I

FFiinnaall RReeppoorrtt

Siawash Sayad

TTrraannssmmiissssiioonn ffoorr aa

PPoowweerr AAssssiisstteedd BBiiccyyccllee

MMEEnngg EEnneerrggyy EEnnggiinneeeerriinngg

SScchhooooll ooff EEnnggiinneeeerriinngg aanndd MMaatthheemmaattiiccaall SScciieennccee

22001111//22001122

SSuuppeerrvviissoorr::

PPrrooff.. KKeeiitthh PPuulllleenn

CCoo--oorrddiinnaattoorr::

MMrr.. RRoonn DDeennnniiss

II

Acknowledgements

Thanks to Prof. Pullen and Mr. Ron Dennis for giving me this opportunity to work on

one of the most exciting projects. This was probably the best project I have ever worked on.

And I also thank you for supporting me and understanding me during the difficult time I had

when I lost my USB. It was a great experience to work with you and Mr. Ron Dennis. I would

like to thank Dr. Yen, Prof. Nouri, Gary and other lab technicians for their advice and

support. Special thanks to my family and friends who were on my side.

III

Abstract

The aim of this project was to design and manufacture a low cost transmission

system for the power assisted bicycle, which would be used in sub Saharan African countries

to transport patients to the nearest health centre. A Continuously Variable Transmission is

used to provide appropriate speed for different road surfaces. The transmission system is

designed and manufactured. The ambulance bicycle is ready to be tested. Further

suggestions and investigations are provided for future research on this project.

IV

Table of Contents

Acknowledgements II

Abstract III

Table of contents IV

List of tables V

List of figures VI

List of symbols VII

1. Introduction..................................................................................................1

2. Objectives.....................................................................................................2

3. Review of previous work...............................................................................2

4. Road Load Power..........................................................................................3

5. Transmission Design and Selection................................................................5

5.1 Nuvi.nci (CVT).......................................................................................6

5.2 Ninja Pocket Bike (CVT).........................................................................7

5.3 Drive ratio calculations.........................................................................8

5.4 Transmission concept design................................................................9

5.5 CAD Models & Final Design.................................................................11

6. Component Selection ..................................................................................13

6.1 Chain selection......................................................................................13

6.2 Chain testing.........................................................................................14

6.3 Sprocket selection.................................................................................16

6.4 Bearing Selection..................................................................................18

6.5 Shaft Selection......................................................................................18

7. Fatigue Analysis...........................................................................................19

7.1 Shear force & Bending moment............................................................19

7.2 Fatigue & Stress Analysis......................................................................22

7.3 Centre of Gravity...................................................................................25

8. Cost Analysis ..............................................................................................26

9. Manufacturing process.................................................................................27

10. Sustainability of two stroke engine..............................................................30

11. Conclusion ..................................................................................................31

V

12. Recommended future work............................................................................31

13. References.....................................................................................................32

14. Bibliography...................................................................................................33

15. Appendix.........................................................................................................33

Appendix A.....................................................................................................33

Appendix B.....................................................................................................35

Appendix C.....................................................................................................38

Appendix D.....................................................................................................41

AppendixE......................................................................................................44

VI

List of Tables

Table no Title Page no

3.1 Review of previous work 2 4.1 Friction coefficient 3 5.1 Minimum speed 6km/h 8 5.2 Maximum speed 25km/h 8 6.1 Sovereign 08 (ISO 606) Simplex 13 6.2 First chain reduction 13 6.3 Second chain reduction 13 6.4 Pitch circle diameter 16

VII

List of Figures

Figure no Title Page no

1.1 Pregnant woman on a bicycle ambulance 1 1.2 Bicycle ambulance on a rough road 1 4.1 Friction forces acting on the bicycle ambulance 3 4.2 Graph power against velocity 4 5.1 Nuvinci CVT CAD model 6 5.2 Nuvinci CVT 6 5.3 Synchronous belt 7 5.4 Ninja pocket bike CVT 7 5.5 Transmission design 1 9 5.6 Assembly drawing of concept 1 9 5.7 Transmission design 2 10 5.8 Assembly drawing of concept 2 10 5.9 Engine 11 5.10 Continuous Variable Transmission 11 5.11 Bicycle frame 11 5.12 Assembly of transmission system mounted on the rear wheel 11 5.13 Exploded view of transmission design 12 6.1 Chain sample 14 6.2 Chain set up 14 6.3 Chain test diagram 15 6.4 Chain failure 15 6.5 No hub 16 6.6 Hub on one side 16 6.7 Hub on both sides 16 6.8 Stress distribution on 37 teeth sprocket is based on Von Mises method 17 6.9 Stress distribution on 11 teeth sprocket based on Von Mises method 17 6.10 Pillow block bearing 18 6.11 Carbon steel shaft 18 7.1 Shaft design 19 7.2 Free body diagram 20 7.3 Shear force & bending Moment diagram ZX axis 20 7.4 Shear force & bending Moment diagram YX axis 21 7.5 Bending stress 22 7.6 Shear stress 23 7.7 Goodman diagram 24 7.8 Reaction forces 25 7.9 Centre of Gravity including the trailer 25 8.1 Project cost 26 8.2 Parts cost 26 9.1 Materials and components 27 9.2 Base frame 27 9.3 Drilling holes 28 9.4 Testing the bracket on the bicycle 28 9.5 Bracket is welded and ready to mount 28 9.6 Mounting the engine on the rear wheel of the bicycle 28 9.7 Mounting the bearings on the CVT on the main frame 29

VIII

List of Symbols

% percentages

Shear stress

stress ± Plus minus, range between £ pounds money ° degree celcius Ab Bicycle frontal area C of G Centre of Gravity CD drag coefficient CR rolling resistance CVT Continuous Variable Transmission D diameter d diameter fig Figure g Gravity ICE Internal combustion engine Ix second moment of inertia KF stress concentration factor Km/h Kilometers per hour KR Reliability factor KS Size factor KW Kilowatt M Mass, Bending Moment m meter Max Maximum Min Minimum mm millimeters MR, H, V Moment: resultant, horizontally, vertically N Number of teeth, Newton Nm Newton meter P Chain Pitch Pr Power r radius R Reaction forces RH Reaction force horizontally RPM Revolution Per Minute RV Reaction force vertically S Shear force Se Fatigue strength SU Ultimate tensile strength T Tension, Torque V velocity W weight x axis, direction, unknown y axis, direction θ angle ρa density of air Σ Sum

1

11 IInnttrroodduuccttiioonn

Transport is a major issue in rural area of sub Saharan Africa. 65% of the population in Africa

are living over 10 km away from the closest clinic or health centre [1]. In rural parts of Africa

people suffer and die from Aids, HIV, maternal mortality and many more diseases. The main

reason is because there is not much public emergency transport and they cannot afford to

pay for the private transport to take them to the nearest clinic or hospital. The majority of

people travel by foot, bull and cart, and carrying the patients on the bicycle, which is time

consuming, inconvenient and unstable.

Bicycle ambulance is one of the solutions, which had a significant impact to this problem it

saved hundreds of lives. Bicycles are crucial form of transport in developing countries and

are commonly used for transportation and goods.

Developing Technology (DT) [2] is a UK charity which works along with the other workers and

societies to improve access to the clinics and hospitals for people living in rural locations in

Zambia, where there is no transport. Ambulance bicycles are used for shorter journeys.

However, due to poor road condition considerable amount of human power is required to

move the bicycle and the trailer forward. To update this, a supplementary power unit

system can be attached to the wheel via a transmission system.

Figure1.1 Pregnant woman on a bicycle ambulance[3] Figure1.2 Bicycle ambulance on a rough road[4]

2

22 OObbjjeeccttiivveess

The main objective of this project is to design a transmission with gear change for the back

wheel of the bicycle with a small internal combustion engine (ICE), which will be used on the

rough road condition or inclined road to transport the emergency patients to the nearest

healthcare centre.

The power assisted bicycle ambulance obligates to meet the following condition.

Using a small (ICE) engine of 1KW and at the high gear it should not exceed 25km/h

and a low gear 6km/h, the bicycle and the trailer mass should not be more than

300kg.

Low cost manufacturing of £150, easy to repair, parts available in developing

countries.

Using Continuous Variable Transmission to provide suitable speed for different road

surfaces.

Design & mount the engine and transmission assembly on the bicycle.

Making use of pedals in case of failure in the engine or shortage of fuel.

33 RReevviieeww ooff pprreevviioouuss wwoorrkk

Engine (RPM) Power (kW) Torque (Nm) Speed (km/h)

Max Torque 1108 0.44 3.79 6

Max Power 1605 0.59 3.48 25

Table 3.1[5]

These results are taken from the previous work which was done by a colleague.

The maximum power is shown 0.59 kW which produce the maximum road speed of

25 km/h or 6.94 m/s and for the maximum torque the minimum road speed of 6km/s or

1.67 m/s which is the lowest speed required for the bicycle to stay upright in the flat bitumen surface.

‘‘In sand, the maximum speed that engine can produce is 6 km/h or 1.67 m/s at flat

surface and the minimum speed is 2 km/h or 0.56 m/s at 12% incline surface. The

maximum torque which the bicycle ambulance can produce is 3.85 Nm at 0.44 kW at

maximum speed of 21 km/h in the flat bitumen surface.’’[5]

The table 3.1 shows the required power for different inclined road conditions. The first gear

speed limit should be 6km/h and the maximum speed is required to be 25 km/h.

3

44 RRooaadd LLooaadd PPoowweerr

Road load power level is a handy reference to determine power assisted bicycle engine, the

power required to ride a power assisted bicycle on different road conditions and different

speed. Road load power over comes the rolling resistance which arises from the rolling

resistance of the bicycle tires, the aerodynamic drag of the bicycle and slope resistance.

Rolling resistance and drag coefficient CR and CD respectively as it is shown in fig 4.1. [6]

[Equation 4.1]

Drag Force

Slope resistance

Rolling Resistance Force

Figure 4.1 Friction forces acting on the bicycle ambulance

Generally the road condition in Zambia is extremely poor. Mainly in the countryside, less

than a quarter of the road network is in a good condition and more than 60% of the country

is in a poor condition [7]. There might be improvement in the future but in recent times it is

not in a good condition. The research is mainly on four types of road conditions. The four

rolling frictions of the bicycle tires were provided by (Mr Ron Dennis) [8].

Road condition

Rolling friction coefficient (CR)

Asphalt 0.01

Gravel 0.016

Rough road 0.021

Soft sand 0.1

Table4.1

The total mass of the bicycle ambulance was estimated to be 260kg (see excel power calculations).

The density of the air is varying. As the temperature increases the density decreases for the constant

altitude. The average annual temperature in Zambia is around 25°C and the air density is 1.18Kg/m3

[9]. The frontal area of the bicycle ambulance is 1.1m2. The drag coefficient of a bicycle upright

commuter including the trailer was set to be 1.2[10]

4

Figure 4.2 Graph Power against velocity

5

The max power speed limits can be read from the fig 4.2. Travelling at 5% inclined on a

rough road the speed of the bicycle can reach the required speed limit of 6km/h. look at the

point of travelling at 0% inclined on gravel surface the bicycle can speed up to 25km/h.

According to the graph for the maximum power of 0.59 KW the equivalent velocities of

6km/h and 25km/h can be achieved without any difficulties. The transmission design can be

designed and calculated for the required speed limits. (See excel file power calculation for

detailed calculations.)

55 TTrraannssmmiissssiioonn ddeessiiggnn aanndd sseelleeccttiioonn

An efficient and corresponding transmission gear ratio is required for different road surfaces

and different speed. CVT (Continuous Variable Transmission) is a transmission that changes

through an unlimited number of gear ratios between minimum and maximum.

Continuous Variable Transmission provides efficient fuel economy with more power, fluent

and quiet driving experience. CVT reaches the maximum torque of the engine and continues

it over a limitless of bicycle speeds by changing the transmission. CVT gives more or less

infinite number of engine speeds to the bicycles speed ratio. [11]

Types of CVTs that can be used for bicycle ambulance: [12]

Frictional

Electrical

Hydrostatic

Cone

Toroidal

Variable planetary (Nuvinci)

Variable Diameter

There are multiple ways to achieve a continuously variable speed ratio. The most common

ones for the bicycle and scooters are Nuvinci and pocket bike CVT.

6

55..11 NNuuvviinnccii ((CCVVTT))

Nuvinci is designed for bicycles with motor power

and human power. Using a set of rotating balls

positioned around the centre point. Tilting the

balls changes the contact diameter and varies the

speed ratio of the bicycle. The blue ring

represents the output and the red ring represents

the input as it is shown in fig 5.1. Figure 5.1 Nuvinci CVT CAD model [13]

The red ring is being driven by the pedals or by an attached engine. The controlled rod

moves the idler back and forth. As the rider adjusts the shifter the idler moves from left to

right which changes the transmission ratio. In under drive the input disk rotates faster than

the output disk. As the rider changes the shifter the disks rotate at the same time which is

1:1 gear ratio. And for lower gear the output disk rotates faster than the input disk shown

in fig 5.2. The other unique future of the Nuvinci CVT is the way torque is transferred, using

a special fluid that fills the inside of the hub. The cost of Nuvinci CVT exceeds the budget for

this project. Therefore the selected CVT will be Pocket Bike.

Figure 5.2 Nuvinci CVT[13]

Input

disc

output

7

55..22 NNiinnjjaa PPoocckkeett BBiikkee ((CCVVTT))

This type of CVT is mainly used on the scooters. The variable transmission has three

fundamental mechanisms.

Two pulleys, one of them is input driving pulley and the other one is output driven pulley

The pulleys are connected through a high power rubber belt

The gear ratio and the speed ratio changes to an infinite number

The pulleys are made of fine alloy metal. The

pulleys are made in a shape of cone opposite each

other. A belt is rotating in between the two cones.

There are different types of belt shapes such as[14]:

V-belts, wedge belt, synchronous belt and many

more. The chosen CVT has a synchronous belt

shape which is shown in fig 5.3. Figure 5.3 Synchronous belt

The driving pulley is connected directly to the engine shaft and the energy is transferred

from the engine to the transmission. When the driving pulleys are close together and

rotating simultaneously the diameter of the belt around the pulleys increases, but when the

input pulleys and the output pulleys are rotating equivalent. The radius of the belt loop

going around the pulleys will be the same see fig 5.4.

When the two cones are spread from each other the diameter of the belt around the pulleys

decrease. As one pulley decreases its radius the other pulley increases its radius to keep the

belt in tension. A spring tension is attached to the CVT to form the required force and move

the pulleys.

Figure 5.4 Ninja pocket bike (Continuous Variable Transmission) Ratio 1:1 Under drive 2:1 Over drive 1:2

8

55..33 DDrriivvee rraattiioo ccaallccuullaattiioonnss

An efficient gear system ratio and design is essential to determine the required maximum

speed of 25km/h and minimum speed of 6km/h on 0% asphalt and 5% inclined soft sand

surface respectively. From the table 3.1 the maximum engine power equals to 1605 RPM.

For the required maximum speed the gear ratio was worked out to be 9.75, which is too

high for single chain reduction therefore it is necessary to design two chain reduction

systems. (See appendix A)

The first chain reduction system exists of a small sprocket made of 11 teeth and 37

teeth

This gives a gear ratio of 3.36

The second chain reduction is also with a small sprocket of 11 teeth and 44 teeth.

This gives a gear ratio of 4

Minimum speed 6 Km/h

Max torque 1108 RPM

CVT

1st chain reduction

2nd chain reduction

19.5 :1 gear ratio needed for 6km/h speed

8:4 37:11 44:11

2

3.36

4

Gear ratio

Table 5.1

Table 5.2

Maximum speed 25 Km/h

Max Power 1605 RPM

CVT

1st chain reduction

2nd chain reduction

6.72 :1 gear ratio needed for 25km/h speed

4:8 37:11 44:11

0.5

3.36

4

Gear ratio

9

55..44 TTrraannmmiissssiioonn CCoonncceepptt DDeessiiggnn Two concepts were designed for the transmission system. The concept one will be

compared with concept two the most favourable one would be chosen and manufactured.

Concept: 1

Fig 5.5 Transmission design 1

fig 5.5 shows the two chain reduction systems. The

2 stroke engine is directly connected to the CVT

and the output drive of the CVT is connected to a

small sprocket of 11 teeth. The first chain

reduction exists of an 11 teeth and 37 teeth

sprocket. The bearings are mounted on the frame,

a key shaft is going through the bearings and on

the left hand side the shaft is connected to a 37

teeth sprocket. The second chain reduction starts

with an 11 teeth sprocket, which is adjusted to the

chain and the 44 teeth sprocket on the rear wheel

of the bicycle. The whole transmission system is

mounted on the simple square frame.

Fig5.6 Assembly drawing of concept 1 (See appendix for more drawings)

1. 2 stroke engine 2. CVT 3. Shaft 4. 2 x 11 teeth sprocket 5. 2 x chain 6. 37 teeth sprocket 7. 2 x pillow block bearing 8. 44 teeth sprocket 9. Rear wheel of the bicycle 10. Frame

10

1. stroke engine 2. CVT 3. 2 x Shaft 4. 2 x 11 teeth sprocket 5. 37 teeth sprocket 6. 44 teeth sprocket 7. Rear wheel of the bicycle 8. 2 x chain 9. Metal box frame 10. 4 x bearings

Concept: 2

Fig 5.7 Transmission design 2

Fig 5.7 shows the two chain reduction systems.

The 2 stroke engine is directly connected to the

CVT and the output drive of the CVT is connected

through a shaft to a small sprocket of 11 teeth. The

first chain reduction exists of an 11 teeth and 37

teeth sprocket. The shaft on the second chain

reduction is rotating the inside sprocket, which is

adjusted to the chain sprocket and the rear wheel

of the bicycle. The shafts are supported by four

bearings. The whole transmission system is

mounted on the metal box.

(See logbook for more sketches)

Fig5.8 Assembly drawing of concept 2

11

Concept 1 was chosen in the favour of concept 2, comparison points:

Reduction in complexity during manufacturing, the metal box in concept 1 has to be

manufactured very precisely as the shafts inside the box has to be aligned perfectly

to avoid damage to the transmission system and the mismatch of the bearings.

Reduction in number of components, design 1 requires 2 shafts, 4 bearings, design 2

requires only 1 shaft and 2 bearings.

By reducing the number of parts it decreases the cost of the system. So therefore

concept two is more suitable.

55..55 CCAADD mmooddeellss && ffiinnaall ddeessiiggnn

Figure 5.9 Engine Figure 5.10 Continuous Variable Transmission Figure 5.11 Bicycle frame

The CAD designs were made on Solid Works. Each of the mechanism was made separately.

Figure 5.12 Assembly of transmission system mounted on the rear wheel of the bicycle.

12

FFiigguurree 55..1133 EExxppllooddeedd vviieeww ooff ttrraannssmmiissssiioonn ddeessiiggnn

13

66.. CCoommppoonneenntt SSeelleeccttiioonn

66..11 CChhaaiinn SSeelleeccttiioonn

The next step is the design of the chain drive layout and selection of the standard

component available from chain manufacturers. Renolds Transmission Chain drive

programme was used for this purpose. For the first and second chain reduction Renold

suggested to use Sovereign 08 B (ISO 606) Simplex, with a life time of 15000 hours. After

approximately 2 and half years, 3% wear elongation will be reached. The Pitch chain is

12.7mm [15]. Small pitch makes less noise, less wear and less mechanical losses.

Table 6.1 Sovereign 08 B(ISO 606) Simplex [15]

Table 6.2 [15]

Table 6.3[15]

First chain reduction Pitch (mm) Weight

(kg/m) Chain length (mm)

Centre distance (mm)

Number of links

12.7 0.7 711.2 196.1 56

Second chain reduction for maximum speed Pitch (mm) Weight

(kg/m) Chain length (mm)

Centre distance (mm)

Number of links

12.7 0.7 1092.2 400 92

14

Renolds chain selection is more for industrial use which will run for hours but for bicycle

ambulance it would be used approximately up to 5 hours a day. The selected chain is able to

withstand the effect of dust and harsh environments up to three times than the standard

chain. The other features and benefits are that the chain is a suitable for high speed or

heavy load applications, excellent reliability which reduces the maintenance cost of the

product. [16]

66..22 CChhaaiinn TTeessttiinngg

The main aim of this experiment was to examine when the failure occurs. The tensile test

was employed in this analysis. Material properties play an essential role in engineering

design and also the requirement of this experiment is to know the characteristic of the

material and select the right chain for the required transmission.

Figure 6.1 Chain sample Figure 6.2 Chain set up

First task was to take a small piece of chain place it in the tensile testing machine, where the

chain was inserted to the upper jaws of the machine and fastened as well by another grip at

the bottom. There was no chain holder used for the test. The top jaw was fixed and the

bottom jaw was moving downwards and then applying a continually increasing load with a

constant speed. Fig 6.2 shows the sample during testing process.

15

Figure 6.3 Chain test diagram

The figure above shows clearly the proportional line up to the point of failure. The failure of

the chain occurred at 9118N. The other mechanical properties could not be calculated

because the cross sectional of the chain cannot be defined. The failure takes place mainly on

the joint of the links as it is shown in fig 6.4. Chain damage occurs due to wear between the

plates and the pins but not due to tension in the chain. Renold chain software suggested

after approximately 2 and half years, 3% wear elongation will be reached. Keeping in mind

that the environmental area where the chain is in operation plays a big role.

Figure 6.4 Chain failure

The selected chain would be appropriate for the transmission system application.

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 1 2 3 4 5 6

Load

(N

)

Displacement (mm)

Silver steel chain

16

66..33 SSpprroocckkeett SSeelleeccttiioonn

The pitch circle diameter for all the sprockets can be calculated using the equation below:

[Equation 6.1]

Table 6.4

The output of the CVT at the maximum torque rotates faster than the engine, thus it is

necessary to connect the output to a small sprocket. Roller chain drives are driven by the

sprockets, which are toothed wheels machined to fit the chain roller. There are 3 types of

standard sprockets, which are shown below.

Figure 6.5 No hub Figure 6.6 Hub on one side Figure 6.7 Hub on both sides

For this specific design there will be 2 type of sprocket standards used. The 44 teeth

sprocket is 178mm in diameter with no hub, which will be mounted on the rear wheel of the

bycicle. The 37 teeth sprocket and 11 teeth sprocket would be made of one sided hub with a

keyway.

Pitch circle diameter (mm)

11 teeth sprocket

37 teeth sprocket

44 teeth sprocket

45.08 149.75 178.02

)/180sin( N

Pdiametercirclepitch

17

Figure 6.8 Stress distribution on 37 teeth sprocket is based on Von Mises method

The 37 teeth sprocket will be attached on the key shaft which is shown on fig 5.13

Simulation conservative analysis was done on Solidworks to work out the safety factor of

the component. A tangentianal force of 336.9N was applied on the sprocket. The results

showed a minimum safety factor of 3. The choosen material for the sprocket is carbon steel

with inner diameter of 25mm with pitch circle diameter of 149.75mm as shown on table 6.4

The sprockets will be purchased and assembled on the transmission system.

The 11 teeth sprocket is attached

to the key shaft as it is shown on

fig 5.13, a tangential force of

1123.1N is applied on the

sprocket. The maximum stress is

applied on the key hole see fig

6.9. The bore diameter is 17mm

and the pitch circle diameter is 45

mm from table 6.4.

Figure 6.9 Stress distribution on 11 teeth sprocket based on Von Mises method

18

66..44 BBeeaarriinngg SSeelleeccttiioonn

According to the transmission design in

fig 5.5 light duty pillow block bearing

would be suitable to use. The main

purpose of the bearing is to support the

load which is applied on the shaft. The

pillow block bearings are perfectly

compensated for shaft misalignments, Figure 6.10 Pillow block bearing

two screws are needed to mount the pillow block bearing on the frame. Also there are two

positions for the screws to connect the shaft. The bearings are made of cast Iron. The

selected pillow bearing is able to withstand the dirt resistance. The other features and

benefits are its cheap and reliable.

Care needs to be taken on the following points when mounting the bearings:

The bearings needs to be placed on the flat and rigid surface (Flatness: 0.05 max)[17]

The angle error between bearing mounting face and shaft should be within 2°

Over tightening the mounting bolts will deform the housing bearing. It is

recommended to use washer with the bolts when mounting the housing because

using the bolts only will cause damage to the casing of the bearing.

66..55 SShhaafftt SSeelleeccttiioonn

The selected shaft is made of carbon steel, with diameter of 17mm and 300mm in length.

The right shaft was selected for the pillow block bearing which was provided by the lab

technician.

Figure 6.11 Carbon steel shaft

19

77.. FFaattiigguuee AAnnaallyyssiiss

77..11 SShheeaarr ffoorrccee && BBeennddiinngg MMoommeenntt

The shafts or of the stub type, should be of such proportions and strength that sprocket and

bearing alignment remains unimpaired under load. Shaft sizes should be selected taking into

account combined bending and torsional moments.

29mm 105mm 55mm

D = 150mm Y T1

D = 45mm D = 17mm

A B O

C D Z

T1 X

T2 T2

Figure 7.1 Shaft Design

The shaft is analysed to obtain the maximum stress to determine the design safty margins.

Also to calculate the deflection of the shaft under the tension T1 (336.9N) and T2 (1123.1N)

at point A and C respectively. The shaft diameter is 17 mm. To determine the maximum

stress results shear force and bending moment diagram needs to be worked out.

(See appendix B for further calculations)

20

y 336.8N RH1 A 0.029 B RH2 0.105 z 184 0.055 C D x

RV1 1123.1N Figure 7.2 Free body diagram RV2

Shear force and Bending Moment on the horizontal plane ZX

Free Body Diagram

0 +61N Shear Force Diagram (N)

-336.8N -9.77Nm

Bending Moment Diagram 0

(Nm) Figure 7.3 Shear Froce and Bending Moment diagram

The maximum Shear Force on the ZX-axis equals to -336.8N and 61N as it is shown on the

shear force diagram and the maximum Bending Moment equals to -9.77Nm. The ZX-axis is

where the 37 teeth sprocket is attached to the shaft and connected with the chain to the

output of the CVT. (See appendix B for full calculations).

21

Shear force and Bending Moment forces on the horizontal plane YX

Free Body Diagram

0 +386.1N Shear Force Diagram

(N) -737N

Bending Moment Diagram 0

(Nm) + 40.5Nm Figure 7.4 Shear Froce and Bending Moment diagram

The maximum Shear Force on the YX-axis equals to 386.1N and -73N as it is shown on the

Shear force diagram and the maximum Bending Moment equals to 40.05Nm. The YX-axis is

where the 11 teeth sprocket is mounted on the shaft and connected with the chain to rear

wheel of the bicycle. (See appendix B for full calculations).

22

77..22 FFaattiigguuee && SSttrreessss AAnnaallyyssiiss

Due to forces applied on the shaft it undergoes compression and tension at the same time.

To work out the fatigue of the component bending stress and shear force are required. The

resultant Moment can be worked out from the bending Moment diagrams.

(Detailed calculations are shown in appendix C)

22

VHR MMM [Equation 6.2]

Since it is a shaft the Ix and Iy is the same. When analysing and designing the circular shaft

the following equation can be used:

64

4dI x

[Equation 6.3]

The resultant Moment and the second moment of inertia can be substituted into the

bending stress equation 6.4. The y value is the point from the centroid of the shaft to the

outside edge.

I

yM Rstressbending [Equation 6.4]

Figure 7.5 Bending stress

Due to rotation of the shaft bending stress alternate at 86.37MPa. (See excel file)

-100

-80

-60

-40

-20

0

20

40

60

80

100

Be

nd

ing

Stre

ss (

MP

a)

Bending stress σ

N-Cycle

23

Shear stress:

The shear stress of the shaft can be worked out from the following equation:

3

16

d

T

[Equation 6.5]

The final value of shear stress was calculated to be 26MPa

Figure 7.6 Shear stress

The alternating and the mean stress component equals to 13MPa which is shown in the diagram above. (See excel file)

The stress at a point on the selected

shaft is normal stress σ which is in the

x-direction and the shear stress τ in the

xy direction.

From Mohr’s circle the Maximum

distortion energy criterion theory

equals to:

2

22 3

fs

yp

N

S

[Equation 6.6]

Substituting the shear stress 13MPa and the bending stress 86.37MPa into the equation 6.6

Was worked out to be 89.26MPa

0

5

10

15

20

25

30

0 2 4 6 8 10 12

She

ar s

tre

ss (

MP

a)

N-Cycles

Shear stress τ

24

The final step is to find out the Fatigue strength.

F

Rs

K

KKFs

factorion concentrat stress

limit endurance MODIFIED

Modified endurance limit values and the stress concentration factor depends on

the[geometry, these values were taken from the fatigue analysis website. [18] [19]

The fatigue strength of the shaft was worked out to be 168MPa

The Ultimate tensile strength of the material was assumed to be 540MPa.

Figure 7.7 Goodman Diagram

The following diagram represents the Alternating stress versus Mean stress acting on the

shaft transmission. The red line indicates the failure line, the shaft design should not reach

the danger zone as most likely failure will occur. The green line indicates line design which is

the safe region. Additionally, the fatigue life of the shaft was plotted on the fig 7.7.

Equivalent alternating stress and equivalent means stresses are below the failure line for

the required safety factor. Safety factor is given by ratio of length to failure divided by

length to design point, which is 1.8. These points are below the danger zone. Since the parts

already exist it should not make much difference to the design shaft. Also consider that the

bicycle ambulance is in operation approximately 4 to 5 hours a day.

(See appendix C for full calculations)

89 84

168

0

20

40

60

80

100

120

140

160

180

0 100 200 300 400 500 600

Alt

ern

atin

g st

ress

(M

Pa)

Mean stress (MPa)

Goodman Diagram

22.5 0 270

540 Su

Se

Safe area

Danger Zone

25

77..33 CCeennttrree ooff GGrraavviittyy && RReeaaccttiioonn FFoorrcceess

The centre of gravity is the average location of the bicycle where the weight acts towards

the earth. The purpose of calculating centre of gravity is to find out the balance of the

bicycle and its stability. The principle of moment has been applied to find out the centre of

gravity. (See appendix D). The figure below shows the disturbed loads acting on the bicycle.

The mass of the three objects were assumed to be:

a: transmission & engine mass 40kg b: cyclist mass 70kg c: bicycle mass 30kg d: trailer & patient mass 100kg

b

a

c

R1 R2

145mm 855mm Figure 7.8 Reaction forces

85% of the weight is acting on the rear wheel of the bicycle and 15% of the weight is acting

on the front wheel of the bicycle. When attaching the trailer the position of C of G changes.

(See appendix D)

y

b a c

c c

d

x Figure 7.9 Centre of Gravity including the trailer

mx 687.0

my 61.0

26

88.. CCoosstt AAnnaallyyssiiss

Cost and budget are generally one of the most important aspects that need to be

considered in any engineering design. From the cost analysis it can be worked out if it is

beneficial to manufacture the final design. From the final drawings it can be worked out

what size materials are required and what parts are needed to complete the assembly. The

figure below shows the main cost of the project. (See excel Cost analysis)

Figure 8.1 Project Cost

From the bar chart on fig 8.1 the total cost of the project is £193.44. Additionally, tooling,

fastening and materials were provided by the lab technician in the PTC lab. As it is shown in

the figure above, parts have the highest cost in the diagram. The following diagram will

break down the costs on parts.

Figure 8.2 Parts Cost

£0.00

£50.00

£100.00

£150.00

Cost

£148.41

£32.68

£3.75 £8.60

Parts

Material

Fastener

Tooling

£20.00

£20.00

£45.00 £6.99

£15.50

£9.98

£17.95

£12.99 2 Stroke Engine

Bicycle

CVT

11 teeth sprocket

1500 (mm) chain (new)

Pillow block bearing

37 teeth sprocket

44 teeth sprocket

27

Most of the parts were purchased from the websites online and some of the parts were

provided by the supervisor Prof. Pullen and co-ordinator Mr. Ron. Considering that in the

cost analysis shipping fee is not included. The figure 8.2 shows that Continuous Variable

Transmission was the most expensive part. The sprockets were purchased from different

companies online. [20]

99.. MMaannuuffaaccttuurriinngg pprroocceessss

The first step was to buy an

inexpensive bicycle, then

designing the transmission on cad

models and work according the

drawing designs. (See appendix E)

Materials and components:

2 stroke engine

CVT

4 sprockets

Chain Figure 9.1 Materials and components

Shaft

2 bearings

Square tube

Main Frame:

The base frame is made of mild steel square tube

with dimension of (20mm x 20mm X 3mm) and

the holder is made of black mild steel angle with

the same dimensions as square tube. The square

tube was cut by using band saw then it was

welded together. 6m holes were drilled through

the holder and the base frame, bolts and nuts

were used to fasten the holder on the base

frame. On fig 9.2 the engine is mounted on the Figure 9.2 Base frame

frame with two supports.

28

Brackets:

The steel angle is cut throughout the middle and 3 holes were drilled in the centre by using

milling machine. On each side of the bar another steel angle was welded to make the

bracket more stable and rigid.

Figure 9.3 Drilling three holes Figure 9.4 Testing the bracket on the

bicycle Figure 9.5 Bracket is welded and ready to mount

The purpose of bracket holder is to support the base frame on the bicycle. It is very

important to make this part as accurate and solid as possible because the whole frame is

supported on this part. The next step is to mount the engine on the bicycle which is shown

in figure below.

(a) (b) Figure 9.6 Mounting the engine on the rear wheel of the bicycle.

29

Bearing: Two pillow bearings were mounted on each side of the main frame, drilling machine was

used to make 8m holes through the body frame. It is very important to mount the bearing

housing on the right line in respect to each other, so that the shaft rotates smoothly. The

bearing needs to be mounted firmly on the flat surface to avoid vibration when the bicycle

ambulance is in operation. On the back of the frame supporting bars were attached for

improving the stability. The supporting bars can be adjusted to maintain the chain tension,

see fig 9.7 (a).

(a) (b)

Figure 9.7 Mounting the bearings and the CVT on the main frame.

Continuous Variable Transmission:

Two square metals were drilled and welded against the main frame to mount the CVT. A

coupling was required to connect the engine output to the CVT input. As it is shown in fig

9.7 (b)

30

10. Sustainability of two stroke engine

Engine emission cause pollution in the busy cities and hazard to the health of population

and the surroundings which also may have an impact on the climate change. These

problems can be solved by varies ways, which are less pollution to the environment by using

biofuel, fossil fuel and etc.

One objective while controlling the emissions is to eliminate excess emissions from a two-

stroke engine to a four-stroke engine. However this would involve eminent maintenance

cost. To be able to reduce emissions from a two-stroke engine, meticulous inspection has to

be carried out and maintenance programs have to be performed. Also lubricating oil could

be used with the corresponding quality and quantity. The main disadvantage of two-stroke

engine is that it is less efficient and not economical to run.

The need of population in developing countries is to have a motorised bicycle ambulance,

which does not use human power, on the other hand national policy aim is to improve

human health and reduce emission. Gathering the population and clarify essential to

ensuring socio-centric concerns also instructing the public on the un-sustainability of relying

on 2 stroke engine with gasoline mixture. The national need is to improve the energy

efficiency and developing and promoting the suitable products and services. Using different

and more efficient engines will increase the cost.

Disadvantages of two stroke engine:

There is mixture of fuel involved

Not fuel efficient due to leakage through the exhaust

Due to unburned fuel it is polluting the environment releasing high CO and NOx

Not suitable for long operation period

Advantages of two stroke engine:

Low weight high torque

At every revolution it fires only once, therefore better power to weight ratio.

Can be mounted on varies sides

31

11. Conclusion

The project objective was to design and manufacture transmission system for ambulance

bicycle by using 2-stroke engine and CVT. Two chain reductions were derived from the gear

ratio calculations due to high speed of the engine.

Continuous Variable Transmission is used to provide a good matching speed for different

road surfaces and environment that would be experienced in developing countries.

The cost of the project came up to £194. Majority of the parts were provided. All the theory

part including calculations has been done. The transmission system was designed and

completed, all the components has been purchased. More than the half of the

manufacturing process is finished. While some work still remained incomplete such as

testing the bicycle and collecting the end results.

Due to loosing of files and drawings the project could not be finished on time. Since all the

components are available and more than the half of manufacturing is done, the project

would be completed even after the final report submission.

12. Recommended future work

Use more efficient engine to run the power assisted bicycle.

Decrease the cost of the project if possible, use scrap parts for manufacturing,

become a member of the charity organization, so the parts can be provided.

It would be more reliable to use 1 chain reduction instead of two this will decrease

the cost of the project at the same time.

Avoid using complex design and transmission systems at the same time investigate

the size and the geometry of the selected design.

Cover the transmission system from dust and harmful environment.

32

13. References

Websites

[1]Youtube video http://www.youtube.com/watch?v=nCyTZCY-RSo

[1] http://www.youtube.com/watch?v=3RFVHiJXrrE

[2]DT web site: http://developingtechnologies.wordpress.com/

[3] Bicycle ambulance fig1.1: http://www.rescue.org/blog/saving-lives-mothers-and-babies-photos-

field

[4] Bicycle ambulance fig1.2 http://www.cycleyourheartout.com/charity.html

[5] Power Assisted Bicycle Project (Waradom Tour Voraprawat City University student)

[7]Road Condition Zambia page 9: http://www.eu-africa-infrastructure-

tf.net/attachments/library/aicd-background-paper-14-roads-sect-summary-en.pdf

[8] Rolling friction of bicycle tire provide by (MR. Ron Dennis)

[9] Air density: http://www.denysschen.com/catalogue/density.aspx

[10] Drag coefficient: http://www.engineeringtoolbox.com/drag-coefficient-d_627.html

[11]CVT: http://cars.about.com/od/thingsyouneedtoknow/a/CVT.htm

[12]Types of CVT: http://www.gizmology.net/cvt.htm

[13]Nuvinci CVT: http://fallbrooktechnologies.com/NuVinci.asp

[15]Renold chain drive selector:

http://www.renold.com/Support/Roller_Chain_Selector/Renold_Chain_Selector.asp

[16]Renold chain folder (Renold Sovereign): Disc file

[17]Bearing folder(Bearing Units NTN): Disc file

[18]Fatigue strength: http://roymech.co.uk/Useful_Tables/Fatigue/FAT_Mod_factors.html

[19]Stress concentration factor:

http://roymech.co.uk/Useful_Tables/Fatigue/Stress_concentration.html

[20] Purchasing website: www.ebay.co.uk

[21] Engineering for Sustainable Development: Guiding Principles

33

14. Bibliography [6] Understanding Mechanics, A.J Sadler D.W.S Thorning, Oxford University Press, Second Edition,

Chapter 2 page 25, chapter 3 page 42,chapter 6 page 107-115.

[14] Mechanical Design, Peter Childs, Second Edition, page: 155-157

[22] Mechanical Engineering Design, Shigley, Seventh Edition, Chapter 4, 7, 18

[23] Bicycle Science, Third Edition, David Gordon Wilson

[24] Motorcycle Handling and Chassis Design, the art and science, Tony Foale,

chapter 4 & chapter 14

1155.. AAppppeennddiixx

Appendix A

Drive ratio calculations:

The diameter of the bicycle wheel is 0.559m

Circumference of the wheel m76.1559.0

CVTs maximum gear reduction is 2:1

75.98.56

554

velocityangularTire

velocityangularCVT

RPM

RPMratioGear

out

in

Minimum speed calculations 6km/h

From the (table 3.1) The maximum torque RPM (1108)

88.26436.32

21max:

reductionchainndreductionchainstreductionCVTratiogeartotalThe

RPMratiogearTotal

RPMtorqueMaxThe22.41

88.26

1108

Working out the speed: hkmmrpm /4.46.360

5.7276.122.41

This is very close to the required speed.

Maximum speed calculations 25km/h

From the (table 3.1) the maximum power engine RPM = 1605

34

72.6436.35.0

21min:

reductionchainndreductionchainstreductionCVTratiogeartotalThe

RPMratiogearTotal

RPMPowerMaxThe84.238

436.35.0

1605

Working out the speed: hkmmrpm /22.256.360

36.42076.184.238

This is very close to the required speed.

Appendix B

The maximum engine torque from the CVT output = 7.58Nm

The radius of CVT output = 0.0225mm

Horizontal tension T1 on the 11 teeth sprocket of CVT output Nm

Nm9.336

0225.0

58.7

The torque on the intermediate shaft Nmm

mmNm 27.25

45

15058.7

The vertical chain tension T2 = Nm

Nm1.1123

0225.0

27.25

Shear Force and Bending Moment diagram

Free body diagram y 336.8N RH1 A 0.029 B RH2 0.105 z 184 0.055 C D x

RV1 1123.1N RV2

35

Shear force and Bending Moment on the horizontal plane ZX Z 336.8N 29mm 160mm X A B D

RRHH11 RRHH22

+ 0 xF

+ 08.3360 21 HHz RRF

Working out the Moment on the shaft to find out the reaction forces. Sum of all Moment forces on point D + Free body diagram between point A and B -336.1 x S + S = -336.8 0 < x < 0.029m A B

xxMM 8.336)(

NR

NR

RM

H

H

HD

61

8.397

)8.336)(189.0(160.0

2

1

1

NmMmxat

NmMmxat

77.9029.0

00

36

336.8N x S 0.029m S = 397.8-336.8 S = 61N + A B D 397.8N

054.1161

8.336)029.0(8.397)(

x

xxxMM

The maximum Shear Force on the ZX-axis equals to -336.8N and 61N and the maximum Bending Moment equals to -9.77Nm. Shear force and Bending Moment forces on the horizontal plane YX y 1123.1N 105mm 0.055mm X B C D

RRVV11 RRVV22

+ 0 xF

+ 01.11230 21 VVy RRF

Working out the Moment on the shaft to find out the reaction forces. Sum of all Moment forces on point D +

NmMmxat

NmMmxat

0189.0

77.9029.0

NR

NR

RM

V

V

VB

1.386

737

0)16.0()105.0)(1.1123(

1

2

2

37

Free body diagram between point B and C + S = 386.1N 0 < x < 0.029m B C x

386.1N S xxMM 1.386)(

1123,1N S S = 386.1-1123.1 B S = -737N + A 105 D X

09.7369.117

8.336)105.0(1.11231.386)(

x

xxxxMM

The maximum Shear Force on the YX-axis equals to 386.1N and -73N and the maximum

Bending Moment equals to 40.05Nm.

NmMmxat

NmMmxat

5.40105.0

00

NmMmxat

NmMmxat

016.0

5.40105.0

38

Appendix C

Calculations for failure line on Goodman Diagram:

= 168MPa

Fs = MPaUTS

2702

540

2

Size factor (KS) = 0.90

Reliability factor is a very small number between 0.6 < 1 KR= 0.9 Stress concentration factor depends on geometry and must be found From charts in a book on mechanical design

Stress concentration factor for keyways shaft KF = 3.1

Su of the shaft = 540MPa

Calculations for equivalent alternating stress on Goodman Diagram:

MV

MR

Resultant moment:

Nm

MMM

VH

VHR

66.41

5.4077.9 22

22

MH

Ks=1.189d-0.097 8mm < d < 250mm Ks=(1.189)(17)-0.097 = 0.903

F

Rss

K

KKFSe

factorion concentrat stress

limit endurance MODIFIED

39

Shaft Diameter: 17mm

Second moment of inertia:

444

8.409964

17

64mm

dI x

Since it is a shaft the Ix and Iy is the same.

Bending stress:

Substituting the values of resultant force MR and second moment of inertia Ix equals to:

Due to rotation of the shaft bending stress alternate ±

Shear force: The maximum engine torque from the CVT output equals to 7.58Nm (0.0225 = Radius of CVT sprocket)

The torque on the intermediate shaft

Nmmmsprocketteeh

mmsprocketteethNm 27.25

4511

1503758.7

Shear force: MPa

d

T26

017.0

27.25161633

Alternating stress component: 132

26 MPa

Mean stress component: 132

26 MPa

From Mohr’s circle the Maximum distortion energy criterion theory equals to:

The values of bending stress and shear force can be substituted in to the following equation

22 )13)(3(37.86

= 89.26MPa

MPaI

yM Rstressbending 37.86

8.4099

5.841660

2

22 3

fs

yp

N

S

40

Length to failure:

8.16216040 22

Length to design point:

8.915.2289 22

Safety factor: 8.18.91

9.164

Calculations for equivalent mean stress on Goodman Diagram:

5.02

5.02

)133(

)3(

=22.5Mpa

Calculation for safety factor:

41

a: transmission/engine mass 40kg b: cyclist mass 70kg c: bicycle mass 30kg

a: transmission & engine mass 40kg b: cyclist mass 70kg c: bicycle mass 30kg d: trailer & patient mass 100kg

Appendix D

Centre of gravity for the bicycle: y

b a c 50kg 70kg 30kg x 150mm 375mm 625mm Resolving Moment vertically clockwise:

1471.5N = 30g + 70g + 50g : weight Totall

(50g x 0) + (70g x 0.15) + (30 x 0.375) = x5.1471

mx 145.0 y

b a c 900mm 870mm 600mm x Resolving Moment horizontally clockwise: (50g x 0.87) + (70g x 0.9) + (30g x 0.6) = y5.1471

my 83.0

Centre of gravity for the bicycle including the trailer: 01.14759.2132.1261

0

9.2131

1.1475145.0

2.12611

1.1475855.0

21

2

1

wRR

NR

NR

42

y

b a c d 50kg 70kg 30kg

100kg x 1000mm 150mm 1375mm 625mm Resolving Moment vertically clockwise:

2452.5N = 100g30g + 70g + 50g : weight Totall

(100g x 0)+(50g x 1) + (70g x 0.15) + (30 x 0.375) = x5.2452

mx 687.0

y

b a 900mm c d 870mm 600mm

280mm x Resolving Moment horizontally clockwise: (100g x 0.28)+(50g x 0.87) + (70g x 0.9) + (30g x 0.6) = y5.2452

my 61.0

43

The position of centre of gravity

y

b a c d

x

mx 687.0

my 61.0

44

Appendix E

45

1 Project Gantt chart

46