Abstract This paper acts as a design report describing the overall two seated buggy chassis designs that have been developed as a requirement for the BJF3022 Computer ided !esign 2 course"
Introduction The goal of the pro#ect is to design the two seated chassis model of the $buggy$ $b uggy$ vehicle by means of using using the selected program which supports the design" %t is also necessary to to perform a series of computer calculations in order to simulate the behavior of the structure under the influence of different load conditions" The frame of the vehicle model visuali&ation is performed using utodes' %nventor 20()" *trength calculations are made by means *tress nalysis using utodes' %nventor 20()"
Objective The ob#ectives for this pro#ect are+ i" To design an two seated ated buggy chassis ii" ii" To anal analy& y&ee the the stre stress ss dist distri ribu buti tion on on an bugg buggy y fra frame me
Scopes of Project The scope for this pro#ect consists of i" !esign a two seated buggy chassis" ii" naly& naly&ing ing the frame frame stress stress distri distribut bution ion by using using utode utodes' s' %nvent %nventor or 20() naly nalysis sis *oftware"
Literature Review buggy car is a recreational vehicle vehicle with large wheels, wheels, and wide tires, designed for use on sand dunes or beaches" The design is usually a modified vehicle with a modified engine mounted on an open chassis" ch assis" The modifications usually attempt to increase the power to weight ratio by either lightening the vehicle veh icle or increasing engine power or both" similar, similar, more recent generation of off road vehicle, often similar in appearance to a sand rail but designed for different use, is the $off road go 'art$" The difference between a dune buggy or go 'art and an $off road$ buggy or 'art is sometimes nothing more than the type of tires fitted -sand tires or all terrain tires - but $off road$ go 'arts and buggies are a rapidly developing category of o f their own" They are also often referred to as air buggies, and those with an open op en frame chassis are called sand rails"
Literature Review
Chassis Design Consideration (. /odifying roduction Chassis
• 1hen considering modifying a production-based chassis to mount alternate suspension, engines or drivetrain, spend time studying the unibod y newer vehicle. or ladder-frame older vehicle. structures" The structures formed b y the manufacturers chassis designers have strong areas intended for loads and wea' areas not intended to carry loads" %dentifying the correct parts of the chassis structure to cut or modify is critical"
• Consider using scale models of the vehicle if plastic models were made., to moc'up the changes, or 3! modeling software to do the same" %f the changes involve the suspension, such as lowering the vehicle, mode l the new suspension first" *ometimes lowering the vehicle while using the same suspension pic'up points will create poor handling"
2. Build Chassis /odels
• /odeling a space frame chassis with balsa wood stic's enables you to see firsthand the differences triangulation ma'es to the stiffness of a chassis" 4erb dams, in his boo' 5Chassis 6ngineering7 provides a whole chapter on chassis modeling using balsa and paper" 4is recommendation is for a (8(2 scale model"
• 9i'ewise, using cardboard, paper and glue to build model monocoques can be a very rewarding and low cost learning e:perience as well" The great thing about these materials is that they dont have a lot of strength an d so the deformations that loads create can be easily seen when loads are applied"
• !esign the chassis after the suspension" • %t is much easier to design a tentative suspension according to the rules and go od geometry, and then build the chassis to conform to suspension mounting points and springs8damper mounts" 3. Consider the load paths
• chassis is not about 5absorbing7 energy, but rather about support" 1hen considering placement of tubes, visuali&e the 5load paths7, and consider using F6 Finite 6lement nalysis software. to help analy&e load scenarios" 9oad p aths are defined as the forces
resulting from accelerating and decelerating, in the long itudinal and lateral directions which follow the tubing from member to member" The first forces which come to mind are suspension mounts, but things li'e the battery an d driver place stresses on the space frame structure"
;. /a:imi&e C< placement and vehicle balance
• Center of gravity affects the race car li'e a pendulum" The ideal place for the C< is absolutely between the front and rear wheels and the left and right wheels" lacing the C< fore or aft or left or right of this point mea ns that weight transfers unevenly depending on which way the car is turning, and whether it is accelerating or decelerating" The further from this ideal point, the more one end of the car acts li'e a pendulum, and the more difficult it is to optimi&e handling" The C< is also height dependent" lacing an engine higher off the ground raises the C<, an d forces larger amounts of weight to transfer when cornering, accelerating, or decelerating" The goal of vehicle design is to 'eep all four wheels planted if possible to ma:imi&e grip, so placing all parts in the car at their lowest possible location will help lower the C< height" =. 9ayout the tube members for easy access and maintenance
• /aintaining a race car comes after construction" lacing tubes across openings is a natural way of ensuring a rigid chassis" 4owever, in practical terms you may be ma'ing it difficult or impossible to reach the maintenance demanding components" good chassis design will allow quic' and easy access to all components and will not hamper removal or replacement of any part" ). Chec' out vehicles which are competitive in your class
• >ehicles which are competitive are usually built well, and with appropriate materials and methods" ?bserve them at the trac' and in the pits, and you can infer a great deal about what ma'es them winners" @. ?ptimi&e the tubing shape for the #ob
• *quare tubing is the easiest structural shape to build a chassis from" 4owever, there are circumstances where round tubing can be useful, albeit at a penalty in the comple:ity of construction" ?val tubing is useful in open whe el race cars for wishbones"
A. ?ptimi&e the tubing si&e and gauge for the #ob
• Tubing which is used in tension, can be of a lighter gauge than that used in compression" eeping this in mind can save considerable weight, although it requires additional #oining wor' and variety of tubing"
Materials factor that been consider in building a bugg car !" Lightweight
s there is a high emphasis on greenhouse gas reductions, reduction of emission and improving fuel efficiency this criterion is most important o ne for an automotive company" 9ightweight materials can improve fuel efficiency more than other factors" 6:periments reveal that (0 percent of weight reduction can lead to ) to A percent improvement in fuel usage" 1eight reduction can be obtained by three ways+ •
eplacing materials of high specific weight with lower density materials without reducing rigidity and durability" For e:ample replacement of steel with aluminium, magnesium, composites and foams"
•
?ptimi&ing the design of load-carrying elements and e:terior attachments so as to reduce their weight without any loss in rigidity or functionality"
•
?ptimi&ing the production process, such as reducing spot welding and replacing new #oining techniques"
#" $cono%ic effectiveness
?ne of the most important consumer driven factors in au tomotive industry is the cost that determines whether any new material has an opportunity to be selected for a vehicle component" Cost includes three components+ actual cost of raw materials, manufacturing value added, and the cost to design and test the product" luminium and magnesium alloys are certainly more costly than the currently used steel and cast irons" *ince cost may be higher, decisions to select light metals must be #ustified on the basis of improved functionality" /eanwhile the high cost is one of the ma#or obstacles in use of the composite materials"
&" Safet
The ability to absorb impact energy and be survivable for the passengers is called 5crashworthiness7 of the structure in vehicle" t first two concepts in automotive industry should be considered+ crashworthiness and penetration resistance" %n the more accurate definition of crashworthiness, it is the potential of absorption of energy through controlled failure modes and mechanisms" 4owever penetration resistance is concerned with the total ab sorption without allowing pro#ectile or fragment penetration"
Materials nor%all used in %a'ing bugg car Steel
• The main factors of selecting material especially for body is wide variety of characteristics such as thermal, chemical or mechanical resistance, ease of manufacture and durability" *o if we want to choose a material with these characteristics, *teel is their first choice" There was many developments in irons and steels over the past couple decades that made the steel more light-weight, stronger, stiffer and improving other performance characteristics" pplications include not only vehicle bodies, but also engine, chassis, wheels and many other parts" %ron and steel form the critical elements of structure for the vast ma#ority of veh icles, and are lowcost materials"
• The past several years have seen steady increases in the use of high-strength steels that are referred to as high-strength, low-alloy steels" These materials formed the basis of Dltra light *teel uto Body D9*B." The D9*B car body demonstrated a (E mass reduction in a body structure that had superior strength and structural performance" Comparable mass reductions and other benefits were achieved for doors, hoods, dec' lids, and the hatchbac's"
• The prime reason for using steel in the body structure is its inherent capability to absorb impact energy in a crash situation" Alu%iniu% •
There are a wide variety of aluminium usages in automotive powertrain, chassis and bod y structure" Dse of aluminium can potentially reduce the weight of the vehicle body" %ts low density and high specific energy absorption performance and good specific strength are its most important properties"
•
luminium is also resistance to corrosion" But according to its low modulus of elasticity, it cannot substitute steel parts and therefore those parts need to be re-engineered to achieve the same mechanical strength, but still aluminium offers weight reduction"
•
luminium usage in automotive industry has grown within past years" %n automotive powertrain, aluminim castings have been used for almost (00 of pistons, about @= of cylinder heads, A= of inta'e manifolds and transmission" For chassis applications, aluminium castings are used for about ;0 of wheels, and for brac'ets, bra'e components, suspension, steering components and instrument panels" luminium is used for body structures, closures and e:terior attachments such as crossbeams, doors or bonnets"
•
ecent developments have shown that up to =0 weight saving for the body in white B%1. can be achieved by the substitution of steel by aluminium" This can result in a 20 -30 total vehicle weight reduction"
•
The cost of aluminium and price stability is its biggest obstacle for its application"
Magnesiu%
• /agnesium is another light metal that is becoming increasingly common in automotive engineering" %t is 33 lighter than aluminium and @= lighter than steel8cast iron components" /agnesium components have many mechanical8physical property disadvantages that require unique design for application to automotive products" lthough its tensile yield strength is about the same, magnesium has lower ultimate tensile strength fatigue strength, and creep strength compared to luminium" The modulus and hardness of magnesium alloys is lower than aluminium and the thermal e:pansion coefficient is greater"
• /agnesium alloys have distinct advantages over aluminium that include better manufacturability, longer die life and faster solidification" lso magnesium components have higher machinability"
• Because of its too low mechanical strength, pure magnesium must be alloyed with other elements" The most common alloying elements for room temperature applications is /g-lGn group that contains aluminium, manganese, and &inc" Advanced co%posite %aterials
• Fibre reinforced composites offer a wide range of advantages to the automotive industry" %t has the potential for saving weight offered by their low density" Component designs can be such that the fibres lie in the direction of the principal stresses, and amount of fibre used is sufficient to withstand the stress, thus optimi&ing materials usage"
Carbon(fibre epo) co%posite
• /ost recently, the most of the racing car companies much more rely on composites form whether it would be plastic composites, evlar and most importantly carbon-fibre epo:y composition" %t is because the composite structure is the high strength8low weight ratio" The most common materials used for racing cars are carbon graphite., evlar and glass fibres" 6po:y composites have been the first choice in Formula ( car industries and other race cars" *lass(fibre co%posites
•
Aerodna%ics +asics and Design Consideration erodynamics is the science of how air flows around and inside ob#ects" /ore generally, it can be labeled 5Fluid !ynamics7 because air is really #ust a very thin type of fluid" bove slow speeds, the air flow around and through a race vehicle begins to have a more pronounced effect on the acceleration, top speed and handling" Therefore, in race car design we need to understand and optimi&e how the air flows around and through the body, its openings and its aerodynamic devices" Aerodna%ics Consideration
(. Cover ?pen wheels
• ?pen wheels create a great deal of drag and air flow turbulence, similar to the diagram of the mirror in the 5Turbulence7 section above" Full covering bodywor' is probably the best solution, if legal by regulations, but if partial bodywor' is permitted, placing a converging fairing behind the wheel provides ma:imum benefit"
2. /inimi&e Frontal rea
• The smaller the hole your race car punches through the air, the better it will accelerate the higher the top speed it will have" %t is usually much easier to reduce F frontal area. than the Cd !rag coefficient."
3. Converge Bodywor' *lowly
• Bodywor' which quic'ly converges or is simply truncated, forces the air flow into turbulence, and generates a great deal of drag" s mentioned above, it also can affect aerodynamic devices and bodywor' further behind on the vehicle body"
;. Dse *poilers
• *poilers are widely used on sedan type cars such as H*C stoc' cars" These aerodynamic aids produce down force by creating a 5dam7 at the rear lip of the trun', raising the air pressure over the trun'" 1here a notch left by the rear window e:ists a spoiler can help restore pressure to the void behind the window"
=. Dse 1ings
• 1ings are the inverted version of what you find on aircraft" They wor' very efficiently, and in less aggressive forms generate more downforce than drag, so they are loved in many racing circles" 1ings are best placed in areas that have clear airflow to them" lacing a wing behind an obstruction reduces the downforce the wing can produce"
). Dse Front ir !ams
• ir dams at the front of the car restrict the flow of air reaching the underside of the c ar" This creates a lower pressure area under the car, effectively providing downforce" %n many cases, the air dam also reduces the Cd of the vehicle"
@. Dse erodynamics to ssist >ehicle ?peration
• Dsing vehicle bodywor' to direct airflow into openings, for instance, permits more efficient, smaller openings that reduce drag penalties" Iuite often, with some forethought, you can gain an advantage over a competitor by these small dual purpose techniques"
• nother useful technique is to use the natural high and low pressure areas created by the bodywor' to perform functions" For instance, /ercedes, bac' in the (E=0s placed radiator outlets in the low pressure &one behind the driver" The air inlet pressure which fed the radiator became less critical, as the low pressure outlet area literally suc'ed air through the radiator"
• useful high pressure area is in front of the car, and to ma'e full use of this area, th e nose of the car is often slanted downward" This allows the higher air pressure to push down on the nose of the car, increasing grip" %t also has the advantage of permitting greater driver visibility"
A. eep rotrusions way From The Bodywor'
• The smooth airflow achieved by proper bodywor' design can be destroyed quite easily if a protrusion such as a mirror is too close to it" 1hile it is important to design an aerodynamic mount for a mirror, the mirror itself needs to be placed far enoug h away from the bodywor' to avoid adverse effects"
E. a'e the chassis
• The chassis, as mentioned in the aerodynamics theory section above, is capable of being slightly lower to the ground in the front than in the rear" The lower 5Hose7 of the car reduces the volume of air able to pass under the car, and the higher 5Tail7 of the car creates an e:panding space where a vacuum effect can form" This lowers the air pressure beneath the car, creating down force"
(0. Cover or streamline 6:posed 1ishbones
• 6:posed wishbones on open wheel cars. are often made from circular steel tube to save cost" 4owever, these circular tubes generate turbulence" %t may be worth considering the
use of oval tubing, or a tube fairing that creates an oval shape over top of the round tubing"
Figure 2 + *treamlined wishbone tubing improves the smoothness of the air flow to parts of the car behind and reduces drag"
Chassis ,pes There are multiple types of chassis but all of them can be classified into one of two approaches+ (. Dse lengths of round or square tubing, or other structural metal shapes to form the chassis structure *pace frame, multi-tube, ladder frame. 2. Dse #oined panels to form the chassis structure /onocoque, Dnibody. Both approaches can provide a structure capable of mounting other race vehicle components, but each has its own advantages and disadvantages" Space fra%e Chassis
The *pace frame chassis uses numerous cut and shaped pieces structural metal tubing usually steel. #oined together to form a strong framewor'"
!iagram *pace frame chassis for a 59ow cost7 car
Monoco-ue Chassis
The monocoque chassis is technically an improvement over the space frame chassis" !iagram ( below shows a simple e:ample of the difference between space frame and monocoque design"
!iagram (" Comparing the behavior of a monocoque versus a space frame under tension load The monocoque 5Bo:7 on the left uses a panel of material to structurally 5complete7 the bo:" 1hen the hand pushes against it in the direction shown by the green arrow, it creates a shear force across the panel" This force is effectively handled the same wa y a tension load is by the space frame triangulated bo: on the right" 4owever, if the hand were to push from the other side of the bo:, the space frame tube could potentially collapse in compression, whereas the monocoque bo: would behave the same way it did before"
!iagram 2 Comparing the behavior of a monocoque versus a space frame under compression load" Both types of chassis can be made #ust as strong as each other" 4owever, to ma'e an equivalent strength space frame generally requires more material and therefore more weight" The materials used ma'e a big difference as well" %n !iagram 3 below, both the monocoque 5bo:7 o n the left and the fully triangulated space frame 5bo:7 on the right would handle loads in the same manner the rear of the space frame 5bo:7 to avoid visually complicating the diagram.
!iagram 3 /onocoque bo: and 5equivalent7 triangulated space frame" lthough the monocoque can usually be made lighter and stronger than a space frame, it does have some downsides that ma'e it more complicated to design, build and operate" First, the monocoque requires the structure formed by the panels to be 5complete7" %f you observe the 5bo:7 in diagram 3 that we used to demonstrate the monocoque, imagine one side of it is missing as shown in diagram ; below+
!iagram ;" %ncomplete load handling by a monocoque will cause it to deform and buc'le" 1e can push on the corner of the bo: where three panels meet shown on the left. and it wont warp much., but push on a corner ne:t to where the missing side should be and the bo: will buc'le as shown on the right." 1here an opening e:ists, the chassis must handle loads through a supporting sub-structure" primary goal in monocoque design is to ensure that there are no unhandled load paths that can cause the monocoque structure to buc'le" buc'led monocoque is no better than a buc'ledspace frame tube"
%n the case of poorly handled load paths, the space frame can be more forgiving as the tubing diameter and steel material usually provide a more g radual failure than a monocoque" 4owever, it is better to design the chassis correctly in the first place then to rely upon noticing gradual failures" This brings us to another 'ey point about the monocoque %f it is damaged, it is difficult to repair compared to space frame tubes" %t is also difficult to detect damage on a monocoque whereas bent or bro'en tubing is quite easy to spot"
,orsional Rigidit Torsional rigidity is a property of every race vehicle chassis that determines how much twist the chassis will e:perience when loads are applied through the wheels and suspension" !iagram = below shows the principle"
!iagram = Torsional igidity" The less the chassis twists, the more torsionally rigid it is considered" chassis that has a lot of twist wont handle as predictably as o ne which has very little because by twisting, the chassis begins to act li'e an e:tension of the suspension" The suspension is designed to allow the wheels8tires to follow the roads bumps and dips" %f the chassis twists when a tire hits a bump, it acts li'e part of the suspension, meaning that tuning the suspension is difficult or impossible" %deally, the chassis should be ultra-rigid, and the suspension compliant" Torsional rigidity is measured in lbs-ft8degree or 'g-m8degree" ?ne end of the chassis front or rear. is held stationary and the other end is balanced on a point and twist is applied via a beam" !iagram ) below shows the basic idea
!iagram ) /ethod to measure torsional rigidity"
Design of ,wo Seated +ugg
Stress Analysis Report
Analyzed File:
Part1.ipt
Autodesk Inventor Version:
2016 (Build 2001!000" 1!#
$reation %ate:
12&1&201'" 10:0 P)
*i+ulation Aut,or:
B)*
*u++ary:
Project Info (iProperties) Summary Aut,or
-*/1
Project Part u+er
Part1
%esiner
-*/1
$ost
30.00
%ate $reated
12&1&201'
Status %esin *tatus
4orkInProress
Physical )aterial
Alu+inu+ 6061
%ensity
2.5 &+7
)ass
1'0.68 k
Area
'6!2800 ++72
Volu+e
''!1200 ++7
$enter o9 ravity
;<1.11'6 ++ y<'.01 ++ z<2'2.8' ++
ote: P,ysial values ould e di=erent 9ro+ P,ysial values used y FA reported elo>.
Simulation:1
General objective and settins: %esin ?@etive
*inle Point
*i+ulation ype
*tati Analysis
ast )odiCation %ate
12&1&201'" 10:8 P)
%etet and li+inate /iid Body )odes
o
!esh settins: Av. le+ent *ize (9ration o9 +odel dia+eter#
0.1
)in. le+ent *ize (9ration o9 av. size#
0.2
radin Fator
1.'
)a;. urn Anle
60 de
$reate $urved )es, le+ents
Des
!aterial(s) a+e
Alu+inu+ 6061 )ass %ensity
eneral
2.5 &+7
Dield *trent, -lti+ate ensile *trent, DounEs )odulus
*tress Part a+e(s#
10 )Pa 6!.8 Pa
PoissonEs /atio
0. ul
*,ear )odulus
2'.802 Pa
Part1.ipt
"peratin conditions #orce:1 oad ype
Fore
)anitude
1000000.000
Vetor
0.000
Vetor D
0.000
Vetor G
1000000.000
Selected #ace(s)
25' )Pa
#i$ed %onstraint:1 $onstraint ype Selected #ace(s)
Fi;ed $onstraint
Results Reaction #orce and !oment on %onstraints %onstraint &ame
Reaction #orce
Reaction !oment
!anitude %omponent ('*)
!anitude %omponent ('*)
0 Fi;ed $onstraint:1
1000000
0
66 + 66 + 0 +
H1000000
0+
Result Summary &ame
!inimum
!a$imum
Volu+e
''!12600 ++7
)ass
1'0.68 k
Von )ises *tress
0.00!668 )Pa
!6.!8 )Pa
1st Prinipal *tress
H1566. )Pa
261.6 )Pa
rd Prinipal *tress
H'2.!6 )Pa
60.62! )Pa
%isplae+ent
0 ++
5.'0!' ++
*a9ety Fator
0.051!6 ul
1' ul
*tress
H261.! )Pa
2006.5 )Pa
*tress D
H'8'.186 )Pa
6.2' )Pa
*tress G
H12'.66 )Pa
!08.01! )Pa
*tress DD
H2!20.' )Pa
2'65.'8 )Pa
*tress DG
H16!'.5! )Pa
1110.05 )Pa
*tress GG
H01.' )Pa
!85.'' )Pa
%isplae+ent
H16.!05 ++
1'.'52! ++
D %isplae+ent
H65.5518 ++
0.0528 ++
G %isplae+ent
H2.!20'8 ++
6.!'!1 ++
uivalent *train
0.00000011651 ul
0.0'0018 ul
1st Prinipal *train
0.0000000'6021 ul
0.006 ul
rd Prinipal *train
H0.062!001 ul
H0.0000000216!66 ul
*train
H0.01826 ul
0.02800' ul
*train D
H0.011!8 ul
0.0121! ul
*train G
H0.022182 ul
0.01'6165 ul
*train DD
H0.028!!! ul
0.006!1 ul
*train DG
H0.02'11 ul
0.0212! ul
*train GG
H0.0'1052 ul
0.01262' ul
#iures +on !ises Stress
1st Principal Stress
,rd Principal Stress
-isplacement
Safety #actor
Stress ''
Stress '
Stress '*
Stress
Stress *
Stress **
' -isplacement
-isplacement
* -isplacement
./uivalent Strain
1st Principal Strain
,rd Principal Strain
Strain ''
Strain '
Strain '*
Strain
Strain *
Strain **
Discussion This design data and analysis of is only a start in the long and comple: way of designing and manufacturing a two seated acing Buggy, which could compete with other Buggys" But in my opinion no one can really understand and add on the more comple: mechanism without pass through the starting point and understanding thoroughly the basic functionality, and the theory behind the basic design" *o this starting point is the most essential factor in any designing process" The ne:t step in designing the complete a two seated acing Buggy is to the design the complete rear and front a:les, then the bac' a:e and engine mounting, which also includes the lin'ages between them" The selection of a motor will help in both designing the gear transmission and the bac' a:e" This selection will include also a generator set, a battery set, an e:haust system, gasoline tan' and car accessories" Then will come the selection for the right fasteners" fter that will be the auditing process on all the designing processes which include a through chec'ing of the design data and measurements" Finally will be the manufacturing and assembling of the p arts to form the complete buggy product."
Conclusion Frame design, as most design problems are, comes d own to a series of tradeoffs between various competing aspects" 1ith a chassis, the main aspects are stiffness, weight and cost" There are several ways to ma:imi&e these trade-offs as discussed earlier and this is essentially what the design process consists of" The chassis design incorperated the concepts of triangulation and polar moment of inertia into a coherent chassis design that is representative of a first cut" The actual design process, is an
iterative effort and once the analysis results are in, the design can be twea'ed and updated to accommodate the discovered wea'nesses" This is where the design created currently sits" %t has been created and analy&ed and the ne:t step would be to update the design to address the issues found in the analysis"
References +oo's !" Ba#a Bugs and Buggies by Jeff 4ibbard and on *essions #" Building a !une Buggy The 6ssential /anual+ 6verything Kou Heed to now Build ny >1-based !une Buggy Kourself by aul *ha'espeare .ebsites
(. 2. 3. ;.
http+88www"vw-store"com8Buggy20Frames-20Chassis"htm http+88www"buggyworld"com8parts8products"phpLidM2 http+88www"v-dubstore"com8rticles"aspL%!M(3A http+88trentfabrication"com8chassis8
