the rear axle for propelling the vehicle shifts the point of application

of force near the center since the diameter of the wheel is very large compared to the

diameter of the sprocket

Figure 5.3: Calculation of central force required to roll over the step



In this case the reaction passes through the center of the roller.

Considering equilibrium of vertical forces,

∑

………………………….5.4

Considering equilibrium of horizontal forces,

∑

……………………….5.5

Using equation 5.4 in 5.5 we get,

……………………5.6

To find the minimum force to pull the wheel over the obstacle, differentiate equation 5.6

and equate it to zero.

(

)

Substituting this we get,

Fmin =

( )

Fmin = ……………………………….5.7

CALCULATIONS FOR THE MODEL:

If the vehicle is carrying the load of 20 kg up to the height of 3 meters in 60 seconds then,

Weight of the empty vehicle = 20 kg

Weight carried by the vehicle = 15 kg

Total weight carried by the vehicle W = 35 x 9.81 = 343.35 N

Total time of ascent for the height h = 60 seconds

Energy required for the climb, E = 35 x 9.81 x 3 Joules

E = 1030.05 J



Considering overload and frictional losses

E act = 1030.05 x 3 = 3010.15J

Hence,

Power needed P = Eact / t

P = 3010.15 / 60 = 51.5 Watts

Pulling force required, F =0.866 x W

F= 0.866 x 343.35 N = 297.34 N

Hence, the motor we have used for the model has the specifications which satisfy the

requirements for the necessary power and force of pull.



CHAPTER 6

ASSEMBLY AND SPECIFICATIONS

6.1 DIMENSIONS OF THE VEHICLE

Frame dimensions at base = 46 29 cm

Frame dimensions at back = 46 29 cm

Chair dimensions = 19cm x 19cm x 19cm

Length of the vehicle = 47 cm

Total height of the vehicle = 44 cm

Width of the vehicle = 29 cm

Height of the legs = 46 cm

Radius of the arms of front wheel from center = 9.5 cm

Diameter of the rear wheels = 18.5 cm

Diameter of the roller wheels in front axle = 3.25 cm

Width of the roller wheels in front axle = 1.25 cm

Width of the rear wheels = 4 cm

Average height of the steps = 15 cm

Average width of the steps = 30 cm

Power of motor used = 75 W

Speed of motor used = 30 rpm

Speed reduction = 1:2

Number of teeth in driving sprocket = 14

Number of teeth in driven sprocket = 28



6.2 ASSEMBLY OF THE VEHICLE MODEL

Figure 6.1: Isometric view of the assembly of the vehicle

Figure 6.2: Top view of the assembled vehicle



Figure 6.3: Side view of the assembled vehicle



CHAPTER 6

CONCLUSION

The model was made employing the concept and was tested for the climbing features over

the model stairs. The ascent was successfully achieved except the vibrations which

couldn‟t be eliminated because the shock absorbers were not installed. During the descent

controlling of vehicle was found to be difficult which necessitated braking system on

wheels. The main purpose of this project was to check the validity of the concept in

making the cheap and affordable simple wheelchair. For general population it is very

difficult or almost impossible to afford very expensive modern wheel chair whose price

ranges from 0.5 to 3 lakhs. All the costs incurred in fabricating the model added together

was below 8000 Rupees. By eliminating unnecessary costs, the cost of fabrication can still

be brought down.



CHAPTER 7

FUTURE SCOPE

The future enhancement of our project requires rectifying the problems that we have

encountered during descending of the wheel chair in stairs. We had a smooth travel while

ascending but while coming down from the steps, some difficulties were encountered.

There was some problems regarding vibration and to overcome this springs and shock

absorbers can be used. Constant braking is required while descending the stairs in order to

achieve safe ride. The steering system and braking system can also be added so that wheel

chair will be in a good control.

With the incorporation of suspension system, steering and braking system, this concept

vehicle can be very promising, cheap and useful for real life applications.



REFERENCES

1. Wheelchair skills program (wsp), www.wheelchairskillsprogram.ca.

2. Research Paper - Anthropometry of Indian Manual Wheelchair Users - Vikas Sharma

3. Giuseppe Quaglia, Walter Franco and Riccardo Oderio (2011), “Wheelchair, a

Motorized Wheelchair with Stair Climbing Ability”, Mechanism and Machine Theory,

Vol. 46, No. 11, pp. 1601-1609.

4. Lawn, M.J., Sakai, T., Kuroiwa, M. and Ishimatsu, T. (2001). Development and

practical application of a stairclimbing wheelchair in Nagasaki, International Journal

of Human-friendly Welfare Robotics Systems, vol.2(2), pp. 33-39

5. Wellman, P., Krovi, V., Kumar, V. and Harwin, W. (1995). Design of a wheelchair

with legs for people with motor disabilities, IEEE Transactions on Rehabilitation

Engineering, vol. 3(4), pp. 343-353.

6. Johnson & Johnson (2009), iBOT, URL:http://www.ibotnow.com, access on

03/05/2010

7. Lawn, M.J. and Ishimatsu, T. (2003). Modeling of a stair-climbing wheelchair

mechanism with high single-step capability, IEEE Transactions on Neural Systems

and Rehabilitation Engineering, vol.11(3)



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