Creating Sustainable Water Access in Guinea Bissau
LOVISA GRÖNVIK, MAJKEN DOMICELJ
Examensarbete TRITA-ITM-EX 2018:84 KTH Industriell teknik och management
Bachelor Thesis Spring 2018
Bachelor Thesis TRITA-ITM-EX 2018:84
Creating a Sustainable Water Access in Guinea-Bissau
Majken Domicelj Lovisa Grönvik
Approved
2018-05-14
Examiner
Ulf Sellgren
Supervisor
Ulf Sellgren
Commissioner
UNICEF
Contact person
Fredrik Asplund
Abstract
In Guinea Bissau, one of the third most underdeveloped countries, there are many areas that are hard to reach by any other kind of vehicles than motorcycles – cars struggle with the poor road conditions. This means that many smaller communities, that are at a considerable distance from a larger road or city, become isolated and vulnerable. When the water pumps break down, one of the main issues in the repair process is that the pump mechanics simply struggle to transport their tools and spare parts to these areas. The consequence is that the water pumps are left broken and out of use and people go back to using the water holes instead, where the water normally is of significantly worse quality and often contaminated.
This leads to sickness, diseases and loss of workforce in the entire country.
This project aims to develop a prototype of a monotrailer that can be used by the pump mechanics in Guinea Bissau. A monotrailer is a transport vehicle which is attached behind a motorcycle. Motorcycles have very limited loading options, but with a monotrailer the possibilities can be extended. The road conditions are rough, the area of usage is hard to define and the manufacturing possibilities are limited. Given this, the challenges of this project is to develop the monotrailer in a way that it can be manufactured on site and fulfil its purpose.
The project has been carried out in both Stockholm aa well as in Guinea Bissau and is a cooperation between KTH and Unicef Wash Section.
Keywords: Integrated product development, machine design, monotrailer
Bachelor Thesis Spring 2018
Examensarbete TRITA-ITM-EX 2018:84
Utveckling av hållbar vattentillgång i Guinea-Bissau
Majken Domicelj Lovisa Grönvik
Godkänt
2018-05-14
Examinator
Ulf Sellgren
Handledare
Ulf Sellgren
Uppdragsgivare
UNICEF
Kontaktperson
Fredrik Asplund
Sammanfattning
I Guinea Bissau, som är ett av världens tredje mest underutvecklade länder, finns många landområden som är svåra att nå med något annat fordon än motorcyklar – vägarna är så undermåliga att bilar har stora svårigheter att ta sig fram. Det innebär att många mindre samhällen och byar som ligger på betydande avstånd från en större väg eller stad, blir isolerade och lätt hamnar i en sårbar position. När vattenpumpar i byarna går sönder, har det visat sig att ett av de största problemen kring reparationsprocessen är att pumpmekanikerna helt enkelt har svårt att transportera sina verktyg och reservdelar till dessa platser. Påföljden blir att vattenpumparna står oanvända och befolkningen återgår till att hämta vatten i
vattenbrunnarna, där vattnet är av betydligt sämre kvalitet och ofta kontaminerat. Detta leder till ohälsa, sjukdomar och bortfall av arbetskraft i hela landet.
Detta projekt syftar till att utveckla en prototyp av en monotrailer för bruk av pumpmekaniker i Guinea Bissau. En monotrailer är ett transportfordon som fästs bakom en motorcykel.
Motorcyklar har väldigt begränsade lastmöjligheter och med en monotrailer kan dessa utökas.
Vägförhållandena är tuffa, användningsområdet för monotrailern är svårt att definiera och tillverkningmöjligheterna är begränsade. Givet detta, ligger därför utmaningen i detta projekt att utveckla monotrailern så att den går att tillverka på plats och fyller sitt syfte.
Projektet har utförts både i Stockholm och på plats i Guinea Bissau och är ett samarbete mellan KTH och Unicef Wash Section.
Nyckelord: Integrerad produktutveckling, maskinkonstruktion, monotrailer
Bachelor Thesis Spring 2018
Preface
Initially, we would like to thank Fredrik Asplund, Chef at Unicef Wash section and supplier of this project, for the opportunity to visit Guinea Bissau, for his remarkable passion and for our long nights and fruitful discussions at Caipirinha Bar. Furthermore, we would like to acknowledge our supervisor Ulf Sellgren, for his support, adequate advice, knowledge and wise contributions.
We would also like to thank Zeca Da Silva, consulting constructor to Unicef and this project, for his immense enthusiasm and remarkable knowledge within the field mechanical design and for devoting time to us.
Of course, we would also like to take the opportunity to thank our our classmates for the feedback during the opposition.
Majken Domicelj & Lovisa Grönvik Stockholm, May 2018
Bachelor Thesis Spring 2018
Nomenclature
Symbol Description
F Force [N]
M Momentum of Force [Nm]
L Length [m]
k Stiffness
m Mass [kg]
g Gravity [m²/kg²]
E Elasticitetsmodul [MPa]
r Radie [m]
h Tjocklek [m]
Table 1. Explanations of the symbols used.
Abbreviations Description
CAD Computer Aided Design
UN United Nations
WASH Water and Sanitary Hygiene
3D Three-dimensional
pers. comm. Personal communication
NGO Non-Governmental Organisation
Table 2. Abbreviations.
Bachelor Thesis Spring 2018
TABLE OF CONTENT
1 INTRODUCTION 8
1.1 Background 8
1.2 Purpose 9
1.3 Scope 9
1.4 Limitations 9
1.5 Method 10
1.6 Problem formulation 11
2 FRAME OF REFERENCE 12
2.1 Previous work in the field 12
2.2 Existing monotrailer 14
3 REQUIREMENTS SPECIFICATION 15
4 ANALYSIS OF THE EXISTING ENGINEERING DESIGN 17
4.1 Linkage between the motorcycle and the trailer 18
4.2 The bearing system 19
4.3 The loading area 21
4.4 The suspension and the placement of the wheel 22
5 POSSIBLE DESIGN SOLUTIONS 24
5.1 Linkage between the trailer and the motorcycle 24
5.2 The bearing system 29
5.3 The loading area 30
5.4 The suspension and the placement of the wheel 32
6 DIMENSION AND DESIGNING 34
6.1 Linkage between the trailer and the motorcycle 34
6.2 The bearing system 35
6.3 The loading area 38
6.4 The suspension and the placement of the wheel 39
7 DISCUSSION 41
7.1 Design solutions 42
7.2 Production methods 43
7.3 Chosen Materials 43
7.4 Replicability 44
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8 CONCLUSIONS 45
8.1 Conclusions of the problem formulation 45
8.2 Summarized conclusions of the project 45
9 FURTHER WORK 47
10 REFERENCES 48
APPENDIX 49
Appendix I. Risk Analysis 50
Appendix II. Informational Report 51
Appendix III. Trip Report 53
Appendix IV. Trip Report II 55
Bachelor Thesis Spring 2018
1 INTRODUCTION
Here is an introduction to this Bachelor Thesis Project. Background, purpose, scope, method and problem formulation are explained.
1.1 Background
Access to clean water of good quality is a necessity for all human beings. Unfortunately, this is still a great problem in many parts of the world. In Guinea Bissau, great effort has been made to create better water access. Several actors, such as the Guinean Government and Unicef´s WASH section has been involved and large investments have been made to set up a good structure for sustainable water access. In 2016 six NGOs all over the country started a project which aims to map out the available water points and get a clear picture of the current situation. The work is still ongoing, the mapping is 50 % complete. So far, their work has shown that out of the 703 boreholes visited, only 49 % were fully functioning. This has led to the conclusion that it is not only the access to water points that is the main issue rather than the low level of functionality. (Unicef WASH, 2018)
The project is based around an app were the participants can enter information about the water pumps, such as pump type, level of functionality and surrounding environment. The app then generates a map of all the registered water points in the country. A red mark means a non-functioning water point, yellow means semi-functioning and green fully functioning (appendix II). One of the main reasons the pumps aren’t functioning is because small parts break or get stolen, according to Fredrik Asplund (F. Asplund 2018, pers. comm., 15 Jan).
There are many different types of pumps, which are supplied from different actors. The square parts can only be purchased in the capital Bissau, which has shown up to be a big hurdle for the communities. There is also a significant lack of qualified pump mechanics who are able to access these areas and accomplish the reparations. The two main issues the pump mechanics face is transportation and authority. To solve the authority issue UNICEF and the Government are working on improving their identity by creating a uniform and a logo which will improve the recognition of the mechanics. (Unicef WASH, 2018)
The road conditions are very rough, many places are easier accesses by motorbike than by car. Unicef has provided motorcycles for the mechanics participating in the project, however motorcycles have obvious loading limitations. A monotrailer for the load has therefore been constructed but the existing prototype has several problem areas.
Bachelor Thesis Spring 2018
1.2 Purpose
This project has been made together with the Unicef WASH section in Guinea-Bissau. Their project aims to improve water and sanitary hygiene in the region. This project aims to assist in this bigger purpose by developing a well-functioning monotrailer which can manage both the rough road conditions but also the load of the gears and spares. The existing monotrailer is functioning but has limitations. The project also aims to develop a handbook which will be free to use for everyone, locally as well as internationally. Standard parts and components will be used in order to facilitate reparation and replacement of parts.
1.3 Scope
The project will focus on developing and constructing the trailer in relation to availability.
The availability of production methods, materials and components in Guinea-Bissau are somewhat limited – which sets the frame for the possibilities. Improvements of the design could be made but would not facilitate the targeted group.
Material available Production methods available
Steel Welding
Galvanized pipes (1-2 inch water pipes) Drilling
Bamboo Steel cutting
Sheet metal Lathing
Old cars
Table 3. Summary of the production and material limitations.
1.4 Limitations
Due to regulations from the commissioner, Unicef, no change are allowed to be made on the motorcycles. One of the main ideas about the trailer is that it should be replicable. However, if the trailer require permanent changes to be made to the motorcycle, Unicef can’t guarantee neither the safety or the solidity of the motorcycle. Therefore, they have set the requirement for the trailer not to require any permanent changes on the motorcycle. This affects the possible design solutions for the linkage between the trailer and the motorcycle, which will be discussed throughout this report.
The commissioner, Unicef, also requires the trailer to have one wheel, not poly. This is due to the rough road conditions, it is simply not a possible engineering design to have a two wheeled trailer hence the pumpmechnics will not be able to drive through the terrain. Number of wheels has been evaluated by Fredrik Asplund, before our project.
Bachelor Thesis Spring 2018
The environmental aspects will not be taken into account when designing the monotrailer due to vast requirements and problem formulations that limits the possible engineering design solutions.
1.5 Method
The project has been divided into the following steps – initial research and analyze of the existing model, setting up a relevant requirements specification, obtaining and choosing design solutions, verification, production, testing and documentation.
Initial research and analysis
The initial research started with creating a better understanding of the current situation in the country and the ongoing work to improve the water access. This was made by interviewing our supervisor Fredrik Asplund who is Chief WASH, going through reports and data associated with the project and looking at solutions in similar contexts. A field trip was made to study the trailers that had been in use for the last six months (appendix III & IV). Both usage and wearing of the trailer was looked at and analyzed.
The analyze of the existing monotrailer was made both in a scientific way as well as by actually testing the design psychically. A simple conceptual model was made in CAD to increase the understanding of the design and the problematic areas.
Requirements specification
The requirements specification is essential for the result of the project, which means that creating a relevant profile for the design is crucial. An initial profile was made due to the expected usage of the trailer, the available methods and materials and limitations around costs and expenses. A first version was created in an early step of the project to get an understanding of the framework, however, this version had to be updated several times to fit accordingly to the reality.
Design solutions and verification
The initial step here was to find possible engineering design solutions. Ideas and inspiration from brainstorming, looking at similar designs as well as other vehicles. After a set of different solutions were found they were evaluated in relation to the requirements specification – each solution was analyzed based on its efficiency in combination with effort.
Several aspects had to be considered and the different factors were scaled against each other, such as price and time for production against serviceability and strength.
After choosing the most suitable designing solutions, models were constructed in CAD, verified and given dimensions based on requirements and calculations.
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1.6 Problem formulation
The main object is to design a monotrailer which can manage the road conditions in the rural areas of Guinea-Bissau. The problem statement is a combination of rough road conditions (including nearly non-existing roads) and limited access to materials, components and production methods. In addition to that, it’s difficult to define the exact usage of the trailer.
The main purpose is to transport gears and spare parts to the water points and vaccine boxes, however the trailer could very well be used for several other purposes, such as transporting people or animals.
The struggle to reach remote areas and transport loading such as vaccine boxes, tools and food, are not only a problem in Guinea-Bissau. This seems to be a common problem in large parts of Africa. Therefore, another main part of the project is the documentation of the manufacturing process, in order to enable others to construct the trailer as well. Considering a low level of literacy and very basic level of English – how can the handbook be designed to give as many people as possible the opportunity to read and understand the content? The handbook will be published separately due to desiers from Unicef, however the handbook is still central in this project and adds fundamental requirements to this reports scope.
The problem formulation therefore lies in constructing a trailer which is solid, serviceable and safe. Which is the most efficient and satisfying way to design the trailer given the information above? What are the best solutions considering both manufacturing and usage?
From this broad question, five problem statements are formulated as follows:
Q1 Does the monotrailer constitute as a tool for the mechanics to access remote areas?
Q2 Is the trailer made out of components available at sight?
Q3 Is the trailer serviceable?
Q4 Is the trailer replicable by others?
Q5 Is it possible to link the monotrailer and motorcycle without making any changes to the motorcycle?
Table 4. Problem formulation stated as questions.
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2 FRAME OF REFERENCE
In this chapter our frame of reference is introduced. In section 2.1 gathered information and inspiration of different engineering designs of trailers made by others are presented. In the next section, the existing design solution made by Unicef is briefly presented.
In order to create a satisfying requirements specification relevant information was gathered from different sources. The project supervisor Fredrik Asplund, Chief Wash at Unicef, provided information for the initial information retrieval. Fredrik defined the road conditions and information about the terrain – mainly sand, mud and gravel. The paved roads are relatively flat while driving in terrain means large elevations and road pits. The existing design has a ground clearance of 1 inch, which has worked sufficiently. Material that can be found in Bissau is quite limited. At the mechanic site there are old cars and motorcycles, galvanized pipes, steal etc. Standard components can be purchased at the market in Bissau and the most common manufacturing methods are welding, drilling and lathing.
2.1 Previous work in the field
After gathering some basic information about the framework of the project, inspiration from similar projects was collected. Some basic ideas and categories was framed. The trailer should have either one or two wheels.
Image 1. Inspirational picture of a trailer with two wheels respectively one wheel.
The most common attachment solutions seemed to be in the motorcycle swing (as seen on the picture below), the mud flap (as seen above to the left) or in the frame.
Bachelor Thesis Spring 2018
Image 2. Inspirational picture with an attachment in the frame and in the swing.
The most commonly used suspension solution seems to be either one or two springs attached to the back wheel and the loading area, or to have a vertically attached spring.
Image 3. (left) Inspirational picture with a double spring suspension system and (right) inspirational picture of a vertical suspension system.
Bachelor Thesis Spring 2018
2.2 Existing monotrailer
Fredrik Asplund, Chief Wash at Unicef, have made a first version of the monotrailer that will be referred to as the existing monotrailer. The trailer was designed by Fredrik as a part of their water point mapping project. The existing trailer was analysed, which is presented in chapter 4, to gather information of problem areas as well as benefits with this engineering design.
Image 4. The first version of the trailer.
Bachelor Thesis Spring 2018
3 REQUIREMENTS SPECIFICATION
In the process of specifying the most relevant requirements for the design, three prioritized areas were identified:
● solidity and mechanical functions
● materials and manufacturing
● components, assembly and serviceability.
The formulated concept should fulfil the following:
No. Description Importance*
I The trailer should be constructed to manage the following load:
A. Added load: 100 kg
B. The weight of trailer itself: 40 kg
5
II The trailer should work equally well independently of the placing of the load
4
III The trailer should not demand permanent changes to be made to the motorcycle (such as welding, drilling or cutting).
5
IV The trailer should manage the following road conditions:
A. Very uneven roads of gravel, sand and soil.
B. Rough terrain such as rocks, sandbanks and swamps.
C. Narrow road tracks (commonly occurs after rain period)
4
V Trailer should have a ground clearance of a minimum 10 tum = 25.4
2
VI The length of the trailer should not exceed 200 cm 4 VII The width of the trailer should not exceed 60 cm 4 VIII The trailer should be constructed to manage the following (not
simultaneously):
A. 10 water pipes á 3 m B. 1 tool box
C. 1 pump top part D. 50 m coil of PPE pipes
E. 6 vaccination boxes á 2.7 kg and 27 x 27 x 30 cm (width, length, height)
5
IX Expenses for the trailer should not exceed 4 000 SEK, including material costs
5
X The trailer should be serviceable, of standard measurements and be 4
Bachelor Thesis Spring 2018
easy to replace.
XI The trailer should be manufacturable at sight, considering the availability of manufacturing methods, materials etc.
5
Table 5. Requirements. * The importance of the requirement is graded on a scale 1-5.
Bachelor Thesis Spring 2018
4 ANALYSIS OF THE EXISTING ENGINEERING DESIGN
In this chapter, the existing trailer is analysed to gather information like problem areas of the existing engineering design.
With the requirements for the trailer specified, the process of finding possible design solutions was initiated. The first step was to analyze the existing trailer (image 4), and identify the main issues. The original trailer was designed by Fredrik Asplund, chief WASH, as a part of their water point mapping project. After iterative tests, a single wheeled solution was chosen. The single wheeled managed to follow the track of the motorcycle in a more desirable way. The two-wheeled trailer was more solid in roll and could handle a heavier load but was not able to manage the road conditions to the same extent as the single-wheeled solution. Given the background of the project, that requirement was prioritized.
The existing trailer is functioning in some respects but does not fulfil the set requirements. It can manage a load up to 50 kg but when that is exceeded it loses its torsional rigidity.
The trailer is also sensitive to where the load is placed. If the load is placed closer to the back wheel it functions better than if the load is placed in the front part. For more information about the field trips and the analysis of the existing trailer (Appendix III and IV).
After analyzing the trailer four critical areas was identified:
● The linkage between the motorcycle and the trailer
● The bearing system transferring the movement of the motorcycle to the trailer
● The loading area.
● The suspension and the placement of the wheel.
Figure 2. Global free body diagram
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L 1840 total length of the trailer
L1 485 length between the Centre of the back wheel to the loading area L2 800 length of the loading area
L3 130 length between the loading area and the Centre of the bearing L4 425 length between the bearing and the Centre of the front wheel dh1 660 diameter of the back wheel
Table 6. The dimensions of the trailer [mm]
The active forces was also analyzed and described in an active forces diagram.
Figure 3. Active forces diagram
N g 0
↑ : 1+ N2− m = (1)
mg ( )
↻x : L22 + L3 − M1 = 0 (2)
4.1 Linkage between the motorcycle and the trailer
The linkage between the trailer and the motorcycle is constructed in two parts. Two sockets have been attached on each side of the motorcycle swing – by three screws drilled in pre-existing screw holes. The nuts are welded on the socket and the fork arm is attached in the nuts with bolts. The system allows vertical movement from the arms, which is necessary given that the attachment is fastened in the swing (which is attached directly to the back wheel) (image 5). The main problem seems to be is the distribution of the weight. The design puts a lot of pressure on the nuts as well as the screws in the swing. Also, the nuts are welded on the holder, which is not ideal in a solidity perspective. When the motorcycle is driving
Bachelor Thesis Spring 2018
with the trailer attached, the socket is exposed to both a dragging force and a moment of force, putting a lot of pressure on the screws in the swing.
Image 5. The linkage on the motorcycle swing (right). The attachment on the swing after 6 months.
4.2 The bearing system
The bearing system consists of a vertical roll bearing in which the arms are attached (image 6). The bearing is fastened at the bottom pipe and is supported at the top. The system allows movement in yaw but not vertical movement or movement in roll.
Image 6. The bearing system in profile.
Bachelor Thesis Spring 2018
The arm between the motorcycle and the trailer is vulnerable to movement in roll direction – the torsional rigidity is low. Motorcycles has a lot of movement in roll, while turning for example. However, the trailer should not move too much in that direction – the design should be made to manage that in a more efficient way.
If the trailer could be shorter and have the center of gravity closer to the back wheel of the motorcycle, the trailer would get an increased ability to follow the track of the motorcycle in yaw which would increase the stability. If the trailer is not following the driven track this will result in a larger turning radius as well as a decreased mobility and it will get more difficult to avoid obstacles such as rocks and road holes. This pose both a safety risk and will wear out the components in the trailer faster. This is thus an important prerequisite in order to transport both gears and people in a safe way and an efficient way to increase the durability.
The distance between the bearing and the wheel of the trailer in combination with the loading creates a lever arm which puts an unproportioned pressure on the bottom of the bearing (figure 4). The current design did break during testing, the bottom bolt came off and the bearing folded backwards towards the trailer (image 7). The breakdown did not cause large damages during the testing but could potentially cause a dangerous situation.
Image 7. The broken bearing system.
Bachelor Thesis Spring 2018
One of the arms welded on to the bearing system also broke after about six months. The welded connection was not solid enough to handle the transmitted motion from the motorcycle. It is exposed to a lot of torsional movement as well as vertical movement - making a critical point in the design. When it broke, only one of the two arms broke which better than them both breaking at the same time, in a security aspect. However, when one of the two arms came loose, the stability in the design dropped drastically. Its rigidity towards torsional movement was decreased meaning that it will lower the life expectancy of the design.
Figure 4. Active force diagram in the bearing system.
The bottom of the bearing is exposed to a momentum of force, as shown in (2). This is directly affected by the weight of the loading. It is hard to say exactly how much weight the existing trailer can hold, since there is no testing done and no documentation made of the usage. A qualified guess, after talking to the mechanics using it, is around 100 kg. It also creates a large stress concentration in area where the arms are welded to the bearing, due to the bending moment that occurs when the momental force M1pushes the bearing down in a vertical direction. The led to one of the the arms coming off.
4.3 The loading area
The loading area of trailer consists of hollow, rectangular pipes, welded together forming the frame (image 8). Underneath the frame a thicker pipe is welded to strengthen the base. The base then goes both to the front of the trailer and connects in the bearing as well as to the back part. This system works quite well except from the dimensions and the torsional rigidity.
The dimensions were originally 495 x 780 mm. Since the vaccination boxed measures 273 x 265 mm this means only two boxes can be transported at the time. Changing the dimensions to 540 x 810 mm would increase that number to six at the time.
Bachelor Thesis Spring 2018
The rectangular base pipe has a relatively low torsional rigidity and could potentially break.
The loading area also need to have a simple draining system – the current design is completely waterproof meaning that if it rains, the water stays in the box for weeks.
Image 8. The base pipe and the frame.
The rectangular base pipe is not an ideal choice, considering the amount of torque that occurs when the trailer is loaded and moves in roll.
4.4 The suspension and the placement of the wheel
The spring is attached on each side of the horizontal roller bearing (image 9). Ideally could this be optimized to either be give better support or be made shorter. One of the requirements for the trailer is to make it independent of where the load is placed – this could be improved by overlooking this subsystem.
Bachelor Thesis Spring 2018
However, the spring and the fastening of the spring need to be assessed in relation to the force of the wheel and the load of the trailer. During usage the spring has started leaking, an indication that the load has exceeded the spring force (figure 5).
Figure 5. Active force diagram, suspension system.
N g cos (60°)
↑ : 1− m − Ffj = 0 (3)
The spring force is represented by
Ffj = x · k (4)
x Extension of the spring [m]
k Spring stiffness [-]
Table 7. Definition of the variables affecting the spring force.
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5 POSSIBLE DESIGN SOLUTIONS
The next step, after forming the requirements profile and the analysing of the current design, is to find possible design solutions. The solutions will then be evaluated according to the requirements profile and the most suitable solutions can be chosen.
5.1 Linkage between the trailer and the motorcycle
The function of the linkage system is to transfer movement forward (or backwards) between the motorcycle and the trailer. Possible solutions:
Attaching the linking arm in the:
1.1 In the frame of the motorcycle
1.2 Attaching the linking arms in the premade swing holes (current solution) 1.3 Foot pegs
Table 8. Possible design solutions for the attachment of the linking arm.
Regarding the linking arm:
1.4 Allowing the arm to move vertically
1.5 Not allowing vertical movement, locking the linkage completely.
1.6 Building a truss for the arms, in order to help it take up tension.
1.7 Changing the bushings to roller bearings
1.8 Manufacture the linking arms as one solid piece, rather than four separate ones.
Table 9. Possible design solutions for the design of the linking arm.
The linkage could either be attached in the motorcycle swing or frame (image 10). Attaching it in the frame could be a good way to transfer the moment from the motorcycle without having to attach the trailer directly to the back wheel. However, due to requirements of the commissioner, no modifications are allowed to be made on the motorcycle. In order to get such constellation solid enough, drilling or welding would be necessary. Therefore, the option to attach the arms in the swing is a better option due to original screw holes.
Bachelor Thesis Spring 2018
Image 10. The motorcycle wheel without any changes made to it (left). Underneath the fender of the wheel (right).
Looking at the body of swing, there seems to be two options. Either a solution similar to the current one but strengthened or attach the arms in the foot pegs. The foot pegs are attached to the swing with a threaded screw (image 11).
Image 11. The foot peg on the motorcycle and the hole for the peg and (right)
This could be an efficient solution, considering it would not require any modifications to be made to the motorcycle and would also allow the trailer to easily be detached. However, it was discovered that many of the foot pegs of the motorcycles were actually not intact after usage (image 12).
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Image 12. Non-intact foot pegs.
This is likely due to driving a passenger in a high speed on uneven roads. But even if the foot pegs probably could handle the load of the trailer, twisted foot pegs would make it hard to drive the trailer. Therefore, this does not seem to be a possible solution.
The link arm will drag the trailer forward. While acceleration or retardation there will be a dragging, horizontal force but not during constant movement. As long as the attachment is fastened in the swing (which is directly connected to the back wheel) the arm will need to be movable in vertical direction. When the back wheel goes over road obstacles it moves in vertical direction, up to 50 cm. If the linking arm is not movable in that direction, that movement will be transferred and multiplied due to the lever arm a solid arm would create.
The link arm has to be movable in vertical direction as of the movement that emerge when the back wheel goes over road obstacles. The allowing point of vertical movement can either be placed in the linking arms attachment to the motorcycle or to the bearing between the linking arm and the frame. When the back wheel goes over road obstacles it moves in vertical direction up to 50 cm. If the linking arm is not movable in vertical direction, the movement will be transferred and multiplied due to the lever arm a solid arm would create. Therefor the link arm has to be movable in vertical direction. The allowing point of vertical movement can either be placed in the linking arms attachment to the motorcycle or to the bearing between the linking arm and the frame. In the later alternative, the same problem of a lever arm applies. Therefore, the point allowing vertical movement needs to be placed close to the back wheel of the motorcycle, hence the linking arm has to be movable in its attachment to the motorcycle to minimize the lever arm.
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Another issue with the linkage arm is torsional movement and movement in yaw direction.
This makes the system unstable and transfers unwanted movement to the trailer. Two improvements could help this. Creating a three-dimensional truss for the arms and changing the bushings to roller bearings should limit the transition of torsional movement.
Criteria/Concept 1.1 1.2 1.3 1.4 1.5 1.6 1.7
I 5 −5 5 0 0 5 0
II 4 −4 4 −4 4 5 0
III −5 5 5 0 0 0 0
IV 4 −4 4 4 −4 4 4
V 0 0 0 0 0 0 0
VI 0 0 0 0 0 0 0
VII 0 0 0 0 0 0 0
VIII 5 5 5 0 0 5 5
IX 5 5 5 0 0 0 −5
X 4 4 4 0 0 −4 4
XI 5 5 5 5 5 −5 5
∑ 27 16 37 5 5 10 13
Table 10. Pugh evaluation chart weighed after importance, linkage system.
5.2 The bearing system
The purpose of the bearing system is to transfer movement in desired directions and to stop movement in the unwanted directions. The prevailing system has to transfer movement in yaw, otherwise the turning radius will be extremely large. The question is whether it should allow vertical movement. The current bearing system does not allow vertical movement;
however, the vertically rigid bearing broke after about six months of usage – indicating that the construction does not meet the requirements.
The bearing system
2.1 Cardan joint
2.2 A straight, vertical roller bearing (current solution) 2.3 A tapered, vertical roller bearing
2.4 Manufacturing the linking arms as one solid piece, rather than four separate ones.
Table 11. The possible solutions for the bearing system.
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The Cardan joint connects two inclined axes and transfer motion in vertical and yaw direction but does not transfer torsional movement (Mills, 2007) (image 13). The advantage with the Cardan joint is that it does not transfer vertical movement from the lever arm coming from the trailer.
Image 13. Cardan joint (Mills, 2007)
The vertical roller bearing allows movement in yaw but not in vertical direction. This is acceptable as long as the linking arm is attached in such way that it allows vertical movement from the motorcycle. The cons with vertical roller bearing is the limitation of transmitting load and motion in vertical direction. In the original design a lot of strain from the load hordes on to the connection between the bearing and the carriage, this causes high amount of bending shear stress which after six months of usage resulted in bending of the welded connection. Another con with the original vertical bearing system is the way the system is attached with only one screw in the bottom to the base pipe. After six months of usage the system broke due to a high level of bending shear stress.
A third possible solution is to improve the original solution with a standing tapered roller bearing (image 14). The tapered roller bearing will allow applied force in vertical led thus enables new ways of linkage between bearing, carriage and linking arm. This can be attached to the base pipe in a different way which changes the way the lever arm works on the bottom of the bearing.
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Image 14. The connection of the bearing.
The connection of the arms and the bearing needs to be improved. It could be designed in one solid piece rather than four separate pieces. The arm in one solid piece could be bent around the bearing, resulting in a larger welding area. This should create a more even tension in the whole component rather than putting pressure on one single spot.
Criteria/Concept 2.1 2.2 2.3 2.4
I 5 −5 5 5
II 4 −4 4 0
III 5 5 5 5
IV 4 −4 4 4
V 0 0 0 0
VI 0 0 0 0
VII 0 0 0 0
VIII 4 −4 4 4
IX 4 4 4 4
X 5 5 5 −5
XI 5 5 5 −5
∑ 36 2 36 12
Table 12. Pugh evaluation chart weighed after importance, bearing system
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5.3 The loading area
The loading area is a straight forward part of the design. Following improvements could be made:
The loading area
3.1 Change the dimensions to fulfil the criterion; 540 x 810 mm 3.2 Have a simple drainage system to get water and liquid out.
3.3 Exchange the rectangular base pipe to a circular axis which can manage higher levels of torsion.
3.4 Have a simple system to fasten the load on the trailer .
Table 13. Possible design solutions for the design of the loading area.
All these four improvements could be implemented without further issues. Widening the loading area could have an impact on the trailers stability in roll thus enabling the load to be placed further out from the trailers center of gravity. Nevertheless, widening of the loading area would noteworthy double the transport capacity by fitting two vaccine boxes in width instead of one.
The drainage system can easily be done by drilling a hole in each of the trailers corners. This wouldn’t have an impact on the trailers rigidity because the holes would be made into the sheet metal and not into the frame.
A circular pipe is more rigid for torsion then a rectangular pipe due to geometrics. Changing the base pipe to a circular one would strengthen the trailers whole design. (Sundström, 1998)
Figure 6. Circular base pipe.
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Figure 7. Circular base pipe in cross section.
→ : M − Mv= 0 (6)
Given that the pipe is thin walled ( h << r) the shear stress is assumed to be constant over the cross section. The radius is also assumed to be constant. That results in:
Mv= τ(2π r h)2 (5)
When driving through prevailing road conditions it's important that the load is attached to the trailer for safety and sustainable reasons. In the original design, small hooks are placed on top of each side of the trailer. The cord can then tie the load to the trailer but does not have an impact on attaching smaller objects or the three-meter-long pipes. Therefore, the cords could additionally go through the drainage holes to better fasten the load.
The three-meter-long pipes are difficult to stably load onto the trailer. The pipes wither
“pointing out ” either at front or out back. For safety and sustainable reasons, it is important for the pipes to be stably attached on the trailer. A possible solution is to build a holder on the back wheel for the pipes to lean against. If possible the center point of the pipes, 1,5 meters, should be inside the trailer. One can also tie the pipes at the bottom.
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Criteria/Concept 3.1 3.2 3.3 3.4
I 5 0 5 5
II 4 0 4 4
III 5 5 5 5
IV 4 −4 4 4
V 0 0 0 0
VI 0 0 0 0
VII 4 0 0 0
VIII 5 5 5 5
IX 5 5 5 5
X 4 4 4 4
XI 5 5 5 5
∑ 41 20 37 37
Table 14. Pugh evaluation chart weighted after importance, loading area
5.4 The suspension and the placement of the wheel
The suspension system is supposed to decrease the transition of movement from the wheel of the trailer to the loading area. The following changes could be made:
The suspension system
4.1 Replacing the current current spring to a stronger spring with a higher stiffness.
4.2 The bars which the spring is attached to could be leaning rather than being in a 90° angle.
4.3 Double springs instead of a single spring.
4.4 Shorting the vertical bar, placing the vertical roller bearing closer to the loading area.
4.5 Adding a holder for the PEE pipes.
Table 15. Possible design solutions for the design of the suspension system.
The spring works between the two parts to create smooth movement and avoid fitful movements. The spring force is affected by both the loading and the angle of the spring. The most efficient solution to make the spring manage a larger force is to replace it to with a spring with a higher spring stiffness. A stronger spring will be more expensive (the current
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spring is already one of the most expensive components in the trailer, however, it will still be more cost effective to use a suitable spring initially than changing it every six month.
The bars in which the spring is attached is in the current solution constructed with a 90°
angle. An idea is to construct them leaning to decrease the tension in the bottom of the bar, (figure 8).
Figure 8. The standing bar in a slightly smaller angle in relation to the vertical bar.
Criteria/Concept 4.1 4.2 4.3 4.4
I 5 5 5 5
II 4 4 4 4
III 0 0 5 5
IV 4 4 4 4
V 0 0 0 0
VI 0 0 0 0
VII 0 0 0 0
VIII 5 5 5 5
IX 5 5 5 5
X 4 4 4 4
XI 5 5 5 4
∑ 32 32 37 36
Table 16. Pugh evaluation chart weighted after importance, suspension system
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6 DIMENSION AND DESIGNING
After going through the possible solutions and evaluating those according to the requirements specification and the current design, the most satisfying solutions were chosen.
6.1 Linkage between the trailer and the motorcycle
The following changes was made:
1.2 Attaching the linking arms in the premade swing holes 1.4 Allowing the arm to move vertically
1.6 Building a truss for the arms, in order to help it take up tension.
1.7 Changing the bushings to roller bearings.
Table 17. Changes made to the linkage system.
The way the trailer is attached to the motorcycle was not changed, due to the requirement to not make permanent changes to the motorcycle. All other solutions demanded either welding or drilling in the motorcycle, making this solution the only possible one, even though it scored the lowest in the Pugh evaluation (table 10).
However, the socket was improved and made stronger and more rigid. Instead of having the screws as the only fastening points, the edges were extended to swipe around the swing (figure 9). In that way, the load will be evenly distributed, and the piece will be more closely attached to the swing.
Figure 9. The attachment to the motorcycle.
It was also decided that the arms should be able to move vertically, with the argument that it would not work with stiff arm going from the vertical roller bearing in the back of the trailer to the swing of the motorcycle, even though they scored evenly in the Pugh evaluation (table 10). When the wheel moves vertically, which it does naturally when driving, it would
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multiply the movement of the wheel of the trailer, due to the lever arm. The original idea was to have a cardan joint instead of a standing bearing, which would make it mobile in both vertical and horizontal direction. However, that solution didn’t work for other reasons, which will be presented further down.
A three-dimensional truss was designed in order to distribute the shear stress evenly and to minimize the torsional motion transmitted from the motorcycle to the trailer (figure 10). A truss is an efficient way to handle torsional movement and also to spread the tension that was earlier concentrated to the welded points in the vertical bearing. It is a cost efficient solution as well. The downside is that is was slightly more complicated to manufacture (table 10).
Figure 10. The linkage between the trailer and the motorcycle.
In the previous solution the linking arm was attached in the bult with bushings. However, the bushings was completely worn out after six month and arm was attached straight on the metal bult. That made the fastening untight and unstable. Therefore the linking arms will be attached on the outside of a deep roller bearing. This will provide a smooth motion of the arm and will be a more solid solution. The chosen bearing is a deep groove ball bearing, more specifically 6004 - 2RSH (Skf.com, 2018).
6.2 The bearing system
The following changes was made:
2.3 A tapered, vertical roller bearing
2.4 Manufacturing the linking arms as one solid piece, rather than four separate ones.
Table 18. Changes made to the bearing system.
Concept 2.1 and 2.3 scored the same in the Pugh evaluation chart (table 12). The cardan joint was the prefered solution due to its high solidity and serviceability. However, it turned out to be mechanically challenging to design since it would create a long lever arm from the center
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of the motorcycle wheel to the wheel of the trailer. Therefore, a solution with a tapered, roller bearing was chosen.
The challenges the bearing system was facing was mainly not being able to manage the lever arm from the trailer. The bottom part was not solid enough to take up the main part of the torque – which led to it breaking. That solution was modified so that the base pipe was attached in the middle of the bearing instead of in the bottom. The pipe is welded onto the bearing rather than attached with a screw. That means that the connecting areas are larger.
The linking arms will be manufactured as one single piece with a jig instead of four separate pieces. They will be attached by pointed welding around the bearing, both in the front and in the back. By making the arms in one single piece, the critical points where the arm broke are eliminated. However, this also turned out to be quite complicated for the constructor to make.
Image 15. The tapered roller bearing.
Image 16. The roller bearing.
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Image 17. The final solution for the bearing system during engineering design phase.
Image 18. The final construction of the connection between the wheel and base pipe.
The bearing chosen is tapered, single row roller bearing, more specifically 32004 X (Skf.com, 2018). The bearing was mainly chosen with regards to the diameter, due to the diametrical restrictions in the pipe and to the expected loading.
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6.3 The loading area
The following changes was made:
3.1 Change the dimensions to fulfil the criterion; 540 x 810 mm 3.2 Have a simple drainage system to get water and liquid out.
3.3 Exchange the rectangular base pipe to a circular axis which can manage higher levels of torsion.
3.4 Have a simple system to fasten the load on the trailer.
Table 19. Changes made to the loading area.
All the solutions scored high in the Pugh evaluation chart (table 14) and all of the solutions were possible to make. The loading area needs to be dimensioned after vaccine boxes, tools, pipes and other equipments while still managing a safety aspect. In a loading aspect, it is profitably for the loading area to be as wide and long as possible. However, the trailer can not be wider than the steering and the width also adds instability in roll. The loading area resulted in managing to fit 6 vaccine boxes (image 19). The base pipe was exchanged to a Galvanized, circular axis (image 20).
Image 19. The frame with two vaccine boxes.
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Image 20. During the construction of the base pipe and base plate.
6.4 The suspension and the placement of the wheel
The following changes was made:
4.1 Replacing the current current spring to a stronger spring with a higher stiffness.
4.2 The bars which the spring is attached to could be leaning rather than being in a 90° angle.
4.4 Shorting the vertical bar, placing the vertical roller bearing closer to the loading area.
4.5 Adding a holder for the PEE pipes.
Table 20. Changes made to the suspension system.
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Here, all the solutions scored high in the Pugh evaluation chart as well and they all turned out to be viable (table 16). The sustention system worked quite well in the previous version.
However, there were room for improvements. The way the bars was constructed was changed, so that they are on an angle rather than 90°, in order to improve the solidity. A holder for the pipes was added in order to support the 3 meter long PEE pipes that will be transported with the trailer (image 21).
Image 21. The new suspension system.
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7 DISCUSSION
In this chapter, the results, dimensioning and designing in chapter 5 is discussed and parallels are drawn to the requirements specification in chapter 3, analysis of original trailer in chapter 3 and to the frame of reference in chapter 2. Central during the discussion are the five questions Q1-Q5, formulated in the problem formulation in chapter 1, from which our findings in chapter 6 are discussed and analysed.
7.1 Design solutions
During this project different design solutions has continuously been compared, discussed and revised against the requirements specification to reach the results presented above. Central in this project has been to use materials available at sight in Guinea Bissau and for the final design to be replicable by others in need.
Mono wheeled or poly wheeled trailer
Debatable in the final design is the number of wheels. One wheel clearly affects the stability in a negative way; the loading area and the weight on the linkage on the motorcycle. Two wheels would enable a more stable trailer, the weight would be more easily balanced thus put less weight onto the linkage on the motorcycle and result in an easier design to build. All this would enable to add more weight and create a larger loading are. However, two wheels are not a possible design solution due to the road conditions. The purpose of the trailer is to enable the pump mechanics to access remote areas thus be able to repair the pumps. With two wheels, the trailer and the mechanic cannot reach these remote areas, hence the trailer would not fulfill its purpose. Consequently, in this project the trailer can only have one wheel.
Linkage between the motorcycle and the trailer
Linkage between the motorcycle and the trailer was one of the biggest challenges faced during this project due to the requirements specification and question Q5 formulated in problem statement stating that no change could be made to the motorcycle. The linkage and connection points have to be created into pre existing holes, unfortunately the motorcycle has limited existing connection options (image 10). The final design of the linkage between the monotrailer and the motorcycle is presented in chapter 6.1, where the linkage is connected into pre-existing holes in the swing and is rigid enough to carry the required load while driving through rough road conditions. This answers the problem statement Q5 -It is possible to link the monotrailer to the motorcycle without making any changes to the motorcycle.
Another requirement for the linkage is that the trailer should easily be detached, without the risk of misplacing a nut or two. During the project it was decided the linkage should be attached to the foot pegs (image 11). The linkage was supposed to be attached around the screw of the peg with a bearing. The bearings would then be linked to the arms of the trailer, enabling movement in yaw. The trailer would be attached and detached by unscrewing the peg. This solution fulfilled all requirements.
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During a field trip it was discovered that the foot pegs had broken after six months of usage, (image 12), without carrying the load of the trailer. Most likely, a passenger has been standing on the foot pegs while driving through rough terrain, resulting in the peg bending.
The weight of a grown person is equal or less than the weight of the trailer, thus this solution would clearly not bear the weight of the loaded monotrailer.
After this discover, it was decided the best solution would be a similar one to the already existing design, (figure 9). The goal here was to minimize the pressure onto the bolts by making the linkage go around the swing of the motorcycle, ensuring the pressure from the monotrailer would be focused on to the swing and not only in the bolts.
In order to make the linking arms more rigid, the design of the arms is supposed to imitate a framework (figure 9). This turned out to be a hurdle to build for the constructor, resulting in the arms and framework not to end up as planned. The constructor found it hard to understand the purpose with a framework, had a limited range of tools needed to fulfill the design. This will most likely also be a struggle for others building this design which interfuses question Q4 stating the trailer should be replicable by others. In further work, the linkage between motorcycle and trailer can be improved to gain better rigidity and durability to the monotrailer and for the design to be more easily replicable by others.
The bearing system
Long into the project a Karda joint was thought to be a smart solution for enabling movement between the trailer and the motorcycle, without transferring roll movement to the trailer.
When using a Cardan joint in the new design, the point enabling vertical movement would be transferred back from the linkage between motorcycle and trailer to the Cardan joint, about 30-60 cm further back. Moving the point enabling vertical movement back creates a lever arm. When driving over a bump the lever arm would have a waste impact on the trailers capacity to handle height differences. The exclusion of the Cardan joint led to the final solution for the bearing system (image 15, 16 & 17). Placing the bearing system centered into the base pipe made the final design more rigid than the original design. The linking arms goes around the bearings on top and bottom, creating a more even force load over the bearing system.
The biggest challenge was to prevent and ensure no sand could sweep into the bearing system. The bearing system is placed in a vulnerable place hence the bearing system constantly is exposed to big amount of sand, water and mud coming from the motorcycles back wheel. By using rubber seals and filling the tube with oil, the bearing system got more resistant for expositor of sand and water.
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7.2 Production methods
The result of the design was not only affected by the solutions - low accuracy and tolerances from the constructor had a negative impact on the result. Due to communication limitations and different points of view, it was revealed that the constructor found it too to difficult to make in a proper way. This made the design process take longer time than estimated. The delay was also due to funding difficulties and poor planning from the constructor. Image 20 is an example of bad tolerances and accuracy during the design. The hole between base pipe and the base plate was later filled with welding material.
During the design process it was discovered that the monotrailer´s wheel was crookedly attached to the bearing and base pipe (image 18). Having the wheel constructed tilted and, in an angel, contradicts the purpose in making the constructed design more stable in roll.
7.3 Chosen Materials
The problem statements Q2, Q3 and Q4 composes fundamental aspects during the process of choosing materials. When choosing materials for the monotrailer, the material resources where limited due to the requirements specification and the lack of shops because of the impossibility to produce or import materials and components in Guinea Bissau. Therefore, the materials and components had to be found in Guinea Bissau. This means the materials and components had to be found on the market, in old cars and motorcycles or in the dump.
The requirement specification also states the used components has to be of standard parts, Q2, thus the ability to repair the monotrailer is crucial, Q3, and for the design of the monotrailer to be replicable by others, Q4.
Galvanized pipes are used in the waterholes for the water pumps. The Galvanized pipes has several positive aspects such as their rigidity and availability in Guinea Bissau and similar places. Therefore, the Galvanized pipes were chosen to compose the base pipe of the monotrailer. Alternative materials for the base pipe was a pipe with U profile. The U profiled pip would be assembled to a square shaped pipe in order to be more rigid and prof, which the base pip requires. This assembly requires the two U profiled pipes to be welded together.
This was seen to be an inferior alternative, hence of experience the welds often brake. One reason the welds are not tough enough is because of the limitations in tools and the lack of knowledge of how materials react when welding. Avoiding as much welding as possible was preferred.
When choosing materials for the monotrailer, the environment aspects was considered negligible. As mentioned, the material resource was limited, materials used was whatever could be located in Guinea Bissau hence no materials nor parts could be ordered from outside the country due to the requirements specification. The environment aspects as an additional requirement would further limit available supplies. However, the majority of used material
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are from old cars, motorcycles etc., resulting in the monotrailer being constructed out of 100% recycled materials.
7.4 Replicability
The struggle to reach remote areas and transport loading such as vaccine boxes, tools and food, are not only a problem in Guinea-Bissau. This seems to be a common problem in large parts of Africa. Therefore, another main part of the project was the documentation of the manufacturing process, in order to enable others to construct the trailer as well. The documentation is gathered in a handbook, with step by step guidance. This also entails question Q4 formulated in the problem formulation, chapter 1, stating the monotrailer needs to be replicable by others. The criteria of replicability has been central throughout this project and had vast impacts on the engineering design. Q4 has been a fundamental aspect during the engineering design process and when choosing materials and components, as discussed above. However, the handbook will be published separately together with Unicef.
