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Team ARMY Design Project |
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John Oliver, Michael Harrison, Dhruvraj Choudhary |
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Section A The objective of this design project is to build a vehicle that is powered only by stored elastic potential energy. Our vehicle will be designed to travel twenty-five feet from a start gate, cross a marker at the midpoint gate, reverse direction, and return to the starting as quickly and as accurately as possible. |
When building our car, we focused on the two main problems in order to fulfill the criteria of the design project: 1)enough power to propel the car forward twenty-five feet and 2) enough power to return the car back to the starting line.
Our method of propelling the car forward is very simple. A screw was drilled into the frame of the car for a cut rubberband to be fastened around. The rubberband is then wound very tight around the front axle and released to turn the axles and propel the car forward.
The return trip is much more complicated. Alongside the front axle of the car is a geartrain, intentionally built for the purpose of the return trip. On the frame of the car are two mousetraps with a plastic lever arm attached to the middle of the two mousetraps. A small metal rod is placed on top of one of the gears on the gear train that is used to set off the mousetraps after a certain number of rotations of the gearset. Once the car reaches twenty-five feet, the small metal rod will set off the two mousetraps, which in turn release the attached lever arm. This lever arm has a string drilled into it, which is wound around the rear axle. The string, lever arm, two mousetraps, and small metal rod are the components for the return trip. However, for the metal rod to set off the mousetraps at exactly twenty-five feet requires much testing.
Overview of the trip
The rubberband wound around the front axle propels the car forward the thirty feet of distance required. Once the car reaches the distance of twenty-five feet, the metal rod attached to the geartrain sets off the two mousetraps on the base of the car. These mousetraps spring forward the lever arm with the string rolled around the rear axle. This starts the return trip.
Testing and Different Prototypes
We made three different vehicles for the duration of this project:
Our first vehicle was more or less a complete failure. Our idea for the forward propulsion was to utilize a propeller. We took a significant amount of time in building this car only to find out that it did not move anywhere after testing it just once. We decided to scratch the propeller idea and completely start over.
Our second vehicle was not a complete success, but not a failure either. It was more of a test model. There were some very obvious problems to our second car: 1) it was built very sloppy, 2) the frame for the car was not very reliable, 3) the wheels were misalligned, 4) the geartrain was not always rotating in unison, and 5) the car's performance was very inconsistent. Sometimes it would travel the required twenty-five feet and return back to the starting line. Other times it would travel to the midpoint line and the mousetraps would be set off, but the string sround the rear axle would get caught up or the geartrain would lock up. Nonetheless, this was a great example of how we need to improve our next and final car for the competition.
Because this car was so inconsistent, we tested it numerous times in hope that it would perform well for the design reviews. The majority of the tests resulted in this car traveling twenty-five feet, but only returning three or four feet towards the starting line. However, we did get the car to perform the way we hoped at least once. One night we tested the car on the first floor of New House after we made some minor changes to the lever arm and string, making sure the string did not restrict the return trip by catching up on the rear axle. On this particular test the car traveled twenty-five feet and returned to the starting line in less than twelve seconds. That was the best time our second vehicle ever traveled and it never repeated that time again.
Learning from the mistakes of our first and second prototypes, we made our third car more reliable by building it very carefully. The frame is sturdy, the wheels are alligned straight, the geartrain rotates in unison, and the car performs more consistently. After testing our second vehicle more than twenty times, we found that it completes the course is less than twelve seconds very consistently. On average, our car will fault one time out of five or six trials and not return all the way to the starting line. Nonetheless, this is much more accurate and efficient than our first and second vehicles.
Our car works well because it is a simple design. Many times we thought of different ways to build our car that could work, but they were very complex ideas and were far-fetched. While working in the design lab, we noticed that some of the groups could not even get their car to move forward because they tried to utilize such a complex design. We stuck to the motto: "keep it simple stupid" and we are proud of how well our car performs, even if it is a simple model.
However, our idea for springing the mousetraps that are responsible for the return trip was a very novel idea. We attached a small metal rod on top of one of the gears on the geartrain, which was responsible for setting off the double mousetrap system. This is a very unique way of using the geartrain in more than one way. Of course, in order to use this idea, our geartrain must be properly constructed and it must be perfectly alligned with the corresponding mousetraps. This was very hard to construct because everything, even the small things, must be placed perfectly on the car in order for it to perform.
This project required hours of work and brainstorming. We can't even recall how many times we were excited to see our car built the way we wanted, but soon felt the effects of failing after our car did not perform the way we hoped and planned. The hardest part of this project was not the physical labor of building this car, or the time consumed, but it was the mental part. Our car failed us so many times, even after we reconstructed and tested numerous times. Succeeding in this project meant to keep a positive outlook and be mentally tough. We were downtrodden a lot because we thought we were never going to be able to make a car that works. We learned a lot about mental perseverance and finally built a car that performs adequately.
