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BAJA SAE 2010. Conceptual Design Review. Statement of Work.

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BAJA SAE 2010

Conceptual Design Review


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Statement of Work

  • Baja SAE is an international collegiate design competition sponsored by the Society of Automotive Engineers. The program simulates real-world engineering design projects and the related challenges with the goal of developing and building a small off-road vehicle. Teams from around the world compete in static and dynamic events to have their design accepted for manufacture by a fictitious firm.


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Team Responsibilities

  • Sam Moran – Chief Executive Officer; Frame Designer; Welder/Grinder

  • Michael Guilfoy – Steering Engineer; Chief Financial Officer; Welder/Machinist

  • Sam Weitkemper – Drivetrain Engineer; Executive Secretary

  • Ben McNealy – Braking Engineer; Analyst; Director of Internet Services

  • Matt Wantland – Analyst; Materials Acquisition Specialist; Fabricator

  • Dan Pickering – Suspension Engineer; Chief Mechanic

  • Ahmed Al-Gattan – Chief Safety Officer


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Customers

  • SAE Competition Fictitious Firm

    • Safe vehicle

    • Maneuverability, Traction, Suspension, Acceleration

    • Design/Manufacturability

    • Cost

  • Sponsors

    • Competitive vehicle

    • Promotion

  • Faculty Advisors

    • Competition success

    • Educational experience


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Benchmarking

  • Vehicle Engineering Specifications

    • Front Track Width

    • Rear Track Width

    • Wheelbase

    • Weight

    • Suspension

    • Drivetrain

  • Data from 2009 Baja SAE Alabama competition


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Benchmarking

2010 TU car

2009 TU car


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Benchmarking

2010 TU car

2009 TU car


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Benchmarking

2010 TU car

2009 TU car


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Benchmarking

  • Analysis of top 11 overall performing cars from 2009 Baja SAE Alabama competition


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Frame Concept 1 – The Nose Box

  • Advantages:

    • simple

    • few packaging constraints

  • Disadvantages:

    • inefficient use of space


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Frame Concept 2 – Integrated Cockpit

  • Advantages:

    • more legroom

    • efficient use of space

    • light

  • Disadvantages:

    • Complicated design


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Frame Concept 3 – “The Cage”

  • Advantages:

    • simple design

    • requires the least amount of planning

    • allows for last-stage drivetrain changes

  • Disadvantages:

    • heavy

    • difficult drivetrain maintenance


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Frame Concept 4 – Double Loop

  • Advantages:

    • lightweight

    • efficient

    • easy drivetrain maintenance

  • Disadvantages:

    • difficult to design

    • not conducive to double a-arm suspension

    • stuck with drivetrain choices


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Frame Concept & Design

  • Front

    • Length designed for the reach of the team’s smallest driver

    • Clearance designed for the 95th percentile male

    • Integrated cockpit design

  • Rear

    • Double loop design inspired by Queen’s University

    • Frame members do not interfere with removal of drivetrain components

  • Weight: 73 lbs

  • Length: 80.5”

  • Width: 31.0”

  • Height: 52.9”


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Final Frame Design


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Frame Material

  • Given in 1018 PCS

  • 2 different specifications -Strength/Stiffness

    • Critical Components – Roll Cage

    • Non-Critical Components – frontal/side impact



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Tubing Possibilities

  • Hi Performance – Expensive/Light

  • Economical – Cheap/Heavy

  • Compromise – In between


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Frame Specifications

*http://www.airpartsinc.com/products/4130-steel-tubing.htm


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Drivetrain Benchmarking


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Drivetrain Concept #1

  • CVT with chain drive

  • Pros: lightweight, simple, cheap

  • Cons: no reverse gear, requires tensioning system


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Drivetrain Concept #2

  • Motorcycle gearbox with chain drive

  • Pros: easy to find, includes reverse gear

  • Cons: more difficult for the driver


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Drivetrain Concept Chosen

  • CVTech CVT with Dana H-12 transaxle

  • Pros: Simple, proven reliability, F/N/R, auto-locking differential

  • Cons: Heavy


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Drivetrain Layout



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Drivetrain Specifications


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Front Suspension

  • Double A-arm configuration

    • The front suspension system for a majority of the cars at last year’s competition

  • Benefits

    • The length and orientation of the arms can be designed for the vehicle’s application.

    • Computers can be used to design the suspension geometry


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Front Suspension

  • The vehicle was designed around the suspension mounting points

    • To prevent conflicts between the suspension and other vehicle components

    • Mechanism synthesis was performed in SolidWorks with the help of Dr. Daily


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Front Suspension

  • Mounting points

    • Geometric constraint analysis was performed to determine the suspension mounting points for a given tie rod length and designed for no bump steer

    • Constraints: 5 degrees of camber and 10 inches of vertical travel for a 52-inch front track width

    • Top arm length: 16.375”

    • Bottom arm length: 16.50”


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Front Suspension

  • Roll center

    • The front roll center was determined using SolidWorks

    • For the desired mounting points, the roll center was found to be about 3.05 inches above the ground


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Rear Suspension

  • Solid Rear Axle/ Swing Arm

    • Top finishers such as Queen’s University and Michigan University used a swing arm with a solid rear axle.

  • Double A-arm

    • A majority of the cars at last year’s Mini Baja used a double wishbone configuration.

    • More appropriate for cars without a solid rear axle

    • Simple

    • After discussing options with the team, a double wishbone configuration was chosen


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Rear Suspension

  • Mounting points

    • Geometric constraint analysis was again performed to determine the suspension mounting points

    • Constraints: no camber change and 8 inches of vertical travel for a 50-inch rear track width

    • Top arm length: 16.50”

    • Bottom arm length: 16.50”


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Rear Suspension

  • Roll center

    • The rear roll center was determined using SolidWorks given parallel equal length arms

    • For the desired mounting points, the roll center was found to be at the ground


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Shocks and Springs

  • The shock mounting points were set by the frame design and restrained by the control arm movement.

  • The ideal shock travel for the given wheel travel was determined from mechanism synthesis.


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Steering Concepts

  • Power Steering

    • Additional components

    • Requires power

    • Complicated integrationinside steering box

  • Four-Wheel Steering

    • Challenging integration

    • Untested in competitionconditions


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Steering Concepts

  • Rack and Pinion Steering

    • Simplified system

    • Light

    • Ease of integration with suspension

    • Used by nearly every Baja SAE team


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Ackerman Geometry

51”

62.5”


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Modeling Steering Angles

27.73°

45.49°

Outside Wheel Lock Position

Inside Wheel Lock Position



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Steering Specifications

  • Chosen Concept: Rack and Pinion

    • 14 inch length; 4.5 inches of travel

    • 1.5 turns lock-to-lock

    • Turning radius of approximately 10.5 feet

    • Ackerman Geometry

    • Tie Rod Connection

    • Rack mounting to minimize lateral loads

    • Rack mounting considered in frame design

    • Front Suspension design clearance issues addressed


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Braking Concepts

  • Rules require two independent hydraulic systems

  • Disc brakes

    • Light

    • Compact

    • Used by nearly all Baja teams

  • Drum brakes

    • Heavy

    • Bulky


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Braking Concepts

  • Single cylinder, dammed reservoir

    • Pros: simple, packaging flexibility

    • Cons: longer than dual cylinders

  • Dual cylinders, overhead mount

    • Pros: shortest overall length

    • Cons: aesthetics

  • Dual cylinders, floor mount

    • Pros: elegant packaging

    • Cons: longer, may conflict with steering components


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Braking Concepts

  • Rigid lines

    • Pros: Rigid, look good

    • Cons: Difficult to install

  • Braided flex lines

    • Pros: Flexible, easier to install

    • Cons: Heavier


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Braking Concept Selected

  • Polaris discs and calipers

  • Dual US Brake master cylinders

  • Wilwood reverse mount pedal

  • Braided steel flex line


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Safety

  • Braking

    • Two independent hydraulic braking systems

    • Capable of locking the wheels

    • No plastic brake lines

  • Drivetrain

    • CVT cover – made of polymer

    • Gas catch – made of polymer

  • Kill Switches

    • Two kill switches required

    • One in cockpit, one in rear


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Safety

  • Frame pads

    • The minimum required thickness is ½”.

    • The cost is $17.95 per 3 feet.

    • Need 6 feet.

  • Safety helmet

    • Motor cross style, Snell M2005 specification


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Safety

  • Fire extinguisher

    • Two 5 B-C extinguishers.

    • One must be mounted next to the driver and the other in the pit area.

  • Head restraint


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Goals and Deadlines

  • January 25 – complete design

    • stress analysis

    • CAD models

  • February 28 – drivable vehicle

    • rolls under its own power

    • basic safety gear

  • March 28 – competition-ready vehicle

    • meets all rules

    • fully functional, painted, polished, done.

  • April 8-11 – 2010 Baja SAE Carolina competition