PT1.2 - Engineering Goals

Part 1: Brainstorm design criterion
1. Weight
  • Strong so that it can withstand the force of the wound up the mousetrap spring yet light so that it would not create so much air resistance and friction
  • However, it cannot be too light as weight is needed for the wheel to be in contact with the ground at all times
2. Wheels
  • Number of wheels
    • 4 wheels improve stability
    • 3 wheels
      • Tadpoles: 2 wheels at the front, 1 at the back. Because they taper off towards the back, they let air flow past them. The air parts at the front of the car, and flows smoothly inwards towards the back. The car is extremely aerodynamic, especially at higher speeds. The two wheels in the front make the overall design stable while the back wheel is attached to the engine and accelerates the car.
      • Deltas are the opposite, 1 wheels at the front, 2 at the back.
  • The diameter of the wheels
    • Large diameter makes fewer turns over the same distance compared to smaller diameter wheels. Therefore, less energy is needed to overcome friction and hence, allow a vehicle to travel longer distances.
    • However, large wheels mean that amount of torque necessary to begin rotation increases as well. A smaller wheel is, therefore, easier to turn.
  • Traction
    • Smooth Tires: Smooth tires produce less friction which increases the distance of the mousetrap car. 
    • High-friction tires will produce more traction. The highest acceleration of the mousetrap car is affected by the traction of the wheels on the surface it is on.
3. Gears
  • Useful for long distance as they increase the overall torque
  • Disadvantage for when speed is needed as they principally serve to create more friction between the components
4. Materials
  • Wheels
    • Thin and light
    • Try to remove mass from the wheels, the wheels would then require less force and energy to accelerate. This will allow the car to travel further and hence improve its performance. 
  • Arm 
    • Inflexible so that it can pull the string without flexing and therefore, it might affect the distance travelled. However, it must then be strong so that it will not break.
5. Shape
  • Shape of chassis
    • Aerodynamic so as to produce minimal air resistance
6. Size
  • Lever Arm
    • Short: Shorter distance moved by the arm while the mousetrap is releasing. However, the distance travelled after the mousetrap is fully released the distance is larger that a long lever arm
    • Long: Larger distance moved by the arm while the mousetrap is releasing. However, the distance travelled after the mousetrap is fully released the distance is smaller that a short lever arm. However, if the lever is too short, it will spin out.
- Axle
    • Smaller diameter than the wheels so that it will increase the distance travelled by car but only when a large wheel is used too as it will allow the same amount of string to make more revolutions around the axle and therefore, more distance covered than a larger axle. 
    • Larger diameter axles paired with small wheels results in less force to accelerate the car
7. Conclusion
  • Long distance but slow build
    • long lever arm
    • small axle with large wheels with little traction
    • gearing
  • Short distance but fast build
    • short lever arm
    • large axle with small wheels with high traction
    • Direct connection between arm and drive axle
Part 2: Engineering goals
Using the Engineering Design Process, come out with 3 unique mousetrap car designs that fulfil the following competition specifications:

  1. Uses only the MouseTrap provided as the only energy source
  2. Has a maximum length of 30 cm, width of 10 cm, and a height of 10 cm
  3. Mousetrap car must move off from the rest powered by the drivetrain without any push/pull from student

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