Modelling (1)

Advanced Engineering Design Modelling | Mark Antoni Georg
Tutor: Dr.Sajid Khalifa
Tutor:Dr.Dani Harmarto
BSc (Hons) Mech Eng
Advanced
Engineering
Design
Modelling
Offroad Buggy
Mark Antoni Georg

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Abstract
The advanced modelling course required the design of a 4WD off-road buggy (Fig 1).
This process involved researching the principle function of the buggy and key points involved in design, hand
calculations covering a wide range of engineering principles were used to primarily find the requirements and
functionality of components before proceeding with the 3D design process, and secondly to meet the assignment
requirements, these included:
 Thermodynamics
 Engineering Science/mechanical principle equations
The assembly process is also covered, use of FEA to validate design decisions, and 2D manufacturing drawings
created to Bsi8888 to meet a ISO standard in drawing interpretation and achieve accurate manufacture.
Figure 1Complete off-road buggy

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Contents
Abstract.............................................................................................................................................................................1
Index Of figures.................................................................................................................................................................3
Introduction ......................................................................................................................................................................5
Design Challenges .........................................................................................................................................................5
Hand Calculations .............................................................................................................................................................6
Piston ............................................................................................................................................................................6
Piston Diameter, Compression Ratio, and Piston Clearance ....................................................................................6
Piston Height, Gudgeon Pin Height, Con Rod Length ...............................................................................................7
Engine Thermodynamics...........................................................................................................................................7
Heat Due to Compression.........................................................................................................................................7
Heat Due to Combustion, Combustion pressure, and Force Achieved ....................................................................8
Gudgeon Pin..................................................................................................................................................................9
Crankshaft...................................................................................................................................................................10
Crankpin..................................................................................................................................................................10
Prop-shaft ...................................................................................................................................................................11
Torsional Stress.......................................................................................................................................................11
Gearbox.......................................................................................................................................................................12
Gear Ratios..............................................................................................................................................................12
Gear Sizes................................................................................................................................................................13
Output Shaft Torsional Stresses..............................................................................................................................14
Wheel Studs................................................................................................................................................................15
Static Beam Stresses .......................................................................................................................................................16
Design process/Intent.....................................................................................................................................................18
2D Block Engine and considerations...........................................................................................................................18
Key considerations..................................................................................................................................................18
2D, Blocks, and 3D: .....................................................................................................................................................19
Buggy size................................................................................................................................................................19
Engine......................................................................................................................................................................19
Chassis.........................................................................................................................................................................20
Tyres/Wheels ..........................................................................................................................................................23
Suspension ..............................................................................................................................................................24
Steering...................................................................................................................................................................25
4W Drivetrain..........................................................................................................................................................28
Controls...................................................................................................................................................................29
Assembly Process............................................................................................................................................................29
Part Assemblies and Constraints ................................................................................................................................29

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Para metrics ................................................................................................................................................................31
Finite element analysis software ....................................................................................................................................32
Engine..........................................................................................................................................................................32
Piston ......................................................................................................................................................................32
Gudgeon pin............................................................................................................................................................35
Con-rod ...................................................................................................................................................................36
Crankshaft...............................................................................................................................................................37
Chassis............................................................................................................................ Error! Bookmark not defined.
2D Manufacturing drawing of … to BSi8888...................................................................................................................39
Critical Analysis ...............................................................................................................................................................39
References ......................................................................................................................................................................40
Appendices......................................................................................................................................................................41
Index Of figures
Figure 1Complete off-road buggy.....................................................................................................................................1
Figure 2engine design.....................................................................................................................................................19
Figure 3space frame parameters (SAE, 2015).................................................................................................................20
Figure 4space frame parameters (SAE, 2015).................................................................................................................20
Figure 5 Space frame parameters (SAE, 2015) ...............................................................................................................21
Figure 6Space frame parameters (SAE, 2015) ................................................................................................................21
Figure 7sketched outlines...............................................................................................................................................22
Figure 8 Chassis...............................................................................................................................................................22
Figure 9tireand wheel (mountain, n.d.) (wickedalloys, n.d.) Respectively.....................................................................23
Figure 10 tire creation.....................................................................................................................................................23
Figure 11Wheel creation.................................................................................................................................................23
Figure 12 Suspension layout ...........................................................................................................................................24
Figure 13Ackerman principle (www.rctek.com, n.d.).....................................................................................................25
Figure 14Ackerman Principle (www.rctek.com, n.d.).....................................................................................................25
Figure 15 Ackerman geometry in the buggy layout........................................................................................................25
Figure 16 steering conection...........................................................................................................................................26
Figure 17 Steering universal joints..................................................................................................................................26
Figure 18steering centerpoint ........................................................................................................................................26
Figure 19 Steering rack and pinion .................................................................................................................................27
Figure 20 UJ steering column..........................................................................................................................................27
Figure 21Differential.......................................................................................................................................................28
Figure 22keyed drive shaft and axle arrangement .........................................................................................................28
Figure 23 mates...............................................................................................................................................................29
Figure 24 mates...............................................................................................................................................................29
Figure 25mates ...............................................................................................................................................................30
Figure 26 mates...............................................................................................................................................................30
Figure 27 mates...............................................................................................................................................................30
Figure 28Parametric example.........................................................................................................................................31
Figure 29Piston material type FEA..................................................................................................................................32
Figure 30Piston constraints and pressure FEA................................................................................................................32

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Figure 31Piston Mesh FEA ..............................................................................................................................................33
Figure 32Piston Min Max Stress FEA...............................................................................................................................33
Figure 33Piston Displacement FEA .................................................................................................................................34
Figure 34Piston FOS FEA .................................................................................................................................................34
Figure 35Gudgeon pin FEA..............................................................................................................................................35
Figure 36Con rod FEA......................................................................................................................................................36
Figure 37 Crank FEA ........................................................................................................................................................37
Figure 38 2D Manufacturing drawing .............................................................................................................................39

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Introduction
The 4WD off-road buggy is an all-terrain vehicle that can cope with the stresses presented whilst being driven off-
road such as jumps, large scale suspension impacts, and extreme track surfaces. The design process to meet the
assignment’s tasks involved the theoretical hand calculations before the design process takes place, the actual
design of the buggy, and validation of the components using FEA.
Key points are defined in the assignment as to which aspects of the buggy must be hand calculated, for example
engine size design and H&S aspects.
Design Challenges
Initially the type of buggy to be designed needs to be established, to achieve this a number of key points are
established and considered.
Key consideration Parameter
Engine size, large enough to drive the buggy over rough
terrain
1000cc
Number of pistons 4 minimum
Suspension travel including compression and droop 400min
Drive to wheels 4WD
Chassis design Spaceframe
Turbocharging Naturally aspirated
Strength of materials Achieve a required FOS
It was recommended in the assignment that the SAE BAJA style buggy site be used as a frame of reference. This
route provided a number of considerations that will be described throughout this report.

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Hand Calculations
Piston
To calculate many of the engine components it is first necessary to establish the key engine parts such as: diameter
of the piston, connecting components, and positional values based on the 1000cc 4 cylinder engine size.
Piston Diameter, Compression Ratio, and Piston Clearance
To calculate the piston size for a 1000cc 4 cylinder engine, the equation is calculated as ¼ of the total engine size.

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Piston Height, Gudgeon Pin Height, Con Rod Length
Engine Thermodynamics
To further calculate the other engine components it is necessary to establish the loads the engine will be applying to
these, so thermodynamic processes within the cylinder are calculated.
Heat Due to Compression

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Heat Due to Combustion, Combustion pressure, and Force Achieved

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Gudgeon Pin
Now that the forces in the engine have been established, further components can be calculated.
Gudgeon pin area, Outer Diameter, and Inner Diameter

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Crankshaft
Crankpin
The forces acting on the crankpin must be considered when calculating its size (V.B.Bhandari, 2010) states a method
for calculating these sizes.

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Prop-shaft
The prop shaft is used to transmit force ultimately to the wheels and should be able to react safely to the torsional
force output of the engine.
Torsional Stress

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Gearbox
Gear Ratios
Gear ratios are used to vary the output speed of the gearbox shaft allowing different speeds to be achieved. The
following calculations show how this may be calculated.

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Gear Sizes
As the gears run on parallel shafts at a fixed distance, it is necessary to achieve appropriate gear sizes that meet the
distance and ratio criteria.

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Output Shaft Torsional Stresses
When calculating the output shaft size it is important to consider the torsional stresses it will be subjected to
An alternative material or CSA may be necessary to achieve a higher FOS

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Wheel Studs
Impact stress
If the car falls from a height onto one wheel the studs will need to be able to resist these forces, the impact force
and distance is dampened by the suspension system by converting some of the force into moving a fluid in the
dampener these points are included in the following calculations.

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Static Beam Stresses
(Unfortunately during this assignment I had limited time due to personal issues and could not calculate any static
beam scenarios for this project, I have included some tutorial examples I had completed which illustrate how these
are calculated and may be used in the buggy application)

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Design process/Intent
After completing the hand calculations, the next step was to start the design of the buggy. This was done using
extensive research and a mixture of 2D and 3D design processes. 2D was used to generate the outlines and limits,
blocks were used to check the mechanical/fit and function aspects of the design, and 3D to finalise the process.
The following sections will discuss the intent, process, limitations, and methods used to achieve the objectives for
key aspects of the buggy design.
2D Block Engine and considerations
After establishing the engine values and dimensions through hand calculations the drawing process can proceed.
Each of the components, to create the engine, were created in 2D and converted into blocks to check the mechanical
aspects to ensure it would function in principle, and to check clearances for the housing. (A video is available of the
block animation)
Key considerations
Whilst carrying out this process the key points that were considered were:
 Valve clearance at TDC, ensuring there were no collisions
 Casing clearance
 Pulley Ratios
 Piston/Head clearance
 Timing
After running the 2D simulation, it seemed in principle that the engine functions from a mechanical motion
standpoint worked as intended.

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2D, Blocks, and 3D:
Buggy size
The assignment referred to SAE BAJA for information, after referring to this site the decision was made to create the
buggy partially under the SAE rules process. According to (SAE, 2015) the engine size needed to be under a size that
was not in line with the assignment so this aspect was ignored, however buggy size limits and safety aspects were
included in the design process.
According to (SAE, 2015) the buggy must have:
 4 wheels
 The engine capacity to carry 1 person
 Vehicle dimensions not exceeding W1620mm, L2740mm
 Suitable ground clearance must be suitable
 The capability to travel on all terrains conditions
 Spaceframe dimensions that fall within outlined limits (discussed later)
Many other aspects fell out of the assignment requirements, such as electrics.
Engine
After the block simulation was carried out the engine design (fig 2) was carried out in 3D following the hand
calculation parameters.
Figure 2engine design
The cam creation involved orientating the lobes as such that the engine would function as a 4 stroke Otto cycle type.
Mates were added to each component limiting the degrees of freedom to simulate a real world mechanical scenario,
concentric mates were placed on the crank, con rod, and parallel constraints were added to limit the drift of the con
rod along the shaft. After all the required mates were added the engine was rotated to TDC and the Camshaft
orientated appropriately.
The timing process ultimately yielded a 1,4,3,2 firing cycle, and under simulation (turning the crank) the intake valve
opened appropriately, the compression stroke in the cylinders had both valves closed, and the exhaust stage
functioned as intended.
After the mechanical function of the engine was completed the casing was designed to enclose the engine
components.
Material selections were based on lightweight materials that could withstand the applied loads, these are discussed
further later in this assignment.

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Chassis
According to (SAE, 2015) the chassis had to follow certain criteria, this would create a safe and functioning space
frame.
Figure 3space frame parameters (SAE, 2015)
Figure 4space frame parameters (SAE, 2015)

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Figure 5 Space frame parameters (SAE, 2015)
Figure 6Space frame parameters (SAE, 2015)

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With this data the basic outline for the chassis was created in Solidworks (fig 7) using 2D and 3D sketches following
the dimension parameters and driver considerations including head height and width.
Figure 7sketched outlines
After the sketching process, tubular material was added and trimmed in weldments (fig8).
Figure 8 Chassis
The tube material was decided to be 33.4 dia x 3.2 wall thickness s355 as steel is reletivley cheap currently and the
FEA showed that this would be the minimum yield (355Mpa) to withstand the buggy rolling withing a acceptable
FOS.

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Tyres/Wheels
After researching a desirable ride height on enthusiast websites it was established this is subjective and
circumstantial , so the decision was made to make a nominal figure of some of the stated heights(not referenced as
not deemed completely reliable) that would achieve the objective, the ride height would be 300mm. With this
information appropriate wheels and tyres were researched.
A number of tyres and wheels were suitable but the Carlisle 489 A/T ATV Tire (fig 9) was chosen as it suited the ride
height (mountain, n.d.), full documents on these products is available in the appendix.
Figure 9tireand wheel (mountain, n.d.) (wickedalloys, n.d.) Respectively
These were then modelled in Solidworks using rotation, mirror and extrusions.
Figure 10 tire creation
Figure 11Wheel creation
The bolt hole pattern and offset was then added using (tirerack.com, n.d.) and (wheelsupport, n.d.) as reference.
Details in appendix

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Suspension
The design criteria of the suspension is that the droop and compression of the suspension should achieve 400mm of
travel. The geometry for this was calculated using blocks and block animation (fig12) with constraints in the model.
Once the geometry was calculated the 2D sketch was used to create the 3D assembly of the suspension, concentric
and parallel constraints were used in this design, also travel limits were added.
It was calculated on the basis that ultimately the wheel will travel the full range of the suspension maintaining a
vertical alignment. To achieve this the upper and lower arms were placed on a parallelogram and are the same
length.
Figure 12 Suspension layout
Considering the mounting points on the chassis would apply load to these points additional plates were added for
mounting and strengthening.

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Steering
The steering system for the buggy was approached with the Ackerman principle in mind. According to
(www.rctek.com, n.d.) (Heisler, 1989)When a vehicle turns the innermost wheel needs to turn more than the outside
wheel (fig 13), this allows the car to turn effectively and not cause the road surface to shear across the tire.
Figure 13Ackerman principle (www.rctek.com, n.d.)
This is achieved by laying out some geometry between the steering arms mounting points on the hub and the center
of the projected rear axle center-line
Figure 14Ackerman Principle (www.rctek.com, n.d.)
The layout detailed shows a method for creating a turning circle without toe out/in states (www.rctek.com, n.d.)
These principles were adopted during the design of the buggy steering system and the geometry included in the
layout.
Figure 15 Ackerman geometry in the buggy layout
Although the diagram shows the lines intersecting the center axis of the front wheels the mounting point falls on this
line and not at the intersection with the axis (fig 14)

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Figure 16 steering conection
As the wheels need to turn left and right and also be moveable during suspension movement, a number of universal
joints were added (fig 17)
Figure 17 Steering universal joints
To avoid the wheels turning during suspension travel (bump-steer) due to the connection not being on the focal
point of the suspension travel, additional layouts were created. The focal points were established by a creating 3
point radius from the mounting point on the hub. This showed the idea position intersection for the centreline of the
steering rack axis and pivot point (fig 18)
Figure 18steering centerpoint

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The rack and pinion aspect of the rack were created using the Solidworks tool box and mated using mechanical
mates taking into consideration the gearing ratio, or how much the rack will travel in a linear direction during the
rotary angular motion of the pinion(fig 19). The angles in the steering column were achieved by using UJs this
allowed room for the driver, and yields a comfortable steering wheel position (Fig 20).
Figure 19 Steering rack and pinion
Figure 20 UJ steering column

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4W Drivetrain
The drivetrain has 2 differentials, these were designed in a separate sub assembly and mechanical mates used to
create the interactions between the various gears. The differential allows each wheel to turn at different rates, this
allows the car to turn without dragging the outer or inner wheel depending on which has traction states (Coombes,
2004).
The design process involved using Solidworks toolbox components and breaking links allowing them to become
editable parts. The gears and pinion were constrained and mechanical mates used to achieve the degrees of
freedom required for a differential to work through the spider gear and respective bevel gears (fig 21)
Figure 21Differential
After the sub-assembly was created the prop shaft and universal joint connections were added. As the suspension
and steering moves the wheels, and due to positioning of the drive shafts. The connection between the drive shaft
and hub is keyed and is allowed to slide in and out of the hub maintaining a suitable interaction whilst driving the
wheels (fig 22)
Figure 22keyed drive shaft and axle arrangement

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Controls
The controls in this assignment are purely pictorial apart from the steering wheel.
Assembly Process
Part Assemblies and Constraints
During the assembly process of the buggy a number of sub-assemblies were created. These all carried internal
mating systems to limit degrees of freedom and simulate real life motion. Example (fig23-27)
1) Free components
Figure 23 mates
2) Con-rod and piston are aligned
Figure 24 mates

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3) Concentric mates are added.
Figure 25mates
4) Concentric mates again to align the piston and bore
Figure 26 mates
5) Finally a concentric and coincident mate are added.
Figure 27 mates

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Para metrics
Para-metrics were used in the process of creating this model, one example is the spring in the suspension.
The spring was created by turning a profile along a line, this line was linked at one end to a fixed component and
linked to another moving part.
Figure 28Parametric example
When the free component is extended along its un-constrained line the spring updates to reflect the changes.

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Finite element analysis software
The next step in the design process is to validate the components used. One of the methods for validating
components is Finite element analysis or FEA, this process allows the designer to check the amount of deflection,
stress within the system, strain, and FOS.
The software achieves this by meshing the component and considering the reaction of each small section, similar to
the spring style hand FEA.
Engine
As requested in the assignment, various components in the engine require FEA. The following section will detail this
process.
Piston
After establishing the pressure in the engine during combustion it is possible to constrain the piston and apply this
pressure to validate the design. (Fig 29-34)
Figure 29Piston material type FEA
Figure 30Piston constraints and pressure FEA

Page 33 of 43
Figure 31Piston Mesh FEA
Figure 32Piston Min Max Stress FEA

Page 34 of 43
Figure 33Piston Displacement FEA
Figure 34Piston FOS FEA
As the maximum stress is < the min Yield of the material and the FOS=1.5 this components passes the
requirements. Further analysis will include only one diagram.

Page 35 of 43
Gudgeon pin
As the force acting on the con-rod was hand calculated, this value is used in the next analysis.
Figure 35Gudgeon pin FEA
Applied force 26340N
Material Alloy Steel 620 MPa min Yield
Stress Max 563.5 MPa
Deflection 0.06mm
FOS Min 1.1
The factor of safety is very close to 1 which may not be suitable as deviations in force or manufacturing may cause
failure, alternative materials or CSA may be necessary.

Page 36 of 43
Con-rod
The force on the Con-rod was hand calculated, this will be applied when the crank is at 25 degrees as (V.B.Bhandari,
2010) states when the crank is at 25 degrees this will be the maximum torque.
Figure 36Con rod FEA
Applied Force 26340N
Material Alloy Steel 620Mpa
Stress 611 MPa Max
Displacement 1mm
FOS 1.01
Again, the factor of safety is very close to 1 which may not be suitable as deviations in force or manufacturing may
cause failure, alternative materials or CSA may be necessary.

Page 37 of 43
Crankshaft
Similar loading constraints and forces were added to the crank-shaft as the con rod.
Figure 37 Crank FEA
Force 26340N
Material Plain Carbon Steel 220Mpa Min Yield
Stress 197MPa Max
Displacement 0.03mm
FOS 1.1Min
This component is very close to acceptable (@1.3), but the CSA may need adjusting to increase the FOS.

Page 38 of 43
Chassis
Applied Force 26340N
1060 ALLOY 1060 Alloy Min yield 275Mpa (later adjusted to s355)
Stress 285Mpa Max
Displacement 2.5mm
FOS 0.96
The chassis failed initially in the FEA, later the material was adjusted to S355 and the FOS result = 1.2

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2D Manufacturing drawing of … to BSi8888
As instructed by the course tutor, a 2D manufacturing drawing was created using projected views and an isometric
view. GDT was applied along with tolerance dimensions for manufacturing accuracy.
Figure 38 2D Manufacturing drawing
Critical Analysis
During the creation of the off-road buggy quite a few hand calculations were required, initially I was curious as to
why this was when we have expensive software to carry out the process. After completing the design and carrying
out some FEA on various components it became clear that hand calculations not only reinforce an understanding of
how components react to stresses, give a better understanding of what the FEA software is reporting, but also
ultimately save time.
One of the post design hand calculations I carried out, that was not required during the assignment, showed that
one of my key components was not suitable for the application to such a degree that I would have to use rare,
extremely strong material to resolve it without redesign. If this had been in a commercial environment, this would
have caused major issues with deliver times as I process 3D designs from the top down, meaning that many other
components were not suitable as a result of this one part
Another concern I discovered during my research with FEA is that it is very accessible to anyone using the software
and there is a danger that the interpretation of the analysis could be misconstrued as safe where as in reality other
factors may cause the application to fail. It is vital that any simulation and analysis is validated by a professionally
registered engineer as failure in the field could result in injury or worse. Many senior engineers believe that "FEA will
make a great engineer from a good one, but it will make dangerous one from a bad engineer" (eng-tips, n.d.)
These instances of cascading errors and FEA cautions has altered my interpretation of design process and technical
software. Software is not a substitute for experience or manual calculation, it is just a tool.

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References
Coombes, V. H. &. P., 2004. Hillier's Fundermentals pof motor vehicle technology. 5th ed. Cheltenham: Nelson
Thornes Ltd.
eng-tips, G., n.d. eng-tips. [Online]
Available at: http://www.eng-tips.com/viewthread.cfm?qid=296596
[Accessed 02 01 2016].
Heisler, H., 1989. advanced Vehicle Technology. 1st ed. London: Edward Arnold.
mountain, R., n.d. rockymountainatvmc.com. [Online]
Available at: https://www.rockymountainatvmc.com/p/1602/320/Carlisle-489-A-T-ATV-Tire
[Accessed 02 01 2015].
SAE, 2015. BAJA SAE Rules, Tennesse: SAE BAJA International.
tirerack.com, n.d. /techpage.jsp?techid=92. [Online]
Available at: http://www.tirerack.com/wheels/tech/techpage.jsp?techid=92
[Accessed 02 01 2016].
V.B.Bhandari, 2010. Design of machine elements. In: Design of machine elements. Pune: Tata Mcgraw Hill, pp. 889-
891.
wheelsupport, n.d. offset. [Online]
Available at: http://www.wheelsupport.com/offset/
[Accessed 02 01 2016].
wickedalloys, n.d. 12x7-atv-utv-matte-black-rampage. [Online]
Available at: http://wickedalloys.com/products/12x7-atv-utv-matte-black-rampage
[Accessed 02 01 2016].
www.rctek.com, n.d. ackerman_steering_principle. [Online]
Available at: http://www.rctek.com/technical/handling/ackerman_steering_principle.html
[Accessed 02 1 2016].
Bibliography
Coombes, V. H. &. P., 2004. Hillier's Fundermentals pof motor vehicle technology. 5th ed. Cheltenham: Nelson
Thornes Ltd.
Heisler, H., 1989. advanced Vehicle Technology. 1st ed. London: Edward Arnold.
SAE, 2015. BAJA SAE Rules, Tennesse: SAE BAJA International.
V.B.Bhandari, 2010. Design of machine elements. In: Design of machine elements. Pune: Tata Mcgraw Hill, pp. 889-

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Appendices
(wickedalloys, n.d.)

Page 42 of 43
(mountain, n.d.)

Page 43 of 43
(wheelsupport, n.d.)

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