Mechanical Engineering Group Design: EGA214 (2018-2019)

Final Design Report

Group No: 17

Student Name Student Number Part SPLD

Sam Prestwich 956633 Drivetrain o

Zayd Neseyif 952682 Chassis/Frame o

Mesaud Algow 841826 Seats o

Dulanaka Welandawe 971665 Steering o

Daniel Anyanya 959646 Body o

Omar Alkindi 891535 Suspension o

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Contents
Introduction: ........................................................................................................................................ 5
Design specifications: ...................................................................................................................... 5
Design evolution: .............................................................................................................................. 6
Weighted matrix:............................................................................................................................... 8
SWOT analysis ............................................................................................................................... 11
1.0 Chassis ........................................................................................................................................ 12
Design Specifications .................................................................................................................... 12
Design Concepts and Development ............................................................................................ 12
Pugh’s Matrix .................................................................................................................................. 14
Material Selection ........................................................................................................................... 15
Tube Size Selection ....................................................................................................................... 16
Joining Method ............................................................................................................................... 17
Stress Test of the Chassis ............................................................................................................ 18
FMEA ............................................................................................................................................... 19
Reflection of Design ....................................................................................................................... 19
2.0 Drivetrain ..................................................................................................................................... 22
Part Requirements ......................................................................................................................... 22
Drivetrain Design Specification ................................................................................................ 22
Option of assisted electric drive, must conform to EU Directive 2002/24/EC. .................. 22
Initial Concept Designs .............................................................................................................. 22
Development of Design ................................................................................................................. 24
Freehub vs Differential .............................................................................................................. 24
VR Prototyping ............................................................................................................................ 25
Design Calculations ....................................................................................................................... 25
Gear Ratio ................................................................................................................................... 25
Design Simulation .......................................................................................................................... 26
Material Selection ........................................................................................................................... 27
Manufacturing Specifications ....................................................................................................... 28
FMEA ............................................................................................................................................... 29
Reflection of Design ....................................................................................................................... 30
.............................................................................................................................................................. 32

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3.0 Seats: ............................................................................................................................................ 33
3.1 Requirements: .......................................................................................................................... 33
PDS: ............................................................................................................................................. 33
3.2 Concept evaluation:................................................................................................................. 34
Weighted matrix:......................................................................................................................... 35
3.3 Material selection:.................................................................................................................... 35
3.4 Manufacturing process: .......................................................................................................... 37
3.5 Failure mode and effect analysis (FMEA): .......................................................................... 38
3.6 design reflection:...................................................................................................................... 38
4.0 Steering ........................................................................................................................................ 41
Concept evolution........................................................................................................................... 41
DESIGN EVOLUTION ................................................................................................................... 43
Results from Stress Analysis ........................................................................................................ 44
Material specifications ................................................................................................................... 47
Manufacturing processes .............................................................................................................. 47
Joining process ............................................................................................................................... 47
FAILURE MODE AND EFFECTS ANALYSIS ........................................................................... 48
REFLECTION ................................................................................................................................. 49
5.0 BODYWORK................................................................................................................................ 52
1. The body on frame concept .......................................................................................... 52
2. Monocoque construction ............................................................................................... 52
3. Unibody design................................................................................................................. 52
4. Tubular space frame ....................................................................................................... 53
5.1 BODYWORK SPECIFICATIONS (FROM PDS) ................................................................. 53
5.2 DESIGN EVOLUTION ............................................................................................................ 54
5.3 STRESS ANALYSIS (SOLIDWORKS SIMULATION) ....................................................... 55
5.4 DESIGN STUDY ...................................................................................................................... 56
5.5 MATERIALS AND MANUFACTURING .............................................................................. 57
Material Selection..................................................................................................................... 57
Manufacturing ........................................................................................................................... 57
Joining ........................................................................................................................................ 57
Environmental Considerations............................................................................................. 57
5.6 FAILURE MODE AND EFFECT ANALYSIS ....................................................................... 58
5.7 REFLECTION OF DESIGN REVIEW ................................................................................... 58

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6.0 Suspension ................................................................................................................................. 61
6.1 Design specifications: ............................................................................................................. 61
DESIGN CONCEPTS: ................................................................................................................... 62
Concept matrix:............................................................................................................................... 63
6.2 Design evaluation : .................................................................................................................. 64
6.3 Materials and manufacturing process: ................................................................................. 65
6.4 Failure mode and effects analysis: ....................................................................................... 67
6.5 Reflection of design review: ................................................................................................... 67

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Introduction:

Design specifications:

Specification Standards
1.1 Taxi to transport a driver and two passengers Project brief
1.2 Human powered Project brief
1.3 Comfortable Project brief
1.4 Ease of Manufacture Frame requirement
1.5 Light weight Project brief
1.6 Durability throughout life cycle Drivers focus group
1.7 Ease of Maintenance Drivers focus group
1.8 Adjustable cabin Passengers focus
group
1.9 Wear resistant long-term Frame requirement
1.10 Weather resistant Frame requirement
1.11 Taxi must carry up to 400 kg of load Frame requirement
1.12 Maximum distance per trip: 5 miles Wear criterion
1.13 Cabin must be weather resistant Frame requirement
1.15 Traditional taxi platform Frame criterion
1.16 Seatbelts and handbrake Interior criterion
1.17 Product must withstand minor impact (e.g. drops of curbs, Physical requirement
minor bumps into bollards)
1.18 Product must remain stable in all weather conditions Physical requirement
1.19 Cabin must be adjustable for different situations Physical requirement
1.20 Product lifespan of 5 years Physical requirement
1.21 Use of readily available materials Manufacturing
guidelines
1.22 Use of safe materials according to standards Manufacturing
guidelines
1.23 Manufactured from CAD drawings provided Manufacturing
guidelines
1.24 Minimal manufacturing cost Manufacturing
guidelines
1.25 Safety regulations for bicycles BS 6102-1 : 1981
1.26 Environmental friendly materials PD ISO/TR
17098:2013
1.27 Bolts and screws must obey standards and regulations BS ISO 885:2000
1.28 Parts must be able to withhold loads (i.e. seats) EN 1728:2012
1.29 Welding must follow certain regulations PD ISO/TR
18786:2014
1.30 Chassis regulations and standards BS EN ISO 4210-
6:2015
1.31 Other regulations for other parts BS EN ISO 4210-
3:2014

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Design evolution:
Concept overview Description
1) Two separate cabins: one
for the driver, and one for
the passengers.
Cargo space behind the
passenger seats.

Rectangular frame
consisting of square
beams, with the seat
mounts on the middle and
rear crossbeam.
Front crossbeam
provides stiffness to the
front

Pedals linked to a
differential, driving a prop
shaft connected to rear
differential, driving the
rear wheels (rear-wheel
drive)

Rack and pinion steering

mechanism

2) Pedal powered with

assistive electric drive to
rear wheel

Two rear wheels and one

front wheel, with steering
on the front.

Both the driver and

passenger are
undercover with the driver
at the front and two
passengers at the rear.

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 3) A 3 wheeled human
powered taxi, with back-
to-back seats to minimise
the size of the taxi

Generating electricity
from pedalling to power
the accessories in the taxi

The taxi is designed with

a closed compartment,
(doors and roof) to
protect the rider from rain
and wind.

4)

Comparing these four concepts has resulted in the determination of the optimal design,
which incorporates the most notable features of each concept. The prototyping workshop
further accentuated the pros and cons of each concept, and therefore aided in the
development of the final design.

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Weighted matrix:

Concept 1 Concept 2 Concept 3 Concept 4

Selection Weighting Rating Weighted Rating Weighted Rating Weighted Rating Weighted
Criteria Score Score Score Score

Weight 12% 2 0.24 2 0.24 3 0.36 3 0.36

Ease of 5% 2 0.10 3 0.15 4 0.20 3 0.15

Manufacture

Durability 10% 3 0.30 3 0.30 3 0.30 3 0.30

Dimensions 15% 2 0.30 2 0.30 2 0.30 4 0.60

Ease of 5% 3 0.15 3 0.15 4 0.20 4 0.20

maintenance

Ease of 12% 3 0.36 3 0.36 2 0.24 3 0.36

operation

Sustainability 10% 2 0.2 3 0.3 2 0.10 3 0.30

Comfort 18% 3 0.54 2 0.36 2 0.36 4 0.72

Safety 13% 3 0.39 3 0.39 2 0.26 3 0.39

Total Score 100% 2.58 2.55 2.32 3.38

Rank 2 3 4 1

From this decision matrix, the most suitable concept for our final design turned out to be
concept 4. Adopting this concept as the basic form of the taxi, the evolution process was
commenced.
The overall body shape was altered, the most notable alteration being the extension of the
roof to cover the entire vehicle. Alongside this, the taxi will have doors
The profile of the vehicle was changed to a single, aerofoil-esque shape, in the interests of
aerodynamics and aesthetics.
The passenger compartment is accessible through doors, conveniently placed at the centre
of the vehicle, which allows for easy access to the sizable passenger compartment.

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Assembly Instructions
1. Assemble into jig and weld together.
2. Insert crank frame and weld to frame.
3. Install fixture for suspension, rear axle and drivetrain.
4. Install drivetrain.
5. Install suspension.
6. Weld fork frame to frame.
7. Install fork, steering arms and wheels.
8. Place seat into frame and bolt to the floor.
9. Attach body panels to frame.

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SWOT analysis
Strengths:
 The costumers and the driver are protected from the rain and wind as it is a closed
cabin.
 Large luggage area, and passenger’s seats, for better costumer experience.
 A modern design that would stand out from other competitors.
 The vehicle has an independent suspension system, and thick tires to overcome all
terrains.
 Has the ability to drive in narrow streets and bicycle lines because of its narrow body.

Weaknesses:
 The vehicle is quite large so may struggle down narrow streets
 Due to the fact it is well protected, material costs are relatively high as there is more
material being used

Opportunities:
 The ability to use the vehicle as a normal taxi and to give tourist tours.
 Because of its narrow body, tours by the seaside are possible.
 There is sufficient space where the current drive train is to incorporate a small
motor. This would either make pedalling considerably easier or take away the
need for it completely.
 The vehicle has the potential to adapt a solar panel, or a paddling energy
converter.

Threats:
 Weather could have a huge impact on the costumers need and wants for taking a
human powered taxi, especially in areas that are rainy and windy.
 Standers and regulations could change, that would affect the dimensions, or the
trade of the human powered vehicles. Such as after the Brexit.

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 Zayd Neseyif Chassis 952682

1.0 Chassis

Design Specifications

The chassis of the Human Powered Taxi needs to be to flexible enough to absorb
vibrations and small bumps while at the same time provide enough rigidity and
support to minimize chance of failure.

The mass of the chassis contributes largely to the overall mass of the vehicle and
needs to be kept as low as possible while keeping up a respectable value of
strength. It needs to be strong enough to have a large carrying capacity as well as
being able to resist light impacts e.g. curbs. A way this can be done is in the design
of the frame as a solid design will allow for less material to be used, keeping mass to
a minimum and resulting in a more sustainable product.

Design Concepts and Development

Inspiration for the chassis came from
the Ariel Atom. The chassis of this
car is a tubular steel frame that
provides sufficient strength for
extreme acceleration while remaining
both flexible and light enough to
produce high quality handling in
corners. The Human Powered Taxi
won’t be put under the same high
stresses of the Atom therefore, a
lighter material can be used for the
frame.

An initial sketch of the chassis shows

a potential way the tubular frame
could be incorporated into the taxi. A
rear wheel drive vehicle with the
driver in the front and a single wheel
for steering.

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 The final concept drawing is an
evolution of the initial sketch, keeping
the three wheeled design and adding
an advanced version of the coverage
for the driver and passengers

A first sketch of the chassis in

SolidWorks using the final concept
drawing and rough estimates for the
dimensions. The front of the chassis
contains extra supports to provide
protection for the driver in the event
of a crash. Cross beams at the rear
introduce rigidity into the passenger
cabin.

Virtual Reality (Gravity Sketch) was

used to provide a real-world
perspective, helping to see where the
frame needed altering. These were
the edits made as a result of the VR
sessions:

● The width of the passenger

cabin was deemed too wide
and an area where weight
could be saved. The width was
cut down from 1500mm to
1250mm.

● The length of the vehicle

appeared unnecessarily long
therefore was cut from
3000mm to 2750mm.

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 ● Opened up drivers’ field of
view

● Opened up headspace for

passengers

● Remove unneeded round

section at front
The final sketch in SolidWorks of the
chassis. All adjustments from the VR
sessions have been made and it is
ready for tubing to be added.

Pugh’s Matrix

Round Tube Square Tube Round Bar

Selection Weightin Ratin Weighte Ratin Weighte Ratin Weighte

Criteria g g d Score g d Score g d Score

Weight 30% 3 0.90 2 0.60 1 0.30

Ease of 20% 1 0.20 3 0.60 3 0.60

Manufactur
e

Durability 20% 2 0.40 1 0.20 3 0.60

Sustainabilit 10% 3 0.30 2 0.20 1 0.10

y

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 Safety 20% 3 0.60 2 0.40 2 0.40

Total 100% 2.4 2.0 2.0

Score

Rank 1 2 2

Material Selection

Yield Strength / Density vs Price per unit mass

The majority of the strength of the Human Powered Taxi is provided by the chassis
and therefore, material selection for this part is very important. To make this decision
CES EduPack was used and the chart above was produced.

The density needs to be kept as low as possible since the vehicle is only being
powered by a single human. Additional weight will require more energy to accelerate

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and brake therefore, reducing handling, efficiency and potentially safety. For these
reasons the density of the material was constrained to 3000 Kg/M^3.

The vehicle is required to take small impacts e.g. curbs and still be fully functional.
That is why the fracture toughness is an important factor in the selection of the
material and was constrained to a minimum of 15 MPa.m^0.5.

The intended use of the vehicle is in the city of Swansea in which water is
guaranteed to come into contact with the frame. It stands to reason that the material
used for the frame needs to be resistant to corrosion both from salt and fresh water.
The restraints for fresh were set to excellent and acceptable for salt.

The flexibility of the chassis is important as too brittle a material would create a very
harsh and potentially unusable vehicle. Too much flexibility would result in a frame
unable to support the required weight. For this reason, the Youngs Modulus of the
material was limited to a minimum of 50GPa and a maximum of 200GPa.

Using the CES EduPack chart a suitable aluminium alloy was singled out: Aluminium
6061 T6. This alloy is a very versatile metal that allows good welding opportunities
and while the yield strength is reduced during welding, the strength can be regained
by a heat treatment and aging process

Tube Size Selection

The inside and outside diameter of the tubing control the yield strength and mass of
the entire chassis. While the yield strength needs to be as high as possible, a minor
increase in the tube wall thickness has a dramatic affect on the overall mass of the
chassis therefore, a compromise has to be made. For the static study the tube was

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set to a length of 1m and fixed at either end as would be the
case in the chassis. A force of 4000N was distributed along
the length of the tube and then the tube was meshed and
run to find the data necessary for the design study. To find
the optimal-dimensions, the design study was created with
the inside and outside diameters as variables. A few runs of
the study were completed to reduce the ranges where
necessary and then a final study was completed. The
resulting dimensions were: Outside Diameter = 50mm,
Inside Diameter = 46mm. The stress was 85.028 N/mm^2
and the mass 814.301g

Joining Method

The material used in the tubing of the frame is Aluminium therefore decreasing the
options for joining methods. The method used to join the tubing of the chassis was
gas metal arc welding or MIG welding. It is a heavy-duty welding process that
instead of using flux replaces it with a stream of inert gas. MIG has the advantage
over torch welding that there is no flux, slag and provides a smart weld. The
disadvantage of MIG welding is that the inert gas that it requires is more expensive
and is difficult to transport.

There are opportunities to automate the process meaning the chassis of the taxi
could be mass produced if required.

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Stress Test of the Chassis

Stress testing was completed on the frame in SolidWorks using a force of 4000N as
well as that of gravity. The fixed geometry was set at the wheel attachments, one at
the front and two at the back, and the force was distributed throughout the base of
the chassis. The yield strength of the chosen material for the frame (aluminium alloy
6061, T6) is shown in SolidWorks as 2.750e+008Pa. The visualisation of the stress
is the image on the left and shows the distribution through the frame with a maximum
of 6.742e+007Pa at the rear wheel attachments. This is a difference of
2.076e+008Pa and provides a safety factor of 4.08 for the frame at the maximum
point of stress. This high safety factor is in anticipation of a significant increase in the
mass of either/both passengers and any extra luggage that may need to be
transported.

The displacement of the chassis is displayed in the image on the left, it shows the
majority of the displacement concentrated around the centre of gravity and has a
maximum of 5.221mm at the centre bar. This is a small value that is expected to
have no impact on the performance of the vehicle but does show that there is an
element of flex in the chassis. While this can be considered a bad thing when there
is too much displacement occurring, with the small values obtained it can be
expected that the frame is going to absorb the majority of bumps and vibrations that
may occur while being used on the road.

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FMEA

Failure Potentia S Potentia O Chance D RPN

Mode l Impact l Cause of
Severit Occurrenc Detection Detectio
y e n

Crack in Very 8 Vehicle 2 Full 5 80

the frame Limited Collisio vehicle
use of n service
vehicle

Dislocate Unable 10 Vehicle 1 Vehicle 3 30

d Tube to use Collisio Inspectio
vehicle n n

Reflection of Design

Overall, I am happy with the design of the chassis. The stress tests showed very
good results and I am confident that this frame could withstand a lot of abuse. The
chassis has a total mass of 35.31kg which is respectable however, the safety factor
is very high. If I were to do it again, I would give minimizing mass a higher priority in
the design study over minimising stress resulting in a lighter frame but a lower safety
factor. Doing this would also reduce the material used so when it came to
manufacture the chassis would be cheaper and more sustainable to produce. I am
very happy with the use of VR during the design process as it notified me of some
necessary adjustments that would have been missed without it. With further practice
this resource could become invaluable to future design processes.

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Drivetrain – Sam Prestwich - 956633

2.0 Drivetrain

Part Requirements
The drivetrain of the human powered taxi is required to convert energy from the driver into
forward drive of the vehicle via the rear axle and the wheel. The cranks are situated near the
front of the vehicle so the drive system is required to be quite long in order to transmit the
up/down motion of the driver’s legs to the rear axle.

Drivetrain Design Specification

1.1 Lightweight All parts of drivetrain must be a light as
possible to keep the overall product
lightweight.
1.2 Human powered Option of assisted electric drive, must conform
to EU Directive 2002/24/EC.
1.4 Ease of manufacture
1.18 Product to withstand outside use, This is very important for the drivetrain, rust
including rain, dirt, salt. and dirt will affect the efficiency.
1:7 Ease of maintenance User must be able to carry out simple
maintenance.
1.17 Withstand minor impacts Withstand drops of curbs.
1.34 Can withstand temperatures between -
10°C and 45°C.
1.33 Can be repaired using existing off the
shelf tools.
1.20 Product lifespan of 5 years.
1.32 Worn parts can replaced. Such as
bearings, chain, cassette.
1.27 Bolts and screws must obey standards BS ISO 885:2000
and regulations
1.33 Most if not all materials used are
recyclable.
Design Evolution

Initial Concept Designs

Concept 1 – Electric assisted drive with chain: a
long chain runs from the cranks to the rear axle.
The system is single speed with an electric motor
above the rear axle to assist drive when needed.

Concept 2 - Belt drive: Belt drive from cranks

to the rear axle. Belts come in limited sizes so
more than one belt and a pulley system is
required.

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Concept 3 – Chain and derailleur: A set up like a traditional
bike, some existing human powered taxis run this system. The
derailleur is situated at the rear axle
and allows a large range of gear ratios.

Concept 4 – Driveshaft: A driveshaft

and bevel gears is used to convert
drive from the cranks to the rear axle. It
is contained in a casing.

Belt Chain Driveshaft

Efficiency 93-98% at high 75-97% , decreases 94%
tension with wear
Weight 87 grams 260 grams Heavier than belt
and chai
systems
Requires lubrication No Yes, requires No
monthly lubrication
Frame must split to Yes No No
remove drive
Readily available Harder to source in Yes, available No, but don’t
developing countries everywhere need replacing
Sufficient length Would require more Yes, can be Yes
than one belt for extended link by link
human powdered
taxi
Needs cleaning No Yes, oil on chain will No
pick up dust and dirt
Requires tensioning Yes No No
Easy to replace Harder than chain Yes Very difficult
Repairable on No Yes No
roadside
Lifetime 10000+ miles 3000 miles 75000+ miles

Pugh’s Concept 1 – Concept 2 – Belt Concept 3 – Concept 4 -

Matrix Chain Electric Drive Chain and Driveshaft
Drive Derailleur
Selection Wei Rat Weighte Rating Weighte Ratin Weighted Rating Weighted
Criteria ghtin ing d Score d Score g Score Score
g
Manufact 0.2 2 0.4 2 0.4 3 0.6 2 0.4
urability
Weight 0.3 1 0.3 3 0.9 2 0.6 2 0.6

Lifespan 0.2 2 0.4 3 0.6 2 0.4 4 0.8

Dimensio 0.1 1 0.1 3 0.3 2 0.2 3 0.3

ns
Maintena 0.2 2 0.4 3 0.6 2 0.4 4 0.8
nce
Net Score 1.6 2.8 2.2 2.9

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From the above Pugh’s matrix we can see the driveshaft design is the preferred for the
human powered taxi. Due to the taxi being used on flat ground in and around Swansea’s city
centre it doesn’t require gears – single speed will be sufficient enough for all gradients it will
cover. The main benefits of a driveshaft system is the very low maintenance it requires and
its overall lifespan. Therefore, its sustainability is also high as waste is minimal.

Pugh’s Matrix Bevel Gear Hobson’s Joint Worm Gear

Visual
Representation

https://www.youtube.com/watch?v=0cU5
oB8V_08

Selection Weig Rati Weighted Rating Weighted Rating Weighted

Criteria hting ng Score Score Score
Manufacturabili 0.2 3 0.6 1 0.2 2 0.4
ty
Weight 0.3 2 0.6 2 0.6 3 0.9

Lifespan 0.3 2 0.6 3 0.9 1 0.3

Dimensions 0.2 3 0.6 1 0.2 3 0.6

Net Score 1 2.4 1.9 2.2

Development of Design
There are a number of ways to transmit the energy 90 degrees from the driveshaft to the
rear axle.

Using Pugh’s design matrix, it was found that bevel gears are the most suitable to convert
the drive from the driveshaft 90 degrees to the rear axle. Bevel gears come in four different
forms; straight, spiral, hypoid and zerol. For the human powered taxi, straight bevel gears
will be used, as they are; the easiest to manufacture, can be designed to take up minimal
space and to be lightweight.

Freehub vs Differential
Due to there being two rear wheels in the design, the design has the problem that if the
vehicle is being driven whilst turning a corner, and the axle is fixed, both wheel will be
turning at the same speed but the outside wheel will be traveling further than the inside
wheel. This therefore creates a problem and the wheels will either jump forward, the taxi will
not turn or a part will simply break.

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Every motorised road vehicle uses a differential to overcome this problem by allowing each
rear wheel to spin at speeds independently to one another whilst still delivering power to
both.

This is also possible by using a freewheel hub in each wheel, a freehub works by a ratchet
system When the drive is engaged the pawls in the freehub push against the teeth and the
wheel is driven. When the drive is not engaged or, like in this case, when the vehicle is
turning a corner the teeth move backwards in relation to the pawls and the wheel does not
engage.

A freehub is much lighter than a differential so will be used within the hub of each rear
wheel.

VR Prototyping
Virtual reality gravity sketch meant the
frame and size of the taxi could be
modelled against the size of the driver and
passengers. This help determine where
the cranks should sit within the frame and
therefore the dimensions of the drivetrain
included the crankshaft.

Design Calculations
The rear wheels being used are 24inch, with a Schwalbe Marathon 24” x 1.75” tyre mounted
on it. The Schwalbe Marathon was chosen because of the ability of the tyre to last up to
18000km and effectively resist punctures. This is an important factor for city riding due to the
problem of broken glass, hedge cuttings and dirt.

Conversion of inches to metres:

24" ∗ 0.0254 = 0.6096𝑚

Calculating circumference:

𝐶 =𝜋∗𝑑

𝐶 = 𝜋 ∗ 0.6096 = 1.9𝑚

Thus, for one rotation of the wheel the taxi will travel 1.9 metres.

Gear Ratio
To choose the correct gear ratio for city riding a bike was tested around Swansea city (see
figure 1), in the areas identified by the questionnaire. It was found that with a 42 tooth front
chainring the best rear cog was 16t. Therefore, the gear ratio was found to be:

42𝑡
= 2.625
16𝑡

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Therefore, the gear ratio chosen for the taxi will be 2.5 to keep manufacture simple.

Figure 1

As a driveshaft has two sets of bevel gears, the gear ratio changes twice. For the shaft bevel
gear to fit on the shaft it must have 10 teeth, therefore to achieve a 2.5 gear ratio from the
crank gear to the axle gear the crank gear must have 20 teeth and the crank gear 50 teeth.

10t
10t
20t
50t

This means for one rotation of the cranks the taxi will travel 4.75 metres.

1.9 ∗ 2.5 = 4.75𝑚

Design Simulation
Due to the driver of the human powered taxi being sat in a recumbent position, the force
through the pedals is not affected by the weight of the driver just the force delivered by their
legs. An average cyclist generates an average wattage of 150W per hour and can peak at
around 1000W.
120𝑟𝑝𝑚
If the peak cadence for an average person is 120rpm, 60
= 2 revolutions per second.
The cranks being used in the design are 175mm long so the pedals will travel 1 metre per
second. As the peak wattage is 1000W, the maximum force that will be applied through the
pedals is 1000 Newtons. Using a safety factor of 2 the driveshaft and gears must be able to
withstand 2000N of force.

A safety factor of 2 was chosen due to the a well-known material being used in an
reasonably constant environment. It is hard to determine the loads and stresses to a high
accuracy due to efficiencies but they can be determined.

Due to the primary constraint of the gear being the size and the number of teeth, stress
testing was used to ensure the design could withstand 2000 newtons. As you can see from

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figure 2 the max stress was 270MPa far below the 305MPa yield stress of medium carbon
steel.

Figure 2

Material Selection
When choosing a material for to manufacture the bevel gear, the primary constraints are:

 High tensile strength – the gear teeth must be able to withstand the static load.
 High surface durability – The surface does not wear easily when under repeated loads.
 Low coefficient of friction – a low coefficient of friction will reduce the friction between
the moving parts of the gears meaning better efficiency for the system.
 Manufacturability – due to the above constraints, manufacturing gears can be
expensive so ease of manufacture is important to reduce cost and time.

The programme CES EduPack was used to decide on the best material for used in the bevel
gears. Its aerospace package provides a highly comprehensive catalogue of materials.
Limits were used to narrow down the most appropriate material.

Figure Young's Modulus/Density against Price Graph

0.1
Young's modulus / Density

Low alloy steel Stainless steel

0.05
High carbon steel

Nickel-based superalloys

0.02

Medium carbon steel

Tungsten alloys
0.01

0.2 0.5 1 2 5 10 20 50
Price (GBP/kg)

27 | P a g e
 Young's Modulus against Price

250

240

Medium carbon steel

230
Young's modulus (GPa)

220

210

200 Low alloy steel

190

High carbon steel

180

0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8

Price (GBP/kg)

Medium carbon steel will be used for the manufacture of the bevel gears due to the good
price, ductility, high tensile strength and high young’s modulus. In particular, medium carbon
steel AISI 1045 will be used. To ensure the steel is optimised for use in gears it must be
normalised and through hardened. Normalising is when the steel is heated and allowed to air
cool, this reduces residual stresses and means the steel is easily machinable. Through
hardening involves heating and cooling the steel whilst maintaining a certain level of carbon
in the surrounding air. These processes ensure the 1045 steel is ductile enough it will not
crack and can be machined effectively but hard enough that it won’t wear under use as a
gear. Steel is preferred over materials such as carbon fibre as it can be recycled easily
increasing the sustainability of the design.

Manufacturing Specifications
When manufacturing a bevel gear, the correct size stock bar is bought in from material
suppliers and then cut to size. Using a lathe a blank is produced, this is the gear body
without the teeth cut out. Sometimes when extreme strength to weight ratio is required the
blank is forged. Next the teeth are cut from the blank, this is a difficult process due to the
complex mathematics behind bevel gear designs (figure 3 shows the the equations involved
to draw a bevel gear on solidworks). There are two methods, the Gleason system and
Oerlikon and Klingelnberg method. The Gleason systems uses a milling machine to cut gap
out separately. The curvature along the face of each tooth is a circular arc whereas the
Oerlikon and Klingelnberg method cuts a face like an extended epicycloid by using the face

28 | P a g e
hobbing method. As the design uses a straight bevel the Gleason system will be used. The
gear is then hardened and finished.

Figure 3

For this design, the gear is joined to the shaft by a key and spline. The key is sunk into the
both the gear and shaft so it is strong enough. The axle bevel gear and crank bevel gear
uses grub screws to attach the gears to the axles.

FMEA
Using the SOD method, the potential risk and likelihood of failure is measured so steps can
be taken to reduce the possibility of these problems.

Failure Potential Sever Potentia Occu Chance of Detectio Risk

Mode Impact ity (S) l Cause rrenc Detection n Rating Priority
e (O) (D) Number
(RPN)
Drivesh - Loss of 8 Damage 2 Checking 7 112
aft drive to shaft the drive
Breaks system prior
- Journey to journey.
unable to
be Feeling
completed problem
when in
transit.

Flat -Delayed 5 Damage 6 Checking 1 30

Tyre Journey to tyre or the drive
wheel system prior
to journey.

Avoiding
glass and
similar
sharp
objects

29 | P a g e
Reflection of Design
Overall I have very much enjoyed the design process of this human powered taxi. I am
pleased with the final design or both my section – the drivetrain – and the final product. I
found the VR and physical prototyping sessions enjoyable and with a bit more experience
these resources could be even more useful.

I am particularly proud of my Solidworks drawing of the bevel gear, I spent a lot of time
improving my Solidworks skills and learning new features. Using the equations function, I
have linked the parts of the bevel gears so you can input the number of teeth, pitch
diameter, angle of action and length of the teeth and a new design is out-putted. As size was
the primary factor for the bevel gear, the number of teeth was chosen to be 10. Ideally I
would also research and test the driveshaft but with limited space this was unattainable.

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31 | P a g e
32 | P a g e
Mesaud algow Seats 841826

3.0 Seats:

3.1 Requirements:
Seats are one of the most essential parts of the vehicle; it is the primary factor driving the costumer’s
experience. When designing seat it is important to take under consideration space saving, and from
information gathering, customer prefer that their luggage is as close to them as possible. Therefore, the
luggage area is designed to be under the seats.

PDS:

3.1 Fits three or more passengers

3.2 Able to have luggage area underneath

3.3 Comfortable

3.4 Safety, design must pass the safety requirements (BS 6102-1 : 1981)

3.5 Ability to hold a load of (>981N/person)

3.6 Can withstand external load (BS EN 12727:2016)

3.7 Lightweight materials

3.8 Eco-friendly materials (PD ISO/TR 17098:2013)

3.9 Width = >37 cm, average person’s width in the UK is 37 cm

Safety and durability are the two key elements of the seat design, to ensure that, some factors must be
taken under consideration:

1. Accurate assembly.
2. Must meet the standers and regulations.
3. Reach a proper safety factor.

Additional improvement to the design could be by adding cup holders, and arm rests.

33 | P a g e
 Mesaud algow Seats 841826

3.2 Concept evaluation:

Concept evaluation is key when designing a product; it starts with comparing the concepts in
a broader view. Then, a weighted matrix with specific terms, to weigh the concepts and
choose the most suitable one. A weighted matrix is shown below, as weight, Durability, and
luggage area, have the highest grade in the matrix.

Concepts Merits Disadvantages

1)wood seat  Flexible, when  Requires external
considering changing material on top of
design wood to protect it from
 Large seating area rain

 Hard to produce
 Expensive

2) leather seat  Comfortable  Expensive

 Leather material will  Requires extra
make it durable attention(cleaning)


3)alloy seat  Luggage can be stored  Hard to change design

underneath the seats in the future
 High mechanical  Sharp edges
properties.
 Good impact
resistance

34 | P a g e
 Mesaud algow Seats 841826
Weighted matrix:
Criteria Weighting Concept 1 Concept 2 Concept 3

Weight 20 6 12 16

Durability 20 7 11 15

Luggage area 20 13 9 15

Ease of manufacture 10 5 8 8

Cost 15 6 7 10

Safety 15 6 10 11

Total score 100 43 57 75

Rank 3 2 1

3.3 Material selection:

Material Advantages Disadvantages Mechanical properties
1060 alloy  Low in price  Weak in  Yield strength
 Good mechanical =27.57 N/mm^2
conductivity strength  Density =2700
kg/m^3
 Cost =0.493
GBP/kg
 Tensile strength
=68.94 N/mm^2
2014-t4  Moderate  Expensive  Yield strength
mechanical  Fragile =290 N/mm^2
properties  Density =2800
 Easy to kg/m^3
manufacture  Cost =
1.51GBP/kg
 Tensile strength
=425 N/mm^2

35 | P a g e
Alloy steel  Good for  Density  Yield strength =
mass 620.42 N/mm^2
production  Density =7700
 Cheap in price kg/m^3
 Good  Cost
mechanical =0.531GBP/kg
properties  Tensile strength
=723.83 N/mm^2

Stainless steel  Corrosion  Very  Yield strength =

(ferritic) resistance expensive 170 MPa
 Density
=7.6e3kg/m^3
 Cost =
4.31GBP/kg
 Tensile strength =
480MPa

A case study carried out by SOLIDWORKS to analyse stresses in four different material, to
choose the most suitable one. The simulations are done with a load of 981 N acting as the
weight of the passenger. The results of these studies are below:

Materials Alloy steel Stainless steel Aluminium 1060 alloy aluminium 2014 -
(ferritic) T4
Factor of safety 19.215813 6.74793 2.015093 21.19289
Stress (psi) 4682.8 3704.2 1984.7 1984.7
strain 0.000057 0.00007 0.000154 0.000147
Displacement 0.00012 0.00013 0.00036 0.00035
(cm)
Mass (g) 36351.1 36351.1 26351.1 26351.1

Figure 4 2014-T4 Figure 5 1060 alloy

36 | P a g e
 Figure 6 alloy steel Figure 7 stailless steel (ferritic)

Taking under consideration, mass, price, and mechanical properties. Aluminium

1060 alloy, showed the best-companied result, therefore, it is the selected material.

3.4 Manufacturing process:

Seat: manufactured using injection moulding, where at first a cast is printed using 3D
printing, after that a melted 1060 aluminium is poured into it. Which is a composition mostly
from aluminium and other materials added into it.

Base: Rotational moulding, its best used for circular part. Therefore, the middle part (pipe)
will be produce using this method.

Bottom: produced using High Pressure Die Casting, were the liquid metal injected at high
speed and high pressure into a metal mould to create the desired part.

Holes: Electric drill used after manufacturing the seat, drilling must be in a slow rate to
prevent any cracks from happing.

37 | P a g e
 Mesaud algow Seats 841826

3.5 Failure mode and effect analysis (FMEA):

Failure Potential Severity Potential cause Occurrence Chance of Detection RPN

mode impact detection
Over-  Seat 7  Un- 3  Not 2 42
loading bending expected allowing
heavy heavy
objects stuff on
the seat
Incorrect  Seat will 8  Inaccurate 2  Double 2 32
insulation fall apart assembly checking
and
having
instruction
sheet
Exceeding  Material 6  Using the 2  Eye 3 36
life spam corrosion product inspection
over the
expected
life spam

3.6 design reflection:

Visual reality sessions were very helpful as it made it possible to see the dimension of the
design in a real scale, moreover, good in seeing trouble or difficulties ahead.
Physical prototyping were good also, but, not as helpful as the VR sessions. Because there
was so little of time and if a mistake has happened there is no coming back, we must start
again.

38 | P a g e
39 | P a g e
40 | P a g e
Dulanaka Welandawe Steering 971665

4.0 Steering
In order to control the taxi’s trajectory, a steering system is necessary. This allows
the vehicle to move in almost any desired direction.
For the three-wheeled layout of the taxi, the most effective steering method is front-
wheel steering. Since the front wheel will be mounted on a fork, the fork will need to
rotate around its axis to accomplish the steering.

The fork is positioned in front of the driver’s cabin, so a system will be required to
steer the vehicle.
The steering system must meet the following requirements:

Steering system requirements (From PDS)

1.5 Lightweight Project Brief

1.6 Durable Drivers focus group

1.7 Easy to use Manufacturing guidelines

4.2 Stability at all times Drivers focus group

4.3 Controls adjustable to driver’s preference Drivers focus group

Figure 6.1: Steering system requirements

Concept evolution

The initial product design comprised of two front wheels, which were steered by a
rack-and pinion steering system. However, this system adds complexity to the
design, which would increase the cost of manufacture and increase weight.
Therefore, the platform was changed to a 3-wheel layout.
The steering of a 3-wheel vehicle can be accomplished by turning either the front or
the rear wheels. However, the passenger seats are positioned directly above the

41 | P a g e
rear wheels, which makes rear-wheel steering impractical because the wheels have
insufficient space to facilitate steering. Also, the unconventional nature of rear-wheel
steering would create complications in vehicle control.
Therefore, a front-wheel steering layout was selected.

By means of a decision matrix, the most favourable steering system was determined:

Design Mas Durabilit Eas Tota Ran Continu

s y e of l k e
use
+ + - 1 2 No

- 0 + -1 3 No

0 + + 2 1 Yes

42 | P a g e
Figure 6.2: Steering system decision matrix

Since the vehicle is to be rear-wheel drive using a foot-propelled drivetrain, the main
requirement of the steering system is that it is hand-operated. Due to the conical
front end of the vehicle, the system also needs to be compact in size and easy to
use. The last concept in figure 6.2 satisfies most of these requirements and is
therefore the most favourable steering system.

DESIGN EVOLUTION

The initial geometry of the front fork: Final geometry of the front fork: reduced
Steering rods will be welded onto the thickness (weight reduction measure).
indented mounting points on the fork. Steering rods will be bolted onto the fork,
and wheel mounts have indents for a
more secure fit.

43 | P a g e
 Initial and Final geometry of the Steering rod.

Initial geometry of the fork-to-frame connector Final geometry of the connector:

triangular bracket with three mounting
points (two for the frame, one for the
fork).

Figure 6.3: Design Evolution

Results from Stress Analysis

The improved part geometries listed in Figure 6.3 have been developed by analysing
the maximum Von Mises stress encountered within each component under a certain
load, keeping a minimum safety factor of 1.25.

44 | P a g e
 Part Simulation Results Conclusion

Fork: Initial Unsuitable:

design High mass
(2295g).
Load: Safety factor:
2500N 2.93
Material:
6061-T6
Aluminium
alloy

Fork: final Mass greatly

design reduced
(1190g), with
a safety
factor of
2.848.

45 | P a g e
 Steering Stresses
rods: Initial below yield
Design stress, with a
safety factor
Load: of 1.43
400N Mass: 1253g
Material:
6061-T6
Aluminium
alloy

Connector Unsuitable:
rod: Initial Yield
design strength
exceeded
Load:
2500N
Material:
6061-T6
Aluminium
alloy

Connector Stresses
rod: final below yield
design strength, with
a safety
factor of 1.64
Mass:
2392g.

Figure 6.4: Simulation results

46 | P a g e
Material specifications
The materials used in the steering assembly will be the same as the frame:
Aluminium 6061-T6. This decision was made due to the combination of light weight,
corrosion resistance, low cost and adequate strength this alloy exhibits. Since the
taxi will operate in Swansea – a humid and windy coastal environment – it is
imperative that the steering system needs to be corrosion resistant for the sake of
durability.
Using lightweight materials for the steering system helps keep the overall weight of
the taxi low and also makes the steering easy to operate, as less force is required to
make a turn.
Additionally, since the material of the steering system and the chassis are identical,
cost is greatly saved because all components can be manufactured from a single
material.

Manufacturing processes
The manufacturing method for the fork will be casting, because of its rounded shape.
After casting, the slots and notches for the steering rods and the wheel are machined
out of the casted part. CNC machining can used for this, considering its advantage of
providing a good surface finish.
Casting can also be used for the steering rods, as these also have a rounded shape.
Mounted on the ends of the steering rods are rubber grips, which would be made of
rubber, or any similar soft material.
The connecting bracket could be casted, but due to its triangular shape and three
mounts it would be more practical to combine casting and welding. Three cylindrical
bars will be welded to form the triangular structure. Then, the outer part of the
cylindrical mounts is machined, after which the triangular framework is welded onto
it. Drilling the holes in the circular parts will finish the connector’s forming process.
The excess metal in this process can be melted and used for the casting process of
the other parts, which will aid in lowering manufacturing waste.

Joining process
The steering rods will be mounted to the fork using a 10mm bolt and wing nut, which
facilitates easy assembly and disassembly. The headset, a set of bearings, will be
press fitted onto the steerer on the fork, after which the connector bracket will be
pressed onto the headset, thereby facilitating rotation. A second bracket, also

47 | P a g e
 Where: S= Severity, O= Occurrence, D= Detection, RPN= Risk Priority Number (S x
including a bearing, will be press fitted slightly higher on the steerer to provide extra
support. Once the brackets are fitted, the top end of the steerer will be plugged with

Component Failure mode Potential S Potential O Chance of D RPN

Impact causes detection
Fork Fracture Loss of 10 Excessive 2 Regular 3 60
control loading inspection
an end cap, which prevents disconnection of the fork from the frame.

Loss of Noise
wheel
FAILURE MODE AND EFFECTS ANALYSIS

Stuck Inability to 6 Excessive 2 Regular 1 12

turn wear maintenance
Damaged Tight
headset steering
Connector Fracture Loss of 10 Excessive 2 Regular 1 20
control loading inspection
Figure 6.5: Failure Mode Effects Analysis

Loss of
balance
Steering Disconnection Loss of 7 Improper 3 Regular 1 21
rods control assembly inspection
General Play in
wear steering rods
Fracture Loss of 7 Improper 1 Regular 2 14
control assembly inspection
Excessive

48 | P a g e
loading

O x D)
Deformation Possible 4 Excessive 3 Regular 1 12
loss of loading inspection
control
REFLECTION

This rod steering system was selected because of its simple form and ease of use.
Other steering systems may have advantages over this system, but are more
expensive to implement, or more complicated in structure. Through the use of an
established concept design matrix, this rod system stood out as the most favourable
steering method for the Human Powered Taxi.
The steering rods are adjustable, permitting easy and comfortable control for any
driver. As a result of simulation testing, this steering method, although primitive, is
certain to withstand the loads acting upon it under normal operating conditions.
The use of symmetrical parts like the steering rods allows for easy manufacture and
maintenance since the parts can be fitted in any orientation; the left steering rod can
be used on the right side of the fork and vice versa.
Aluminium 6061-T6 has been chosen as the material forming the steering system,
due to its corrosion resistance and low weight, with an added advantage being that it
is also used for the frame.

49 | P a g e
50 | P a g e
51 | P a g e
5.0 BODYWORK
The body of the human powered taxi is composed of multiple sheet metal panels that are
welded to the frame of the taxi. The body must resist and ease the impact of a crash to
protect the occupants. It also needs to be as lightweight as possible for optimal fuel
economy and performance. The body designs have evolved over the years and the various
designs have their benefits and drawbacks. A lot of these designs were considered including
the following:

1. The body on frame concept

This was used until the early 1960s by almost all cars worldwide. The material used
in the original frames changed from wood to steel ladder frames in the 1930s. The
frame resembles a ladder with two longitudinal rails bridged by many lateral and
cross braces. The weight of the frame design is a drawback as it is usually heavy and
the two dimensional structure results in unideal torsional body stiffness. The frame
causes the centre of gravity to rise. There are also safety concerns in the occurrence
of a crash as the rails do not deform under impact meaning that a greater proportion
of the energy from the impact is transferred into the cabin and other parts of the
vehicle.

2. Monocoque construction
This is a construction technique in which the external skin supports some or most of
the load (in contrast to the body-on-frame concept where the frame is covered with
cosmetic body panels). The integral floor pan serves as the main structural part to
which all the mechanical components are fixed. The monocoque body structure
allows for crumple zones to be built into it enabling good crash protection. As the
whole structure is an outer shell, this design has the advantage of space efficiency.

3. Unibody design
The monocoque structure is very suited to robotic mass production. Due to high
tooling costs, small scale production is not ideal. The pure monocoque structure is
relatively heavy. A prime compromise of weight and stiffness is achieved through the
shaping of the shell with key consideration of space efficiency rather than a focus on
strength. Sheet panels, unlike tubes, other closed structures and three dimensional
parts, are not very stiff. As a result, the majority of modern vehicular body designs
are not true monocoque designs. Rather a unitary construction method is employed,
commonly referred to as unibody design. The bulk of the vehicle’s strength is
obtained through the use of a system of tubes, box sections and bulkheads. In this
scenario, the stressed skin contributes minor stiffness and strength.

52 | P a g e
 4. Tubular space frame
Specific applications employ the tubular space frame. A three dimensional design
was developed because motor racing engineers due to the ladder chassis not being
strong enough for racing purposes. The tubular space frame design uses many tubes
and other rod shaped components, situated in different directions to provide the
required mechanical strength against forces from originating from any location. This
results in a very complex
welded structure.

A tubular space frame is employed for the design of this taxi as it is allows for the realisation
of lightweight design suited to requirements.

5.1 BODYWORK SPECIFICATIONS (FROM PDS)

SPECIFICATIONS STANDARDS
1.4 Ease of manufacture Frame requirement
1.5 Lightweight Project brief
1.10 Weather resistant Frame requirement
1.17 Product must withstand Physical requirement
minor impact
1.21 Use of readily available Manufacturing
materials guidelines
1.24 Minimal Manufacturing Manufacturing
costs guidelines
1.26 Environmentally friendly PD ISO/TR
materials 17098:2013

CONTINUES ON NEXT PAGE

53 | P a g e
5.2 DESIGN EVOLUTION
Design Description
This is an initial concept design that is
modular, with detachable rails that can
connect the driver’s cab to the passenger
cab. The passenger cab is plastic moulded.
There is no roof.

A roof has been introduced in this iteration

of the design when considering the
environmental operating conditions of the
taxi. The passenger cab is made of sheet
metal when considering the cost and ease
of manufacture in comparison to the plastic
mould. A bag hold has also been
introduced to carry the passengers’ bags.

The rails connecting the roof to the driver’s

cab have been taken away from the design
as they are unnecessary components that
would increase the total mass of the taxi.

The hold is refined to allow for better space

management and leg room for the
passengers.

A roof was designed with consideration with

how the water would run off the component
if it rained. The water was expected to run
off the roof but due to the slope of the roof it
would run down and fall through the gap,
splash in the passenger’s cab and the
driver’s cab.

In order to channel the direction of water

from rainfall on the roof in a better way, a
sheet panel has been designed that acts as
a drain that directs the water away from the
passenger cab off the sides of the roof.

As minimising weight is a major design priority, there is an avoidance of unnecessary

physical body design features. Therefore most of the body is designed to be manufactured
from sheet metal.

54 | P a g e
5.3 STRESS ANALYSIS (SOLIDWORKS SIMULATION)

Design Study 1
Scenarios/Iterations: 13
Parameter Constraint or Initial Optimal Scenario
Goal Format Unit Value Value 1
Thickness2 mm 3 1.2 0.6
< 120
Stress1 N/mm^2 N/mm^2 26.9207 118.16 430.049
Displacement1 Monitor Only mm 0.000311 0.000725 0
Mass1 Minimize g 896.127 358.451 179.225
Displacement2 Minimize mm 0.000311 0.000725 0
Stress2 Minimize N/mm^2 26.9207 118.16 430.049

Scenario Scenario
Scenario 2 Scenario 3 Scenario 4 5 Scenario 6 7
Calculated Calculated Calculated Calculated Calculated Calculated
0.8 1 1.2 1.4 1.6 1.8
178.974 141.77 118.16 91.8077 82.7553 63.6392
0.015144 0.004522 0.000725 0.000802 0.000709 0.000632
238.967 298.709 358.451 418.193 477.934 537.676
0.015144 0.004522 0.000725 0.000802 0.000709 0.000632
178.974 141.77 118.16 91.8077 82.7553 63.6392

Scenario Scenario Scenario Scenario

Scenario 8 Scenario 9 10 11 12 13
Calculated Calculated Calculated Calculated Calculated Calculated
2 2.2 2.4 2.6 2.8 3
53.027 45.4985 39.5491 34.4639 30.2931 26.9207
0.00054 0.000459 0.000429 0.000379 0.00034 0.000311
597.418 657.16 716.902 776.644 836.385 896.127
0.00054 0.000459 0.000429 0.000379 0.00034 0.000311
53.027 45.4985 39.5491 34.4639 30.2931 26.9207

55 | P a g e
5.4 DESIGN STUDY
When designing the body panels of a vehicle, the major design consideration is bending
stiffness. The first major design consideration is bending stiffness. Bending stiffness is the
resistance of a member against bending deformation. Bending stiffness can be determined
analytically from the equation of beam deflection when it is applied by a force.

K = p/w
Where K is the resistance of a member against bending deformation, p is the applied force
and w is the deflection.
There are two types of body panels, interior body panels and outer body panels.
The outer body panels have two other design requirements, resistance against oil canning
(high elastic modulus) and resistance against denting (high yield strength).
To select the final design, the optimal thickness of the outer body sheet metal plates has to
be determined by considering the design exhibiting the ideal combination of the three design
requirements discussed above alongside the mass value to achieve a lightweight design.
In the Design study ran, thickness was a parameter that ranging from 0.6 mm to 3 mm. The
yield stress of Aluminium 6061 T6 is a minimum of 240 MPa. Using a safety factor of 2 (as
the body panels are non-critical components of the vehicle), a constraint is set to fail an
iteration in which the thickness of the body panel results in the design having a yield stress
of below 120 MPa.
Based on goals to minimise the displacement in the direction of the force, stress and mass,
the design study determined the optimal thickness to be 1.2 mm. This optimal panel weighs
360g, has a yield stress of 118 MPa and experienced a displacement of only 0.000725 mm.
The focus of the design study on minimising the displacement when determining the optimal
plate thickness resulted in the selection of a panel design displaying good bending stiffness
and high resistance against oil canning. The constraint on yield strength allowed for the
selection of a body panel with the optimal thickness to have high resistance to denting.

56 | P a g e
5.5 MATERIALS AND MANUFACTURING
Material Selection
Aluminium is a material that is compatible with existing manufacturing processes and
possesses ideal properties such as low density, good mechanical properties, and high
corrosion resistance. Aluminium 6061 T6 has high to moderate strength, good formability for
sheet and good corrosion resistance. It has to be heated for optimal properties and is good
for manufacturing automotive sheets. Aluminium 6061 T6 has been selected as the frame is
also manufactured from tubing in this material therefore a high quality weld can be obtained
between the body sheet metal panels and the frame as they are the same material. The
operating conditions have also influenced the material selection as the body of the taxi will
be exposed to the rain due to Swansea’s typical climate and salty sea water of when
operating around the marina. Therefore it was necessary to select a corrosion resistant
material.

Manufacturing
There are two main commercial metal forming processes: sheet forming processes and bulk
forming processes. Sheet forming processes constitute of sheet metal blanks stretched
under tensile loads to be formed into the required shapes. Some key advantages to using
metal forming processes are the relatively short cycle time, forming at room temperatures
which allows for improvement in the strength of the manufactured part by work hardening
and particularly in the design of vehicles it is one of few metal manufacturing processes that
can produce class A surfaces that are visible to customers.

The aluminium panels will be manufactured by room temperature stamp forming. During
stamping, the sheet metal blanks will undergo manufacturing methods on a press,
experience shearing(blanking, piercing, trimming). The sheet metal blanks will also be drawn
and bent. These processes will transform the sheet metal blanks into the form for use as
body panels on the vehicle.

Joining
The panels will be joined using resistance spot welding. Resistance spot welding is generally
created by robots now-a-days and as a results eliminates human error. Resistance spot
welding does not require any filler material to form the weld. It is also aesthetically pleasing
as the nugget joining the two sheets is completely internal and therefore invisible from the
outside.

Application of lubricants on aluminium sheet surfaces aid formability. These lubricants must be
removed before spot welding as the electrical resistivity of the surface can be changed leading to
weld defects such as porosity and cracks.

Environmental Considerations
Aluminium’s impact on the environment can be minimised by recycling. This can be done
through vehicle recycling centres and take back vehicle programmes. The body sheet metal
panels could be disassembled and retained separately or re-melted.

57 | P a g e
5.6 FAILURE MODE AND EFFECT ANALYSIS

Component Failure Failure Failure S* O* D* RPN Preventive

Mode Case Effect Actions
Body Structural Colliding Loss in 4 4 2 48 Choose
Panels failure of aesthetics material of
foreign high FOS
object,
Impact
loading

5.7 REFLECTION OF DESIGN REVIEW

Due to the nature of the design brief, minimal mass was a requirement for the taxi. A
tubular frame was employed to minimise weight and therefore the body design
involved mostly sheet metal working to fit the frame and still maintain a low mass.
This in turn influenced the choice of material, Aluminium 6061 T6. Although savings
in mass are ideal, structural integrity of the vehicle’s bodies cannot be compromised
as safety is the most important design factor in a taxi. Therefore a design study was
run to help select the optimal thickness of a sheet metal panel that could withstand
the expected collision forces and impact loads.

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6.0 Suspension

6.1 Design specifications:

Suspension system requirements

1 Cost of the suspension system must be low.

2 Weight should be minimum as by itself.

3 Suspension system will be designed such that it can minimize the

tyre wear.
4 With required stability deflection must be minimum.

Suspension 260- Material High strength

length 265mm
Suspension 45-50 mm Cost Low cost
width
Fitting Type Bolt & Nut Assembly & Easy
Disassembly

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DESIGN CONCEPTS:
Concepts Advantages Disadvantages

1) spring shock absorber  High strength  Num of part is

 Easy to more
manufacturing  Due to
 Easy assembly hydraulic
 High impact maintenance
Resistance is High

2) leaf spring  High strength  Heavy

 Installation is
 Extra support very difficult
for the chassis  Not compact
Design

3) Rubber bush  Low weight  Low strength

 Simple design
 Small size  Less durable
 Easy to fit
 Low load
applicable

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Concept matrix:

Concepts
1 2 3
Criteria Weight Ratin Weighte Ratin Weighte Ratin Weighte
g d score g d score g% d score
% %
design 0.15 90 12 50 7.5 80 15
weight 0.2 80 8 45 8.5 75 10
size 0.11 70 10 60 8 85 12
durability 0.16 75 10 65 8.5 80 9
Cost 0.10 80 11.5 95 7 68 9.5
Maintainabil 0.12 90 9.5 75 9.5 95 15
ity
Function 0.16 75 11.5 75 9 75 9.8
Total 1 71.5 58 80.3
Rank yes no no
decision

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6.2 Design evaluation :

1 Maximum value of total deformation is

1.137e-2 mm and minimum value is 0.0
mm. Color indication is shown as rainbow
style in which red color indicates maximum
deformation while dark blue color indicates
minimum deformation.

Some probes are shown at different nodes

in total deformation.

2 The stress distribution on the suspension

system geometry with the probe indication.
Maximum value of the stress is 2.84e+7
n/m2 and minimum value is 1.81e+3 N/m2.
The safety depends on the material
property and allowable maximum stress.
Yield strength of given material is 250 MPa
and produced maximum stress is 28.4
MPa, hence the design is safe.

3 This figure provides maximum strain

produced in the suspension system
1.073e-4 and minimum value as 1.28e-8.

4 While the factor of the safety for system is

high as 3.4e+5 and minimum as 2.18 e+1.

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6.3 Materials and manufacturing process:

Steel alloys are the most commonly used spring shock absorber
materials. The most popular alloys include Medium-carbon, chrome
vanadium and stainless steel.

Material Density Young's modules

Medium carbon steel 7.84 g/cm^3 205 GPa
Chrome vanadium 7.86 g/cm^3 195 GPa
Stainless steel 7.85 g/cm^3 190 GPa

From above table the preferable material is high carbon steel because it
has lower density as well as good young's modules. Moreover carbon
steel will be easier for manufacturing and low cost material among the
others. The manufacturing process for this part will be as following:

Part Machine to be used Process

1) Piston Lathe machine + This part can be
milling machine manufacturing by using
lathe machine the
various steps such as
facing, drilling and
cutting.
2) Spring Spring winding The first step to
machine manufacture the spring
is coiling the metal
using spring winding
machine. Then the coil
will be heat treated to
maintain its
characteristic resilience
3) Cylinder Lathe machine + This part is the same as
milling machine the first one so the
same process can be
done in order to
manufacture it.

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6.4 Failure mode and effects analysis:

Failure Potential S Potential O Chance of D RP
mode impact severit cause occurrenc Detection Detectio N
y e n
Lose bolts Suspensio 2 Incorrect 4 Use torque 4 25
n damage torque wrench to
insure the
right bolts
tightening,
double
check the
installation.
Suspensio Taxi 5 Excessiv 3 Calculate 3 48
n damage damage e weight, and test the
Incorrect suspension
assembl load
y of parts capacity,
check the
assembly.
Spring Suspensio 6 Crack, 3 Preventive 3 41
damage n damage fatigue maintenanc
e.

6.5 Reflection of design review:

From the overall anaylsis it is concluded that using physical and

virtual prototype will save time that is wasted during
manufacturing and will also help predict the error obtained.

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