PT 2.2 3 Designs and Decision making matrix

Design Criteria

Design Criterions we create will affect the distance travelled by the car

1) Size of the wheels
  • Use large rear wheels. Large wheels have greater rotational inertia than small wheels. In practical terms, this means that once they start rolling, they're harder to stop rolling. This makes large wheels perfect for distance-based contests — theoretically, they'll accelerate less quickly than smaller wheels, but they'll roll much longer and they'll travel a greater distance overall. So, for maximum distance, make the wheels on the drive axle very large.The front wheel is a little less important — it can be large or small. 

  • Use thin, light wheels. It's also important to take the weight of the wheels themselves into account any unneeded weight will ultimately slow our car down or lead to added friction. In addition, wide wheels can even have a small negative effect on the car's drag due to air resistance. For these reasons, we have to use the thinnest, lightest wheels available for our car
    • .Old CDs or DVDs work fairly well for this purpose — they're large, thin, and extremely light. 
2) Frame of the Mousetrap car 

  • Building the lightest frame. Our car should be light. The smaller the mass of our car, the better.  We will try not to have any extra frame material beyond what's necessary to keep our mousetrap and wheel axles in place. We will also want to use the lightest material possible for your frame. Here are just a few suitable ones:
    • Balsa wood
    • Hard plastic sheets
    • Thin, light metal sheets (aluminium/tin roofing material, etc.)
    • Building toys (K'NEX, Legos, etc.)
  • Making the frame long and narrow. When the frame of our car is narrower, there will be lesser air resistance acting on the mousetrap car.  For the purposes of our mousetrap car, this will mean making our frame both narrow and vertically skinny.
3) Power for the mousetrap vehicle 

  • Long arm for increased leverage.  Most mousetrap cars work as follows: the mousetrap is "set", a string tied to the arm of the mousetrap is carefully wrapped around one of the wheel axles, and, when the trap is sprung, the swinging arm of the trap transfers its energy to the axle to turn the wheels. Since the arm of the trap is fairly short, if the car isn't carefully constructed, it can pull on the string too rapidly, causing the wheels to slip and energy to be lost. For a slower, steadier pull, we will try attaching a long pole to the arm to act as a lever, then tying the end of the string to this, better than to the arm itself
  • Positioning the trap as far forward as possible. Assuming that our trap will be turning the rear wheels, we will want our car's mousetrap to be far forward on the frame as it can be without touching the front wheels. The longer distance between the trap and the wheels, the better — more distance means we will be able to loop more string around the axle for just a little extra slow and steady pulling power.

We have come up with a few designs with different capabilities :

Design 1
Design 2
Design 3

Here is our evaluation and decision matrix

Evaluation matrix                                                            Decision matrix

We chose design 3 in the end

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