8/6/2019 Baja2009

1/14

Car No. 83

Union College SAE Baja Vehicle Design Report

Matthew Beenen, Jon Wilson and Ned LincolnUnion College Dutchmen Racing

Union College, Schenectady NY

ABSTRACT

An SAE Baja vehicle is a single-seat, all-terrain vehicle

powered by a ten horsepower Briggs & Stratton engine.

Undergraduate students at Union College from multiple

academic fields collaborated to design and manufacture

a safe, high-performance, cost-efficient Baja vehicle to

serve as a prototype for mass production. The students

utilized and refined both financial procedures and

engineering analyses to complete this objective while

conforming to the prescribed SAE rules.

INTRODUCTION

The Union College SAE Baja vehicle was designed as a

prototype for manufacture by an outdoor recreation firm.

The ideal vehicle is safe, simple and inexpensive: safe

for its occupant to be protected during use, simple for a

novice rider to operate and maintain, and inexpensive to

allow for general production and purchase. Additionally,

the vehicle should be attractive to potential buyers in

both its visual appearance and performance. These

characteristics were considered in design of the

following major vehicle systems: frame, drivetrain,

flotation, suspension, steering, and braking.

LIST OF FIGURES, TABLES AND SYMBOLS

Figure Description Page

1 2008 Frame Schematic 2

2 2009 Frame Schematic 2

3 Drivetrain Components 4

4 Foam Model 6

5 Front Suspension 7

6 Trailing Link Cosmos 8

7 Trailing Link Assembly 8

8 Rear Suspension Analysis 8

9 Tire Selection 10

Table Description Page

1 Gearbox Specifications 3

2 Floatation Calculations 5

Symbol Definition

A area m2

% percent

C.G. center of gravity

CV constant velocity [axel]

CVT continuously variable transmission

F.O.S. factor of safety

FEA finite element analysis

ft feet

g acceleration due to gravity, m/s2

HDPE high density polyethylene

ksi 1000 pounds per square inch, ksi

L length, m (ft)

lb pound

Mpa mega pascal

MPH miles per hour

N newton

RPM rotations per minute

SAE society of automotive engineering

TIG tungston inert gas [welding]

VEHICLE DESIGN

FRAME

Objective - The purpose of the frame is to provide a safe

environment for the occupant while supporting othe

vehicle systems. Several steps were taken to ensure

this objective was met. Tungsten Inert Gas (TIG) electric

arc welding was used to guarantee solid joints and a

rigid foundation to support the main components of the

vehicle. In addition, extensive finite element stressanalysis proved the car would remain intact and protec

the driver under the most strenuous of crashes. The

frame was designed to comfortably accommodate a six-

foot, three-inch tall driver.

Overview of the Design In order to conform to the SAE

frame requirements, major redesign was decided upon

rather than alteration of the existing frame. For the 2008

season, several positive modifications were made to the

frame, including a shortened wheelbase, a seven-inch

front-end rake, and new cockpit layout. The front wheels

were moved six inches back, reducing the cars turning

radius and improving the weight distribution, which hadpreviously been heavily rear biased. In the 2009 season

the team has redesigned the rear section of the frame to

accommodate new rear suspension and drivetrain

components.

Figures 1 and 2 display the frame schematics from 2008

and 2009, respectively. The changes to the rear half o

the frame can be seen. The elimination of the solid 1x1

steel slugs in the rear greatly reduces frame weight.

8/6/2019 Baja2009

2/14

Figure 1: 2008 frame schematic.

Figure 2: 2009 rear frame schematic

The decision to increase driver safety resulted in several

frame improvements. The side impact members were

widened and located higher from the bottom of the frame

to better protect the driver from side impacts and ensure

that taller drivers remain enclosed by the roll cage at all

times. The new design also includes bracing that was

not present in the previous frame design. This bracing in

the rear eliminates the need for triangulation in the front.

In addition to preventing visual obstruction, it also allows

the driver to egress more quickly should he or she need

to. Supports on the roof of the car and verticalreinforcements in the cockpit made the new frame safer

in a rollover situation. At the front of the car, a sub-frame

that had supported the pedals, brake master cylinder,

and suspension was eliminated, placing the drivers seat

farther forward and improving the use of space in the

car. Lastly, the steering frame was rebuilt to

accommodate a new steering layout and driver position.

The frame is made of 1.25 inch 4130 Chrome

Moly round tubing with 0.065 inch wall thickness which

has a higher strength to weight ratio than the required

material. These characteristics maintain the equivalen

area moment of inertia and provide a reduction in weight

The rear frame section is made of the same material

The frame was TIG welded using Certanium 72 as filler

rod.

CosmosWorks, a Finite Element Analysis

package, was used to ensure the frame could withstand

a significant impact. There were three impact scenariosanalyzed each with a 3g impact with a car weigh

estimation of 600lb; this provided for a 10,700N force

The max stress of any member was 18 ksi, while the

yield strength of the steel is 80-90 ksi resulting in a facto

of safety between four and five. The impacts were front

side, and rear, applied to the front lateral cross member

the side impact member, and the rear lateral cross

member, respectively. Renderings of these data can be

found in Appendix A, and confirm that the driver

compartment would remain safe in the event of an

accident. A more serious, worst case scenario type

situation was also analyzed with a 10g force of ove

20,000N and resulted in a maximum stress of 62 ksi or323Mpa. This is lower than the yield strength of 435Mpa

See appendix A for figures.

DRIVETRAIN

Objective The drivetrain for this years car has been

radically overhauled to improve overall car performance

and correct vulnerabilities of previous designs. Pas

drivetrain designs have been double-reduction, open

chain designs, based around a CVT, chains, sprockets

and a jackshaft mounted in an open sub-frame. The

system benefited from simplicity and low cost, at the risk

of premature failure due to misalignment and direct

exposure to water and dirt. Adhering to recommended

wrap angles and center distances for chain drives

requires the system to occupy a large volume, thereby

increasing frame weight. Reducing the number of chains

in the transmission was a logical choice to

simultaneously address issues of reliability, performance

and size.

Additionally, the overall drivetrain ratio was re-examined

to optimize top speed and acceleration, and a new chain

tensioning system was designed to reduce

misalignment.

Discussion of Alternatives Reducing the number o

exposed chains required some form of self-contained

lubricated subsystem to take the place of the 1st

stage

open-chain reduction. The car still operates with a fina

drive chain connecting the 1st

stage system to the CV

drive axles. Several alternatives were evaluated agains

the following design requirements:

8/6/2019 Baja2009

3/14

1) Increased Reliability Over Open Chains: Protecting

the first reduction stage from water and dirt is critical to

decreasing wear. The new system must isolate the

components of the 1st

reduction stage from the off-road

environment. Shafts and bearings must be robust

enough to handle the power and torque delivered by the

engine-CVT combination.

2) Decreased Component Volume: Reducing the space

requirements for drivetrain components allows the frameto be smaller, lighter and more resistant to buckling.

3) Precise Component Alignment: Misalignment in

sprockets, chains and bearings dramatically decreases

component life. Enclosing components in a machined

case reduces the number of components that must be

checked for proper alignment, and reduces the chance

of misalignment.

Alternatives:

1) Sealed, Lubricated Chain Box Enclosing the existing

first stage reduction components would eliminate thepotential for wear due to exposure to dirt and water.

Chain tensioning would remain an issue, however.

Additionally, the overall size of the drivetrain would not

improve due to required sprocket center distances and

diameters.

2) Enclosed Gears Gears are capable of higher

operating speeds, load capacity and reliability compared

to chains. The major tradeoffs are increased cost and

manufacturing time, as the gears must be custom

fabricated. Component volume is reduced over chain

drives, but weight may not improve. The gains in

drivetrain durability and efficiency are significant,

however.

Toothed belts were not given serious consideration due

to reported issues with slipping / skipping from other

teams.

A helical gear train was ultimately chosen as the

new 1st

reduction stage. The potential for car

performance improvement outweighed the increase in

cost. It is also important to keep in mind that gear

manufacturing costs drop rapidly with quantity, so in

terms of mass-production of a Baja vehicle, gear driveswould not be out of the question and in fact, appear to be

the teams best option.Overview of the Design A Comet 790 CVT transmits

power from the Briggs & Stratton Intek 305 engine to a

custom helical reduction gearbox. The CVT is capable of

ratios from 3.38:1 (Low) to 0.54:1 (High) between its two

pulleys. 1st

stage drivetrain components must be able to

handle both the maximum input torque and RPMs of the

secondary CVT pulley. Based on the Briggs & Stratton

specifications for their Intek 305 engine, maximum CVT

torque is approximately 47 ft-lb, and maximum CVT

speed is 7000 RPM. These occur at opposite ends of the

CVT engagement range, low and high, respectively.

The CVT secondary drives the integrated pinion-shaft o

the custom helical gearset, designed in-house at Union

College. Unfortunately, a 4th

Axis indexer was no

available in Unions CNC mill in time for in-house

production of the gearset. Kamar Industries in BuffaloNew York, was selected for gear cutting. Shaf

machining was done in-house. The basic specifications

of the gearbox are found below, in table 2

Diametric Pitch 12

Pressure Angle 20

Helix Angle 15

N, Pinion 16 teeth

N, Gear 64 teeth

Material 4340 Ht Trtd Stl

Max Input Torque 50 ftlb

Max Input Speed 7000 RPMMinimum Factor of Safety, Bending 2.5

Minimum Factor of Safety, Wear 1.2 (1000 hrs)

Inside the gearbox, an integral 16T pinion-shaft engages

a 64T gearwheel, mounted to a 5-bolt hub on the outpu

shaft. An MITCalc design suite was used to aid gea

design and analysis, The software references ISO 6336

and AGMA standards to calculate gear strength and

wear characteristics. COSMOS FEA was also run on

both pinion and gear to check tooth strength. Based on

the heat treatment performed on the gears, expected

yield strength is at least 150 ksi, giving a F.O.S of 2.5 orgreater.

All gearbox shafts are supported with precision bal

bearings. 40 angular contact bearings handle the thrust

loads generated by helical gears, and sealed radia

bearings support the shafts on the zero thrust-load ends

The gear housing consists of two symmetrical halves

machined from 6061 aluminum, and features grade 8

fasteners and an integral mounting bolt pattern. Oi

addition is done via a side-mounted plug, and a breathe

valve allows for thermal expansion of the air inside the

gearbox. Sealing is assured with a nitrile gasket between

the two case halves and double-lipped shaft seals at theinput and output. High gear speeds and the compac

case make splash lubrication a sufficient mechanism fo

getting oil to the meshing teeth and open angular

bearings.

The output shaft was designed to carry a bore, 3/16

keyed sprocket. The gearbox output and rear driven

sprockets are connected with 420 RK Gold Racing

chain, rated at 3300lb, giving a factor of safety of 2.5 - 3

during maximum drivetrain torque. Chain load and

Table 1: Shows basic gearbox and drivespecifications

8/6/2019 Baja2009

4/14

F.O.S. range slightly depending on rear sprocket

diameter.

The final drive shaft is mounted rearward of the gearbox,

approximately 15.5 center-to-center from the gearbox

output. Driven sprockets from 40 to 54 teeth can be

mounted on the shaft hub, offering a wide range of

ratios. New for this season is the Polaris Outlaw final

drive system. This system integrates the CV shafts with

the drive shaft to produce a single, easily serviceableand replaceable alternative to a custom setup. The

shafts were lengthened by 3 to accommodate the wider

track of the baja car. Figure 3 shows the assembly fitted

to the frame with a tensioning mechanism very similar to

the factory Polaris design.

This system utilizes two large bearings with the drive

axle built inside of a cast aluminum housing. This

housing, mounted on the bottom with a single pivot axle,

is easily tensioned using the upper mounting points.

Tensioning is accomplished using a large bracket and

bolt between the axle case and the rear of the frame.

This allows up to 1.25 of forward/rearward travel.

Previous designs used outdated Arctic Cat CV axles that

were not only very worn, but were irreplaceable. The

inboard female splines on those units are nearly

obsolete now and needed to be replaced.

Driven sprockets were purchased as blanks from Martin

Sprocket. Bolt patterns and major weight removal

patterns were cut using Unions abrasive waterjet.

COSMOS analysis of the sprockets showed that by

using these patterns, sprocket weight was almost halved

with no significant loss in strength. The sprockets are

mounted to the final drive system using the integrated

bolt pattern and tapped holes. This integrated sprocket

mount on the hub eliminates any trouble with alignment

and any issues with slippage and the previous need for a

custom axle.

Figure 3: All major drivetrain components are present

except for the engine. The chain side gearbox case has

been hidden to show internal detail. A 10T/48T sprocket

combination is shown.

Design Advantages Starting with a race-proven

drivetrain from last season, this years improvements

focus mainly on maintainability and integrating more

modern systems. This will not only offer better

performance and efficiency, but will also ensure that if a

part of the system fails replacement parts will be readily

available.

Since only one chain is present in the new drivetrain, the

new rear frame is smaller and more compact than anyprevious Union College Baja car. Cantilevered CVT and

sprocket shafts in the gearbox make safety guards

easier to construct, and more effective against the wate

intrusion that can cause CVT belt slippage. Chain

tensioning is much more robust than in previous years

and a wide selection of chain ratios is available. The

drivetrain is easier to work on, adjust and protec

compared to previous years. Higher speed and

acceleration is expected due to higher transmission

efficiency, and the risk of chain failure has been more

than halved by replacing previously used #40 chain with

a 420 racing chain. This system is designed for at least

1000 hours of operation before the gears should beinspected for wear. Lastly, the drivetrain offers a

continous range of overall ratios from 57.5:1 to 9.2:1

Such a wide range makes the drivetrain well-suited to

off-road driving; one system can provide both a 30MPH

top speed and over 800 ft-lb of axle torque at takeoff.

FLOTATION AND PROPULSION

Objective - The goal of the flotation system is to provide

the buoyant force necessary to keep the vehicle and

driver afloat in an aquatic environment. This must hold

true at both a horizontal orientation and up to at least a

30-degree roll situation. While the car is floating, the rear

wheels function as the means of propulsion, with the

treads of the tires acting as paddle wheels. In the past

it was believed that fenders close to the tires were

necessary for propulsion. We learned last year that thick

mud can easily render these fenders not only useless

but harmful to the drivetrain. We have therefore decided

against fabricating fenders tight to the tire. This is

covered more carefully in the flotation section.

Design Requirements - The flotation system must firs

and foremost support the weight of the car and driverwhen in the water. Second, it is important that the

flotation system keep the rear wheels at an optimum

height in the water without sacrificing ground clearance

on land.

Safety was considered the first priority over al

other design requirements. The flotation and body

should not impede a drivers ability to exit the cockpit in

fewer than five seconds. There should be easy access to

all the kill switches and there should not be sharp edges

8/6/2019 Baja2009

5/14

The foam must be durable and protected from debris the

car may encounter during routine use. The flotation

system should be easily removable for repair and

maintenance.

The flotation material on the bottom of the car

should not interfere with the full travel of the suspension,

and the front and rear approach angles should be kept

as high as possible. Finally, the flotation system must

be integrated into the body of the car to produce aprofessional look to the vehicle, keeping in mind that the

bottom should be streamlined to reduce drag in the

water.

Discussion of Alternatives Previous designs employed

a flotation system involving Polystyrene billets. While

this foam was successful in floating the vehicle for a

short period of time, its physical characteristics proved

ineffective over extended testing and abuse. The nature

of the Polystyrene material caused the foam to hold

water and weigh down the car. In addition, its fragile

makeup did not withstand the rocky, unforgiving

conditions of off-road terrain. For these reasons air filledpontoons were decided against, as a puncture would

render the system useless.

This years system is comprised of foam side

pods and a block underneath the car, which attaches to

the frame. Rather than using three separate blocks, use

of one solid piece makes installation and removal easy.

A foam piece underneath the drivetrain and behind the

car adds additional support. Durable, water resistant

Polyethylene foam was chosen. Polyethylene is a closed

cell, rigid structure foam product.

In addition, great emphasis was placed on

optimal ground clearance. Previous designs performed

exceptionally in the water, but lacked the necessary ride

height to excel on land. As a result, calculations were

performed to place the car slightly lower in the water, at

a level where it propels efficiently and safely, but does

not sacrifice clearance on land. See Appendix B for

calculations and analysis.

Overview of the Design - The final design was evaluated

with safety being the most important factor followed by

performance and styling.

The car is designed to float in both calm water

and adverse conditions with a driver having a maximum

weight of 220 lbs. The foam planks used for the vehicle

are particularly suitable for flotation. The system is

comprised of Polyethylene foam commonly used in

industrial applications. Two inch planks were heat

treated together to form larger thicknesses. One cubic

foot of foam will provide 60 pounds of buoyant force

before considering the foams own weight. It will not

hold water and will not lose its buoyant characteristics if

punctured. The foam is also resistant to chemicals and

heat.

Foam

Bouyancy of foam (lb/sqft) 58

Center of Gravity (in from firewall) 13

Surface Area forward of C.G. 7.58

Surface Area behind C.G. 9.66

Total Surface Area 17.24Distribution

Front (%) 44

Back (%) 56

Volume

Depth Below Frame (ft) 0.667

Volume of Foam below waterline (ft^2) 11.499

Distribution (ft^3)

Front 5.056

Back 6.443

Weight Distribution

Maximum Driver Weight (lb) 220.00

Front (lb) 260.00

Front (%) 40.63

Back (lb) 380.00

Back (%) 59.38Results

Foam to be placed behind C.G. 10.24

Foam to be below waterline (ft^3) 11.499

Buoyancy foam is located under the drivers

compartment, under the engine compartment and rear

suspension components, behind the engine

compartment similar to a rear bumper, and on the sides

of the drivers compartment. The foam in the side pods

is the most essential part of the flotation system. The

side pods not only provide a majority of the buoyan

force but also provide transverse stability. The sidepods allow the car to easily recover from a 30 degree

induced tilt from either side. This is accomplished by

keeping the buoyant force as close to vertical with the

center of gravity even in a rolling situation. Submerging

the side pods in a roll will help do this. A total of 11.5 ft3

of foam is incorporated into the flotation system, which

has been designed with the center of buoyancy directly

under the center of gravity of the car. All figures from

calculations are shown to the left, in table 2. The

metacenter is found directly above both the center o

mass of the car and the center of buoyancy. This is the

point of pivot when the vehicle heels to one side or the

other. During the analysis it was discovered that the tiresalso provide a buoyant force. The tires buoyant force

will be considered a factor of safety incorporated into the

design. Figure 4 shows a SolidWorks model of the

undercarriage foam section.

Table 2: Shows calculations and figures forflotation design.

8/6/2019 Baja2009

6/14

Figure 4: Foam underbody model

To ensure that the system is durable, it has

been fitted with an HDPE (high density polyethylene)

shell. Not only is this shell extremely durable, but being

smooth as it is, it will greatly reduce drag caused by the

un-sealed foam cells on the surface of a cut. An

aluminum angle sub-frame that bolts directly to the main

frame supports the entire system. With this flotation

system bolted to the car securely, an individual is able to

stand on the flotation pods with no risk of harm to the

vehicle. This frame makes the system both structurally

sound and easy to remove should repairs or

modifications need to be made.

Propulsion is a key part of this vehicles design.

With the tread of the tires providing the thrust, the car is

able to move and steer in the water. Using fenders

mounted above the rear wheels, the car is able toconvert the energy created by the water being kicked up

by the tires into a useable amount of thrust. These

fenders are constructed of HDPE, a durable, lightweight

alternative to aluminum of fiberglass. In addition to

helping with propulsion, the fenders help guard the

engine from the inevitable splashing that the tires create.

Steering is done using the steering wheel. While

other methods can be used, the added complexity and

opportunity for failure far outweigh the benefits. The

shifting of the drivers weight can also be used to aid in

cornering. With more of the outside rear tire/wheel in the

water, the turn is completed more quickly. Sometimesoverlooked by previous teams, flotation and water

maneuverability are very important to performing well not

only in a competition setting, but in a recreational setting

as well.

SUSPENSION

Objective The objective of the suspension system is to

provide the vehicle with the means to keep all four

wheels planted on the ground with the maximum tire

contact patch in any driving situation. The front and rea

suspension must work as a unit to keep the tires on the

ground as well as possible so that the drivetrain can

continue moving the car with maximum efficiency and

the driver can comfortably control the car.

Discussion of alternatives The main options

considered for the front suspension were a few

variations on the double a-arm suspension setup. These

included parallel a-arms, un-parallel a-arms, equalength and unequal length. These offer various pros and

cons. The main goal is to keep the tires planted firmly on

the ground in all driving conditions. To do this, the tire

and wheel need to gain negative camber in a rolling

situation, keeping the tire flat on the ground. This leaves

only a limited number of options, the best being

unparallel double a-arms.

For the rear suspension several alternatives

were considered. These included independent unequa

A-arms, trailing link with locators, and swing arm

designs. A rear swing arm consists of a solid axle which

is connected to the wheel at either end. This design isstrong and simple but yields a combination of poo

ground clearance, unruly camber change and high

unsprung mass, all of which make it less than ideal

Independent unequal length A-arms are widely accepted

as one of the best alternatives for off-road suspension

due to the fact that camber change can be nearly

eliminated. A-arms can provide large amounts of trave

and usually match the front suspension set up which is

almost always an A-arm type. A-arm systems can add

unwanted unsprung mass to the suspension and are

prone to failure due to the number of parts involved. The

suspension type chosen for this vehicle is a trailing link

with locating links. This simple design is comprised of a

pair of arms (trailing links) which are connected to the

chassis just behind the driver on the lower part of the

rear roll hoop. These extend outward and back to the

position of the output shaft where it connects to the drive

axle. Additionally, there are two locating links attached to

the hub end of each trailing links. These links can be

adjusted so that the system acts similarly to a double a-

arm system, geometrically. A 2006 Polaris Outlaw 500

hub and bearing carrier is integrated into the end of the

trailing link. This accommodates the use of the Outlaw

final drive as well as more standard wheel sizes. The

dampers are connected to the arm and mounted to theroll cage above. This system is ideal because it provides

a combination of significant ground clearance, relatively

low unsprung mass, simplicity, and better access to

drivetrain area.

Overview of the design The vehicle features front

unequal length A-arms that attach to the frame with a

rake of 15 degrees from the horizontal. This provides

better transmission of shock forces when the vehicle

lands after jumps and when approaching steep inclines

8/6/2019 Baja2009

7/14

The front shock absorption is supplied through two

independent Fox Air Sox 2.0 shocks that have 8.5

inches of travel. Opting for a non-coil-over setup

provides significant weight reduction compared to a

more conventional coil spring design and increased

travel. The front spindles come from a Polaris Predator

ATV. They were chosen for their high strength-to-weight

ratio based on their cast aluminum design: using a

prefabricated spindle allows for easy brake and steering

integration.The A-arms are fabricated with 1 inch 4130

Chrome Moly tubing, which is a strong, lightweight, and

workable material. This adds durability to the

suspension, thus improving the reliability and safety of

the vehicle. A finite element analysis was run in

CosmosWorks with the same force as the rear and the 1

inch tubing proved to be more than adequate with a

factor of safety of well over 1 for both the front and the

rear. The ball and helm joints are attached to the tubing

using tube ends of their respective diameters and thread

sizes. These A-arms can be seen in Figure 5.

Figure 5: View of front suspension

The front suspension setup was designed and

modified from starting parameters based on the cars

ride height and track width. Such a methodology makes

certain the car is as stable and efficient as possible. The

lower A-arms are designed with force transmission as

their main priority. Thus they are the main structural

members of the front suspension. The lower a-arms are

further reinforced using a 1/8th

inch plate to not only

strengthen the part, but to also provide a flat, solid

mounting point for the front shocks. Their connection

with the frame is made through two unidirectionalbushings for rigidity. The ball joint that is used to

connect the lower A-arm to the spindle has a limited

amount of travel. To maximize the cars suspension

capabilities and travel, a bend of 20 degrees was placed

in the A-arm to allow for a more horizontal relationship

with the spindle mounting point. This ensures that the

travel of the front suspension is not hindered by the

limited travel of the ball joints. A similar approach was

taken when designing the upper A-arms; however

adjustability was considered more important than

strength because it is not required to transmit forces to

the shock. This led to mounting the upper A-arms 5

inches above the lower A-arms using heim joints instead

of bushings. This allows for easy camber adjustment

Like the lower A-arms, the uppers also are bent to

provide a more level mounting angle with the spindle

The ball joints are mounted on the spindle 1 inch furthe

apart than the mounting points on the frame to reduce

the overall camber change throughout the working arc o

the suspension.

The shocks are connected as close to the

spindle as possible to help decrease body roll and stress

on the arms. The Fox Air Shox 2.0 provides gas

pressure specialization that is not available in a standard

coil spring. They permit specific pressure adjustmen

based on the weight distribution of the car and the

desired spring rate. This allows the suspension to

compensate for the additional weight of the driver while

still providing the user a comfortable ride over rough

terrain. The shocks have been re-valved to

accommodate the approximate 128 pounds per whee

sprung weight estimate. The vehicle obtains a maximumunloaded ground clearance of 14 inches without flotation

and 10 inches when the flotation is attached.

The rear suspension uses a trailing link design

and has many positive characteristics, one of which is

the significant weight savings over the alternatives. The

links are constructed from the same 1-inch diameter

0.065-inch wall thickness Chrome Moly tubing that the

front a-arms are made of. This provides more than

adequate strength and durability without the added

volume and bulk of similar aluminum trailing links. A

simple and effective system was designed and built with

minimizing unsprung weight in mind. Two symmetrica

parts were TIG welded together to form the arm portion

of the link. Additional tabs and mounting brackets are

found at the hub end of the arm.

The members were modeled using SolidWorks

3-D solid modeling software. FEA analysis was then

conducted using CosmosWorks modeling software. The

members were subjected to shock loading of 90,000n

assuming a bottomed out shock and very high impact on

a single trailing link. The member was also subjected to

a simulated 4 G rear impact, which could occur if another

car hit the vehicle at full speed. Both of these modes oloading produced a factor of safety in excess of 3. The

stress plot of the shock loading analysis can be seen in

Figure 6:

8/6/2019 Baja2009

8/14

Figure 6: Cosmos Stress plot with 90000N shock loading

and deformation scale of 22. Max Stress = 20KSI

The locator links were constructed using the same

tubing mentioned above, with ultra high-strength heim

joints at each end. These allow for smooth, easy travel

and up to 2.5 inches of length adjustability. This allows

the team to carefully tune camber change and track

width using only a single crescent wrench.

This member, in addition to the wheel, hub and locator

links, constitutes the entire unsprung weight of the rear

suspension. The links are shown installed on the chassis

in figure 7:

Figure 7: rear trailing link members on chassis.

Most standard trailing link suspension designs

have one major drawback. The angle of the tire relativeto the trailing link never changes. This means that

excessive body roll will effectively induce unwanted

camber change at both wheels. The suspension

designed and built for the 2008 season eliminates this

issue by using two locator links on each side. Instead of

using a bushing and hinge type attachment to the frame

for the trailing link, an ultra high-strength heim joint has

been used. As stated earlier, this allows adjustment of

static and dynamic camber change. A demonstration of

camber change (gaining negative camber) is shown in

figure 8. Appendix B contains a figure showing the car in

a hard left turn, demonstrating how the rear suspension

reacts and keeps maximum tire contact with the ground

Not only does this increase the stability, it increases the

tire patch on the ground, increasing cornering ability.

Figure 8: Rear suspension shown at full droop and ful

bump

To compensate for excessive body roll, the dampers

used are highly adjustable Fox 2.0 Airshox. Thesedampers use internal nitrogen gas pressure to determine

spring rate as opposed to conventional steel springs

The stock nitrogen pressure in these shocks is 200 psi

The necessary pressure to achieve 8 inches of ride

height with all flotation components has been estimated

180 psi. This is based on gross vehicle and driver weight

as well as expected fore/aft weight distribution in the

chassis. This adjustable damper set up is absolutely

necessary with the trailing link suspension and allows

the user to adjust ride characteristics at will. Another

benefit of the trailing link system is the ground clearance

that can be achieved. As shown in Figure 1 the closescomponent to the ground at full droop is the end of the

trailing link. This is an improvement over double a-arms

where a drop angle can occupy otherwise free ground

clearance.

STEERING

Objective - The main objectives of the steering system

are to provide the driver with an accurate, predictable

and reliable method for navigating a Baja vehicle ove

rough terrain. A small turning radius provides the drive

with a responsive and controllable ride. The rack and

pinion system is a proven method of steering that isdirect and reliable. The tie rods must be protected from

impacts and move with the two A-arms while the whee

stops limit the steering radius and reduce wear on the

system. In addition, the steering system does no

interfere with the suspension, allowing for optima

negotiation of off-road conditions.

Discussion of Alternatives - The steering linkage system

had two options. The first option was to place the tie rod

attachment point in front of the spindle, and the second

8/6/2019 Baja2009

9/14

option was to place it on the back side of the spindle.

The tie rods are attached to the rear of the spindle to

provide more protection from impact and easy

integration into the Polaris knuckle.

Overview of the Design - A 14 inch rack and pinion

system was selected for the steering of the vehicle. This

industry-proven steering method is reliable and was

chosen to ensure the safety of the driver. The position

of the steering rack was carefully positioned for minimalmovement over the suspensions entire arc. This was

accomplished by modeling all the components in

SolidWorks. This gave a base for optimizing under both

bump and droop conditions. The wheels were aligned

forward and the displacement of the rack was measured

at both extremes. This procedure was repeated

iteratively for a matrix of potential steering rack positions.

By following this procedure the position of minimum

bump steer was determined.

The three-dimensional modeling programs

SolidWorks and COSMOSWorks, and a two-dimensional

modeling program, Working Model, were used toperform a stress analysis of the tie rods. This test

determined that the rods will endure expected

conditions. An axial compression force of 1200 lbs. was

applied, giving a factor of safety of 3. Analysis of the

buckling force also showed that with this design, neither

buckling nor axial failure will be an issue.

Design Characteristics - In order to properly achieve the

main objectives, numerous technical aspects were

considered. Camber and toe setting were other

important issues addressed. The camber is adjusted to

a slight inward, or negative, tilt of two degrees from static

ride height. This setting optimizes the tires contact with

the road surface, maximizing steering feel, response,

tracking, and tire life. Through threaded rod ends and

heim joints, the system is adjustable to optimize steering

geometry and performance. To enhance the turning

radius, the wheel base was minimized. With a shorter

wheel base and wide track the car is both stable and

steers as directly as possible.

BRAKING

Objective - The brakes are one of the most important

safety systems on the vehicle. The car uses three discbrakes, one on each front wheel and one on the rear

axle, to bring the vehicle to a quick and safe stop

regardless of weather conditions or topography.

Discussion of Alternatives - A braking system that acts

on all four wheels was chosen for optimum safety and

performance. Two methods for accomplishing this

objective were considered. Both options made use of

dual front disc brakes, but the rear setup could vary.

The first option with regard to the rear system wasthe

use of a single disc brake located inboard of the wheels

It would act to stop the rear tires by braking the fina

drive axle. The second alternative was locating the disc

brakes at each rear wheel. The first option was chosen

because it simplifies the rear trailing link design and fully

utilizes the capabilities of the Outlaw 500 final drive

system. Additionally, it converts the rear brakes from

previously unsprung weight to now sprung weight. With

newer, pre-fabricated CV axles and hub, a single rea

disc brake can be used without worrying about the abilityof the axles to withstand the added torque, similar to the

Polaris Outlaw 500 ATV.

Overview of the Design - The braking system uses two

CNC master cylinders of the same bore size to supply

hydraulic pressure to the brake calipers. All three

calipers are driven by a 5/8 inch bore. The front two

share one cylinder while the rear has its own A

balancing bar at the pedal allows for the allocation of

front and rear braking pressures. The dual cylinders and

reservoirs are easy to access, providing ease of

monitoring and maintaining brake fluid levels. The brake

calipers are connected to the master cylinders by acombination of both hard line and flexible braided brake

line. The steel braided lines are used for their flexibility

and resistance to wear. Thus, they are located in

sections where suspension travel occurs. Both the hard

lines and braided lines are protected from possible

damage because they are placed inside the rol

envelope.

The independent front and rear brakes systems

ensure that there should always be at least one mode o

braking in the case of a line or caliper failure

Additionally, the system is properly sealed such that it

will remain fully functional in the event of a collision o

roll.

The disk brakes, calipers, and caliper mounts

are made by Polaris. The rear calipers are designed fo

an Outlaw 500; a vehicle of similar size and weight while

the front calipers can be found on a 2006 Polaris

Predator. The spindles are also from the Predator and

were chosen for their availability and proven design

strengths. Utilizing parts already in production reduces

cost and lessens the cost of repair for the end user

should something break. The tie rod mounts, and caliper

mounts were designed and manufactured in-houseThese parts are composed of 4130 steel for strength.

Design Characteristics - It was deemed critical that the

front and rear brakes lock up at the same rates. This

would maximize deceleration, prevent front-end dive

and offer the best vehicle control. All brake calipers and

discs are mounted to factory mounts on a Predator ATV

and an Outlaw ATV. This is for a couple of reasons. The

first is that it ensures that the pieces are designed to

withstand a very significant force. The second is that i

8/6/2019 Baja2009

10/14

makes replacement and maintenance much easier

should a part need to be replaced. A brake fluid analysis

of the different bore sizes of master cylinders was

completed. From this analysis, the best combination of

braking forces for the front and rear brakes was

selected.

TIRE SELECTION

The rear tires are a 25 outer diameter by 10wide ITP Mud Lite model mounted on aluminum rims.

They are the lightest six-ply rated tires available which

give the durability needed to withstand rugged terrain.

The large outer diameter of the tire provides an increase

in ground clearance which is vital in traversing off-road

conditions. The treads provide ample water propulsion

when mounted correctly, which means the tires are used

in their proper orientation for optimum traction on rough

terrain. These tires were also chosen for their ability to

perform in mud, a clear requirement when off-road in

anything but a very dry terrain. The front tires are Maxxis

Razr tires mounted on 10 aluminum rims. Aluminum

wheels were chosen for their durability with minimalweight. Minimizing the amount of unsprung weight on the

car is a major goal when designing suspension

components and saving weight anywhere possible

allows for added strength elsewhere. The Razr features

a wide tread pattern to reduce tread squirm and the

sipes tighten up under acceleration and braking forces.

These sipes are small cracks in the tread, designed to

move water away from under the tire quickly. Under a

sliding force, they lock together and prevent the treads

from shifting. These front tires have a less aggressive

tread pattern than the rear tires. A 10-inch wide rear tire

was chosen for its capabilities in mud and water. This

size was chosen over the available 12-inch model to

reduce the amount of friction the car must overcome in

cornering. Without a rear differential, the outside tire

must drag across the ground, or break loose in

aggressive cornering. The ITP mudlite offers an

excellent middle ground, as proven in the mud pit of the

2007 competition. The chosen tires, both front and rear,

are shown in Figure 9.

Figure 9: Rear Mud Lite tire & Maxxis Razr

CONCLUSION -

The Union College Mini Baja vehicle has been designed

to appeal to customers and manufacturers by effectively

meeting the initial objectives and offering a safe

affordable recreational vehicle to fill an otherwise emptymarket segment. The current frame yields high factors o

safety and drive comfort. The drivetrain was improved

upon to further optimize the vehicles performance and

enhance reliability and ease of maintenance. The

flotation system has been revised and lightened to

effectively traverse water without sacrificing land

maneuverability. The steering systems design yields a

responsive and controllable car with no noticeable bump

steer. The braking system affords maximum overal

braking force on the front and rear wheels. The

suspension has been designed to provide ten inches o

ground clearance with the flotation, ample for nearly any

off-road terrain. The tires were selected to run on nearlyany terrain. The resulting vehicle is safe, attractive

reliable, economical and fun to drive.

ACKNOWLEDGMENTS

Brad Bruno - Union College Mechanical Engineering

Faculty

Paul Tompkins Union College Machine Shop

Technician

James Howard - Union College Machine Shop

Technician

Roland Pierson - Union College Machine ShopTechnician

Quality Drive System Alhambra CA, Parts Distributor

REFERENCES

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

(3/05/09)

2. http://parts.polarisind.com/Browse/Browse.asp

(3/05/09)

3. http://www.hoffcocomet.com/

(3/05/09)

4. http://www.martinsprocket.com

(3/05/09)5. Callister, William. Material Science and Engineering

an Introduction. 7th

edition, 2006

CONTACTS

Matt Beenen beenenm@union.edu

Jon Wilson wilsonj@union.edu

8/6/2019 Baja2009

11/14

Appendix A:

10G Frontal Impact (29430N) Max Stress = 62 KSI

4G Side Impact 10700 N. Maximum Compressive Axial Stress = 16,140 PSI

Maximum Tensile Stress = 7,133 PSI

8/6/2019 Baja2009

12/14

Rear Impact, 4G 10700 N

Max Stress (compression) = 18,330 PSI

Rear Impact 125000 N

Max Deformation (buckling) = .0006m

Deformation scale = 181.694

8/6/2019 Baja2009

13/14

Static Load 90,000 N

Max Deformation (deformation scale 22.6)= .0021m

Static Load 90,000 N

Max Stress = 20.5 KSI

8/6/2019 Baja2009

14/14

Appendix B: Suspension Roll Analysis