Report - Old Dominion University

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OLD DOMINION UNIVERS
ITY

SAE Baja

Midterm Report





Frame

Suspension

Drivetrain

Dan D’Amico

Pe瑥r Morabi瑯

Oenne瑨 Nlliot

䍵r瑩V May

MicUael Paliga

Pa瑲ick Mooney

Greg
ScUaffran

Brian RoVV

Mylan Quinn


Facul瑹 ATviVor㨠Mr. Nl浵V瑡fa


i


Ta
ble of Contents

Section











Page #

List of Figures………………………………………………………………………………………………………………………………
.
……
.

.
.
ii

Abstract……………………………………………………………………………………………………………………………………………
.
……
i
ii

Introduction…………………………………………………………………………………………………………………………………………….1

Background……………………………………………………………………………………………………………………………………………
..1

Background
-
Drivetrain……………………………………………………………………………………………………………………………
.2

Methods

& Results
-
Drivetrain………………………………………
……………………………………………
…….
…………………
..
2
-
5

Discussion
-
Drivetrain…………………………………………………………………………………………………………………………
…5
-
7

Background
-
Suspension……………………………………………………………………………………………………………………….7
-
8

Methods
-
Suspension……………………………………………………………………………………………………………………………….
9

Results
-
Sus
pension………………………………………………………………………………………………………………………………….
9

Discussion
-
Suspension………………………………………………………………………………………………………………………
.9
-
10

Background
-
Frame………………………………………………………………………………………………………………………………
.10

Methods
-
Frame……………………………………………………………………………………………………………………
………….
10
-
11

Results
-
Frame…………………………………………………………………………………………………………………………………….…
11

Discussion
-
Frame………………………………………………………………………………………………………………………..…...
11
-
13

Appendix A…………………………………………………………………………………………………………………….………………...
14
-
20

Appendix B………………………………………………………………
…………………………………………………………………………….
21

References……………………………………………………………………………………………………………………
..
........................
22






ii


List of Figures

Figure











Page #

Figure 1.

Gear Train Model …………………………………………………………………………………………………………….……….4

Figure 2.
Differential ……………………………………………………………………………………………………………………….………5

Figure 3.

Double Reduction Gear Schematic …………………………………………………………………………………….…….5

Figure 4.

CVT Image …………………………………………………………………………………………………………………………….….6

Figure 5.

Camber Diagram ………………………………………
………………………………………………………………………….…..7

Figure 6.

Castor Diagram …………………………………………………………………………………….………………………………….7

Figure 7.

Toe Diagram ……………………………………………………………………………………………………………………….……8

Figure 8.

Roll and Steering Behavior ………………………………………………………………………………………………………
.8

Figure 9.

SAE Axes Terminology ………………………………………………………………………………………………………………8

Figure 10.

ODU, Cornell, and Oregon State SAE Bajas …………………………………………………
..
………………………12












iii


Abstract

The
Society of Automotive Engineers (SAE) Baja

senior design project
enables students to gain real
world experience in the

design, analysis, and manufacture of a vehicular product. Specifically, our

team
has been organized into frame,

drivetrain
,

and suspension subgroups to allow a thorough and original
design of all

major
components. The frame team will be responsible for the creation of a

new frame
design that must be concurrent with all SAE competition rules.

Special consideration will be given to
weight and cost reduction. The suspension

team will focus primarily on the
rear suspension. A reliable
trailing arm

design will be utilized for rear suspension applications, while the front

suspension will
consist of a standard double

A
-

arm

setup. The

drivetrain

team will design a double

reduction gearbox,
with an emphasis on ef
ficiency and weight reduction. The

transmission will be a continuously varying
transmission (CVT). The purpose

of this project is to design a SAE Baja vehicle from scratch so that this

design can be utilized in the
2014

SA
E Baja Competition.



1


Introduction

The SAE Baja senior design project is a semester long project intended to allow senior
mechanical engineering students to design an off
-
road vehicle for competition. This project

allows
students to apply engineering theories and concepts that have been presented to them in previous
courses. The purpose of this project is to further the design, manufacturing, teamwork and
communication skills of the team members to prepare them for

working in industry. The team has been
divided into three subdivisions in order to design all the main aspects of the vehicle. The subgroups are:
the drivetrain team, suspension team, and frame team.

The drivetrain team will focus on designing a more effi
cient powertrain design. This will be
achieved by replacing the existing chain driven system with a gearbox. A gearbox will greatly improve
the vehicle’s reliability and efficiently as well as reduce the overall weight of the car. The gearbox will be
paire
d with a CVT transmission to provide a range of gear ratios to improve the vehicle’s maximum
torque and top speed.

The suspension team will develop a more reliable and predicable suspension system. The front
suspension will consist of a double A
-
arm set up
, similar to previous years, to function with the new
frame design. The rear suspension will consist of a four link trailing arm set up to allow for dynamic
camber and the greatest possible suspension travel. This will be more reliable than last year’s des
ign and
should provide the same steering and suspension capabilities.

The frame team will focus on producing a frame that is lighter than last year’s frame. This team
has focused on shortening the frame so that less material is used and a smaller turning r
adius can be
achieved. Additionally, this team has been working to provide the optimum suspension mounting points
and rear end of the frame to accommodate the drivetrain and suspension team’s needs.


Background

The first Mini Baja competition started in 19
76 at the University of South Carolina with only 10
teams. Now more than 30 years later, the competition is formally known as Baja SAE and has expanded
into 3 sub
-
regions: East, Midwest, and West. The Baja SAE competition has even grown into an
internation
al affair with competitions in Brazil, Korea, and South Africa.

This year’s competition will be in Rochester, New York. The competition will include five
dynamic events: Acceleration, Hill Climb, Maneuverability, Suspension & Traction, and Endurance. Thes
e
events will put each vehicle through an intense test of performance and durability. The teams will also
be judged on the vehicle’s styling and cost report.

This competition is used to simulate real world engineering design projects and their related
chal
lenges, therefore, the purpose of the project is for each team to design, build, test, promote, and
race an off
-
road vehicle that can survive the punishment dished out by each event, while keeping costs
low and making it aesthetically pleasing.

2


Background
-

Drivetrain

The SAE BAJA 2013 rule book specifies that all teams shall use a Briggs & Stra
tton 1450 series
engine (
Figure A.1
). This engine produces a peak of 14.50 ft l
bs of torque as shown in
Figure A.2

and is
rated at ~10 horsepower. The engine is tune
d at competition by Briggs & Stratton technicians to insure
that every team is running the specified engine without modifications at 3600 rpm. This is a single
cylinder four stroke engine that is fed from a carburetor and manual choke. The only modificatio
n
allowed to the engine at competition is a remote intake that must be specifically ordered from Briggs &
Stratton and installed according to their instructions.

The transmission we have chosen to pair with this engine is at Continuously Varying
Transmiss
ion (CVT). This transmission is a variable diameter pulley system where the sheaves primary
and secondary pulleys move in and out thus changing
diameter and gear ratio. Figure
A.
3
demonstrates
the extremes of the gear ratios that the CVT will travel throug
h. CVT’s are ideal for the SAE Baja
competition because the CVT adjusts to provide the best ratio depending on the speed of the input and
output shafts thus providing max torque when needed and adjusting to the top speed ratio when
needed. This type of CVT

is adjustable with a system of springs and brass weights to allow tuning for
specific events allowing for top speed or lower end torque bias.


Methods & Results


Drivetrain


One of the primary goals of the powertrain team is to develop a fixed ratio gea
rbox design to
compliment the performance of the Briggs & Stratton engine and Gaged CVT system. The gearbox will
be optimized to provide maximum vehicle performance throughout the range of events incorporated in
the SAE Baja competition. The gearbox desi
gn process consists of three major areas:



Gear train and differential design



Bearing and Shaft design



Gearbox Housing design


Each of these areas requires vastly different design methods in order to produce a gearbox that will
enhance the p
erformance of
the Baja vehicle.

Gear train and differential design is crucial to the reliability of the gearbox and represents a
large amount of the calculations thus far in the project. A precise overall reduction ratio is required in
order to achieve the acceptable p
erformance out of the whole drivetrain system. This can be seen in
Figure
A.
4. The most challenging event in the competition for the powertrain team is the hill climb. At
the Rochester venue the hill is 36
-
37 degrees, the steepest of all the locations th
e Baja competition
takes place at. The vehicle must produce enough torque with the chosen ratio to propel the vehicle up
the incline from a stop with a margin of safety. Based on this, a conservative incline angle of 40 degrees
was determined as well as
an overestimated vehicle weight.



3


In order to overcome the incline a minimum gearbox ratio of 7.7551:1 coupled with the initial CVT
reduction is required. Based on this calculation it was decided that an 8.0:1 ratio would be chosen. This
provides a ma
x torque at the wheels of 446.6 lb
-
ft with the initial CVT ratio. In order to provide a margin
of error the incline angle, vehicle weight, engine torque output and chosen reduction ratio were
all
conservatively estimated.

A total safety factor for the d
rive ratio of the vehicle as required on the hill climb competition was
calculated to be 1.277, as seen in Figure
A.
5. This acts as a buffer to account for parasitic loss due to
friction and rotating mass in the driveline, as well as surface conditions an
d traction issues on the hill.


The final drive ratio of the car throughout the band of CVT manipulation is key to success at all
of the events at the SAE Baja competition. The 8.0:1 gearbox ratio should provide good results in the hill
climb and accele
ration events, but it must also allow for a competitive top speed for the endurance
race. The Briggs & Stratton engine is tuned at competition to have an RPM limit of 3600. Based on
achieving this RPM, a theoretical top speed of 35.7 MPH was determined a
nd can be seen in Figure
A.
6.
This should allow the ODU car to keep up with similarly funded teams on the faster sections of the
course, as well as provide good low end power in the technical portions.

There are many constraints in gear train sizing and s
election. The gear combinations must achieve
many design characteristics:



Desired reduction ratio (8.0:1)



Maintain compactness of the overall design



Allow for housing of the selected differential



Maintain reliability under heavy use


Spur style gears will provide the most efficient transfer of power as well as the simplest bearing and
support design due to the lack of lateral forces. They are also significantly cheaper than comparable
helical gears and there is a larger, more availabl
e selection of size and pitch combinations. The gears
being used will have a modern pressure angle of 20 degrees and a pitch of 12. The gear train will be split
into two reductions in order to save space in the overall size of the gearbox. A single redu
ction box
would require a very large spur gear to compliment the pinion gear in order
to achieve the desired ratio.










4





Stage 1 Reduction: (2.0:1)

o

Pitch = 12, Press Angle = 20°



Pinion Gear: 20 Teeth

-

D
p

= 1.6667



Spur Gear: 40

Teeth

-

D
p

= 3.3333




Stage 2 Reduction: (4.0:1)

o

Pitch = 12, Press Angle = 20°



Pinion Gear: 20 Teeth

-

D
p

= 1.6667



Spur Gear: 80 Teeth

-

D
p

= 6.6667


In order to aid in the selection of gears in the
train a table of potential combinations was created. Included were available face widths, bore sizes and
pitches. To ensure the chosen gear combinations would work well together, interference was calculate
d
for each selection based on the following equation where K=1 for full teeth engagement and m=ratio.
The selection of gears mesh without interference based on the results. Using the equation below a gear
selection table can be made. This table is shown i
n
TableA.1
.



N
p

= (2K/(1+2m)*sin20 deg)*(m+ sqrt(m^2 + (1+2m)*sin20 deg)



To determine the strength and reliability of the gear setup the following calculation methods
were employed for each of the gears:



Lewis Bending Stress



Barth Velocity Factor



Lewis
Safety Factor



Barth Factor of Safety



AGMA Stress and Strength


Based on the calculations that are shown in Figure
A7
, a gear material of AISI 1020 was selected.
This material provides an adequate safety factor, is readily available and easily machinable.

The
performance t
o cost ratio is also very high.






Gear Train Model

5


A differential will be housed in the large output gear in the
gearbox. The differential will allow for more maneuverability and
better handling characteristics in the endurance competition by
allowi
ng a bias between the rear drive axles. The large gear will
have to be machined to secure the differential.



After gear selection and calculation is complete a bearing
and shaft system and housing will be developed. The shafts will rely
on a shoulder co
upled with snap rings to secure the gears in a lateral
direction. A standard keyway will mate the gears to the shaft
rotationally. The shafts will also contain shoulders to house bearings. The gearbox housing will be split
horizontally into two sections

along the centerline of the bearings allowing for access and support.


Discussion
-

Drivetrain

The baja’s drivetrain

will undergo a number of upgrades this year. The objective of this year’s
gearbox design is to create a two
-
stage, double reduction gearbox. This type of gearbox will replace the
belt drive system used in the previous car. The new vehicle will not have an

updated transmission;
however, a differential will be incorporated into the gearbox design. These modifications will hopefully
enhance the performance of ODU’s baja vehicle at compe
tition.

In order to achieve success and compete in not only a few, but al
l of the events at the
competition, a more versatile gearbox design was chosen. After reviewing the types of events that the
vehicle will likely encounter; a gearbox ratio of 8:1 was decided upon. A large reduction ratio was
chosen to correspond with an em
phasis toward acceleration rather than top speed. Also, the large ratio
will be more adequate for completing the hill climb course. Spur gears will be used throughout the
gearbox because they are more efficient and simpler to manufacture compared to helica
l gears. A two
-
stage compound gear train like the one in Fig. 13
-
28 below, shows a design similar to the one that will
be integrated in this year’s baja design.



6


In the quest for excellence, a decision was made to incorporate a more advanced design tha
t
includes a differential. A differential was added to the design to increase the vehicles maneuverability. It
will allow for the wheels to rotate at different speeds when making turns. This should allow the car to
excel in certain, more technical, events.

The addition of a differential will definitely benefit the vehicle’s
maneuverability, especially since it la
cks a reverse drive operation.

The transmission was chosen to be a Gaged GX
-
9 continuously variable transmission (CVT). This
type of transmission
will be able to transmit power at optimal efficiency while maximizing performance.
It accomplishes this by being able to shift smoothly and continuously through an infinite number of gear
ratios within a given range of 3.85:1 initial drive to 0.9:1 final d
rive. A picture of the Gaged GX
-
9 CVT
without the belt is shown below. This system also removes the need for a clutch as the belt slips
allowing the engine to spin freely when the secondary shaft is held.





The powertrain design of this year’s vehicle has some similarities but more differences when
compared with previous vehicles. This year’s gearbox is radically different than last year’s design
because issues that arose at competition were discovered and co
rrected. A gear driven setup was
chosen in order to adhere to the complaints of the previous team about the added weight and noise of a
chain drive. Difficulties in maneuverability in previous vehicles created a need to add a differential to the
design. In

doing so, the new car will be able to move more quickly in and out of turns. Both this year and
last year’s teams have the same transmission. No problems were detected by the previous team so the
same CVT will be used again.



7


Several limitations of this

study are present and effect the possible conclusions that could be
made. It is hard to say how effective the gearbox design actually is because the powertrain will not be
physically tested at competition until next year. Although the project has limitati
ons, its future
implications create a meaningful assignment. Future teams will be able to analyze the performance and
durability of past designs and make modifications and improvements to them. This type of project
allows for ODU’s baja SAE vehicle to prog
ress with each generation.



Suspension

-

Background

The Baja’s suspension design has shown a marked progression through the years. The
suspension has evolved from utilizing parallel double wishbone coil
-
over systems of unequal length on
both the front an
d rear to unequal double wishbone systems on the front, and a trailing arm setup on
the rear. The trailing arm rear suspension is advantageous in that it imbues greater platform stability
and, as an added bonus, dynamic kinematic properties, such as toe an
d camber. Dynamically, criterion
pertaining to toe, camber, castor, track width, wheelbase, weight transfer, roll center, and suspension
travel are crucial elements of a successful suspension design.


According to the textbook
Race Car Vehicle Dynamics
,
camber is defined as the angle between a
tilted wheel plane and the vertical

[11]
. It is one of three terms used to describe a suspension’s
alignment. The camber angle, γ, can have negative or positive orientations, where camber is considered
positive if t
he top of the wheel leans outward, and negative if the top of the wheel leans inward.
The
figure below

serves as a visual representation of positive and negative camber. If a vehicle’s wheels are
properly cambered, a beneficial thrust force is produced. Th
is thrust force, aptly named camber thrust,
contributes a lateral force in the direction of the tire’s tilt. In other words,
it ensures stability by pulling
the bottom of the tire in the same direction the top is leaning.








Castor, or the angle in side elevation of the kingpin axis with respect to the vertical plane, is
another stability oriented kinematic property. The chief benefit of castor is th
at it is responsible for a
8


steering centric restoring force, meaning that the amount of castor affects how the steering feels and
the amount of effort required to turn the wheel.
The figure to the right above

depicts positive castor.

Toe is the final par
ameter used to describe a vehicle’s alignment. From
Bosch’s Automotive
Handbook
, toe specifies the degree to which non
-
parallel front wheels are closer together at the front
than at the rear

[12]
. Tire wear is heavily dependent on toe distances.
The
f
igure
s below

shows what is
meant by a toe
-
in alignment setup.




The roll center has a significant impact on a suspension’s steering response; moreover, there is

a
direct correlation between roll center location and oversteer, understeer, or neutral steer suspension
behavior. In the book
Tune To Wi
n, author Carroll Smith defines the roll center as a point, in the
transverse plane of the axles, about which the spru
ng mass of that end of the vehicle will roll under the
influence of centrifugal force, where the sprung mass is the portion of the vehicle’s total mass that is
supported by the suspension springs

[13]
. Furthermore, vehicles designed to understeer will requ
ire
more steering input, whereas vehicles inclined to oversteer will require less steering input. Vehicles
equipped with a tinge of oversteer are ideally suited for applications that demand maneuverability. The
slight oversteer enables maximum agility whil
e maintaining a forgiving nature, thus would be perfect for
Baja applications.
The right side figure above

shows how varying the inclination of the roll axis affects
steering behavior.

Wheelbase is the longitudinal distance from the center of the front wh
eel hub to the center of
the rear hub. Similarly, track width is the lateral length from wheel centerlines. The length of the
wheelbase is of utmost importance when considering weight transfer and the vehicle’s center of gravity
(CG). From a performance pe
rspective, the center of gravity must remain as low as possible.

The figure below summarizes

the SAE axes terminology and serves as a snapshot for many of the
aforementioned dynamics and definitions.


9


M
ethods

-

Suspension

The suspension design has been broken down into two sections: front and rear. Mounting points
of the suspension on the frame and hubs are used for suspension analysis. These points can be
interpreted by suspension analysis

software; a commonly used one is Optimum K

(OptimumG, Denver,
CO, USA)
. The front suspension mounting points were pulled off of the design from last year using a
solid works drawing. The points were then imported into the analysis software. From there tes
t points
can be used to get desired results. The design for the rear suspension has been researched and
geometry has been decided on. Future designing consists of finding the optimum mounting points for
the desired dynamics of the suspension. It will invol
ve a trial and error type analysis in order to find the
optimum solution.


Results

-

Suspension

The front suspension has been modeled in Optimum K and was then put through a series of
different simulations. The simulations are comprised of adjusting heave, roll, pitch and steering. Once
the parameters are set for the run the simulation is played and
an excel spreadsheet is developed with
the results. These results will help in analyzing whether or not the suspension will be able to withstand
the design requirements of the Baja. A final run through has not yet been developed for the front
suspension bu
t the program has been studied to do so.


D
iscussion

-

Suspension

The suspension design of the 2014 ODU Baja will remain largely unchanged with respect to the
2012 Baja car. Polaris RZR wheel hubs and parts from a Honda 400EX ATV will continue to be utilized.
However, the rear trailing arm must be redesigned such that dy
namic toe is eliminated. Theoretically,
dynamic toe is a great idea because it enables a certain amount of rear steering and is inherently agile.
Unfortunately, the rear trailing arm system was not durable and the design was not rewarded at
competition, so

for greater simplicity, the link that controls dynamic toe must be eliminated. A new
trailing arm setup must be designed and analyzed to meet this goal. The front suspension setup is being
finalized and has been used to train the group on the proper use o
f OptimumKinematics suspension
analysis software. The center of gravity for the 2012 Baja car was calculated using rudimentary materials
and the results are included in
Figure
A.
10

The center of gravity was found to lie approximately 10
inches above the ax
ial center, and can be shortened by using lower mounting locations.

Additionally, Fox Float Racing Shocks have been selected over re
-
using the Custom Works
Shocks of previous years. The Float Racing Shock is an air shock that offers superior cost effective
ness. A
pair of Fox Float Shocks cost $521.25 and the Custom Works Shocks cost approximately $859 per pair.
Figure
A.
8

and Figure

A.
9

serve as a verification of similar performance envelopes, so the compromise
on behalf of cost will not severely impact per
formance. Qualitatively, compression and rebound force
10


versus velocity curves are highly linear. Linear damping rates are acceptable, and one can see how the
shock copes with the transition from minor to major undulations.

Work is currently revolving arou
nd the front A
-
arms. The A
-
arms must be drawn is SolidWorks
and subjected to stress analyses. The team must also simultaneously begin design and analysis work on
the rear trailing arm.


Background

-

Frame


The SAE Baja has a large list of minimum requireme
nts for frame design. These regulations must
be met in order to ensure design integrity and driver safety. The purpose of the frame is to provide a
protected space from which the driver can control the car. All of the frame requirements in the rule
book ha
ve been set to ensure the driver will be as safe as possible in the event of an accident. The
firewall is in place in case of a problem with the engine or drivetrain to protect the driver from fire or
flying shrapnel. In the event of the car rolling over t
he roll cage is designed to withstand the weight of
the car and keep the operator from being crushed. Sidebars provide support in case of a side impact and
the nose section is designed to hold up in the event of a front end collision.

Previous years frame
s were large, heavy and over engineered. There was far too much material.
Frames of past years have weighed around 330 lbs where as another other school's entire car weighed
306lbs. While the past two years have been essentially the same design, the SAE ru
les require the entire
vehicle to be at least 50% different if the same design has been previously used consecutively. The aim
of this year's frame design is to reduce the overall weight and size of the car while meeting this
difference requirement.


Methods
-

Frame

The first step in the design was selecting a suitable material. These are the minimum material
specifications required by SAE. The metals were analyzed for their strength to weight ratio as well as
their cost. The material chosen was 4130 c
hromoly steel.

The initial steps in designing the frame was getting boundary dimensions form the SAE Baja
rules. These minimum dimensions maintain a certain degree of safety for all drivers and ensuring that
the vehicle is rigid enough.

The firewall was th
e first feature designed. It was angled to the maximum tilt of 20 degrees from
vertical to decrease the air resistance and maximize available space for the engine and transmission as
low on the frame as possible. The design was such to give a lateral bread
th of 29 inches at 27 inches
above the seat bottom as required in the SAE rulebook (SAE RULEBOOK). Diagonal bracing members
were added no more than 5 inches from the end horizontal members of the firewall.

Working forward, the front end was designed accord
ing to suspension mounting points
predetermined by the suspension team. Members were drawn to accommodate the double A arms of
11


the front suspension as well as a shock mounting point. Also in consideration was leaving space for the
brake reservoirs. Consid
eration was also made for length for a driver's legs, leaving 44 inches between
the seat bottom and the front most point on the car.

The roll cage was designed by simply connecting the roll cage to the highest point on the front
end. Consideration was made

for minimum head clearance for driver safety. The horizontal portion of
the roll cage was designed to maintain a 41 inch vertical clearance and a 12 inch forward clear
ance from
the rear seat bottom.

The vehicle's rear end was designed with consideration f
or the engine size and orientation.
Gearbox and suspension mounting points were also considered. Only a tentative design is complete. The
design will be finalized on completion of the gearbox and suspension designs. Further work is needed
once the gearbox
design is finalized and the suspension mounting points are decided.

This finalizes the initial design. PATRAN analysis is needed to determine if this preliminary design
is sufficient. Rollover and collision analysis will be performed. The design will be st
rengthened where
necessary and members may be removed to save weight if the design can maintain a sufficient safety
factor without them.


Results
-

Frame

The design of the frame is nearly complete. The firewall, front end, and roll cage have all been
completed along with a tentative design for the rear end. Every member was designed with reducing
vehicle weight in mind. The roll cage has also been designed to minimize vehicle weight and reduce
overall chassis flex while cornering. The length of the veh
icle was reduced by eight inches in comparison
to last year's design for a shorter wheelbase, more precise handling, and reduced weight. This will also
help with driver comfort, as last year's car left the driver with legs full extended. We selected 4130
'
Chromoly' steel tubing with an outside diameter of 1 inch and wall thickness of 0.12 inches for all of the
frame members [6][1]. This steel was chosen over other options such as 1020 steel or 1026 steel
because 4130 has the highest strength to weight ratio

[2][3][4][5]. Chromoly steel is also within the
budget and more readily available than other types [1].

Future work includes finalization of the rear end design based on gearbox and suspension design
and finite element analysis in MSC PATRAN. Testing must

be done for rollover as well as front, side and
rear collision testing. Members will be added should the design fail or removed should it prove to have a
very large safety factor.


Discussion
-

Frame


The goal for the frame team is to reduce the size and
weight of the frame without compromising
structural integrity or performance of the vehicle. Size is a big factor in the weight difference

between
Old Dominion’s 2012 vehicle and the top competitors.

Old Dominion’s frame was
considerably

larger
than the ot
her top competitors who favored a more compact vehicle.

I
t can be seen

in Figure 10

the
length differences between the Old Dominion University, Oregon State, and Cornell vehicles. The driver
12


of ODU’s Mini Baja has his legs almost fully extended and the ste
ering column juts out a considerable
distance. Both Cornell’s and Oregon State’s drivers have their knees bent and the steering column barely
juts out from the front end.


Figure 10.

Ol d Domi ni on mi ni Baja [
9
] (top l eft),
Oregon State Uni versi ty mi ni Ba
ja [
10
] (top ri ght),
Cornel l Uni versi ty mi ni Baja [
10
] (bottom).






This

large ODU Baja design was a result
of concerns about the required driver clearances and
exit time. These other teams have shown that all the required clearances and the exit test ca
n be met
while designing a smaller vehicle. The length and width of the car are the main focuses for reducing the
frame size. Height will also be examined, but it is not believed to have as much room for reduction.
Another possibility is the presence of re
dundant members built into previous frame designs. Identifying
any members that are structurally unnecessary will help optimize the design. It is important that the
power to weight ratio is improved so that the team can be more competitive in events such a
s
acceleration, hill climb, maneuverability, and endurance.


There are

not

many results yet seeing as how the frame design is still in development, but some
preliminary conclusions can be drawn as to what can be expected. A reduction in frame weight, when
compared to the 2012 ODU Mini Baja, can be expected due to several reduct
ions in frame dimensions
and changes in member configuration. These improvements will also increase the handling of the
vehicle.
Reduced weight and increased handling will allow for better performance in competitions
where

past performances can be improved
.

At this time the frame weight reduction is unknown, but will
be available after the final design is put into SolidWorks
(Dassault Systemes Soildworks Corp., Waltham,
Massachusetts, USA)
and a mass analysis is conducted. The structural integrity of the ca
r will be
maintained as the design is similar to the previous vehicle. A finite element analysis will be performed in
PATRAN once the final frame design is completed.
One conclusion that can be drawn is which particular
13


material the frame will be used in c
onstruction.
The frame will be constructed with chromoly 4130 steel

due to its high strength to weight ratio and good weldability

[
1
]
. It was used for past Old Dominion cars
and is the popular steel of choice for many other competing teams.

The past Old D
ominion University Mini Bajas have mostly placed in the middle of the pack in
terms of competition ranking. Last June the team took 55
th

place out of 102 ranked teams
.

It is
important to examine the previous Mini Baja to identify parts of the design that a
re not performing as
well as they should. Potential areas of improvement can be identified by comparing Old Dominion’s
2012 car to other top performing schools. One of the main concerns is the overall weight of the vehicle.
Last year the ODU car weighed 47
9 pounds compared to the 3
rd

place car from Cornell at 306 pounds

[
8
]
. The Old Dominion frame alone weighed a
bout

330 pounds, meaning Cornell’s total car was around
24 pounds lighter than the ODU frame.
Table A.
2

displays the event scores for the top four
competitors
and Old Dominion University from the SAE Wisconsin 2012 competition. The events where Old
Dominion’s performances were much lower depended on high power to weight ratios. A lighter weight
vehicle will improve the performances in acceleration, p
ulling, and endurance the most.


The Baja SAE rulebook lays out many of the specifications that the designed vehicle must stay
within in order to be considered eligible for competition. The maximum allowable width is 64in at the
widest point of the car, w
heels included [
6
]. With the suspension staying mostly unchanged, the car will
fall well within the maximum allowable width. While there is no limit to the length, SAE suggests a
maximum length of 108in [
6
]. The current design sits at 74.5in and is unlikel
y to change very much. The
roll cage has been designed around the template driver that is supplied in the rule book. The first step in
the design was to record all specification requirements to ensure that all were met. Barring any changes
to the 2014 rule

book, the designed Mini Baja will be fully eligible for the competition.


There are quite a few limitations to how much the design can be improved and performance
enhanced, some are within control and some outside of it. Money is one limitation that canno
t be
helped very much. The school is unlikely to drastically change the budget allotted to the Mini Baja team
which leaves sponsors as the only other source of income. Without a dedicated marketing team and
more impressive competition record it is unlikely

that the income from sponsors will change much. This
leaves the team without many of the advantages that better funded schools have, such as dedicated
machine shops and the ability to manufacture parts from carbon fiber. These allow teams with such
facili
ties and budgets to have large advantages over other teams.


A limitation that can be controlled is the transfer of designs and information from one year’s
design team to the next. This would be a great advantage in being able to perform necessary
modific
ations to improve a design instead of starting a new one from scratch. However for this to have
any effect the shop team actually needs to construct the vehicle that the design team drew plans for.
There has been little communication between the shop team
and the design team in previous years.
This has led to design teams that have failed to meet the proper requirements and shop teams that have
decided to design their own Mini Baja. This is less than optimal and results in little design information
being pa
ssed on to the next year’s design team. It would be very beneficial for the faculty advisor to
facilitate communication between the two teams and emphasize the passage of design information.



14




Appendix A




Figure A.1

Engine.



Figure
A.2

CVT Diagram.











15



Figure A.3

Torque Curve
.

Figure A.4

Factor of Safety Calculations.



Figure A.5

Top Speed Calculations.










Factor of Safety (Reduction Ratio)

VALUES: ESTIMATE / A
CTUAL

GEAR RATIO: (8.0

/

7.7551) = 1.0326

VEHICLE WEIGHT: (650

LBS / 600 LBS) = 1.0
833

INCLINE
ANGLE: (40 DEG / 37.
5 DEG) = 1.0667

TORQUE: (15 LB
-
FT MAX / 14 LB
-
FT AVG) = 1.0714

TOTAL FS = (1.0326)
*
(1.0833)
*
(1.0667)
*
(1.0714)


-----
>TOTAL SAFETY FACTOR

=
1.2772


Top Speed Calculations

3600 RPM Max ENGINE SPEED → 216,000 ROT/HOUR

0.9:1 FINAL CVT RATIO

TIRE RADIUS = 1.0 FT

TIRE ROLLOUT: (2π)*(1.0 FT) = 6.28319 FEET

DISTANCE PER ROT
ENG
= (6.28319 FT) / (0.9*8.0) = 0.872665 FT/ROT
ENG


(216,000 ROT/HR)*(0.872665 FT/ROT) = 188,496 FT/HR

(188
,496 FT/HR)*[(1 MILE) / (5280 FT)] = 35.699 MPH

-----
>
TOP SPEED

@ 3600 RPM =
35.7 MPH




16





Figure A.6

Minimum Gear Ratio
.


Table A.1

Ge
ar Specifications for Reduction Ratio.





Minimum Ratio (X) to Overcome Incline Angle

ENGINE TORQUE: 14 LB
-
FT

CVT RATIO (INITIAL):

3.85:1

TIRE ROLLING DIAMETE
R: 1.0 FEET


[VEH
ICLE

WT]*[SIN(INCLINE

ANGLE)] = REPELLING
WEIGHT

[650 LBS]*[SIN(40 DE
GREES)] = 418 LBS

REP
ELLING

WT = (TIRE RAD
IUS
)*(CVT RATIO)*(ENGIN
E TQ)*(X MIN)

418 LBS = (1.0 FT)*(
3.85)*(14 LB
-
FT)*(X MIN)


-----
>XMIN=
7.7551


17



Figure A.7

Loads, Stresses, and Safety Factor Calculations.


Figure A.8

Shock Compression Behavior.



18



Figure

A.9

Shock Rebound Behavior


19



Figure A.10

Baja Center of Gravity Calculations



20


Rank

1

2

3

4

55

School

Uni versi te
Laval

Oregon State
Uni v
ersi ty

Cornel l
Uni v
ersi ty

EDTS

Ol d Domi ni on
Uni v
ersi ty

Overall (1000)

913.77

896.63

893.62

880.21

530.74

Overall Dynamic (300)

266.59

256.18

232.58

227.13

185.54

Overall Static (300)

245.18

236.45

258.04

252.08

183.04

Cost (100)

90.80

74.45

83.54

80.45

71.29

Design (200)

154.38

162.00

174.50

171.63

111.75

Acceleration (60)

60.00

51.72

53.95

47.92

32.24

Land Maneuverability (60)

60.00

58.06

56.44

54.04

48.06

Mud Bog (60)

50.04

60.00

46.34

34.91

43.22

Pulling

(60)

36.55

30.31

22.29

36.11

15.16

Suspension & Traction
(60)

60.00

56.09

53.56

54.15

46.86

Endurance Race (400)

402.00

404.00

403.00

401.00

162.16

Table A.1

Score

Breakdown of Top Four School s C
ompared

to Resul ts for ODU Mi ni Baj a T
eam

[7]
.



















21


Appendix B



Figure B.1
Current Gantt Chart.
22


References

[1]

4130 Alloy Tube Round

[Online]. Available: http://www.onlinemetals.com/merchant.cfm?

id=250&step=2


[2]

Aerospace Specifications: AISI 4130 Steel
[Online]. Available:

http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=m4130r


[3]

ASTM a513 alloys 1020
[Online]. Available: http://www.onlinemetals.com/alloycat.cfm?alloy=A513


[4]

a513 Type 5 Steel Tube DOM

[Online]. Available:

http://www.
onlinemetals.com/merchant.cfmid=283&step=2


[5]

OnlineMetals Guide to Steel
[Online]. Available: http://www.onlinemetals.com/steelguide.cfm


[6]

2013 Collegiate Design Series: Baja SAE Series Rules
, SAE International, Warrendale, PA,

pp. 19
-
32.



[
7
]

Baja SAE Results.
SAE International. Available:



http://students.sae.org/competitions/bajasae/results/

[
8
]
Cornell Baja: The Cars.
Cornell University. Available:

http://baja.mae.cornell.edu/about.php

[
9
]
ODU Baja.
ODU Baja Facebook Page. Ava
ilable:

http://www.facebook.com/ODUBaja/photos_stream

[
10
]
Baja SAE Oregon.
Baja SAE Oregon 2012 Competition. Available:


http://www.facebook.com/BajaSaeOregon/photos_stream

[11]
Milliken, W. F., & Milliken, D. L.,
Race Car Vehicle Dynamics
. Warrendale: Society of Automotive

Engineers, Inc., 1995.

[12]
Smith, Carroll,
Tune To Win
. Rolling Hills Estates, CA: Carroll Smith Consulting Incorporated, 1978.

Automotive Handbook
, 2
nd

ed., Bosch, Stuttgart, GmbH, 1986, pp. 480
-
481.