Midterm Final Draft

8/13/2019 Midterm Final Draft

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OLD DOMINION UNIVERSITY

SAE BajaMidterm Report

Frame Suspension Drivetrain

Dan DAmico Peter Morabito Kenneth ElliotCurtis May Michael Paliga Patrick Mooney

Greg Schaffran Brian Ross Dylan Quinn

Faculty Advisor: Dr. Elmustafa


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Table of Contents

Section Page #

List of Figures....ii

Abstract.iii

Introduction

Background..1

Background- Drivetrain.2

Methods & Results- Drivetrain...2-5

Discussion- Drivetrain-7

Background- Suspension-8

Methods- Suspension9

Results-Sus pension9

Discussion- Suspension.9-10

Background- Frame.10

Methods- Frame10-11

Results- Frame11

Discussion- Frame11-13Appendix A.14-20

Appendix B21

References..........................22


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List of Figures

Figure Page #

Figure 1. Gear Train Model

Figure 2. Differential

Figure 3. Double Reduction Gear Schematic .

Figure 4. CVT Image

Figure 5. Camber Diagram

Figure 6. Castor Diagram .

Figure 7. Toe Diagram

Figure 8. Roll and Steering Behavior .8

Figure 9. SAE Axes Terminology

Figure 10. ODU, Cornell, and Oregon State SAE Bajas ..12


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AbstractThe Society of Automotive Engineers (SAE) Baja senior design project enables students to gain realworld experience in the design, analysis, and manufacture of a vehicular product. Specifically, our teamhas been organized into frame, drivetrain, and suspension subgroups to allow a thorough and originaldesign of all major components. The frame team will be responsible for the creation of a new framedesign that must be concurrent with all SAE competition rules. Special consideration will be given toweight and cost reduction. The suspension team will focus primarily on the rear suspension. A reliabletrailing arm design will be utilized for rear suspension applications, while the front suspension willconsist of a standard double A- arm setup. The drivetrain team will design a double reduction gearbox,with an emphasis on efficiency and weight reduction. The transmission will be a continuously varyingtransmission (CVT). The purpose of this project is to design a SAE Baja vehicle from scratch so that thisdesign can be utilized in the 2014 SAE Baja Competition.


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IntroductionThe 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 allowsstudents to apply engineering theories and concepts that have been presented to them in previouscourses. The purpose of this project is to further the design, manufacturing, teamwork andcommunication skills of the team members to prepare them for working in industry. The team has beendivided 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 efficient powertrain design. This will beachieved by replacing the existing chain driven system with a gearbox. A gearbox will greatly improvethe vehicles reliability and efficiently as well as reduce the overall weight of the car. The gearbox will bepaire d with a CVT transmission to provide a range of gear ratios to improve the vehicles maximumtorque and top speed.

The suspension team will develop a more reliable and predicable suspension system. The frontsuspension will consist of a double A-arm set up, similar to previous years, to function with the newframe design. The rear suspension will consist of a four link trailing arm set up to allow for dynamiccamber and the greatest possible suspension travel. This will be more reliable than last years des ign andshould provide the same steering and suspension capabilities.

The frame team will focus on producing a frame that is lighter than last years frame. This teamhas focused on shortening the frame so that less material is used and a smaller turning radius can beachieved. Additionally, this team has been working to provide the optimum suspension mounting pointsand rear end of the frame to accommodate the drivetrain and suspension teams needs.

BackgroundThe first Mini Baja competition started in 1976 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 expandedinto 3 sub-regions: East, Midwest, and West. The Baja SAE competition has even grown into aninternational affair with competitions in Brazil, Korea, and South Africa.

This years competition will be in Rochester, New York. The competition will include fivedynamic events: Acceleration, Hill Climb, Maneuverability, Suspension & Traction, and Endurance. Theseevents will put each vehicle through an intense test of performance and durability. The teams will alsobe judged on the vehicles styling and cost report.

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


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Background- DrivetrainThe SAE BAJA 2013 rule book specifies that all teams shall use a Briggs & Stratton 1450 series

engine (Figure A.1). This engine produces a peak of 14.50 ft lbs of torque as shown in Figure A.2 and israted at ~10 horsepower. The engine is tuned at competition by Briggs & Stratton technicians to insure

that every team is running the specified engine without modifications at 3600 rpm. This is a singlecylinder four stroke engine that is fed from a carburetor and manual choke. The only modificationallowed 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 VaryingTransmission (CVT). This transmission is a variable diameter pulley system where the sheaves primaryand secondary pulleys move in and out thus changing diameter and gear ratio. Figure A.3 demonstratesthe extremes of the gear ratios that the CVT will travel throug h. CVTs are ideal for the SAE Bajacompetition because the CVT adjusts to provide the best ratio depending on the speed of the input andoutput shafts thus providing max torque when needed and adjusting to the top speed ratio whenneeded. This type of CVT is adjustable with a system of springs and brass weights to allow tuning forspecific events allowing for top speed or lower end torque bias.

Methods & Results DrivetrainOne of the primary goals of the powertrain team is to develop a fixed ratio gearbox design to

compliment the performance of the Briggs & Stratton engine and Gaged CVT system. The gearbox willbe optimized to provide maximum vehicle performance throughout the range of events incorporated inthe SAE Baja competition. The gearbox design 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 willenhance the performance of the Baja vehicle.

Gear train and differential design is crucial to the reliability of the gearbox and represents alarge amount of the calculations thus far in the project. A precise overall reduction ratio is required inorder to achieve the acceptable performance out of the whole drivetrain system. This can be seen inFigure A.4. The most challenging event in the competition for the powertrain team is the hill climb. Atthe Rochester venue the hill is 36-37 degrees, the steepest of all the locations the Baja competitiontakes 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 degreeswas determined as well as an overestimated vehicle weight.


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

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

The final drive ratio of the car throughout the band of CVT manipulation is key to success at allof the events at the SAE Baja competition. The 8.0:1 gearbox ratio should provide good results in the hillclimb and acceleration events, but it must also allow for a competitive top speed for the endurancerace. The Briggs & Stratton engine is tuned at competition to have an RPM limit of 3600. Based onachieving this RPM, a theoretical top speed of 35.7 MPH was determined and 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 thecourse, as well as provide good low end power in the technical portions.

There are many constraints in gear train sizing and selection. The gear combinations must achievemany 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 andsupport design due to the lack of lateral forces. They are also significantly cheaper than comparable

helical gears and there is a larger, more available selection of size and pitch combinations. The gearsbeing used will have a modern pressure angle of 20 degrees and a pitch of 12. The gear train will be splitinto two reductions in order to save space in the overall size of the gearbox. A single reduction boxwould require a very large spur gear to compliment the pinion gear in order to achieve the desired ratio.


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Stage 1 Reduction: (2.0:1)o Pitch = 12, Press Angle = 20

Pinion Gear: 20 Teeth- Dp = 1.6667

Spur Gear: 40 Teeth - Dp = 3.3333

Stage 2 Reduction: (4.0:1)o Pitch = 12, Press Angle = 20

Pinion Gear: 20 Teeth- Dp = 1.6667

Spur Gear: 80 Teeth - Dp = 6.6667

In order to aid in the selection of gears in thetrain a table of potential combinations was created. Included were available face widths, bore sizes andpitches. To ensure the chosen gear combinations would work well together, interference was calculatedfor 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 gearselection table can be made. This table is shown in 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 methodswere 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. Theperformance to cost ratio is also very high.

Gear Train Model


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A differential will be housed in the large output gear in thegearbox. The differential will allow for more maneuverability andbetter handling characteristics in the endurance competition byallowing a bias between the rear drive axles. The large gear willhave to be machined to secure the differential.

After gear selection and calculation is complete a bearingand shaft system and housing will be developed. The shafts will relyon a shoulder coupled with snap rings to secure the gears in a lateraldirection. A standard keyway will mate the gears to the shaftrotationally. The shafts will also contain shoulders to house bearings. The gearbox housing will be splithorizontally into two sections along the centerline of the bearings allowing for access and support.

Discussion - Drivetrain The bajas drivetrain will undergo a number of upgrades this year. The objective of this years

gearbox design is to create a two-stage, double reduction gearbox. This type of gearbox will replace thebelt 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 hopefullyenhance the performance of ODUs baja vehicle at compe tition.

In order to achieve success and compete in not only a few, but all of the events at thecompetition, a more versatile gearbox design was chosen. After reviewing the types of events that thevehicle will likely encounter; a gearbox ratio of 8:1 was decided upon. A large reduction ratio waschosen to correspond with an emphasis 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 thegearbox because they are more efficient and simpler to manufacture compared to helical gears. A two-stage compound gear train like the one in Fig. 13-28 below, shows a design similar to the one that willbe integrated in this years baja design.


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In the quest for excellence, a decision was made to incorporate a more advanced design thatincludes a differential. A differential was added to the design to increase the vehicles maneuverability. Itwill allow for the wheels to rotate at different speeds when making turns. This should allow the car toexcel in certain, more technical, events. The addition of a differential will definitely benefit the vehiclesmaneuverability, especially since it lacks a reverse drive operation.

The transmission was chosen to be a Gaged GX-9 continuously variable transmission (CVT). Thistype 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 gearratios within a given range of 3.85:1 initial drive to 0.9:1 final drive. A picture of the Gaged GX-9 CVTwithout the belt is shown below. This system also removes the need for a clutch as the belt slipsallowing the engine to spin freely when the secondary shaft is held.

The powertrain design of this years vehicle has some similarities but more differences whencompared with previous vehicles. This years gearbox is radically different than last years designbecause issues that arose at competition were discovered and corrected. A gear driven setup waschosen in order to adhere to the complaints of the previous team about the added weight and noise of achain drive. Difficulties in maneuverability in previous vehicles created a need to add a differential to thedesign. In doing so, the new car will be able to move more quickly in and out of turns. Both this year andlast years teams have the same transmission. No problems were detected by the previous team so thesame CVT will be used again.


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Several limitations of this study are present and effect the possible conclusions that could bemade. It is hard to say how effective the gearbox design actually is because the powertrain will not bephysically tested at competition until next year. Although the project has limitations, its futureimplications create a meaningful assignment. Future teams will be able to analyze the performance anddurability of past designs and make modifications and improvements to them. This type of project

allows for ODUs baja SAE vehicle to prog ress with each generation.

Suspension - BackgroundThe Bajas 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 onboth the front and rear to unequal double wishbone systems on the front, and a trailing arm setup onthe rear. The trailing arm rear suspension is advantageous in that it imbues greater platform stabilityand, as an added bonus, dynamic kinematic properties, such as toe and camber. Dynamically, criterionpertaining to toe, camber, castor, track width, wheelbase, weight transfer, roll center, and suspensiontravel are crucial elements of a successful suspension design.

According to the textbook Race Car Vehicle Dynamics , camber is defined as the angle between atilted wheel plane and the vertical [11] . It is one of three terms used to describe a suspensionsalignment. The camber angle, , can have negative or positive orientations, where camber is consideredpositive if the top of the wheel leans outward, and negative if the top of the wheel leans inward. Thefigure below serves as a visual representation of positive and negative camber. If a vehicles wheels areproperly cambered, a beneficial thrust force is produced. This thrust force, aptly named camber thrust,contributes a lateral force in the direction of the tires tilt. In other words, it ensures stability by pullingthe 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, isanother stability oriented kinematic property. The chief benefit of castor is that it is responsible for a


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steering centric restoring force, meaning that the amount of castor affects how the steering feels andthe 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 vehicles alignment. From Boschs AutomotiveHandbook , toe specifies the degree to which non-parallel front wheels are closer together at the frontthan at the rear [12]. Tire wear is heavily dependent on toe distances. The figures below shows what ismeant by a toe-in alignment setup.

The roll center has a significant impact on a suspensions steering response; moreover, there is adirect correlation between roll center location and oversteer, understeer, or neutral steer suspensionbehavior. In the book Tune To Wi n, author Carroll Smith defines the roll center as a point, in thetransverse plane of the axles, about which the sprung mass of that end of the vehicle will roll under theinfluence of centrifugal force, where the sprung mass is the portion of the vehicles total mass that issupported by the suspension springs [13]. Furthermore, vehicles designed to understeer will requiremore steering input, whereas vehicles inclined to oversteer will require less steering input. Vehiclesequipped with a tinge of oversteer are ideally suited for applications that demand maneuverability. Theslight oversteer enables maximum agility while maintaining a forgiving nature, thus would be perfect forBaja applications. The right side figure above shows how varying the inclination of the roll axis affectssteering behavior.

Wheelbase is the longitudinal distance from the center of the front wheel hub to the center ofthe rear hub. Similarly, track width is the lateral length from wheel centerlines. The length of thewheelbase is of utmost importance when considering weight transfer and the vehicles center of gravity(CG). From a performance perspective, 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 theaforementioned dynamics and definitions.


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Methods - 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 beinterpreted 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 asolid works drawing. The points were then imported into the analysis software. From there test pointscan be used to get desired results. The design for the rear suspension has been researched andgeometry has been decided on. Future designing consists of finding the optimum mounting points forthe desired dynamics of the suspension. It will involve a trial and error type analysis in order to find theoptimum solution.

Results - SuspensionThe 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. Oncethe parameters are set for the run the simulation is played and an excel spreadsheet is developed withthe results. These results will help in analyzing whether or not the suspension will be able to withstandthe design requirements of the Baja. A final run through has not yet been developed for the frontsuspension but the program has been studied to do so.

Discussion - SuspensionThe 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 dynamic 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 atcompetition, so for greater simplicity, the link that controls dynamic toe must be eliminated. A newtrailing arm setup must be designed and analyzed to meet this goal. The front suspension setup is beingfinalized and has been used to train the group on the proper use of OptimumKinematics suspensionanalysis software. The center of gravity for the 2012 Baja car was calculated using rudimentary materialsand the results are included in Figure A.10 The center of gravity was found to lie approximately 10inches above the axial center, and can be shortened by using lower mounting locations.

Additionally, Fox Float Racing Shocks have been selected over re-using the Custom WorksShocks of previous years. The Float Racing Shock is an air shock that offers superior cost effectiveness. Apair 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 compromiseon behalf of cost will not severely impact performance. Qualitatively, compression and rebound force


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

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

Background - Frame

The SAE Baja has a large list of minimum requirements for frame design. These regulations mustbe met in order to ensure design integrity and driver safety. The purpose of the frame is to provide aprotected space from which the driver can control the car. All of the frame requirements in the rulebook have been set to ensure the driver will be as safe as possible in the event of an accident. Thefirewall is in place in case of a problem with the engine or drivetrain to protect the driver from fire orflying shrapnel. In the event of the car rolling over the roll cage is designed to withstand the weight ofthe car and keep the operator from being crushed. Sidebars provide support in case of a side impact andthe nose section is designed to hold up in the event of a front end collision.

Previous years frames 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 weighed306lbs. While the past two years have been essentially the same design, the SAE rules require the entirevehicle to be at least 50% different if the same design has been previously used consecutively. The aimof this year's frame design is to reduce the overall weight and size of the car while meeting thisdifference requirement.

Methods - FrameThe 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 astheir cost. The material chosen was 4130 chromoly steel.

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

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

Working forward, the front end was designed according to suspension mounting pointspredetermined by the suspension team. Members were drawn to accommodate the double A arms of


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the front suspension as well as a shock mounting point. Also in consideration was leaving space for thebrake reservoirs. Consideration was also made for length for a driver's legs, leaving 44 inches betweenthe 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 frontend. Consideration was made for minimum head clearance for driver safety. The horizontal portion ofthe roll cage was designed to maintain a 41 inch vertical clearance and a 12 inch forward clearance fromthe rear seat bottom.

The vehicle's rear end was designed with consideration for the engine size and orientation.Gearbox and suspension mounting points were also considered. Only a tentative design is complete. Thedesign will be finalized on completion of the gearbox and suspension designs. Further work is neededonce 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 designis sufficient. Rollover and collision analysis will be performed. The design will be strengthened wherenecessary and members may be removed to save weight if the design can maintain a sufficient safety

factor without them.

Results - FrameThe 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 reducingvehicle weight in mind. The roll cage has also been designed to minimize vehicle weight and reduceoverall chassis flex while cornering. The length of the vehicle was reduced by eight inches in comparisonto last year's design for a shorter wheelbase, more precise handling, and reduced weight. This will alsohelp 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 theframe members [6][1]. This steel was chosen over other options such as 1020 steel or 1026 steelbecause 4130 has the highest strength to weight ratio [2][3][4][5]. Chromoly steel is also within thebudget and more readily available than other types [1].

Future work includes finalization of the rear end design based on gearbox and suspension designand finite element analysis in MSC PATRAN. Testing must be done for rollover as well as front, side andrear collision testing. Members will be added should the design fail or removed should it prove to have avery large safety factor.

Discussion - FrameThe 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 betweenOld Dominions 2012 vehicle and the top competitors. Old Dominions frame was considerably largerthan the other top competitors who favored a more compact vehicle. It can be seen in Figure 10 thelength differences between the Old Dominion University, Oregon State, and Cornell vehicles. The driver


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of ODUs Mini Baja has his legs almost fully extended and the ste ering column juts out a considerabledistance. Both Cornells and Oregon States drivers have their knees bent and the steering column barely juts out from the front end.

Figure 10. Old Dominion mini Baja [9] (top left),

Oregon State University mini Baja [10] (top right),Cornell University mini Baja [10] (bottom).

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

There are not many results yet seeing as how the frame design is still in development, but somepreliminary conclusions can be drawn as to what can be expected. A reduction in frame weight, whencompared to the 2012 ODU Mini Baja, can be expected due to several reductions in frame dimensionsand changes in member configuration. These improvements will also increase the handling of thevehicle. Reduced weight and increased handling will allow for better performance in competitionswhere past performances can be improved. At this time the frame weight reduction is unknown, but willbe 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 car will bemaintained as the design is similar to the previous vehicle. A finite element analysis will be performed inPATRAN once the final frame design is completed. One conclusion that can be drawn is which particular


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material the frame will be used in construction. The frame will be constructed with chromoly 4130 steeldue to its high strength to weight ratio and good weldability [1]. It was used for past Old Dominion carsand is the popular steel of choice for many other competing teams.

The past Old Dominion University Mini Bajas have mostly placed in the middle of the pack interms of competition ranking. Last June the team took 55 th place out of 102 ranked teams. It isimportant to examine the previous Mini Baja to identify parts of the design that are not performing aswell as they should. Potential areas of improvement can be identified by comparing Old Dominions2012 car to other top performing schools. One of the main concerns is the overall weight of the vehicle.Last year the ODU car weighed 479 pounds compared to the 3 rd place car from Cornell at 306 pounds[8]. The Old Dominion frame alone weighed about 330 pounds, meaning Cornells total car was around24 pounds lighter than the ODU frame. Table A.2 displays the event scores for the top four competitorsand Old Dominion University from the SAE Wisconsin 2012 competition. The events where OldDominions performances were much lower depended on high power to weight ratios. A lighter weightvehicle will improve the performances in acceleration, pulling, and endurance the most.

The Baja SAE rulebook lays out many of the specifications that the designed vehicle must staywithin in order to be considered eligible for competition. The maximum allowable width is 64in at thewidest point of the car, wheels included [6]. With the suspension staying mostly unchanged, the car willfall well within the maximum allowable width. While there is no limit to the length, SAE suggests amaximum length of 108in [6]. The current design sits at 74.5in and is unlikely to change very much. Theroll cage has been designed around the template driver that is supplied in the rule book. The first step inthe design was to record all specification requirements to ensure that all were met. Barring any changesto 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 performanceenhanced, some are within control and some outside of it. Money is one limitation that cannot behelped very much. The school is unlikely to drastically change the budget allotted to the Mini Baja teamwhich leaves sponsors as the only other source of income. Without a dedicated marketing team andmore impressive competition record it is unlikely that the income from sponsors will change much. Thisleaves the team without many of the advantages that better funded schools have, such as dedicatedmachine shops and the ability to manufacture parts from carbon fiber. These allow teams with suchfacilities and budgets to have large advantages over other teams.

A limitation that can be controlled is the transfer of designs and information from one yearsdesign team to the next. This would be a great advantage in being able to perform necessarymodifications to improve a design instead of starting a new one from scratch. However for this to haveany 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 havedecided to design their own Mini Baja. This is less than optimal and results in little design informationbeing pa ssed on to the next years design team. It would be very beneficial for the faculty advisor tofacilitate communication between the two teams and emphasize the passage of design information.


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Appendix A

Figure A.1 Engine.

Figure A.2 CVT Diagram.


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Figure A.3 Torque Curve.

Figure A.4 Factor of Safety Calculations.

Figure A.5 Top Speed Calculations.

Factor of Safet Reduction Ratio

VALUES: ESTIMATE / ACTUALGEAR RATIO: (8.0 / 7.7551) = 1.0326VEHICLE WEIGHT: (650 LBS / 600 LBS) = 1.0833

INCLINE ANGLE: (40 DEG / 37.5 DEG) = 1.0667TORQUE: (15 LB-FT MAX / 14 LB-FT AVG) = 1.0714TOTAL 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 RATIOTIRE RADIUS = 1.0 FTTIRE ROLLOUT: (2)*(1.0 FT) = 6.28319 FEET DISTANCE PER ROTENG= (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


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Figure A.6 Minimum Gear Ratio.

Table A.1 Gear Specifications for Reduction Ratio.

Minimum Ratio (X) to Overcome Incline Angle

ENGINE TORQUE: 14 LB-FTCVT RATIO (INITIAL): 3.85:1TIRE ROLLING DIAMETER: 1.0 FEET

[VEHICLE WT]*[SIN(INCLINE ANGLE)] = REPELLING WEIGHT[650 LBS]*[SIN(40 DEGREES)] = 418 LBSREPELLING WT = (TIRE RADIUS)*(CVT RATIO)*(ENGINE TQ)*(X MIN)418 LBS = (1.0 FT)*(3.85)*(14 LB-FT)*(X MIN)

----->XMIN=7.7551


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Figure A.7 Loads, Stresses, and Safety Factor Calculations.

Figure A.8 Shock Compression Behavior.


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Figure A.9 Shock Rebound Behavior


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Figure A.10 Baja Center of Gravity Calculations


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Rank 1 2 3 4 55

SchoolUniversiteLaval

Oregon StateUniversity

CornellUniversity EDTS

Old DominionUniversity

Overall (1000) 913.77 896.63 893.62 880.21 530.74Overall Dynamic (300) 266.59 256.18 232.58 227.13 185.54

Overall Static (300) 245.18 236.45 258.04 252.08 183.04Cost (100) 90.80 74.45 83.54 80.45 71.29Design (200) 154.38 162.00 174.50 171.63 111.75Acceleration (60) 60.00 51.72 53.95 47.92 32.24Land Maneuverability (60) 60.00 58.06 56.44 54.04 48.06Mud Bog (60) 50.04 60.00 46.34 34.91 43.22Pulling (60) 36.55 30.31 22.29 36.11 15.16Suspension & Traction(60) 60.00 56.09 53.56 54.15 46.86Endurance Race (400) 402.00 404.00 403.00 401.00 162.16

Table A.1 Score Breakdown of Top Four Schools Compared to Results for ODU Mini Baja Team [7].


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Appendix B

Figure B.1 Current Gantt Chart.


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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. Available:

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 , 2nd ed., Bosch, Stuttgart, GmbH, 1986, pp. 480-481.
http://www.facebook.com/BajaSaeOregon/photos_streamhttp://www.facebook.com/BajaSaeOregon/photos_streamhttp://www.facebook.com/BajaSaeOregon/photos_stream

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