pt2.3 - construction of car

Construction process:

in the beginning, we decided to make a 3-wheeled car with 2 bigger rear wheels and 1 smaller front wheel. we used wood for our axles and chassis. however, during the testing, the axle where the string was pulling on bent, so the wheels misaligned and the chassis warped. we then realised that the wooden axle would not be able to support the force of the mousetrap pulling on it, thus we decided to make a few modifications.

first, we decided to change to metal axles, so that it would be able to withstand the force of the mousetrap string pulling on it. we also decided to use 4 wheels instead, as the car with 3 wheels was quite unstable, wobbling from side if we exerted weight on it. lastly, we also decreased the size of the wheels, so that it would increase the speed of the car.

Final Design:

Wheels: we decided to use styrofoam discs for the wheels as they were the cheapest and lightest material that we could find. however to further improve it, we stretched balloons and placed them around the discs to increase traction, as the styrofoam itself was quite tractionless.

Chassis: Balsa wood pieces with a wooden plank connecting them to support the mousetrap. we decided to use balsa wood pieces and a hard wooden cardboard as they were also the cheapest and lightest material that we could think of.

Lever arm and string type: Carbon Rod for Lever arm and Cotton twine for string. the carbon rod was strong so it would be able to withstand the constant snapping of the mousetrap and at the same time, not break into two. we also used cotton twine as it was soft and rough, so that it could wrap around the axle smoothly but yet be able to have enough friction between the string and axle so that the axle would move.

Axles: Metal rods for axles. they are actually aluminium tubes with carbon fibre rods in them, so this strengthens the axle to be able to stay together and withstand the strength of the mousetrap and string pulling on it.

Positioning of mousetrap: Front-mid to allow longer lever arm but still maintain good centre of balance.

  • mass of mousetrap car: 190g
  • mass of each wheel (or one if they are all the same): 5g per wheel; 20g for 4 wheels
  • wheel diameter: 6cm Diameter
  • axle diameter: 3mm
  • axle length: 12cm
  • length of string (from end of lever to axle): 30cm
  • length of lever extension: 12.5cm
  • overall length: 26.5cm
  • overall width: 15cm
  • overall height: 6cm


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