PT2.3 - Construction of car

Prototype:
Mass of mousetrap car
180g
Mass of each wheel
15g
Wheel diameter
12cm
Axle diameter
1cm
Length of string
33.5cm
Length of lever extension
0cm
Overall length
31.7cm
Overall width
14cm
Overall height
12cm

Photos of prototype:



Test Run 1:
Run Number
Test Run 1
Total time of test run / s
2
Total distance of test run / m
2.3
Observation 1:
Was the car in steady and stable motion throughout?
Yes
Observation 2:
Was the car moving in a straight line mostly
No
Observation 3:
Did the lever and string operate smoothly as well as expected?
Yes
State area for modification
Add more glue on the wheel onto the axle and add duct tape


Rational for modification

Although we had already added glue to the wheel in order to stick it onto the axle, the wheel still moved flimsily and caused the car to change directions. In order to improve on this, we had to add more glue on the wheel onto the axle, increasing the surface area of glue that is attached to the CD, this would then allow the wheel to stick more firmly onto the axle and thus, prevent the car from moving flimsily.We also found out that the testing site for the mousetrap car was made of tarmac which was rough and uneven this could have broken the wheels of our mousetrap car which were CDs. We then decided to surround the car with duct tape to hold the discs together and prevent it from breaking. Duct tape was also thin and durable, thus not affecting the shape of the wheels that much.


Video



Test Run 2:

Run Number
Test Run 2
Total time of test run / s
2
Total distance of test run / m
2.6
Observation 1:
Was the car in steady and stable motion throughout?
Yes
Observation 2:
Was the car moving in a straight line mostly
Yes
Observation 3:
Did the lever and string operate smoothly as well as expected?
Yes
State area for modification
Increase length of string













Rational for modification

The car went further this time, roughly 3.5 metres. This improvement was achieved with the use of a lever arm. We theorised that by adding a lever arm, this would increase the amount of string that would be able to coil around the axle thus increasing the number of times the wheels would turn and hence increasing the distance travelled.

Test Run 3:

Run Number
Test Run 3
Total time of test run / s
3
Total distance of test run / m
3.5
Observation 1:
Was the car in steady and stable motion throughout?
Yes
Observation 2:
Was the car moving in a straight line mostly
Yes
Observation 3:
Did the lever and string operate smoothly as well as expected?
Yes
State area for modification
Reduce friction and increase the distance travelled by adding a flinging action so that the car could continue to move after string unwounded.











Rational for modification 

Our group realised that the attachment of the string on the rear axle by hot glue would cause the car to come to a complete stop once the mousetrap closes and the string runs out. Initially, we wanted to increase the length of the lever arm to allow more string to be coiled and thus increasing the distance but this would cause the mousetrap car to exceed the length requirements. In the end, we managed to come up with an idea that would allow the car to move further than before, even after the mousetrap closes. This was achievable by adding a metal pin to the rear axle. The end of the string would poke into the metal pin and coil around the axle and when the string runs out, it would unhook from the metal pin which was attached to the rear axle and fling forward. The moment created by the flinging action would then cause the car to continue to move forward even after the mousetrap closes. We also realised that due to the fact that we had hot glued the wheel to the axle, it also increased friction exponentially. Therefore, we added WD-40 (A very powerful lubricant) onto every single axle.  Thus, we would be able to attain better results with these final improvement.


Video


Graph

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