PT 2.3 - Construction Of Car

Construction of Initial Prototype

The picture above shows the materials that we bought from Art Friends for this Mousetrap Car experiment, these materials include:

         -    3 large styrofoam wheels
          -    3 small styrofoam wheels
     -    2 large wooden boards
-    2 long wooden rods
  -    1 long wooden plank

Cutting out the chassis

The picture above is one of our members cutting the block of wood, to create a frame for the mousetrap. 

Steps to do this :
1. Measure a few centimetres away from the edge of the wood 
2. Cut away the wood in the middle.

After cutting away the middle part of the wooden block, we had to create holes for the axle of the car to pass through, as shown in the picture above. We created the holes by drilling through the wooden block. First off, we started by using a small drill bit to make the marking on the block to ensure that it is centralised. Afterwards, we increased the size of the drill bit and continued to drill the wooden block until we created the holes for the axle. 

Designing the wheels 

After creating the holes for the axle, we had to start creating the wheels of the entire mousetrap car. One of our members started by cutting thee styrofoam wheels in half as they were too thick and would cause the entire mousetrap car to be out of size. Another member would then mark the center of the styrofoam wheel and drill a hole in the middle for the axle to pass through.

As we soon realised that our initial design will not be able to work, we changed our idea but we still adopted some parts of our initial design.

Construction of 2nd Prototype

Chassis of the car
In the initial design of the frame, we realised that by using so much wood, we will be weighing the mousetrap car down, thus, we changed the frame to the one in the picture above.

Since we changed the frame of the mousetrap car, we had to figure out a way how to attach the axle to the frame. An idea that we came up with was to cut tiny pieces of the wooden plank and drill hole in them and attach them to the frame and put the axle through them, with the wheel. 

For this design, we had to create an axle holder to hold the axle which will be used to hold the axle that will be attached to the wheel itself. Thus, we decided to use straws to be the axle holder. However, the problem lies with the size of the straws that would fit the axle that we have. We searched high and low, going into shopping malls and drink stalls just to collect different type of straws to find the perfect one that fits the axle. 

In order to prevent the wheels from moving towards the frame when it is on the go, we added a small cut out piece of straw which was put into the axle between the frame and the wheel. We also hot glued the wheels to the axle to ensure that they do not move away from their position.

The basic structure of our second prototype

The picture above shown is what was done after we completed the basic structure of the prototype.

Construction of Final Robot

When we assembled the entire mousetrap car together, we decided to change the small styrofoam wheels to lego wheels with gear ratios to increase the speed and distance. 

This picture above was what we prepared for the next day to test out the next day in school. We had some CDs prepared to be put onto the car in the case where the 2 large styrofoam wheels are not able to function well in enough to get the required score.

The picture above was when we are in school, and as we expected, the styrofoam wheels did not work well in the testing field even though on flat ground, it managed to reach a distance of 6.6m in just about 5 seconds.

As soon as we settled out final prototype which we thought need not need to be changed, we realised the mousetrap car was out of size. It exceeded the 30cm length limit.

One of our team members had to then bring the mousetrap car back home and figure out a way to make the entire mousetrap car smaller to fit the size limit of 30cm length. She then took out the gear ratio and moved everything back by a few centimetre, and the entire mousetrap car was in size! 

Final Mousetrap Car
Overview of the mousetrap car

Top View of the mousetrap car

Bottom View of the mousetrap car

Front View of the mousetrap car

 Back View of the mousetrap car

 Side View of the mousetrap car


Mass of mousetrap car332 g
Mass of each front wheel29g x 2 = 58g
Mass of each back wheel23g x 2 = 46 g
Wheel diameter (Front)8.4 cm
Wheel diameter (Back)12 cm
Axle diameter0.4 cm
Length of string28 cm
Length of lever extension10 cm
Overall length30 cm
Overall width15 cm
Overall height12 cm

Personal Testing Process of the Robot

Test Run 1Test Run 2Test Run 3
Total time of test run / s5s5s6s
Total distance of test run / m2.1m4.8m6.6m
Observation 1: Was the car in steady and stable motion throughout?YesYesYes
Observation 2:
Was the car moving in a straight line mostly?
Observation 3:
Did lever and string operate smoothly as well as expected?
State 1 area for modification.We changed the lever by extending it with a wooden stickWe changed the back wheels, from the friction lego wheels to the styrofoam wheels
State rationale(s) for the above proposed modification.To increase the amount of tension in the string, resulting in more distance travelled.There was too much friction in the back wheels causing in the lost of distance travelled, so we changed it to a styrofoam wheel which has lesser friction

Personal Test Run 1

Personal Test Run 2

Personal Test Run 3

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