First prototype: It did not move forward as there was no traction on the wheels. I came to the conclusion that this was as there was no weight pushing down the wheels. When the weights were added, the cart moved more than when there wasn’t weight.
From the previous trials, I came to the conclusion that possibly it was the result of the wheels not being good enough. I put in small wheels that had traction, were bigger, and actually meant to be used in this sense. I also thought, that if small metal rods that would be used to connect the wheels would run more efficiently as there would be less friction between the metal and the straw. This idea did not work as the rubber band had no grip on the metal rod. Even with glue, the grip was very weak, which resulted in no movement.
I went back to using wooden skewers as the axle. I still used the rubber band to build up the tension. After getting some feedback from other people, I was able to come to the conclusion that the cart could go further. There was another issue that was brought to light: the car would go backward after it went forward. I was unsure of how to fix this issue, so I build a pulley system that would pull up when pulled back but would drop once the car began to move forward. This system was very complicated, fragile, and malfunctioning often. With time running out I decided to try a different approach to the issue. I asked my teacher who gave me the idea that possible it was the rubber band that was causing this issue. With this in mind, I decided to focus on the rubber band and how it dictated how the car moved.
I’m not one hundred percent sure of why the rubberband would continuously have the car go backward, but I came to the conclusion that there was so much tension that was built up in the band when released it created the force to pull the car forward. But often there was a lot of energy created so the momentum would keep the car moving forward, which would then rewind the band. Once the band would reach its limit it would propel the car backward. Though with this explanation I’m still confused as to why the first prototype (when the weights were added) did not go back as well. I think that it didn’t go backward because there wasn’t enough force or tension.
This prototype was more of an accident in the way that it came about. I was using a little bit of elastic band to push down a stopper in the pulley (from the third prototype.) When I began to fiddle with the elastic band, which gave me the idea that possibly the elastic band could replace the rubber band. I also made the skewer smaller so the wheels would be closer to the body. This prototype is the most efficient one, as it goes the furthest, the fastest and is very resilient.
This is a video that shows the prototypes that I created.
Final thoughts/Reflection: I think that the first prototype was a very naive approach to this project, as I only looked at three similar creations other people did. I don’t think though that it added much to the later on prototypes though. The second prototype was a better starting position than the first prototype. The third prototype by far was the most tedious on out of all the prototypes; it was very confusing, not well planned, very different than what my original plan was, and took a very long time to create despite there being no benefit of it. The fourth is what I would also like to consider as my final product as it is the most efficient prototype that I created in this time limit. I still think there are areas where I could do more though to improve it, I would need to do more research on what other people have done and compare the results. Also, I’m a little saddened by the fact that I was unable to create a top for the car.