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Gravity Vehicle Science Olympiad 2012. Coaches Workshop October 22, 2011. Egg-less Scrambler. Similar to former event “The Scrambler” Come closest to reaching target Scoring based on time and distance Lowest score wins Distance announced after impound Braking mechanism can be employed

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gravity vehicle science olympiad 2012

Gravity VehicleScience Olympiad 2012

Coaches Workshop

October 22, 2011

egg less scrambler
Egg-less Scrambler
  • Similar to former event “The Scrambler”
    • Come closest to reaching target
    • Scoring based on time and distance
      • Lowest score wins
    • Distance announced after impound
    • Braking mechanism can be employed
    • No electrical components
  • Major Differences:
    • Propelled only by its own mass

(gravitational potential energy)

    • Teams must build ramp with release mechanism
construction the ramp
Construction: The Ramp
  • Material: smooth to reduce friction (waste energy)
    • Plastic, metal, wood, plexiglas, etc
    • Too smooth=bad tracking
  • Ideally adjustable
    • Perhaps hinged to adjust slope (i.e. lounge chair)
  • Shape: Where is mass concentrated?
    • Flat- simple design, easily adjustable
    • Curved- maximize PEg
construction vehicle chassis
Construction: Vehicle— Chassis
  • Rigid is good– propulsion will cause stress
  • Material: plastic, wood, metal, plexiglas, etc
  • Structure: flat board, box style…
    • Make sure axles are ‘square’ to direction of travel and parallel to each other
  • Design idea:
    • Build car in 2 halves with bolt connecting axles
construction vehicle axles
Construction: Vehicle — Axles
  • Rigid and straight
  • Crooked axle = crooked path
  • Materials: wooden/plastic dowels, metal rods
  • Axle-Chassis attachment:
    • 1.) Drill holes in chassis, feed axle through
    • 2.) Attaches tubes to chassis– straws
construction vehicle wheels
Construction: Vehicle — Wheels
  • Friction is the enemy
    • Straight and light-weight
  • Ideas:
    • CDs- spin well, but need traction
      • Strips of latex balloon
    • Hobby airplane wheels
    • Home-made– only if perfectly circular
  • How many? 3 or 4?
  • Thick or thin?
    • Depends on chassis design
braking general principles
Braking — General Principles
  • Braking mechanism can’t be used to propel vehicle
  • Don’t lose contact/normal force
  • Higher normal force=faster braking
    • Keep center of mass closer to front axle
  • Minimize Skidding
    • Kinetic friction dependent wheel-surface friction instead of braking mechanism
    • Decreases stability
    • Fix it by relocating/adding mass- modeling clay
  • Brake pads for smoother stops
  • Too much brake=Newton’s 3rd Law
  • Take tips from Scrambler
construction braking systems string method
Construction:Braking Systems — String Method

String from one axle unwinds and wraps around the second axle. Fed through, axles lock, car stops. Distance traveled controlled by the amount of string.

  • Easy construction
  • Easy to implement
  • Easy length adjustment
  • Poor accuracy
    • wrapping variation
  • Backlash
    • When string goes taut
  • Skid
    • Relies on wheel traction
construction braking systems threaded rod method
Construction:Braking Systems — Threaded Rod Method

Uses a threaded rod for the axle, wing nut on the axle. Rotation of wheels = horizontal motion wing nut. Wing nut reaches a barrier, stops the axle. Distance set by wing nut placement.

  • High accuracy
  • Consistency
  • Easy length adjustment
  • Little backlash
  • Harder to build
  • Axle friction
  • Skid
general tips
General Tips
  • Test on various surfaces—gym floors, hallway tile
    • Chart data for each; better idea on race day
  • Clean floor— dirt/dust affects braking
  • Calculations– divide race length by wheel circumference to get # of rotations
  • TEST and TEST AGAIN!
  • Don’t DQ! Read rules carefully
    • Dimensions include starting point
    • Release mechanism- actuated by pencil
    • No loose pieces
    • Vehicle mass < 2.500 kg
  • Have fun!
  • Event Coordinator: Betsy White– bwhite6@utk.edu