Mechanical Climbing Wheelchair

DESIGN AND FABRICATION OF STAIRCASE

CLIMBING WHEELCHAIR

INTERNSHIP PROJECT REPORT

Submitted by

NITISH KUMAR

JANMEJAY JAISWAL

IN

AEROSPACE ENGINEERING

INDIAN INSTITUTE OF SPACE SCIENCE AND

TECHNOLOGY

THIRUVANANTHAPURAM

July 2011

IIST Thiruvananthapuram Page ii

BONAFIDE CERTIFICATE

This is to certify that this project report entitled DESIGN AND FABRICATION

OF STAIRCASE CLIMBING WHEELCHAIR submitted to Indian Institute

of Space Science and Technology, Thiruvananthapuram, in connection with the

institute internship program is a bonafide record of work done by Nitish Kumar

and Janmejay Jaiswal under my supervision at the Indian Institute of Space

Science and Technology from 27th

June 2011 to 5th

August 2011

Dr. K. Kurien Issac

Senior Professor and Head, Department of Aerospace Engineering

Indian Institute of Space Science and Technology

Place: Thiruvananthapuram Date: 8th August, 2011

IIST Thiruvananthapuram Page iii

Table of Contents

ACKNOWLEDGEMENT _______________________________________________ v

ABSTRACT ___________________________________________________________ vi

LIST OF FIGURES ___________________________________________________ vii

LIST OF TABLES _____________________________________________________ ix

Chapter 1 Introduction and Objectives ____________________________________ 1

Chapter 2 Working of mechanism ________________________________________ 2

Chapter 3 Detailed Design of Mechanism __________________________________ 6

3.1 Design of Slider _________________________________________________________ 6

3.1.1 Strip 1 ______________________________________________________________ 6

3.1.2 Strip 2 ______________________________________________________________ 7

3.1.3 Spacer ______________________________________________________________ 8

3.1.4 Steel Ball____________________________________________________________ 8

3.2 Design of link of four bar mechanism _______________________________________ 9

3.2.1 Drawing of link of 4 bar mechanism ______________________________________ 9

3.2.2 Drawing of connecting rod of 4 bar mechanism ____________________________ 10

3.3 Specification of gear ____________________________________________________ 10

3.4 Specification of Lever arm _______________________________________________ 11

Chapter 4 Fabrication of Slider __________________________________________ 12

Chapter 5 Experiment _________________________________________________ 14

Chapter 6 Conclusion & Recommendation ________________________________ 16

References ___________________________________________________________ 18

APPENDIX __________________________________________________________ 19

1. Drawing of Outer Plate _________________________________________________ 19

2. Drawing of Intermediate plate ___________________________________________ 20

IIST Thiruvananthapuram Page iv

3. Drawing of Inner plate _________________________________________________ 21

4. Drawing of slot connected to intermediate plate _____________________________ 22

5. Drawing of slot connected to Inner plate ___________________________________ 23

6. Drawing of strip1 of slider ______________________________________________ 24

7. Drawing of strip2 of slider ______________________________________________ 25

8. Solid Model of Stair climbing Mechanism__________________________________ 26

9. Complete Solid Model of Stair climbing Wheelchair _________________________ 28

IIST Thiruvananthapuram Page v

ACKNOWLEDGEMENT

The completion of this project and this report owes itself to the invaluable help and support of

Dr. K. Kurien Issac, Senior professor and Head, Department of Aerospace Engineering, Indian

Institute of Space Science and Technology. We would also like to express our gratitude towards

Mr. Thomas Varghese, Manufacturing lab in-charge, Indian Institute of Space Science and

Technology, for his assistance in fabrication and other valuable inputs.

IIST Thiruvananthapuram Page vi

ABSTRACT

In this project, we aim at designing and fabricating the entire mechanism. The basic working of

mechanism is explained. We made a detailed design of mechanism for climbing wheelchair.

Solid model of entire mechanism is also made. We also fabricated slider part of mechanism.

Finally all the fabricated parts of slider is assembled.

IIST Thiruvananthapuram Page vii

LIST OF FIGURES

Figure 1: Isometric view of mechanism of staircase climbing wheelchair

Figure 2: Initial configuration

Figure 3: Descending of wheelchair

Figure 4: Sliding up the outer column

Figure 5: Rising of wheelchair

Figure 6: Sliding up of wheelchair

Figure 7: Top view of Strip 1

Figure 8: Front view of Strip 1



Figure 11: Cross sectional view of assembled slider

Figure 12: Link of mechanism

Figure 13: Connecting link of mechanism

Figure 14: Top view of fabricated Strip 1

Figure 15: Top view of fabricated Strip 2

Figure 16: Front view of fabricated slider

Figure 17: Top view of fabricated slider

Figure 18: Skeleton view of Slider

Figure 19: Sine bar along with slip gages (gauge blocks)

Figure 20: Sine Table

IIST Thiruvananthapuram Page viii

Figure 21: Isometric view of I-shape slider

Figure 22: Front view of stair climbing Mechanism

Figure 23: Top view of stair climbing Mechanism

Figure 24: Side view of stair climbing Mechanism

Figure 25: Isometric view of stair climbing Mechanism

Figure 26: Isometric view of stair climbing Wheelchair

Figure 27: Front view of stair climbing Wheelchair

Figure 28: Top view of stair climbing Wheelchair

Figure 29: Side view of stair climbing Wheelchair

IIST Thiruvananthapuram Page ix

LIST OF TABLES

Table 1: Specification of Lever arm

Table 2: Specification of gear

Table 3: Value of µ between different surfaces

IIST Thiruvananthapuram Page 1

Chapter 1 Introduction and Objectives

The invention of wheelchair has given independence to many people who would normally have

been totally dependent on other. However problem with wheelchair comes when people have to

go through stairs. In order to address this problem, many people have made mechanism of

different design to climb wheelchair along stairs. One of the designs is patented by G.H.Green.

His wheelchair uses ingenious mechanism to climb by making two arms move along a trajectory

similar to that of a foot. This includes complex mechanism driven by motor. This mechanism is

simplified by Supratim Naskar in his B. Tech. project at IIST in 2011.

The aim of our project is to make a detailed design of this simplified mechanism of staircase

climbing wheelchair and fabrication of its parts. This includes fabrication of different parts of

mechanism which would be done in manufacturing lab, modifying some of the existing design.

The solid modeling of different parts of mechanism would be made using CAD software.


Chapter 2 Working of mechanism

The figure below shows how this mechanism is designed to make the wheelchair climb up a

staircase.

Lever arm 1

Lever arm 2

Stell ball hole

Gear 1 Gear 2

Intermediate column

Outer slider column

Inner column

Protrusion

Vertical Prismatic joint

Platform for wheel

chair

Figure 1: Isometric view of mechanism of staircase climbing

wheelchair


Figure 2 shows the initial configuration. Now, lever arm 2 is pulled down. This descends the

wheelchair on the staircase. The inner plate can easily move vertically down along the vertical

prismatic joint between the intermediate plate and the inner plate. The wheelchair is attached to

the inner plate directly, hence as the inner plate moves down the wheelchair also moves down.

When the chair has completely moved down, lever arm 2 is locked at that position so that the

chair is locked in this position. In this configuration (fig. 3), the inner column is on the staircase

and is supporting the entire weight of the system.

Figure 2: Initial configuration

Figure 3: Descending of wheelchair


Now when the wheelchair is locked in this position, outer column can only slide along the slope

of the staircase through the intermediate column. As lever arm 1 is pushed backward, gear 1

rotates in anti-clockwise direction, forcing gear 2 to rotate in a clockwise direction. The link

connecting gear 2 and the slider (outer) column is fixed with gear 2 and is pivoted at the center

of gear 2. So as gear 2 rotates clockwise, the link also rotates clockwise and this causes slider

column to slide up along the intermediate column. When the slider column has moved along the

slope of the staircase, lever arm 1 is locked at that position and the slider column stays there as

shown in fig.4.

We unlock lever arm 2 and push it up. This raises the wheelchair from the staircase. The raising

happens as the bearings forces the protrusions on the inner plate to move up. When the chair has

completely moved up, lever arm 2 is locked at that position so that the chair is locked in that

elevated position. In this configuration the slider column is on the staircase and is supporting the

entire weight of the system (fig.5).

Figure 4: Sliding up the outer column


Now when the wheelchair is locked in the lifted position, it can only slide along the slope of the

staircase through the slider column. As lever arm 1 is pushed forward, gear 1 rotates in a

clockwise direction, forcing gear 2 to rotate in an anti-clockwise direction. Due to this, the link

also tries to rotate anti-clockwise but the slider column on the other end of the link is supported

on the stairs and cannot move. This provides a reaction force on the shaft of gear 2. This causes

the chair to slide up along the slider column and the initial configuration is restored as shown in

fig.6.

Figure 5: Rising of wheelchair

Figure 6: Sliding up of wheelchair


Chapter 3 Detailed Design of Mechanism

Design of different parts of mechanism like outer plate, intermediate plate, inner plate, slot

connected to intermediate and inner plate and links of four bar mechanism are included in the

Appendix section. In this chapter, we give the design of slider which has to be fabricated.

3.1 Design of Slider

Slider is designed using Steel balls and Aluminium strips. Steel balls are kept on 3.5mm thick

Aluminium strip (strip 1) by making a tapered hole. In order to make ball rotate in its place, thin

Aluminium strip of 1.5mm strip (strip 2) is used as a cage.

3.1.1 Strip 1

Design of strip 1 is shown below.




As shown in above figure, Steel ball of 6mm diameter is kept on tapered hole of strip 1. Taper

angle of hole is 45 . Also, through hole of 3mm diameter is made at equal interval to fix strips 1

& 2 using countersunk bolt M3x6.

3.1.2 Strip 2

Strip 2 acts as a cage to keep the ball in tapered hole. Its drawing is shown below.

Since we are using countersunk bolt, tapered hole is made to fit the bolt. Another inverted

tapered hole is made so that upper face of ball will come out of hole.

CSK bolt hole Stell ball hole




3.1.3 Spacer

To prevent the contact of ball with strip 2, we use nylon spacer of 1.7mm thickness. If spacer is

not used, ball would be in contact with both the plates and pure rolling of ball would not be

possible.

3.1.4 Steel Ball

Steel balls are placed on 45 chamfer, so that it makes only point contact in 2D which makes it to

roll when chair slides over the slider. The idea behind placing balls at 45 chamfer is to convert

the sliding friction into rolling friction, when tangential force is applied which makes it to roll in

its place and hence reduce the friction.

Stell ball Strip 2

Strip 1

Spacer

Figure 11: Cross sectional view of assembled

slider


3.2 Design of link of four bar mechanism

It has been observed during designing process that as four bar mechanism is moving, connecting

link was obstructing with prismatic joint. To avoid it, we design connecting link of C-shaped.

3.2.1 Drawing of link of 4 bar mechanism

In this link, one end is connected using Mx10 nut and bolt to the intermediate plate while other

end is connected to connecting link of four bar mechanism.

Figure 12: Link of mechanism


3.2.2 Drawing of connecting rod of 4 bar mechanism

This connecting link is connected to link shown in section 4.2.2.

3.3 Specification of gear

Module 2

Diametrical Pitch 12

Nominal face Width 25mm

Diameter of gears 100mm

Pressure angle 20

Teeth Depth 10mm

Figure 13: Connecting link of mechanism

Table 1


3.4 Specification of Lever arm

We use two lever arms 1 and 2 for horizontal and vertical movement respectively.

Lever arm Length (mm)

1 600

2 900

Table 2


Chapter 4 Fabrication of Slider

Strip 1 of slider of 6082 T6 grade Aluminium of size 40mm x 3mm cross section and 1000mm

length was available. Since we required 35.6mm x 3mm cross section, vertical milling operation

is used to reduce width of Aluminium flat bar from 40mm to 35.6mm.

Due to non-availability of 35mm x 2mm cross section Aluminium flat bar, Aluminium L-bar of

35mm width on both sides and 2mm thickness is obtained. From this L-bar, we obtained 35mm x

2mm cross section strip 2 flat bar by cutting L-bar using hex saw.

Steps involved in making slider

Using Height gage, marking on strip 1 is done at equal interval where hole is to be made

as shown in fig.7.

Then using C-clamp, we clamp both the strips at three points along the length.

First, we drill through hole of diameter of 2mm at the marked points, where steel ball

would be kept, through the entire length of clamped strips.

Through holes of diameter 2.5mm is drilled at the marked points where countersunk bolts

would be fitted.

Since standard drill bit have 118 tool angle, we grind it to obtain 90 tool angle.

Now we chamfer the ball hole using 6.5mm drill bit with 90 tool angle on strip 1 as

shown in fig.8.

Tapping of all 2.5mm diameter holes in strip 1 is done using M3 tap manually.

Figure 14: Top view of fabricated

Strip 1


Strip 2


Using same 6.5mm drill bit, we chamfer CSK bolt hole in strip 2 as shown in fig.9.

We also chamfer ball hole in strip 2 using 8mm drill bit with 90 tool angle.

To make 1.7mm thick and 10mm diameter spacer having 3mm hole at center, we use

Nylon rod of 50cm length and 10 mm diameter. Then using turning process in lathe we

drill hole of 3mm diameter through the center of Nylon rod. Again using turning process

we cut 1.7mm thick spacer from rod.

Assembly of the parts of slider is done


slider Figure 16: Front view of fabricated

slider

Figure 18: Skeleton view of Slider


Chapter 5 Experiment

In order to know how much advantage slider giver over without slider, we found experimentally

the coefficient of friction (µ) between slider and Aluminium strip & coefficient of friction (µ)

between two Aluminium strips.

Experiment

To find µ, we use Sine table and slip gages are used to measure height as shown in figure. Now

on the Sine table, slider is clamped and it is kept at some angle using slip gages. Aluminium strip

is kept on inclined slider such that it doesn’t slide over slider. Now height ‘h’ is increased by

1mm in steps using slip gages until Aluminium strip starts moving on the slider. At this height,

height ‘h’ is measured. Since the distance between centers of ground cylinder of sine table ‘l’ is

150mm, inclined angle (also called ‘angle of repose’) is found using

=arcsine (

)

Figure 19: Sine bar along with slip

gages (gauge blocks) Figure 20: Sine Table


Same procedure is repeated by clamping Aluminium strip on sine table and keeping another

Aluminium strip on it.

Now we can find coefficient of friction µ using

µ=tan

Observation

Metal Pair Height ‘h’(mm) (degree) µ

Slider-Aluminium Strip 29.5 11.34 0.2

Aluminium-Aluminium

Strip

41 15.86 0.284

Result

From the above experiment, it is observed that coefficient of friction is decreased by 0.084 by

using slider in mechanism.

Table 3: Value of µ between different surfaces


Chapter 6 Conclusion & Recommendation

The solid model of mechanism is successfully done to meet the objective of project. We have

also fabricated the slider. Due to time constraint, all the parts of mechanism could not be

fabricated. But now since the detailed design is made, other parts of mechanism can be made.

After designing and fabricating the slider, we observed following drawbacks.

The material we have used to make slider is aluminum which is much softer then steel balls, due

to which when large load is applied on the slider, chamfer on which steel ball is kept will be

deformed and it will form shape in which the ball will just fit which will cause jamming and

hence friction will increases.

Also for drilling holes on strip, machine does not have long bed which causes some part of strip

to hang out of the bed. This also causes mismatch during assembly of different part of slider.

In course of using the slider, wear and tear will we more which causes increase in friction.

Following are remedy to overcome above problem.

Material used must be harder than steel ball which will decrease friction and reduce wear and

tear. We could have used mild steel instead of Aluminium in slider but then machining of mild

steel would be difficult and caused lots of vibration. This would create dimension mismatch

between two strips of slider.

For machining, long bed must be used and work piece must be tightly clamped and sharp tool

must be used and burrs should be removed manually.

Improvement in design

Design can be improved by using ball bearing instead of slider by making I-shaped slider and

place ball bearing at the ends of I and place this structure in the track which ensures the free

rotation of ball bearing and also provide the track for the movement of chair. This design will

reduce manufacturing cost significantly and also reduces the friction drastically and hence less

effort will we required for movement.


Ball Bearing

Figure 21: Isometric view of I shape slider


References

[1] John J. Uicker, Gordon R. Pennock ,Joseph E. Shigley, Theory of Machines and

Mechanisms, Oxford University Press, New Delhi,2009

[2] http://www.catia.com.pl/

[3] Supratim Naskar, Design of a wheelchair capable of climbing staircases using only user

effort, IIST, 2011

http://www.catia.com.pl/


APPENDIX

1. Drawing of Outer Plate


2. Drawing of Intermediate plate


3. Drawing of Inner plate


4. Drawing of slot connected to intermediate plate


5. Drawing of slot connected to Inner plate


6. Drawing of strip1 of slider


7. Drawing of strip2 of slider


8. Solid Model of Stair climbing Mechanism

Figure 22: Front view

Figure 23: Top view


Figure 24: Side view

Figure 25: Isometric view


9. Complete Solid Model of Stair climbing Wheelchair

Figure 26: Isometric view

Figure 27: Front view


Figure 28: Top view

Figure 29: Side view

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Mechanical Climbing Wheelchair

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