# GROUP M – Pedal Powered Car

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```					GROUP M – Pedal Powered Car

Report

2008-2009

This document is based on the work on the 5th year mechanical engineering group M which
were set the task of developing a working prototype of a pedal powered car. Improvements
were made the steering, brakes, suspension, seating and drive train of the pervious pedalpod.
New features were added included a hand brake and adjustable seating. The completed
vehicle was then tested where these improvements were found to be successful

Mechanical Engineering Department

James Weir Building, Montrose Street, Glasgow, G1 1XJ
Acknowledgements

We would like to thank Dr. Ian Craighead for his guidance and advice throughout all stages
of the project.

Thanks to Jim Doherty for general advice, assistance with ordering new parts and providing
tools required in the manufacture stage.

Thanks to Frank McKenna for providing the workspace, lockers and toolbox used throughout
the project. And also for manufacturing components as needed by the group.

Finally thanks to Gerry Johnson for assistance with the risk assessments, Steven Black for the
welding done on the seats and Christopher Cameron for his advice during the project.
Notation
Section 5 - Suspension                              Section 8 - Braking

θ cam = Camber Angle (degrees)                        : Initial velocity (m/s)

θ cas = Castor angle (degrees)                       : Velocity after accelerated (m/s)

a: Acceleration (m/s2)
UBJ = upper ball joint
LBJ = lower ball joint                              S: Distance (m)
M: Total mass of body of the car, people
RCH =roll centre height (mm)
W = track width (mm)
m: Mass of a pair of tyres (rear and front)
KL = Kingpin length (mm)                            (kg)

FVSA =front view swing arm                          r: radius of tyres (m)

IC=instant centre                                     : Horizontal distance from centre of
mass to front tyre from side view (m)
Fspring = force exerted by spring (N)
: Horizontal distance from centre of
kspring = Spring stiffness (N/mm)
mass to rear tyre from side view (m)
δ spring
= Spring displacement (mm)               y: distance from centre of mass to four
tyres (m)
Fwheel = force exerted by ‘wheel’ (N)
: Friction coefficient between brake rim
Kwheel = wheel stiffness (N/mm)
and disc
δ wheel = wheel displacement (mm)                     : Friction coefficient between tyre rim
Ccrit = critical damping coefficient
(Ns/mm)                                                  : Diameter of disc for brake (m)
ζ = damping ratio
: Diameter of tyre (m)

Section 6 - Steering

W = wheelbase (m)

lt = distance of applied load from the centre of the wheel

t = track (m)

Φ = steering angle (°)
Contents

1.0      Introduction and Background ................................................................................................. 1
1.2         The 2008-09 Group.................................................................................................................1

2.0      Previous Year’s Work .............................................................................................................. 2
3.0      Group Structure........................................................................................................................ 4
4.0      Design Procedure ...................................................................................................................... 5
4.1         Product Design Specification..................................................................................................5

5.0      Suspension ................................................................................................................................. 8
5.1         Original Suspension set-up. ....................................................................................................8

5.2         Initial Research .....................................................................................................................10

5.3         Analysis.................................................................................................................................12

5.3.1 Initial Considerations ...........................................................................................................12
5.3.2 Geometry of Suspension ...................................................................................................... 15
5.3.3 Springing Requirements – theoretical..................................................................................17
5.3.4 Damping Requirements – theoretical...................................................................................18
5.3.5 Springs and Dampers -Reality .............................................................................................21
5.4         Construction..........................................................................................................................22

6.0      Steering Mechanism................................................................................................................ 25
6.1.1 2006 Steering ......................................................................................................................25
6.1.2 2007 Steering .......................................................................................................................26
6.2         Steering Mechanism Research ..............................................................................................27

6.2.1 Rack and pinion....................................................................................................................27
6.4 Analysis.......................................................................................................................................29

6.5         Construction and Evolution of Design..................................................................................30

7.0      Drive train................................................................................................................................ 34
7.1         Pedals ....................................................................................................................................34

7.1.1          Previous Pedal Arrangement.........................................................................................34
7.1.2          Pedal Analysis...............................................................................................................35
7.2         Drive Chain...........................................................................................................................36

7.2.1          Analysis.........................................................................................................................36
7.2.2          Previous drive chain...................................................................................................... 38
7.2.3          Problems .......................................................................................................................38
7.2.4          Solutions .......................................................................................................................39
7.3          Differential and rear axle ...................................................................................................... 41

7.3.1      Previous year differential and rear axle ............................................................................41
7.3.2          Differential....................................................................................................................42
7.3.3          Problems .......................................................................................................................43
7.3.4          Solution .........................................................................................................................43
8.0      Braking System ....................................................................................................................... 44
8.1          Background ...........................................................................................................................44

8.2 Conventional system and our purpose in brake part ...................................................................44

8.3          Specifications of pedal powered car .....................................................................................44

8.4          Analysis of brake system ...................................................................................................... 45

8.5          Analysis of the stopping brake system..................................................................................45

8.6.         Development of parking brake system..................................................................................48

8.7          Necessary torque for parking the car on a slope ...................................................................48

8.8          Construction..........................................................................................................................51

9.0      Seating...................................................................................................................................... 54
9.1          Original Seating Position ...................................................................................................... 54

9.2          Initial Research .....................................................................................................................54

9.3          Analysis.................................................................................................................................56

9.3.1          Previous Studies............................................................................................................56
9.3.2          Relevance......................................................................................................................57
9.4          Construction..........................................................................................................................58

10.0 Storage ......................................................................................................................................59

11.0     Testing...................................................................................................................................... 60
12.0     Marketing ................................................................................................................................ 62
12.1         Competition...........................................................................................................................62

12.1.1         4 cycle red ....................................................................................................................62
12.1.2         Bikecar ..........................................................................................................................63
12.2      Comparison ...........................................................................................................................65

12.3      Questionnaire ........................................................................................................................65

12.4      Target market for the pedal pod............................................................................................66

12.5      Retail Price ...........................................................................................................................67

13.0     Future Recommendations and Conclusions ......................................................................... 69
13.1      Initial Thoughts.....................................................................................................................69

13.2      Current frame ........................................................................................................................69

13.3      New frame.............................................................................................................................70

13.4      Conclusion ............................................................................................................................70

14.0     References................................................................................................................................ 71
15.0     Appendix A – Breakdown of Cost of Project....................................................................... 73
16.0     Appendix B – Picture of Completed Prototype ................................................................... 74
1.0      Introduction and Background

1.1      Overview

The basis of this project is the development of a pedal-powered car, able to carry two
people and their shopping. This project has significant relevance in today’s environment,
what with oil shortages, the environmental debate and increasing costs influencing some
people not to use a car, and to find some other alternative means of transport.

A bicycle has always been the popular mode of transport amongst the ‘environmentally-
aware’ wave, but it lacks any real luggage space. It is not possible to safely carry any bulky
or cumbersome object on a bike. Somehow if it is possible to combine the benefits of a car
and a bike successfully, then a marketable product may be achievable.

1.2      The 2008-09 Group

The group this year for the pedal powered car consists of 4 Mechanical Engineering
students:

Laurence Dikstra

Daryl Docherty

Shuta Hanagasaki

Donald Ross

Laurence, Daryl and Donald are all completing their final year of a Masters degree at the
University of Strathclyde. Shuta is an exchange student from Japan, and has been in Scotland
since August.

The group are keen to complete a successful project, and are focused in achieving this.

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2.0     Previous Year’s Work

This project has been running for two years, and from this work a car has been
produced, and some development has been carried out. From looking at the previous work
completed, the project was taken forward and improved.

In 2006 the group designed and built the first incarnation of the pedal powered car.
Dubbed the Pedalpod, this was a rather simplistic design, featuring a frame mainly
constructed from box aluminium, and featured bicycle wheels. Braking was on the front
steering was achieved by a simple arrangement akin to a go kart. Two passengers sat side by
side, with a luggage basket on the rear of the car:

Fig 2a: Pedalpod in 2006

From looking at the completed car that year, it was clear that the emphasis was on
keeping the weight as low as possible, which is a major consideration when constructing this
car.

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2007’s group took the Pedalpod, and tried to improve many areas of the car. They
introduced suspension, gearing, a differential system, and also chain driven steering. In order
to include everything the frame of the car was heavily modified, with a completely
redesigned front end:

Fig 2b: Pedalpod in 2007

The result of their hard work was a car that was not useable; it was felt amongst our
group that although their intentions were good, and that their ideas were excellent, they did
not put their plans into action too well. The fact that the best picture of the car (Fig 2.2b)
shows it propped up on axle stands seems to reflect this sentiment.

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3.0     Group Structure

At this point of the project it was decided that each member of the group should be
assigned a subsystem of the car; front suspension, braking, steering, and brakes.

Fig 3a:Group Structure

As it can be seen in Fig 3a the group is organised into a level structure; there is no
hierarchy. Each member is responsible for their subsystem, although members help out each
other when they can. By splitting up the workload, each area is analysed in detail, and
discussed as a group at group meetings.

The group meets up for work every Monday and Wednesday, often for the entire day,
to perform tasks on the car. Each member has access to the group locker containing the tools,
so can come and perform work in any spare time they have available.

In the group locker a logbook is kept, so any work that is performed is documented as
it happens. Also a Google Group was set up for the project, thus enabling a file sharing area
for each member of the group to visit, and add to. Having this page meant that even at home
work could continue as a group. Also through constant use of sms texting and email, the
group was always in touch with one another and communicating. This was particularly
important when Shuta had to leave for Japan mid way through the second semester.

It was decided that to start with the emphasis on creating a sound suspension system
was of the greatest importance initially, as having the car up on wheels would allow other
work to be carried out

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4.0    Design Procedure[1]

The design of any product requires inputs from people from different disciplines and
backgrounds. The pedal pod team was well balanced as it contained members from varying
engineering and cultural backgrounds. However, there was one common goal which was to
produce a working prototype based on sound engineering principles.

History is littered with examples of products that have had excellent marketing with a
poor product and vice-versa. Therefore, it is vital that both components are in place to
produce a successful end product.

4.1    Product Design Specification

All designs begin with several needs and objectives that have to be satisfied and the
pedal powered car is no exception. All aspects of the pedal car design had to be considered
before any construction commenced. The needs of the consumer had to be considered in
addition to needs of the consumer. Therefore, a product design specification (PDS) was
produced as shown below:

Performance

The vehicle is designed as an alternative form of road transport to bicycles, cars and
buses etc. It should travel at maximum speed of 20mph with a normal operating speed of 8-
10mph.

Environment

The vehicle has been designed in the UK for the UK market and it should therefore be
suitable for the climate. The frame is made of aluminium with plastic seats. Therefore,
corrosion is not an issue. However, future models could be fitted with a canopy and or body
panels to provide protection from the elements.

Life In Service

The target audience for the product will be using it as an alternative transport to their
place of work / study over a distance of 5 miles. Therefore, it will only be used for 2-3 hours
per day. It is hoped to cope with this usage for 5 years.

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Maintenance

The vehicle requires minimal maintenance. The seats can be cleaned with soap and
water. The chains will need to be well lubricated to prevent any breakages, the tyres should
be well inflated and all bolts should be tightened before use.

Target Product Cost

The aim is to sell the pedal pod at a cost of £1050. This section has been covered in
more detail in the marketing section; however, the target price is cheaper than the
competitors.

Competition

This section is also discussed in greater detail in the marketing section later in the
vehicles currently in production but there is a gap for the pedal pod in the market.

Quantity

Once again from the marketing section, it is hoped that the company would produce
174 pedal pod models per year with possible expansion in the future.

Size / Weight

Box section aluminium was used to construct the chassis of the vehicle to reduce the
weight as much as possible. The chassis was designed by the previous team and it was felt
amongst the group that this could have been designed to be considerably smaller both in
width and in length. This would have significantly reduced the overall weight of the vehicle
which is currently 300kg with 2 passengers.

Aesthetics

The prototype has not been based around aesthetic appeal. Instead the focus was
placed on producing a successful prototype. However, this is an area which could be
improved in the future with simplification of the design or the addition of colour-coded body
panels. This would make the pedal pod more appealing in the competitive market.

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The design process was conducted over the entire 7 month project period. There was
great flexibility in the design process. As the design progressed, some of the original
specifications were altered. The design activity model in figure 4.1a illustrates this point.

Figure 4.1a – Design Activity Model

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5.0    Suspension

5.1    Original Suspension set-up.

One of the improvements that the last year’s group performed on the car was the
introduction of a simple front suspension, consisting of an uneven wishbone configuration,
and a damper/spring from a mountain bike.           Such an arrangement is a popular design
amongst the kit car fraternity, due to its simplicity and ease of build.

Although the theory for the suspension design was sound, the suspension in practice left
a lot to be desired. It was basically rather very crude, with many flaws:

Fig 5.1a: Car as left by last year’s group,
clearly showing the inadequacies of the suspension.

Fig 5.1a shows that the rather inappropriate angle of the front wheels, caused chiefly
by the suspension construction. It simply wasn’t made properly. More evidence of this can
be seen in Fig 5.1b:

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Fig 5.1.b: Close Up of the Driver’s side front

The wishbones themselves were crudely bolted together, and the wishbones themselves
were bolted to the frame of the car using rather weak brackets. The ‘stubs’ or suspension
‘uprights’ (where the wheels attach to the suspension) were attached to the wishbones by
using lengths of threaded bar. The upshot of using bolts and brackets in the construction of
the suspension was that the whole setup tended not to be robust, and that basically as found, it
was falling apart. This is not desired in a system that should be able to withstand varying
forces over a long period of time

The wishbones were of uneven lengths, but with too severe a difference between them,
which enhanced the atrocious negative camber of the wheels. This can clearly be seen in Fig
5.1.b

.

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5.2    Initial Research[2]

It was decided that the current set up would not be acceptable, so the front suspension
would have to be redesigned. Since at this stage it was not confirmed that the chassis would
be kept in its current configuration, several alternatives to the double wishbone were looked
at.

In car design the MacPherson strut has consistently proved to be the choice of
manufacturers when it comes to front suspension.           Used in Europe since the 50’s, the
MacPherson strut consists of a damper situated within a spring, with the damper at the top
mounted to the car, and the bottom attached to the stub, creating the ‘strut’. When the wheel
is turned, the whole strut rotates round with the wheel.

Fig 5.2.a; Typical MacPherson Strut

It is a commonly – used design largely due to its simplicity, but it was rejected for our
design because of the relative complications sourcing and making the strut (correct weight of
springs, dampers etc). Also, strut ‘towers’ would need to be constructed in order to mount the
strut to the car, again added complication to the project, which would eat into funds and time.

Another design considered for the front suspension for the pedal car was the
transverse leaf spring configuration. The thinking behind why this design may be suitable for
use was the fact that many Hot Rod cars of the 1950’s implemented this design, and many of
these cars were constructed at home.

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Fig 5.3.b; Typical Transverse Leaf Spring

As the name implies, a spring consisting of layers of flat bar are situated across the
width of the car. These acts as the spring of the car and the dampers are attached to dampen
the effect of the spring. Again, this design was discounted due to the fact that the cost in
making an appropriate spring for this application would be rather excessive.

In the end, the final design that was chosen for the car was the uneven double
wishbone configuration. The conclusion was that the idea for the design was good; it was
just that the actual build of the suspension was really poor. As stated in section 4.1, this
design is popular amongst kit car manufacturers, and with good reason. If built correctly, this
can be a durable and reliable configuration.

Fig 5.3.c; Classic Double Wishbone Design

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5.3    Analysis[3]

5.3.1 Initial Considerations

As mentioned at the end of section 5.2 it was decided that a Short Long Arm
Suspension design was to be used. When using this configuration a number of parameters
have to considered:

First of all the wheel camber at the front has to be considered:

Fig 5.3.1.a; Camber of a wheel, θcam
(cross-sectional view-positive camber shown)

There are benefits from negative, zero and positive camber.           Negative camber
improves grip when cornering, and maximises the contact patch area when cornering (on the
outside wheel only). Zero camber allows the greatest straight line speed of the vehicle.
Finally positive camber achieves a lower steering effort from the steering system/driver.

Since the tyres and wheels of the car are very thin (the use of bike wheels-with width
of 50mm, this lends itself to the fact that minimal input is required anyway too turn them.
Also, as it is not a main requirement to produce a car with a great straight line speed (see
PDS), then the need for zero camber is not required. Therefore the decision was taken to
construct the suspension so that the front wheels with a slight negative camber of 5o.

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Castor Angle is another factor to consider when designing the front suspension:

Fig 5.3.1b; Castor of a wheel, θ cas , (side view)

The castor angle of the wheel determines the pivot point of the steering.
Ideally they are angled such that a line drawn through them intersects the road surface
straight ahead of the contact point of the wheel. This provides a degree of self centring,
although too much will mean that the vehicle will be difficult to steer. For this reason it is
decided that a slight castor angle of 3o is decided on.

Track width is basically how wide the front wheels are apart from each other. A
depiction of this can be seen in Fig 5.3.1c:

Fig 5.3.1c; Track Width, w of a vehicle

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Increasing the Track Width has a number of benefits, first of which is that a wider
track reduces the load transfer on turn entry. Also loads are more evenly distributed with a
wider track. More stability is provided is another advantage of setting the track to be large,
but one disadvantage of doing is that a lower top speed is inevitable. This is because the
frontal area of the vehicle is greater, which in turn cause more drag, and so decreasing the
speed. As mentioned before this is not a great requirement of this particular project, and
since the benefits of the wider track outweigh the limitations, then the track width is set
slightly wider than the rear, and is set to be a value of 1346 mm. With this width decided,
then the lower ball joint’s position is found.

The kingpin (also known as a stub) is that the outer ends of the suspension arms are
connected to, and is where the wheel and brakes are mounted onto:

Fig 5.3.1d; Kingpin Length, KL

It is desirable to separate the upper and lower ball joints as much as possible. This
reduces the loads on the control arms. With this in mind, it was decided to make the kingpin
length 320mm, which is 48.5% of the wheel diameter. This meant that the upper and lower
ball joints were positioned a good distance apart, and at the same time kept within the
wheel’s diameter.

A method of attaching the stub to the wishbones is another factor to consider in the
early stages of design. After research it was found the best way to do this was to implement
the use of a rod end, which has a spherical bearing housed within it:

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Fig 5.3.1e; Method of attaching Rod ends to wishbone[4]

In doing so, the rod end still maintains a level of adjustment, thus allowing adjustment
to the camber etc. of the wheel.

5.3.2 Geometry of Suspension[3]

To establish the complete geometry of the front suspension arms, a procedure as
outlined by Milliken and Milliken4 is followed. First the front-view geometry is determined:

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Fig 5.3.2e; Front View Geometry

First the Front View Swing Arm (FVSA) length is calculated using the following
expression:

(w/2)                             wheel camber angle
FVSA =                     , where roll camber =
1 − (roll camber)                        chassis roll angle

The Roll Centre is the next point to be determined. The roll centre is an invisible
moving point about which the car is considered to rotate about in a corner. It is found on the
centre line of the car, and is at a height RCH. This is taken to be at the bottom of the chassis
when looking at the front of the car, and the RCH is decided to be 300mm.

The Instant Centre (IC) can then be found. This is a theoretical point in space about
which a wheel is considered to rotate and when moving in bump and droop. It also allows
the location of the suspension links. Drawing a straight line using the point of contact
between the wheel and the road and the Roll Centre location is the first step; where this line
intersects with the vertical line A-A (determined by the FVSA length) is the location of the
Instant Centre.

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Straight lines are projected from the outer ball joints to the Instant Centre. This
predetermines the inner pivot locations of the wishbones, and so the Front View Geometry is
complete.

]
5.3.3 Springing Requirements – theoretical[5

The requirements of the springs are another factor to consider when designing the
car’s suspension. It has been found that the important characteristics to consider are:

The Wheel Frequency                            The Suspension Leverage

The Coil Rate                                  The Wheel Rate

The Fitted Rate

With the above parameters – in conjunction with the geometry of the suspension – it is
possible to gauge the appropriate spring for this particular application.

First of all the Wheel Frequency has to be decided upon. This is the rate at which the
suspension travels up and down per second. It is well documented [6] that the human body is
adept at dealing with frequencies around 1-1.5 Hz, so it is for this reason that the
suspension’s wheel frequency is decided to be a value of 1.25Hz.

The Suspension Leverage is the leverage exerted on the spring by the suspension
linkages. This can be calculated using the following diagram:

AB
Suspension Leverage=
CB

Fig 5.3.3a Calculating Suspension Leverage for Short Long Arm Suspension

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It had been discovered that if the angle of the spring and damper when fitted and viewed from
the front was too severe, then an adverse effect of a ‘softening spring’ may occur. This
means that to compress the spring a certain length, the chassis has to travel a greater distance
than the length required. A 20o would prevent such an occurrence, and it is for this reason
that the distance CB was set to be 60mm, which would keep the spring as upright as possible.
The length AB was determined to be 340mm as decided in the previous section. Therefore
the Suspension Leverage is found to be 5.67mm

The coil rate of a spring is the amount it compresses under a given load. This
parameter is the value to be sought in order to find a spring suitable for the application. It can
be calculated using the following:

Coil Rate = Wheel Rate x (Suspension Leverage)2

The Wheel Rate is a measure of how strong the spring appears to the wheel bouncing up and
down at the end of its links, and this can be found using the following relationship:

2
 Wheel Frequency 
Wheel rate =                   × Sprung Weight
     187.8       

The Sprung Weight is the Gross Weight of the vehicle (see PDS) minus the Unsprung
Weight. The Unsprung Weight is the weight of the wheel, tyres, hubs brakes etc plus half the
weight of the linkages, coils, dampers etc. By knowing the wheel rate, the coil rate can be
found.

Finally the Fitted Rate is how strong the spring appears to be on the car, taking into
account the leverage exerted on it by the suspension linkage. An expression for the Fitted
Rate is:

Coil Rate
Fitted Rate =
Suspension Leverage

By knowing all of the above parameters, a picture of what the requirements of the
spring can be made, and an appropriate choice can be made for the spring ordered.

5.3.4 Damping Requirements – theoretical[7]

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As well is determining the spring requirements, the damping are another factor to take
into consideration. First of all the dimensions have to be known in order to determine the
physical size of the damper required.

The distance between the top and bottom mounting brackets has to be found. This is
known as the ‘fitted length’, and from the geometry decided upon in past sections, this is
found to be a length of 127mm.          Next the ‘maximum length’ of the damper is to be
determined; this is done by adding 38mm to the fitted length, thus giving the value of
155mm. The ‘minimum length’ is found by subtracting 51mm from the fitted length, giving
76mm.

Furthermore to the information given above, the coil rate (which was found in section
5.3.3) is also required, as is the corner sprung weight of the car whilst loaded. This is to
determine the required damping coefficient for the car. This is achieved by forming a static
model of the suspension.

Fig 5.3.4a: Simplified Static Model of spring system, spring rate of wheel/tire taken into
consideration

As mentioned above, the spring (or wheel) rate provided by the wheel/tyre has to be
determined.   This is achieved by modelling the wheel as an ‘equivalent’ spring acting
between the centre of the wheel and the vehicle body [8]:

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Fig 5.3.4b: Equivalent Spring acting at the Wheel Centre

By performing the following steps an estimate of the wheel rate may be made. First
treating the road spring as linear the basic force displacement relationship is shown to be:

Fspring= kspring x δ spring

Similarly for the equivalent spring it can be shown that:

Fwheel = kwheel x δ wheel

 L spring     
Fwheel = 
L              ⋅ Fspring

 wheel        

Due to the geometry of the suspension, the displacement of the road spring can be
approximated as:

 L spring   
δ spring = 
L            ⋅ δ wheel

 wheel      

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Therefore, from the road spring stiffness and suspension geometry, the wheel rate can be
approximated to be:

Fwheel   L spring               L wheel              L spring  2
k wheel   =        =           ⋅ Fspring  ÷          ⋅ δspring  =          ⋅k
 L
δ wheel   wheel               L                     L wheel  spring
   spring                        

Thus, knowing the above values, a wheel rate can be determined.

For each ‘spring’ (coil and tyre), a damping coefficient can be calculated. First the
critical damping coefficient Ccrit can be expressed as:

Ccrit= 2 2km ⋅

It has been found that for road cars the damping coefficient C in their case is around
0.3 of the critical damping value. This allows for a damper slightly underdamped. The ratio
of C/Ccrit is known as the damping ratio ζ . It is this that is required when specifying the
correct dampers.

5.3.5 Springs and Dampers -Reality

In reality it was not possible to order bespoke shocks and dampers for this project,
since the cost of such items were way out of the project budget. Initial cost investigations
into purchasing tailor-made shocks were that individual units would cost in the region of
£400-500. As a result of this the group decided that cheap coil over units would have to be
used in their place. These were borrowed from mountain bikes available to the group, and
can be seen below:

Fig 5.3.5a; Coilover units used for the construction of the front suspension

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The Coilovers combine both the damper and spring in one unit, with the spring on the
outside of the damper. This means that the unit is both compact and easy to mount, since
each requires only 2 mounting points for both spring and damper, rather than 4 mounting
points if they were separate.

The downside of this is that the correct spring rates could not be used, since these
have a fixed spring rate of 131.35N/mm, and no damper information. Since it was imperative
from the outset that the outcome of this project was to obtain a working prototype, making
the car fit round these Coilovers would have meant tremendous alterations to the car, both
eating into the time and budget. As a result of this it was decided to use these units and make
best of the situation.

5.4     Construction

One of the improvements that were made to the suspension was to improve the way
each wishbone is attached to the chassis. Previously they were attached to the car via crude
brackets bolted to the frame. It was thought that the best way to do this was to create secure
mounting points by bolting flat aluminium plate on the faces of the rectangular front section
of the car. By having the flat plate being 20mm longer on either side of the car than the
width of the car itself, then robust points were created to bolt the wishbones on.

Fig 5.4.a; Mounting point (arrowed) created by lengths of flat bar bolted through box section
of chassis (same on each corner of rectangular front section)

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The original wishbones that were originally on the car were - as mentioned – not of any
standard, and the top wishbones were far too short. Therefore it was felt that new wishbones
had to be made. These were constructed using 20mm diameter mild steel tubing. The
dimension of the wishbones were such that the wheels would be in line with the chassis of the
car, but slightly wider than the rear of the car. Instead of being bolted together, the new
wishbones were welded together, to ensure that they could not slacken.

The wishbones themselves were MIG welded at home to save time and keep the project
costs low. The steel tube was obtained from a local blacksmith for free, which also helped
keep costs low. The ends were gusseted to add strength to the mounting points for the stub.
At the attachment points for the stub (upright) 10mm female rod end bearings were bolted on,
again providing a secure attachment point for the stub.

Fig 5.4b:10mm female rod end bearing

By having the rod ends bolted to the suspension arms, then adjustment could be made
as and when necessary to the camber of the wheels, as mentioned previously

The top wishbones were 20mm shorter than the bottom wishbones, in order to provide
negative camber (and so more grip) when the suspension is in compression. This meant the
camber will go positive in droop and negative in bump. This slight difference in length is
more than adequate, and compared to last year’s effort looks better too.

Suspension is provided by combined spring/damper units from 2 mountain bikes, which
are attached to the chassis. A box section bar is also used to spread the load between the two
mounting points of the spring/damper units.

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The end result was a robust suspension system, with secure mounting points.

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6.0    Steering Mechanism

As stated earlier, this is the 3rd generation pedal-powered car produced by final year
mechanical engineering students. A steady progression has been evident year on year and it is
hoped that this year has been no exception. However, in the previous projects, there were
problems with the steering system. As accurate and reliable steering is a key component to
any vehicle, this area was highlighted as an area where significant improvements were
needed.

6.1 Previous Designs

The two previous steering mechanisms are analysed in the following sections:

6.1.1 2006 Steering

As this was the first year of the project the team had many key decisions to make
combined with a high workload. With regards to the steering they decided that the front
wheels should be held on by forks which allowed the use of bicycle wheels. It was hoped that
the design would reduce the stress on the front wheels axles. The forks that held the wheels to
the frame were able to rotate in a custom made housing to permit unidirectional axial loads.

The steering itself consisted of a basic push and pull rod system using a custom-made
support. The group hoped to use a rack-and-pinion system but budget constraints ruled out
this possibility. The steering wheel was attached to the steering column and as it rotated the
steering arms were pushed or pulled to turn the wheels in the desired direction. The following
picture shows the design:

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Fig 6.1a: 2006 Steering Configuration

6.1.2 2007 Steering

The 2007 ‘Pedal Pod’ team tried to implement many changes on the pedal-powered
vehicle. However, they weren’t able to incorporate all their ideas within the given time-
frame. A push and pull system similar to the 2006 model was used. The steering system was
altered from the previous year as the steering shaft was split in two. Geared sprockets and a
chain connected both shafts with the steering wheel attached to the steering shaft on the right
of the vehicle. This allowed the turning of the steering wheel to be transmitted to the steering
column and subsequently to the wheels.

Fig 6.1b – 2007 steering mechanism- highlighting both shafts

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When the above system was tested it had several problems. The response between
both steering columns was satisfactory; however, the wheels wouldn’t turn. This problem was
heightened due to an insufficient suspension system. Therefore, the area where the wheels
connected to the steering rods had to be redesigned. In addition, the frame of the vehicle
interfered with the chain which connected the steering shafts. The previous group had tried to
solve this issue by using a device to guide the chain. However, this only provided limited
success as friction could still be clearly felt between the chain and the frame when turning the
wheel.

6.2      Steering Mechanism Research

As mentioned previously, it was clear that the steering had to be altered to reach a
satisfactory standard. It was decided that the key objectives were the following:

•   Improve the turning circle
•   Eliminate the friction between the chain and frame
•   Find better way to attach wheels to steering system
•
The push and pull steering system which had been used in the previous 2 years had a limited
turning circle. Therefore, alternative steering options were researched:

6.2.1 Rack and pinion

A rack and pinion design is the most common steering application in small cars and
trucks and it was the most obvious candidate to be incorporated into the pedal-powered car. A
rack-and–pinion gear set is encased inside a metal tube with a tie rod protruding from each
end of the tube. The pinion is then connected to the steering shaft. As the wheel is turned, the
gear spins which moves the rack. A rack-and-pinion gear set converts the rotational motion of
the steering into the linear motion needed to turn the wheels. It also provides a gear reduction
making it easier to turn the wheels. Fortunately, the 2007 group sourced a rack-and-pinion
from the university Formula Student Team. However, they decided not to implement it into
their design. Therefore, in order to use the rack-and-pinion a method would have to be found
to mount it at the front of the vehicle and to connect it to the steering column.

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6.2.2 Recirculating Ball

This steering mechanism is usually found in older cars and trucks. It contains a block
of metal with a threaded hole. The block also has gear teeth cut into the outside which
engages a gear that moves the pitman arm. The steering wheel connects to a threaded rod
which is located in the hole of the block. Therefore, as the steering wheel turns, it turns the
bolt. The bolt is fixed so that when it turns, it moves the block which will subsequently move
the gear which turns the wheel.

6.3     Steering Mechanism Choice

After analysing the types of steering mechanism available, it was decided to use a
rack-and-pinion design on the pedal powered vehicle. This type of steering is the most widely
used in modern vehicles and both of the previous pedal pod groups had stated that the
addition of such steering would significantly improve the performance of the vehicle.

6.3.1 Location of Rack and Pinion

After it had been decided to use a rack-and-pinion method, the next was decision was
to choose a location for the rack-and-pinion. This decision was based on key elements; firstly
it had to avoid the driver’s legs and secondly the avoidance of bump steer.

Bump steer is when either or both of the front wheels start pointing in varying
directions as they move up or down without any input from the driver. This can result in
straight line instability and also a feel of uncertainty when cornering. Therefore, once the
front suspension system had been designed and the location of the front suspension pivots
had been defined, the location of the rack was defined.

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Fig 6.3.1a Determining the Position of the Rack and Pinion[5]

Where, correct R &P Length = F × 2

correct R&P Height = G

The method shown in fig 6.3.1a would have been used if the frame had been designed from
scratch. However, as this was not the case, it is included for reference only. In reality, the
location of the rack and pinion was based on the suspension geometry and the location of the
steering shafts.

6.4 Analysis[9]

The steering system was largely designed in the first semester and in testing had been
shown to be successful. Before any practical work was performed, some simple calculations
were performed to gauge the performance of the steering system.

The equation below can be used to calculate the turning circle (the radius of the smallest
circular turn):

t   W
r=     +
2 sin φ

However, after analysing vehicle data it is assumed that the turning circle for a vehicle of this
size would be 10m. Therefore, this figure was used.

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The chassis had already been designed therefore; the track and wheelbase were known as
shown in figure 6.4a. In low speed applications the turn angle of the inner and outer wheels
would be different when cornering. The average steer angle is called the Ackerman angle δ.
This relates to how much the front wheels must be turned, to R, the turn radius:

Where,

L = 2.1m         R = 10m

L
δ = 5.73 
R

This gave a result of 1.2033º

Fig 6.4a – Explanation of wheelbase and track dimensions[10]

6.5       Construction and Evolution of Design

One of the initial ideas of the group was to change the seating arrangement to be in-
line instead of side-by-side. This would have allowed a central steering position and would
have eliminated the need for 2 separate steering columns. However, this idea was eventually
ruled out as there was insufficient length in the existing chassis. Therefore, it was determined
the side-by-side seating arrangement was the most viable. The suspension system was built
first and the steering was made around it. The steering system has evolved throughout the
course of the year with alterations being made as needed. The development and construction
is summarised in the following pages:

•   The central steering position was scrapped as the team felt the frame had insufficient
length to accommodate in-line seating. As the main requirement from the project

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supervisor was to get the vehicle fully operational, it was decided that time shouldn’t
be wasted altering the chassis.

•   Firstly the steering column built by the 2007/2009 team was connected and tested.
However, when turned the threaded bar at the ends rubbed against the aluminium
frame thus preventing a full turning circle. After a small section of the frame was filed
it was discovered that even with full steering lock the turning circle was poor.

•   This led to the use of the rack-and-pinion (shown if figs 6.5a and 6.5b) which the
2007 group had obtained. The main issues were how to mount it to the frame, how to
attach it to the steering column pinion and how to connect the tie ends to the threaded
bar which controlled the turning of the wheels.

Fig 6.5a: Spline of Rack and Pinion Unit

Fig 6.5b: Rod End of Rack and Pinion

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•   Some creative thinking was needed to solve these issues. In order to secure the rack-
and-pinion to the frame, a simple bracket was made using two pieces of threaded bar.
Holes were drilled at an equal distance from the centre on either side of the front
section of the frame. The brackets then held the rack-and-pinion in a secure central
position.

Fig 6.5c – Rack-and-pinion location

Figure 6.5d – Connection of threaded bar to tie ends and wheel

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•   The tie ends were not wide enough to hold the rod ends which acted as a link with the
threaded bar. However, a small section on each of the tie ends was sawn off to give
the necessary diameter to allow female rod ends to be secured in place. These rod
ends were then connected to threaded bar to complete the steering mechanism.

•   A hollow aluminium bar of 10mm diameter was located from the stores and replaced
the previous central steering column. It was cut to length and it was secured to the
pinion with the addition of a metal bracket which could be tightened appropriately.
Holes were drilled in the new aluminium bar and in the existing steel steering column
further up towards the steering wheel to provide a new location for the gear sprockets.
Extra care was taken to ensure that the holes were parallel and the result was a smooth
steering motion without the slippage or friction from the frame. The position of the
geared sprockets was altered until the optimum position was found. The new position
allowed the tension in the chain to be maintained and eliminated any slippage.

Fig 6.5e – New location of steering mount

•   As the new seating position was higher than the previous models, the steering wheel
was turned around to provide the driver with more leg room when pedalling. A thread
was applied to the steering shaft which allowed the steering wheel to ne attached
securely using a 10mm nut.

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7.0        Drive train

Before any work or design decisions could be made about the transmissions system of
the car the 1st and 2nd year pedal powered cars were looked at. For this the transmission of
the system has been broken down into several section; pedals, drive chain, gears,
axle/differential.

7.1        Pedals

7.1.1      Previous Pedal Arrangement

The pedals used in the second year design were maintained from the original pedals
used in the 1st year design. As there is a single central drive train used the do not have
mountings and sprockets located in-between the crank arms as on a normal bike, instead a
'pedal low' setup is used where the pedals are mounted on bearings at each side of the car plus
two more centrally with the drive sprocket mounted in-between.

Foot
supports

Bearing
housings

Fig 7.1.1a: annotated depiction of pedal layout

The pedals themselves were made from box section with a central arc removed to
allow for rotation of the foot supports around the steel cylindrical bars to which they were

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mounted. These were fixed on with cable ties and a plastic sheet had been rolled round the
bar for a tighter fit. The crank arms were connected to theses steel cylindrical bars via with
bolts in some place and welded in others.

The first simple problem noticed was that a bearing was missing from the pedal unit.
The bearing housings on the outside of the car house 2 bearings at end of the housing
however, only one inside bearing was used on both sides. This problem may have resulted
from lack of funds or the bearings could have been taken off for use on other projects as there
is no mention of this in their report. From testing of the pedals it could be seen that the
pedals where free to move sides ways through the bearings in both directions, leading to a
loss in efficiency in pedalling as well as making the actual pedalling much harder. A final
issue noticed was the weight of pedal unit as the cranks arms and cylindrical bars were all

7.1.2   Pedal Analysis

Two important factors in design of pedals relate to the crank length of the pedals and
the position of the pedals with regards to the seating position. In the pedal powered car the
positions for the pedals were limited if the same setup was chosen, as the height was
determined by the frame, and the pedals could not be brought further forward as the front end
of the frame would interfere with cyclist pedalling motion. This meant that the pedals could
only be moved backwards or the seating changed itself. It was decided that it was best to
keep the pedal mountings as far forward as possible in order to allow for more space in the
frame for storage seating and further improvements.

The seating arrangement is discussed later. Therefore a major consideration for the
pedals was the crank length. Increasing the crank length will increase the moment that can be
applied to the pedals or reduce the effective force required within a stroke. However,
increasing the crank length will result in a decrease in the cadence. For example increasing
an increase of 2.5mm in crank length increases the distance of limb segment motion travelled
in a cycle by 15.7 mm, which results in a lower pedalling speed and can tend to increase
pounding over a fluid stroke and thus deteriorate biomechanical efficiency over the range of
activities. Crank length discussions are further complicated by the fact it is also not only

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dependant on the leg lengths of a person but a complex combination of genetic muscle fibre
traits, condition and application. The other issue with increasing the crank length is the
reduction in minimal angle of knee and hip angles which results in undue strain on the
ligaments and the joints themselves an may cause discomfort to the cyclist. As this vehicle is
design for use by the general public rather than tailored to a specific person choosing a crank
[11] [12]
arm that suits on specific size is not viable. Being guided by various research done
from testing, where a wide range users and crank lengths were compared, it was found that
170-180mm range provided the largest peak and mean power outputs.                Many crank
calculators can be found based on older data which suggest a 170mm crank length to be
changed with a formula linking the inside leg length to the crank length.

crank length(mm) = 1.25 × inside leg length + 65

As this empirical method had given a similar general crank length to that found
through more recent studies it was decided to take the take a crank based on these results.
170mm was chosen as the crank length as it provided the smallest leg movement of the range
which was beneficial due to the frame constraints.

7.2     Drive Chain

7.2.1   Analysis

To know what forces will have to be transmitted by the drive trains of the system and
what the available input to rear wheels will be, the output from a cyclist needs to be known.
The cyclist for this project has to be able to pedal the bike for up to 2 hours at a time at a
constant speed. From testing members of the group it was found that a pedal speed range of
60-90RPM was a comfortable rotational speed to cycle for long durations. Below is a graph
which shows how the torque from an average cyclist varies with increasing RPM of the
pedals, for any cyclist the torque that they can produce is dependent on their leg geometry,
the crank length (which is how far the pedals are from their centre of rotation) and their leg
strength.

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250

200
Torque (Nm)

150

100

50

0
0         50            100               150          200         250
Pedaling RPM

Graph 1: Torque produced by Typical Cyclist

The graph here demonstrates that for a given cyclist there is a given RPM at which the torque
they produce drops off from a maximum. The values from this graph can be used to get the
power from the cyclist with an example shown in graph 2 below

500

450

400

350

300
P er(W)

250
ow

200

150

100

50

0
0      50           100               150          200       250
Crank RPM

Graph 2: Power produced by Typical Cyclist

When comparing this graph with the one above it can be seen that the maximum
power from the cyclist occurs after (at a higher RPM) the torque from the cyclist has reduced

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from its maximum. From these graphs it can be seen that for our assumed pedalling range
(60-90 RPM) the output power from the bike is 160-300watts.

7.2.2   Previous drive chain[14]

The 1st year design contained chain going from the sprocket mounted on the pedal
crankshaft to a sprocket on the rear axle.       The chain was completely unsupported and
nd
unguarded. The 2         year added in a Dérailleur and idler to have a complete bicycle gear
system on the rear axle as seen below.

Fig 7.2.2a: Gear System Introduced

7.2.3   Problems

The chain was still very loose even after the edition of the idler and could easily come
off the sprockets (this was also partly due to the rear axle not being aligned). The chain was
also catching the frame and the guide made using a jockey wheel was not adequate and the
chain came off it all the time.

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7.2.4   Solutions

After initial discussions with technicians about the transmission, they were not approving off
the way it was setup. Some other solutions for a drive train were then discussed.

•    Splitting the chain - This involved adding a new section onto the frame to house more
sprockets just behind where the seats are positioned. This would mean the chain was
replaced with two shorter ones. This would be done with 2 sprockets for each chain
end and 2 gears meshing on the other side of each axle so that the chain would remain
in the same line and no repositioning of the rear sprocket required. However, this

•    Guides and covers - This is based around the fact that in theory the chain of that
length should be work as long as it is built properly. Guides would be added along
the length of the chain to both upper and lower parts similar to that found on the gear
changing mechanism on the rear of a bike. A plastic cover will also be made to house
the entire length of the chain to protect users from catching anything in it

•    A third solution also included chancing the seating arrangements to have a rear and
forward facing incline seat. But this would require a complex reverse of the chain
direction at the rear or the rear passenger pedalling backwards. Neither of which was
ideal, and finally it reduced storage space and meant one rider over hanging the frame.

In the end the simplified solution was also the most beneficial not only in financial terms
but weight saving as well. A pulley wheel housed in box section was used and mounted onto
the cross bar of the frame was used to push the chain downwards on the upper portion. The
box section was also used to guide the chain on either side with the pulley wheel being used
to tighten up the chain.

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Fig 7.2.4.a; chain guide pulley

A guide was also manufactured to keep the chain off of the underside of the frame
using small box section with an 8 mm diameter bolt inserted across section and covered with
rubber pipe to allow the chain to pass under it while being guided again by the surrounding
box section.

Fig 7.2.4.b; chain guide

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7.3      Differential and rear axle[13]

7.3.1    Previous year differential and rear axle

The original design for the rear axle had the wheels mounted onto each end of the rear
axle, with 3 bearings being used to mount the axle to the frame this can be seen in the image
below:

Fig 7.3.1a: Original Design

In the second year of the project the rear axle was shortened to bring it inside the
frame. The 3 bearings were kept as the mounting for the rear axle. At the ends of the axle
free wheelers were located. These were then connected via chains to the rear wheels each on
there own axle and also with another free wheeler. Free wheelers that work in different
directions had to use to have both of them located on the inside of the wheel. The axles for
each rear wheel went through 3 box sections and were different thicknesses being 14mm and
8mm diameter.

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Fig 7.3.2a: Revised Design from Second Year

The decision behind the free wheelers and secondary axles were to include a
differential effect to the rear wheels, as they had found that the inside rear wheel was
dragging during cornering.

7.3.2   Differential

The differential are added because, when cornering the inner and outer wheels travel
different distances and if you have a fixed rear axle then the inner wheel will slip and/or the
out wheel will drag, adding a differential allows the wheels to rotate at different speeds while
receiving the same torque. In the 2nd year project the differential the listed as being included
for this reason however due to budget constraints they were unable to include a differential
such as the one shown in the diagram.

Fig 7.3.2a Cutaway view of a Differential

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Instead ratchets were used on the rear wheels and connected this to the rear axle by
chain. However this method does not allow for the rear wheels to rotate at different speeds
with the same torque going to each. What this methods seems to be doing or used for is to
allow the free wheeling effect that occurs in most modern bicycle when the rear wheel is
connected with a ratchet so the bike can still move forward when the cyclist is no longer
pedal which is extremely useful during downhill periods where input from the cyclist is not
needed.

7.3.3   Problems

The first problem noted with the rear axle was that it was not lined up accurately and
the neither were the end free wheelers. This was caused the chain to slip during cycling
which is not ideal at all. The other issue was that the free wheeler solution did not provide a
differential effect and was instead allow each wheel to free-wheel independently.

7.3.4   Solution

The first solution thought up was so to have the rear gears mounted with a ratchet so
that the rear axle (and therefore wheels) is allowed to rotate ones peddling has stopped, this is
how it was previously working and the addition of differential on the rear axle would then be
needed. However the cost of a differential for the rear axle alone was in excess of the total
budget and deemed as not top priory over all so the 'differential' they had implemented was
kept intact. The rear wheels were wanted to be reattached to the main rear axle as well but
due to the fact the axle had been shortened and the frame modifications meant this was no
longer possible without removing some of the frame. The surrounding frame was to be used
to mount the hand brake and storage so again this design was scrapped.

The rear axle was repositioned along with free-wheels in order to make sure they were
all in line and at the right angle to ensure this no longer caused slipping of the chain. The
axle for the rear wheel which was 8mm was removed as it was bent and clearly strong
enough. The central housing on this wheel was turned to be the same as the right rear wheel.
Then a new 14mm threaded bar was turned to fit to same points on the left wheel as well as
the supports in the frame for the axle was widened to accommodate this.

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8.0       Braking System[15]

8.1       Background

Brakes are obviously an essential component on any vehicle. The functions of a
braking system are to stop a vehicle when in motion, and to keep a vehicle stationary.
Therefore, any braking system must fulfil these criteria

8.2 Conventional system and our purpose in brake part

Although the pedal ‘car’ is called a car, in reality it is closer to a bicycle due to its
mechanism, weight and speed. The brake system of our car was developed taking this into
consideration. There are two common types of braking systems used in bicycles and they
became candidates of our brake system. The first option is a rim brake and the second is a
disc brake. From analysis of the previous system it became apparent that disc brakes were
used on the front wheels, and there was a distinct lack of a braking system on the rear tyres.

The biggest problem with previous system was the absence of a parking brake.
Therefore, after considering all of the above facts, the aim of this years braking system is as
follows:

1. To develop a suitable parking brake for our car

2. Check the existing braking system and modify if required

8.3       Specifications of pedal powered car

Several vehicle specifications are required for the design of the braking system. They
are:

M: 300kg                         m: 5.0kg                       r: 0.33m

: 1.0m                           : 1.0m                       y: 0.5m

: 0.5                            : 0.7                            : 0.08m

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: 0.33m

Additionally, two front wheels are fitted with discs for disc brakes but the rear wheels
do not. The braking system has been designed around this factor.

8.4     Analysis of brake system

In this chapter, necessary braking torque to stop tyres is solved. According to [1],
standard for braking is “30 feet from 20 miles per hour.” In other words, standard for braking
is”9.15 meter from 8.93 meters per second”.        To derive the acceleration in this situation
relationship between velocity, distance and acceleration is used.

Acceleration in this situation can be solved by substituting

into the above equation. As a result, acceleration in
this situation is found to be 4.37m/s2. By using this result, angular acceleration of front tyres
in this situation is solved using relationship between acceleration a and angular acceleration

Finally, necessary braking torque T can be solved as follows.

=3.605N

Our purpose of this procedure is to develop a brake system which can generate
braking torque more than this value.

8.5     Analysis of the stopping brake system

As mentioned before, two front tyres have discs for disc brakes and two rear tyres
don’t have them. Thant’s why the easiest way as the brake system for stopping car is to attach
disk brakes to front tyres. Because of this, analysis considering two disc brakes which are
attached to each front tyre has been done first.

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Firstly, the way of generating braking torque is analyzed. In short, the relationship between
grip strength and braking torque is derived. As a first part, Brake grip is analyzed. (fig8.5a).

Fig 8.5a: Brake grip

From the principle of leverage, grip strength            is transformed to force pulling
wire       with doubling.

(3)

Next, the mechanism of disc brake is analyzed

Fig 8.b5: Disk brake

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From the Principle of leverage, grip strength       is transformed to force pulling wire
with doubling.

Finally, generation of braking torque is analyzed (fig 8.5c).

Fig 8.5c. Generating of braking torque

Pushing force       given by brake pad is transformed to braking torque generated by

friction strength       .

From the above analysis brake torque of disc brake is given as follows.

Each value is given as follows from measured and common data.

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By substituting the above into the Tbrake expression, the brake torque of disc brake can
be derived as 37.68Nm. Although it is assumed that two disc brakes are pulled by same hand
grip, it is enough value for brake of our car. Thus it was proved that to attach disc brakes to
each front tyre is reasonable and to attach brakes on rear tyre is not necessary in terms of
braking.

8.6.    Development of parking brake system

In general, parking brake is attached to rear tyres because of mainly three reasons; to enable
to handle a car when emergency, mainly cars are rear wheel drive and to avoid complication
of mechanism

With respect to the first reason, if a car moves accidentally while parking working, it
cannot be steered and very dangerous. As to for the second reason, it is efficient to lock
driving wheels. Finally the third reason is, because front tyres move due to steering,
mechanism become complicated if parking brake is attached to front tyres. As the vehicle is
rear wheel drive whose front tyre is moved due to steering, it was decided that the parking
brake is attached to rear tyres.

8.7     Necessary torque for parking the car on a slope

At first, it is essential to be calculated the necessary braking torque to park a car.
Because it is obvious that cars have to be parked on a slope, analysis is done in case that car
is parked on a slope whose angle is   as shown Fig 8.7a.

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Fig 8.7a: Parked car on a slope

The equations of force and moment in each part are as follows.

Fig 8.7b: Rear tyre

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Fig 8.7c: Front tyre

Fig 8.8d: Body

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From these equations, necessary brake torque to park our car on a slope is expressed
as follows:

Here, because        is obviously helpful for braking, it is assumed that         =0. By
substituting         , necessary brake torque to park our car on a slope whose angle is      can
be calculated as T=63Nm.

8.8    Construction

To enable necessary torque, the mechanism which transmits and doubles strength
which is given by hand has to be developed. Firstly, since there is no disc for brakes on rear
tyre, rim brake is appropriate for parking brake.

An example of mechanism which transmits and doubles strength is shown as follows.
Equivalent of leverage is used to make the strength doubled in both mechanisms.

Fig 8.8a: Rim brake                          Fig 8.8b: Hand brake

For the handbrake the above figures were attempted to be followed, by constructing a
handbrake using a button release mechanism. A chase was constructed from flat aluminium
plate, as seen below in fig 8.8 c:

In these mechanisms, mechanical parameters are as follows.

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Necessary torque which is given by hand can be calculated as                   by what
is same way as the calculation of disc brake using these parameters, vehicle specifications

fig 8.8 c: handbrake and chase

At the back wheel, the brake blocks were utilised in order to provide a clamping
action. The pins were used from a mountain bike to provide a place to mount the blocks, and
this arrangement can be seen in fig 8.8.d:

fig 8.8 d: brake clamped at the rear

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It was decided that it would be tested to see how well the handbrake worked on one
wheel at the rear first, as opposed to both wheels. The results are discussed in section 10.

For the front wheels braking was provided by the disc/calliper arrangement. A new
brake lever was bought that allowed the fitment of two cables for each wheel:

fig 8.8 e: brake lever attached to wheel

The callipers were mounted onto the stubs using new mountings.

fig 8.8 f: calliper mounted onto stub upright

The effectiveness of these brakes is also discussed in section 10.

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9.0    Seating

9.1       Original Seating Position

It was found that the orientation of the seats on the Pedal Car was that they were
bolted directly onto the chassis, thus meaning that the user’s hips were in line with the pedals,
as depicted below:

Fig 9.1a: Cross-sectional view of original seating position (not to scale)

The chassis proved to be a sound and secure mount for the seats. However it proved
to be nigh on impossible to pedal the car. It was not easy to make the pedals to turn 360o, and
this began the thinking behind the fact that the seating position was to blame.

9.2       Initial Research

First of all vehicles with similar pedalling actions were looked at. The first of which
were pedal boats, also known as ‘pedalos’. These vehicles use pedals to power them through
the water. Its drive system can be seen in Fig 9.2a:

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Fig 9.2a: Drive system of typical pedal boat

As it can be seen above the height of the seat means that the user’s hips are a
considerable distance above the pivot point of the pedals.     Human powered cars were also
looked at for reference:

Fig 9.2b: Human powered car

From the above not only is the driver’s hips above the pedals, but also his seat is
leaning back slightly (i.e. in a recumbent position). Obviously further analysis has to be

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9.3     Analysis

9.3.1   Previous Studies[16]

It was found that much research has been made on the optimal position of the cyclist
in order to obtain the maximum power output. A frequent reference was a paper made by Too
[17], which aimed to determine the effect of hip position on power and capacity in cycling.
16 male subjects were used in testing 5 different seating positions. The seats were angled at
0o, 25o, 50o, 75o and 100o, the respective angles being the angle made between the seat tube
(the tube mounted perpendicular to the seat base) and the vertical. Also the seat back was
kept perpendicular to the ground, thus meaning the seat was rotated as the seat angle was
changed to be at the angles mentioned previously. By using an Ergometer, the power output
could be measured for each seat configuration.

Fig 9.3a Sheet tube angles of 0o and 100o

From the results of the study it was found that the angle at which the maximum power
was achieved when the seat was at an angle of 75o.

Also in a further study by Bussolari and Nadel[18], the effect of reclining the seat was
also taken into consideration. Athletes were used to compare the semi-recumbent and upright

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cycling position. It was found that although the semi-recumbent position had advantages
when it came to aerodynamics (lower frontal area), there was no significant difference in
mechanical efficiency or uptake in oxygen between the two different positions.

9.3.2   Relevance

From research it was clear that the seating position of the car was not correct; the way
it was the seating angle was not great enough, and needed improving. This meant that the
seats would need to be raised a significant amount.

Fig 9.3.1a: Proposed Heightening of Seat

This height increase would mean that it would have to suit the needs of the user, and since
every person is of different heights, would mean that some level of adjustment would be
needed in the seats.

From anthropometry information, it was discovered that the average height of a
British male is 5ft 9in, and the average height of a British female is 5ft 4in. It was felt that
these would be the sizes that would need to be satisfied in order for the seats to be a success.
It was decided to make the seat position adjustable. This was initially chosen to be made
possible by means of channel section, within which a box section sits. This box section was
where the seats were to be mounted. The box section would be able to slide along the
channel section, and the seats could be locked in place by removable pins.

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Fig 9.3.1b: Schematic of adjustable seat proposal, showing seat mount (blue)

9.4    Construction
When it came to building the new seat configuration, it was found that in order to
raise the seats, the simplest way would be to use the original seat legs, which were at the time
being used as a luggage compartment. By using these it gave an ideal place to mount the
seats, since that is what they were originally used for.

Channel section was welded to the chassis, and box section was used to run in the
channel. To mount the seats onto the box section, holes were drilled into the box section to
locate the legs of the seats. The result can be seen below;

Fig 9.4a: Final seat design

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10.0 Storage

The original requirement of the vehicle stated that it had to provide transport for 2
people plus luggage. Therefore, to satisfy this requirement storage boxes were fitted to the
rear of the pedal car. In previous years there was a basket arrangement in place. However, the
group feels that this area has progressed with the addition of 2 plastic storage boxes. They
provide ample storage space for around 6 shopping bags and they can be held securely in
place. This can be seen in greater detail in figure 10.1 below:

Figure 10.1 – Storage Boxes

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11.0 Testing

Upon completion of the manufacture of the pedal powered car a date was set aside to
take the car out of the university to be tested. A wide open tarmac area was required for
testing where other we would not affect nor be affected by other vehicles. Glasgow green
was chosen as the place for testing due to the wide tarmac paths and being generally free
from motorists.

The car was tested in several areas which included the brakes, the steering, the
pedalling, suspension and drive train by each member of the group as they were all different
sizes allowing for a better testing of the pedalling setup.

The front brakes on the car were tested after straight runs and down hills to see if the
car could be brought to rest in a reasonable distance. The front brakes were found to be fine
and managed to stop the car in the desired distance from speed. The brake lever position was
found not to be ideal, but was still comfortable enough to.

The handbrake was tested on several hills while at rest to see if it would keep the car
stationary and also applied just after rolling started to see if it applied enough friction to stop
the car. A video recording of the handbrake test was taken which can be seen here[19]. The
handbrake performed well in all tests as it brought the car to rest from downhill rolling and
also kept the car stationary on several differing hill gradients when it was locked on. The
position was found to be fine with it being easily and reached by the driver.

The steering on the car was tested on several 90 degree corners to in both directions as
well as downhill corners and also on a small roundabout that was located at the testing area.
A video of one of the cornering tests can be found here[20]. While the steering mechanism
itself was found to be function well with both wheels turning together and with not lag from
the steering input, it was noted that the turning circle of the car was inadequate and should be
improved.

The vehicle was pedalled on flat inclines and downhill paths while being peddled by
one or two cyclist. Videos of the tests can be seen here[21][22]. The pedalling from a seating
perspective was fine for all group members however the steering wheel did affect the ability
of the driver to pedal. The guides placed on the chain seemed to work fine as the chain never

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slipped or came off during the testing. The gearing also allowed the car to be pedalled up
inclines when put into 1st gear.

Suspension

The suspension was tested during all the pedalling of the car and on its transport to the Green.
During transport to Glasgow green the car was pushed along the pavement and had to go over
many Krebs and potholes. After the journey the suspension was checked and found to be
good condition with not parts coming lose. The suspension worked well during corners and
braking in the test done at Glasgow green

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12.0 Marketing

The pedal powered car is designed to working prototype with a view to being a viable
product in the market place. First a range of pedal powered cars on the market will be looked
at to discuss their pros and cons.

12.1   Competition

12.1.1 4 cycle red [23]

Fig 12.1.1a: 4Cycle Red

This vehicle can clearly be seen to be a 4 seater with all the passengers being able to
pedal. It has 7 forward gears and one reverse gear. All 4 seats are also adjustable in height.
It has a handbrake as well as disc brakes on all four wheels. It has a length of 2.65m weighs
96kg and is priced at £5,296

This vehicle is aesthetically pleasing as well as light weight and high on features.
However the safety of the design is questionable with the short wheel base and high ride
height which is susceptible to toppling. It also has no luggage space.

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12.1.2 Bikecar[24]

Fig 12.1.2a: Bikecar

Fig 12.1.2a does not show the complete version of this pedal powered car. The space
frame around the car houses a body shell and wind shield so this protects users from the
environment. The cost of the vehicle is listed at £2745 and it weighs 181.2kg. Some of the
features include disc brakes on each wheel, 4 seater and 6 speed gears.

A main benefit of this vehicle is the outer shell allowing use in multiple weather
conditions. However the weight is an issue and so is the lack of luggage space and parking
brake.

This car is 2 seater and based around 2 bicycles joined together too make a pedal
powered car as 2 independent drive trains and rear axles. It has space for luggage at the rear
as well choices for upgrades such as a motor assist which leads to a price range of £816-1700.
It also has brakes on all four wheels and 6 speed gears.

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The benefits of this vehicle are it optional extras to cater for a wider market as well as
its luggage space and its small design. Lack of parking a brake and the fully independent
drive of each rear wheel is a concern.

This vehicle is similar to the Rhoads vehicle in that it has two independent drive trains
and is designed for two users. It has a roof but no side front or rear covers so is more of a sun
screen rather than any weather protection. It also has luggage space and is priced at £900.

This is larger than the previous 2 seater which would be considered a downside as
storage space is the same. The sun cover is useful but shows it is design for specific place or
uses at certain times of year. Not have a parking brake is also a problem along with an
impractical drive train.

Those were the main pedal cars that are actually available to buy, as can be seen from
the inclusion of the 4 seater cars that there is a very small variety of machines on the market
for pedal powered cars and specifically the 2 seater kind described in the objectives of the
project.

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12.2   Comparison

The Pedalpod created was then compared with the competitors discussed too find any

•   Gears; the pedal pod has less gears than all the competitors listed meaning l lower
range of speeds where the cyclist are a t optimal cadence. However, the vehicle with
the largest gear selection was 7 speed which is only 2 more than on the pedal pod

•   Aesthetics; this is often a very important factor to general public when choosing a
product and the most expensive car listed is the most attractive vehicle here. While
judging this is subjective it should be noted that when colleges were asked the pedal

•   Storage; both the 4 seater vehicles gave up room for storage by including a second set
of seats. The two 2 seater ones shown have a smaller volume in storage size when
compared to the pedal pod; this advantage is significant as it allows the 2 teasers to be
used for shopping purchases as well as general transport.

•   Brakes; all competitors shown have brakes disc on all 4 wheels where as the pedal
pod only has front brakes. The pedal pod and the 4 seater vehicles have a handbrake
which opens up more places to leave the vehicle parked when compared with the
other 2 seaters.

•   Weight; another very important factor in which the most expensive car comes out on
top due to its use of expensive lightweight materials. The pedal pod is the heaviest of
the 3 two seater cars which is a definite downside.

•   Cost; The 4 seaters work out vastly more expensive than the rest and the low price of
the pedal pod opens it up to a much larger market in terms of affordability

12.3   Questionnaire
A questionnaire was setup in order to find people’s views on pedal powered cars and
also whether or not they would be interested in buying one. This was done so that it could be
seen if a potential market for the pedal pod exited and also what that market was. As this is a
human powered device and considered ‘green’ technology questions regarding how
environmental a person was to establish if that was a factor in them being interested in the
product.

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Questionnaire

How old are you?

…..............................................................................................

Do you cycle often? (Y/N)

………………………………………………………………

Do your family and friends cycle?

…..............................................................................................

Have you heard of pedal powered cars? (Y/N)

……………………………………………………………….

…...............................................................................................

Are you environmentally active and if so, in what way?

…..............................................................................................

What price do you find reasonable for this product?

….............................................................................................

Would you buy a pedal powered car?

….............................................................................................

12.4       Target market for the pedal pod

With any product is has to fit into or cater to a section of the market available to a
product type. As the pedal pod is 2 seater and has storage space unlike the 4 seaters means
that it can be used for shopping, transport or general cycling. As a normal bike can be
purchased from prices starting at £60 it will be very hard to take any market share directly
away from bikes due to the cost alone. Therefore marketing campaigns show focus on the
unique features and group aspect of the pedal powered car to clearly distinguish itself from
the bike market. It should be aimed at the environmentally conscious section of the public

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first, as this is the group most open to the idea of cleaner technology and will accept some of
the disadvantages of the pedal car more easily. Couples in the 20-30y range as well as for
family groups are also more viable candidates for this product as it is very impractical for
solo use. Also the distance the person has to travel to get to a destination is also a factor in
determining whether they would use this product. The reasoning being is 2 seater means that
its needs to target people who may go out for cycle together and also people who would use
in this instead of a car despite the inconveniences it has due to the environmental reasons. As
we believe this market exists then there this definite scope for turning this prototype into a
production model. Due to the reasons listed above the pedal pod is definitely a contender in
this market when compared to its contenders.

12.5   Retail Price [27]

The cost of production of the pedal powered car has been determined by assuming
production is in Poland. This was chosen for the low labour costs and because it is inside the
European Union therefore allowing for easier operations and less tax associated transporting
and selling the vehicles to other countries within the EU. The average wage was found to be
£5500 (1), with a build time equal to that of the estimated used last year of 120 hours.
Assuming normal holidays that allows for 261 working days per year last years’ model
estimated 312) and with 8 working hours per day that amounts to 2088 working hours per
year meaning. This means that 17cars can be made by each employee. Assuming a small
business at first with 10 employees this allows for 174 units to be made each year under these
conditions.   The Table shown in appendix A shows all the cost attributed with the
manufacture of the vehicle from the third year. The car however was developed over 3 years
and the parts cost during the first two semesters came to £675, bringing the total parts cost to
£884.52. However much of the aluminium and bolts being reorder to for design changes and
also missing items being replaced means the material cost of manufacture comes to £660.

The parts ordered was all done from UK suppliers and at small quantities. Therefore
due to over 100 of each part being order the price of each item can be expected to go down
buy as much as 10% due to mass purchase. A further 5% reduction is assumed again for the
reduced cost of the same materials in Poland in comparison with the UK. This means the
parts cost for each vehicle comes to £561. As the vehicles are to be sold in the UK transport
cost for each unit have to be taken into consideration. Karman shipping[28] gives costs

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estimates of £1500 per container which would cover 18 units putting shipping costs to £83
per unit. Combining the new total unit price, £634, with wage costs it was possible to see
how long it how many units or if at all it would break into profits. It was found that with a
price of £953.70 would mean that the pedal pod would break even after having sold all 174
units made in a year. For a sale price of £1000 it breaks even after 152 units and makes
£8000 net profit after all sales are complete. The final price settled on was £1050 as only
77% of units made need to be sold in order to turn a profit with the end of year profit being a
maximum of £16750

The sale price could be increased higher still but then competitor price becomes a
problem. With a final price of £1050 it puts the pedal car well within the price ranges of the
2 sweater competitors and significantly cheaper than the 4 seater competitors listed. The net
profits do not take into account the development cost of the car which would include the total
parts cost over the 3 years plus technician and student time required input into the project.
The numbers obtained for this should not be taken as the ideal price for a pod car due to the
amount of assumption used in these calculations. However it does give a good indication of
the competitive price the car is able can be sold at with regards to its competitors.

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13.0 Future Recommendations and Conclusions

13.1    Initial Thoughts

From the outset of this project the group as a whole thought that the main design of
the chassis was not appropriate for the application; it was too long and wide, which in turn
added unnecessary weight, and meant that all the important factors for a road-going vehicle
is bound to be affected (turning circle, braking distances, speed etc.). It was felt that much
damage had been done to the progress of the project by the group last year, and the main
attributes of the initial car (lightweight, simplicity) had been lost.

However, it was clear that the main objective of the group should be to complete a
working prototype. If the decision was forced to construct a new chassis, then this objective
would have not been met. As such the group made ‘the best of a bad job’ and continued to
work with the original chassis, although it was clear that this was not an optimum design.

It is felt that next year’s group has two main choices; either continue with the current
frame, or construct a completely new frame from scratch. Within both these choices there are
factors to consider.

13.2    Current frame

Chain guard -If continuing with the current frame one of the improvements that can
be made is to include a guard from the chain mostly like a plastic shell around the top half of
the chain to protect cyclist hands from getting caught. This problem is less significant than
before due to raised pedalling position.

Seats – The current seats are plastic seats which have been used in each year of this
project, an upgrade to a more comfortable and specially shape seat would be ideal, as this
would allow for greater freedom of leg movement without contact with the seats.

Steering frame- The frame upon which the steering column is mounted should be
moved forward or raised to accommodate for the new cycling position adopted in this years
design, this would require the shortening of the two support box sections to move the bar
further forward.

Brakes- Only the front wheels have discs in them for use in a disc brake setup, the

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rear wheels could be replaced or equipped with this to allow for breaking on all four wheels
instead of the front wheels only. The hand brake is only applied to the right rear and could
also be improved by applying to both wheels or clamping onto the rear axle.

Steering – While the steering has improved on last year the turning circle remains
inadequate, to increase this either a different steering approach is needed or a rack and pinion
unit with a larger rack is needed. A further solution would be to increase the Ackerman angle
by increasing the length of the length l brackets mounted on the wheel struts.

Weight – As this is a human powered vehicle weight is a major concern and future
improvements could go into reducing the overall weight of the pedal car. The weight of
rotating parts is of particular concern such as the steel pedals and rear axel, but some
framework at the rear end could also be improved.

13.3   New frame

If a new frame is to be used in future the group should focus on having a much
smaller and much more compact frame as the current ones is far to large for what it is used.
The entire frame should be designed around the pedalling position to be adopted in the car.
This was a particular problem of this years project as every solution thought up or attempt
came into problems with the current frame and compromises had to be made. In the first year
it was designed for recumbent style cycling but the frame for the steering was set to high to
be reached comfortably. The exact volume and location of storage place should be decided in
advance, having one large area for storage is not required but it certainly increases ease of use
for the users. Placement of brakes should be included when designing the frame as the
inclusion of brakes in this years car proved problematic with having to add section to the
frame at each wheel. The wheel base of the car should be reduced and this would allow for
the same rack and pinion to be kept while improving the turning circle of the car.

13.4   Conclusion

After being set the task of constructing a working prototype, it is felt that the group
achieved this goal.     However it is the opinion of the group that the current chassis
configuration is not optimal, and strongly advised to design and construct a new chassis from
scratch if the project is to continue next year.

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14.0 References

[1]    Pugh, Stuart ‘‘Total Design’’ p48-55

[2]    Car bibles – suspension bibles

http://www.carbibles.com/suspension_bible.html

[3]    Milliken and Milliken, ‘‘Race Car Vehicle Dynamics’’,1995 SAE International

[4]    Staniforth, A, Chapter 3 Location ‘‘Competition Car Suspension’’, Haynes Publishing
(p88)

[5]    Staniforth, A, Chapter 7 The Amateur at Work ‘‘Competition Car Suspension’’,
Haynes Publishing

[6]    Autospeed –Springs and Natural Frequencies

http://autospeed.com/cms/title Springs-andNaturalFrequencies/A_108167/article.html

[7]    Staniforth, A, Chapter 9 Dampers ‘‘Competition Car Suspension’’, Haynes Publishing

[8]    Blundell, M, Harty, D, Chapter 4 Modelling and Analysis of Suspension System ‘‘The
multibody Systems Approach to Vehicle Dynamics’’ (p171)

[9]    Stone, R, Ball; Jeffrey K, ‘‘Automotive engineering Fundamentals’’ p307-311

[10]   Wikipedia.org

[11]   On the relation between joint moments and pedalling rates at constant power in
bicycling. Redfield, R. and Hull, M. L. (1986). J. Biomech. 19: 317-329.

[13]   Kinematics and dynamics of machines by George H. Martin, New York, McGraw-
Hill 1969

[12]   The effect of pedal crank arm length on joint angle and power production in upright
cycle ergometry Danny Too; Gerald E. Landwer Journal of Sports Sciences, Volume
18, Issue 3 March 2000 , pages 153 - 161

[14]   The dancing chain : history and development of the derailleur bicycle. Berto, Frank;
Ron Shepherd, et al (2005), Van der Plas Publications/Cycle Publications. pp. 162.

71 | P a g e
[15]   Richard Stone and Jeffrey K. Ball, ‘Automotive Engineering Fundamentals’, SAE,
2004, 397-433

[16]   Abbott;Wilson, Chapter 3 Human Power to Modern Vehicles ‘‘Human Powered
Vehicles’’ p42

[17]   Too, D (1991) The effect of hip position/configuration on anaerobic power and
capacity in cycling. International Journal of Sports Biomechanics, 7 359-370

[18]   Bussolari, S.R.,7 Nadel, E.R (1989) the physiological limits of long-duration human
power production: Lessons learned from the Daedalus project. Human Power, 7(4) 1-
10

video

[22]   http://www.youtube.com/watch?v=f2jDqiRK-yk&feature=channel – two users video

[23]   http://nexus404.com/Blog/2007/07/05/4cycle-red-the-zero-emission-four-seat-pedal-
car/

[24]   http://www.cicle.org/cicle_content/pivot/entry.php?id=1335

a-car

[27]   http://epp.eurostat.ec.europa.eu/cache/ITY_SDDS/Annexes/earn_minw_sm1_an1.pdf

[28]   Karman Shipping Ltd, www.carshipping.co.uk

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15.0 Appendix A – Breakdown of Cost of Project
Parts               Quantity        Cost (£)    Sub Total (£)

Rod ends                 4            £10.03         £40.12

Solid aluminium bar (5m)        1            £20.00         £20.00

Aluminium tube (2M)            1             £0.00          £0.00

Threaded bar (various)        10             £0.00          £0.00

Rack and pinion             1             £0.00          £0.00

Jubilee clip              2             £0.60          £1.20

First semester total                                      £61.32

Second semester              -               -              -

Pedal bearings             1             £3.85          £3.85

Plastic containers           2            £10.75         £21.50

Aluminium Channel section(5m)      2            £17.99         £35.98

Aluminium box section (5m)        2            £18.95         £37.90

Guide pulley              1            £17.99         £17.99

Brake blocks              2             £4.98          £9.96

Brake lever               1            £15.02         £15.02

Brake cable               4             £1.50          £6.00

Second semester total                                      £148.20

Total Budget                                           £400.00

Total expenditure                                        £209.52

Remaining budget                                          £190.48

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16.0 Appendix B – Picture of Completed Prototype

Fig 16a: Prototype at Glasgow Green, Glasgow

Fig 16b: Prototype parked on Montrose Street, Glasgow

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