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Suspension. D.J. Conroy. Last year. Designed with existing frame Did not use suspension analysis programming A-arms not easily adjustable Hard to assemble. This year. Design frame around suspension Find optimum geometry using Lotus Make adjustment, machining, and assembly much easier.

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suspension

Suspension

D.J. Conroy

last year
Last year
  • Designed with existing frame
  • Did not use suspension analysis programming
  • A-arms not easily adjustable
  • Hard to assemble
this year
This year
  • Design frame around suspension
  • Find optimum geometry using Lotus
  • Make adjustment, machining, and assembly much easier
geometry
Geometry
  • Analyzed using lotus software
  • Mounting points dictate much of the frame layout
most important aspects
Most Important Aspects
  • Camber
  • Castor
  • Toe
  • Roll center height
optimum settings
Optimum Settings
  • -1° camber (static)
    • 1° change per inch bump/droop
  • Front toe
    • -1° toe in static (positive with lotus sign convention)
    • Minimal change in bump/droop
  • 5° of castor
    • Minimal change in bump/droop
  • Roll center height of about 2 in
    • Stay positive through bump/droop
  • Converging A-arms
pentagon specs
Pentagon Specs:
  • Roll Center:
    • Static: 0.8in
    • 1 in bump: -1in
    • 1in droop: 0.7in
  • Camber:
    • Static: -1°
    • 1 in bump: -2.05°
    • 1in droop: -0.25°
  • Toe:
    • Static: 1°
    • 1 in bump: -12°
    • 1in droop: 14.5°
    • 1° roll: 6.5°
octagon specs
Octagon Specs:
  • Roll Center:
    • Static: 2.7in
    • 1 in bump: 1in
    • 1in droop: 4in
  • Camber:
    • Static: -1°
    • 1 in bump: -2.2°
    • 1in droop: .1°
  • Toe:
    • Static: 1°
    • 1 in bump: -5°
    • 1in droop: 7°
    • 1° roll: + 2.5°
octagon vs pentagon
Octagon vs. Pentagon
  • Advantages:
    • Lower and shorter (from bottom to top of frame)
    • Lower COG
    • Don’t need to worry about a raised front end
    • Better mounting of steering rack
      • Much less bump steer
  • Disadvantages:
    • Heavier
    • More frame members
my opinion
My opinion:
  • The couple extra frame members and 5 lbs max additional un-sprung weight is worth it to have a much lower center of gravity and much less bump steer.
a arm dimensions
A arm Dimensions
  • Upper:
    • Forward arm 15.08in
    • Trailing arm 14.70in
    • Difference: .38in
    • Angle: 51.7°
  • Lower:
    • Forward arm: 15.73in
    • Trailing arm: 16.09in
    • Difference: .36in
    • Angle: 48.2°
materials
Materials
  • Steel
    • Good:
      • Easy to weld
      • Cheap
    • Bad:
      • Heavy
  • Carbon Fiber
    • Good:
      • Light weight
    • Bad:
      • Expensive
      • Hard to bond to steel
manufacturing and assembly
Manufacturing and Assembly
  • Rod ends with built in spacers
  • Mill push rod mounts
  • Use steel or carbon fiber rods
  • Jig:
    • Accurate
    • 3 points
    • Could use mill table
adjustability
Adjustability
  • Exposed outer rod end:
slide28

Breaking:

    • tyre: 217.7 lb
    • Top arm: 114.3 lb
    • Bottom arm: 332 lb
  • Verticle:
    • tyre: 580.6 lb
    • Top arm: 290 lb
    • Bottom arm: 290lb
  • Lateral:
    • Tyre: 290.3 lb
    • Top arm: 152.4 lb
    • Bottom arm: 442.7 lb