redesigning cycle rickshaw wheel using qfd technique...

SUST Journal of Science and Technology, Vol. 19, No. 5, 2012; P:60-70

Redesigning Cycle Rickshaw Wheel using QFD Technique to

Minimize Accident Probability and Severity

(Submitted: June 10, 2012; Accepted for Publication: November 29, 2012)

K. Nahar1, *M. M. Hossain

2, K. M. A. Haque

3, M. A. Islam

4, K. S. Hossain

5 and M. A. Khan

6

1-5Department of Industrial & Production Engineering, Rajshahi University of Engineering & Technology, Rajshahi, Bangladesh

6Akij Cement Company Ltd., Kadam Rasul, Narayongonj, Bangladesh *E-mail: [email protected]

Abstract

This paper reviews the possible problem areas of non-motorized means of travel in

Rajshahi city, particularly cycle rickshaw, with respect to the view of rickshaw pullers and

passengers; and severity analysis. Accidents are more frequent now a day mainly caused by lack

of rickshaw pullers’ adequate training and design of rear wheels; according to market analysis and

reviews. Violent accidents are occurred while the rickshaws drive beside one another and it is

observed that they made collisions and ultimately accident causes human injuries as well as cut

off several spokes of the wheel. Additionally spokes are generally broken down frequently during

riding on the rough roads. Redesigning of the wheel has been done on the basis of measured

maximum load. The dimension of the new model was decided after studying the carried load of

each spoke of the wheel. As five spokes were being used instead of forty two spokes, the

reliability of the wheel is being increased considerably due to increased rigidity of the spokes.

Hub was designed in such a manner that the extension portion of the wheel is no longer

responsible to make frequent accidents. As a result of changing design the problems are being

solved. This paper is also analyzing the cost factors of rickshaw as the customers are of very

diminutive income. A cost comparison with regular one is made.

1. Introduction

Cycle rickshaw is an important & major means of travel, particularly in small cities and amongst the urban

areas (For short journey lengths) in Bangladesh. These are light weighted environment friendly vehicle. The people

of certain class have these vehicles with affordable price as a principal income source. The mechanism of cycle

rickshaw is served as a technical platform that encapsulates fundamental of problems in mechanics, vehicle

dynamics, stability, motive power, etc. However in Bangladesh most rickshaws are assembled based on the general

ideas without investigating the loads and the load bearing capacities. This causes frequent technical failure of

rickshaws and due to lack of knowledge the rickshaw pullers are also involved in enhancing the accident probability.

There are not many researches related to rickshaw. Chowdhury et al (1996), Vikhashu (2007) and Nahar et al (2010)

addressed some technical problems related to rickshaw. However those are not adequate. This paper examines the

mechanics of the cycle rickshaw by considering the possible factors. Major problem area is identified as the wheel

of the cycle rickshaw. All dimensions and specifications of new model are then developed with computation of

mechanics.

2. Problem Selection

Market research is conducted to understand the present condition. To meet customer needs for the product

survey is done. During the survey some basic questions (See Appendix A) are asked to the rickshaw pullers and as

well as passengers. Based on the survey, problem related to wheels are identified as major problems and minor

problems and shown in table 1. Customer needs and their priority are provided in table 2.

Redesigning Cycle Rickshaw Wheel Using QFD Technique to Minimize Accident Probability and Severity 61

Table 1: Major (A) and Minor (B) problems

A Rear Wheel Axle rim spoke Seat Chain-sprocket

B Light hood Driver seat packing Foot rest

Table 2: Customer needs and their priority

Customer Needs No. of Customer Priority

Light Weight 11 3

Economy Cost 16 1

High Endurance Limit 9 4

Longevity 13 2

Reliability 7 6

Aesthetic 5 7

Comfort 8 5

Through this analysis it is identified that the major problem area is wheel with hub, spoke and ball bearing. 2.2

Process Analysis The Another type of analysis is Cause Effect Diagram (CE Diagram) that depicts defects, errors, or problems

which has been identified and begins to analyze potential causes of this undesirable effect. Among the types of CE

diagram the followings are being used to identify the problem region with their respectable causes i.e. Process

Analysis. This diagram provides the information of the process of making the wheel from idea generation to final

product development.

Fig. 1: Requirements for rim design

3. QFD (Quality Deployment Function)

The customers’ requirements must be translated into measurable design targets to identified critical parameter.

Relation among customers’ requirements and engineering specifications and relation within the engineering

specifications are represented in matrix form as quality function deployment (QFD).

Correlation legend

▲ Strong relationship

■ Medium relationship

● Weak relationship

62 K. Nahar, M. M. Hossain, K. M. A. Haque, M. A. Islam, K. S. Hossain and M. A. Khan

Fig. 2: QFD Matrix

Depending upon functional relationship with quality requirement- further design analysis is conducted.

4. Design Analysis and Selection

To redesign the existing product, the cycle rickshaw wheel, for reducing accident severity & probability, the

initial need is expressed in semantic language as a verbal request or requirement of the customers, in this case the

rickshaw pullers & the passengers. Through graphical and analytical analyses; a physical model is being established.

Some drawings are initially constructed considering possible problems & resolving techniques. Material selection is

done on the basis of some design criteria such as yield strength, ultimate strength, elongation, density, modulus of

elasticity, cost etc. Through mechanical analysis the design specifications are developed & correction over the layout

is made.

Measurements for mechanical property analysis consist of different dimensions of lengths, weight of different

parts and rickshaw self weight. Then the reaction/supporting loads at both rear and front wheels are determined

according to the law of mechanics. By using the reaction loads at each of the rear wheel’s the dimensions of the

spokes are being calculated, i.e., the length and width of each spoke. Length of each spoke is found from the

dimension of outer diameter of the hub. Outer diameter of the hub is determined by calculating the thickness of the

hub according to the law of mechanics as the inner diameter is known from selected bearing’s outer diameter.

4.1 Developing Ideas with Drawing Initially several rough drawings are made to figure out the ideas of resolving problems of cycle rickshaw

wheel.


Fig. 3: Initial drawing of wheel

The drawing shown in fig. 3 is done by only considering the ideas of defined problems of extended portion of

axle that causes the distortion of spokes of the wheels of other rickshaws. In that case the hub is designed in such a

way (in fig. 3) that the axle extension is no longer visible. After that the spokes are replaced by five equally spaced

spokes that are more reliable than spoke and are little subject to distortion.

But after developing this primary idea in the drawing the mechanical properties such as the material selection,

static and dynamic load carrying capacities, bearing life etc. are being considered to compute the specifications of

the spokes used in wheel and the hub’s required dimensions as well. The calculations show that the hub is not

properly designed shown in the fig. 3, because it uses only one bearing that reduces the bearing life much less than

the existing one and also caused by the increased bending moment with spokes at one end of the hub and only one

bearing at another end of the hub.

Fig. 4: Redesigned wheel

Redrawing of the wheel is prepared by taking into account the mechanics for rickshaw wheels and finalized

the drawing with specifications to generate physical model of wheels at fig. 4. The specifications of the modified

model are developed by calculating different force calculations according to the laws of mechanics. The area of each

spoke is calculated for the selected material from load applied to each wheel. The outer diameter of the hub is

determined by computing the thickness of the hub assuming the inner diameter as the outer of the bearings used with

hub. By getting two of the bearings in the hub which retains the bearing life more than the existing one and the

maximum bending moment for the eccentric placement of the spokes the thickness of the hub is being calculated.

4.2 Material Selection

After that the material selection is done considering some significant properties of different possible

materials. Possible materials those are nearly suitable for the wheel manufacturing purpose are selected and then

prioritized them according to the required material property for rim.

Priorities are given under score of 20 for each materials property. Over total priority of each material i.e. 200 score

the % of priority is calculated. Amongst three competitive materials Aluminium Alloy with certain composition,

which is conventionally used for rim manufacturing, is being selected in cycle rickshaw wheel manufacturing.

Properties of selected materials are provided in Appendix B in detail.

4.3 Mathematical Calculation 4.3.1 Design of Spoke

The testing result from universal testing machine for yield and failure of existing wheel shows that it can

sustain about 14000 N loads. On behalf of this capacity the new design of wheel is made.


Fig. 5: Sketch of load on each spoke The wheel is designed with five equally spaced spokes because more than five bars it causes reduction of

cross-section area of each; thus the reliability of each spoke. And for less than that number the cross-section area is

increased and thus the weight is also increased.

At equilibrium,

+∑Fy=0 so F' =3908.79 N

Now,

F' = σA = σbt, thus bt=15.39 mm2. Where, A=area of the wheel bar & σ=254 N/mm

2

If the breadth of each spoke, b=25.4 mm than the thickness of each spoke, t= 1.82 mm.

Having FS=3 for mild sh4ock of ductile material and with trial & error basis the breadth of each spoke is determined

as, b=25.4 mm and the thickness of each spoke, t= 1.82 mm.

4.3.2 Hub Design

Fig. 6: Redesigned hub

As the bearing is of the same number 6204, the designed wheel’s hub diameter (inner) is known.

The designed wheel’s hub diameter (inner) is known from bearing number. The minimum length of hub is

determined by required spaces for two bearings, one nut and clearance between two bearings. To determine the

thickness of hub it is required to calculate the forces on different point of the hub (Fig. 7), applied forces are F1 and

F2 and supporting loads are R1 and R2. Where the distances are AB=0.014m, BC=0.007m, CD=0.027m, DE=0.007m.

Fig. 7: Forces on hub

Fig. 8: Reaction forces on hub

By determining the value of R1 from the figure of right most corner (Fig. 8), the unknown loads over the hub

i.e. F1 & F2 are calculated. Formulating with laws of mechanics, R1=6015 N, F1=5503.7N, F2=8694.29N.


By using those values the thickness of hub is being determined with the established formula of maximum

bending moment. In the Figure 9 the lower portion of the hub is considered as simply supported beam with breadth

as same as the spokes breadth. Having maximum moment and with the known values of material strength and

breadth the part thickness of the hub is being determined. The formula is- Maximum bending moment, M= σI /C=

σbh2/6. By putting the known values, the unknown value i.e thickness of the hub, h, is determined as 7.2mm.

Fig. 9: Shear & Moment diagram for hub

4.3.3 Impact of the loads

Bearing life is calculated on basis of the loads that are practically applied to the wheel, that is, the load those

are calculated in earlier section. In this case existing bearings of number 6204 ball bearing are used.

Fig. 10: Forces on Bearing

Where,

Applied forces on each wheel bearings, F=194.32 kg

Sprocket weight, W=0.5 kg

Rickshaw puller’s pulling force, P=465kg

Distances, d1=d2=0.5715

Vertical reaction forces on bearings are, RV1 & RV2

Horizontal reaction forces on bearings are, RH1 & RH2

According to law of mechanics, over vertical & horizontal forces we get RV1=194.32 kg, RV2=194.57 kg,

RH1=232.5 kg & RH2 =232.5 kg. At point B of the Fig. 10 there are two bearings so that the forces on the bearing are

needed to calculate with respect to practically applied load. Practically applied loads are computed for each bar i.e.

F′ =620.3N & spoke support R1=954.54 N.

In the Fig. 10, F=F1+F2 and F1 & F2 are the loads applied through the bearings at point C and D. again from laws

mechanics we get F1=948.555N & F1=955.780N, where F= 194.32 kg is a calculated value of applied load on

bearings.



By using the forces on bearings the reaction forces of bearings are computed to determine the radial load of the

bearings.


Here the calculated values are Rv1=953.87N, Rv2=952.90N, Rh1= 1689.05N & Rh2=589.4N.

Now, Reaction at bearing D,

Rd=√(Rh12+RV1

2)=1788.93N

Reaction at bearing C, Rc=√ (Rh22+RV2

2)=1120.45N

Basic load rating for 6204 ball bearing,

C= 12700N, Co=6200N

With no axial thrust, X=1 & Y=0

and Frd=Fad = Rd=1788.93N

The equivalent dynamic load,

P = XFrd+YFad= 1788.93N

Bearing life at C,

Ld = (C/1.5P)3= 106.01 million rev

and Lhd = L*106/60*60= 40.9 months

With no axial thrust,

X=1 & Y=0, Frc=Fac = Rc=1120.45N

The equivalent dynamic load,

P = XFrc+YFa = 1120.45N

Bearing life at D, Lc= (C/1.5P)3

= 431.5 million rev and Lhc = L*106/60*60= 166.6 months.

The life of the bearings is 40.9 months and 166.6 months at points D and C respectively.

5 Cost Comparisons

By considering monthly production 2,400 Pc, all fixed costs and variable costs per product is calculated, thus

the total cost is calculated. First set of cost calculation is for existing product and next set shows the cost for

redesigned product.

Fixed cost:

Design: Cost of design: TK 10,000/15 year

Cost per unit production: TK 0.023

Table 3: Machineries cost

Type of M/C: Rim M/C Drill machine Roller machine But welding

machine

Polishing

machine

Office

Furniture

Cost of buying: Tk 170,000/15 yr Tk 80,000/12yr Tk 90,000/12yr Tk 300,000/15yr Tk 15,000/5yr Tk 150,000/15yr

No of machine: 1 2 1 1 2

Total cost: Tk 170,000 Tk 160,000 Tk 90,000 Tk 300,000 Tk 300,000

Salvage value: Tk 25,000 Tk 10,000/12 yr Tk 10,000/12 yr Tk 60,000 Tk 1,000

Total depreciation: Tk 9,666/yr Tk 972/yr Tk 6,666/yr Tk 16,000/yr Tk 5,600/yr

Per unit cost: Tk 0.34 Tk 0.40 Tk 0.23 Tk 0.55 Tk 0.194 Tk 0.35


Total Fixed cost: TK 1.737 per unit

Variable cost:

Table 4: Cost of Raw Material

Raw Material Buying cost per kg Per unit required

material Total cost

Mild Steel Tk 70/kg 1.5kg Tk 105

Nickel Tk 70/kg 100gm Tk 7

Table 5: Other Variable Cost

Total cost of existing product: TK 365.75 per unit.

Fixed cost:

Design Cost:

Cost of design: TK 40,000/15 year

Cost per unit production: TK0.0926

Table 6: Machineries cost

Type of M/C: Lathe machine

High pressure

metallic molding

machine

But welding

machine

Polishing

machine Office Furniture

Cost of buying: Tk 300,000/15yr Tk 500,000/10yr Tk 300,000/15yr Tk 15,000/5yr Tk 150,000/15yr

No of machine: 2 1 1 2

Total cost: Tk 600,000 Tk 500,000 Tk 300,000 Tk 300,000

Salvage value: Tk 40000 Tk 80,000 Tk 60,000 Tk 1,000

Total

depreciation: Tk 34666/yr Tk 42000/yr Tk 16,000/yr Tk 5,600/yr

Per unit cost: Tk 1.2 Tk 1.458 Tk 0.55 Tk 0.194 Tk 0.35

Total fixed cost of the designing product: TK 3.844

Variable cost:

Table 7: Cost of Raw Material

Raw Material Buying cost per kg Per unit required

material Total cost

Mild Steel Tk 70/kg 3.5kg Tk 245

Nickel Tk 70/kg 200gm Tk 14

Table 8: Other Variable Cost

Worker Administration Tax &

Rent Transport Electricity Total

Unit

Cost

Outsourced

Materials

Hub Spoke Set

50000 85000 50000 45000 12000 242000 100.83 Tk 70 Tk 60

Total cost of redesigned product: TK 363.67 per unit.

Worker Administration Tax &

Rent Transport Electricity Total

Unit

Cost Outsourced Materials

Hub Spoke Set

80000 100000 50000 50000 12000 292000 121.66 Tk 70 Tk 60


6. Results

The redesigned wheel is shown in Fig. 4. Specifications of the wheel, hub, bearings are as: number of spokes, 5;

thickness of each spoke, 1.82 mm; breadth of each spoke, 25.4 mm; rim is same as the existing one; hub diameter

(inner) is same as 6204 ball bearing’s outer diameter; hub thickness, 7.2 mm, the expected life of the bearings are

40.9 months and 166.6 months. Costs of existing and redesigned model are around Tk 366 and Tk 364 respectively.

7. Discussion and Conclusion

Redesigned wheels are constructed at the university lab. Although unit cost does not decrease significantly

comparative with existing model it satisfies customer requirement with desired quality. It is tested for functionality.

At the initial stage it is found that the wheels are performing well with comfort to the rickshaw puller. This hub

design does not have any extended portion as the existing extension of rear axle. This will prevent the collision with

the other rickshaws while overtaking each other. It is beyond this study to investigate the reliability, longevity,

product life cycle and accident probability due to long cycle time or product life cycle. However it is believed that

due considering the engineering design criteria, this redesigned wheel will serve the following purposes:

• Redesigned wheel will reduce the accident severity.

• This will minimize the problem of spoke distortion and axle position.

• Wheel longevity will be comparatively high.

• Wheel cost is reasonable.

• Outlook is good enough.

Overall it can be said that the redesigned wheel with accessories are good enough to prevent the accident

severity and the maintenance cost will be reduced.

References

[1] Ullman D. G., The Mechanical Design Process, Second Edition, PP 293-308, McGraw-Hill, Inc.

[2] Beer F. P. and Johnston E. R. Jr., Vector Mechanics For Engineers (Statics &Dynamics), third Edition, Tata

McGraw-Hill, Inc.

[3] Chowdhury A. R., Prahan, C. K. and Mukherjee A. K., (1996), Evaluation of occupational health problem of

cycle rickshaw pullers and redesign of cycle rickshaw on economical principles, Redesign of cycle rickshaw.

[4] Vikhashu S., Cycle Rickshaw Project Research and Finding Product design Department, , Srishti School of

Art Design and Technology, [2007]

[5] Edwards, K. S. Jr. and Mckee R. B., Fundamentals of Mechanical Component Design, [1991] EWD.,

McGraw-Hill, Inc.

[6] Nahar K., Khan M. A. and Hossain K. S., (2010), “Redesigning Cycle Rickshaw Wheel to Minimize Accident

Probability and Severity”, Unpublished B.Sc. Engg. Thesis, Rajshahi University of Engineering &

Technology, Rajshahi.

[7] Pytel A. and Singer F. L., Strength of Materials, Fourth Edition, Harper & row.

[8] Hasin M. A. A., Quality Control and Management, pp 40-48, 84-86, 102-112, Bangladesh Business Solutions.

[9] Montgomery D. T., Introduction to Statistical Quality Control, Third Edition, pp 154-156, John Wiley &

Sons.

[10] Allen J. S., Kirskna D. and Wilson D. G., Human Power, Technical Journal of the IHPVA, Number 53, Spring [2002].

[11] Mondal B. N., Green Solution to the Urban Transport System, Research planning & business Dept), Central

Mechanical Research Institute India.

[12] Gadepalli S, (2006), Rickshaw in the new millennium, daily star june 30, 2006

[13] http://www.nariphaltan.virtualave.net/MAPRA.pdf (17/10/2010)

[14] http://www.alibaba.com/showroom/cycle-rickshaw.html (17/10/2010)

[15] http://www.injuryjournal.com/article/S0020-1383(05)00516-4 (17/10/2010)


[16] http://www.cmse.ed.ac.uk/MSE3/Topics/MSE3-nonferrous.pdf (17/10/2010)

[17] Error! Hyperlink reference not valid.

[18] http://www.Rickshaw/Bicycle%20Components,Bicycle%20Saddles

[19] http://www.Rickshaw/Pedicab%20Rickshaws.mht

[20] http://www.Rickshaw/Rickshaw%20Manufacturing.mht

[21] http://catalog.indiamart.com/cat_ifmare.htm

[22] http://www.tntech.edu/me/courses/Zhang/ME30103110/Chap11pt4.ppt


Appendix A (Questionnaire)

To identify the problems related to cycle rickshaw, some basic questions were asked to the rickshaw puller,

passengers and vendors. The questions are provided here.

1. What are the major problems that you face with your rickshaw?

2. How longer the rickshaw give service?

3. How much reliable it is?

4. What about the failure rate?

5. How much load you can carry?

6. Do you feel that the maintenance cost is ok with you?

7. Do you think rickshaw need improvement?

8. What parts should be modify and why?

Many other effective questions are done to clarify exact needs during market research.

Appendix B (Priority to Materials) SI Materials Property Stainless steel Given priority

1 Tensile strength, MPa 500 12

2 Yield strength, MPa 200 5

3 Endurance limit, GPa 280 14

4 Elongation, % Not found 0

5 Modulus of elasticity, 200 GPa 15 GPa

6 Density, g/cc 7.5-8.5 12

7 Melting temp., ºC 2500 5

8 Cost per lb 0.8-2.5 12

9 Hardness, BHN 52 2

10 Corrosion 10

Total priority 101

% over total priority 40.5

SI Materials Property Al Alloy (Conv.) Given priority




4 Elongation, % 39.9% 5


6 Density, g/cc 7-8 11


8 Cost per lb .2-.5 15

9 Hardness, BHN 150 16

10 Corrosion 7

Total priority 111

% over total priority 55.5

SI Materials Property Al Alloy Given priority




4 Elongation, % 15-25% 8


6 Density, g/cc 3 5


8 Cost per lb 3-4 7

9 Hardness, BHN 52-100 12

10 Corrosion 14

Total priority 86

% over total priority 43

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