2. 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.
3. 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.
4. 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
6. 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
7. 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
8. 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
9. 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]
10. 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.
11. 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]
13. 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.
14. 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
15. 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 1:1Under drive 2:1 Over drive 1:2
16. 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
17. 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
18. 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
19. 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.
21. 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
22. 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.
23. 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
24. 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
P
diametercirclepitch
25. 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
26. 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
27. 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)
28. 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).
29. 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).
30. 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
4
d
I 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
yMR
stressbending [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
BendingStress(MPa)
Bending stress σ
N-Cycle
31. 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
Shearstress(MPa)
N-Cycles
Shear stress τ
32. 24
The final step is to find out the Fatigue strength.
F
Rs
K
KKFs
factorionconcentratstress
limitenduranceMODIFIED
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
Alternatingstress(MPa)
Mean stress (MPa)
Goodman Diagram
22.50 270 540
Su
Se
Safe area
Danger Zone
33. 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
34. 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
35. 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.
36. 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.
37. 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)
38. 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
39. 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.
40. 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
41. 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
75.9
8.56
554
velocityangularTire
velocityangularCVT
RPM
RPM
ratioGear
out
in
Minimum speed calculations 6km/h
From the (table 3.1) The maximum torque RPM (1108)
88.26436.32
21max:
reductionchainndreductionchainstreductionCVTratiogeartotalThe
RPM
ratiogearTotal
RPMtorqueMaxThe
22.41
88.26
1108
Working out the speed: hkmmrpm /4.46.3
60
5.72
76.122.41
This is very close to the required speed.
Maximum speed calculations 25km/h
From the (table 3.1) the maximum power engine RPM = 1605
42. 34
72.6436.35.0
21min:
reductionchainndreductionchainstreductionCVTratiogeartotalThe
RPM
ratiogearTotal
RPMPowerMaxThe
84.238
436.35.0
1605
Working out the speed: hkmmrpm /22.256.3
60
36.420
76.184.238
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 N
m
Nm
9.336
0225.0
58.7
The torque on the intermediate shaft N
mm
mm
Nm 27.25
45
150
58.7
The vertical chain tension T2 = N
m
Nm
1.1123
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
43. 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
44. 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
45. 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
46. 38
Appendix C
Calculations for failure line on Goodman Diagram:
= 168MPa
Fs = MPa
UTS
270
2
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
KKF
Se
factorionconcentratstress
limitenduranceMODIFIED
47. 39
Shaft Diameter: 17mm
Second moment of inertia:
4
44
8.4099
64
17
64
mm
d
I 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
Nm
mmsprocketteeh
mmsprocketteeth
Nm 27.25
4511
15037
58.7
Shear force:
MPa
d
T
26
017.0
27.251616
33
Alternating stress component: 13
2
26
MPa
Mean stress component: 13
2
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
MPa
I
yMR
stressbending 37.86
8.4099
5.841660
2
22
3
fs
yp
N
S
48. 40
Length to failure:
8.16216040 22
Length to design point:
8.915.2289 22
Safety factor: 8.1
8.91
9.164
Calculations for equivalent mean stress on Goodman Diagram:
5.02
5.02
)133(
)3(
=22.5Mpa
Calculation for safety factor:
49. 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:weightTotall
(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
9.213
1
1.1475145.0
2.1261
1
1.1475855.0
21
2
1
wRR
NR
NR
50. 42
y
b
a
c
d 50kg
70kg 30kg
100kg
x
1000mm 150mm
1375mm 625mm
Resolving Moment vertically clockwise:
2452.5N=100g30g+70g+50g:weightTotall
(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
