The first project assigned this year in Survey of Engineering Academy was a warm up project to give us an idea of this class. We were assigned the goal of making a time delay switch. Basically we had to make a switch that will complete a circuit 30 seconds after the release of a marble. We were given certain rules, which we had to abide by. For instance we could not use prefabricated objects for their intended use (i.e. using a wheel off a toy car for a wheel on your project) and no human interaction after release of the marble. Otherwise we were given great room for creativity. Our projects were graded on accuracy, creativity, craftsmanship, cost effectiveness (how cheap it is to build) and use of class time.
When I embarked on this project I knew I wanted to keep it as simple as possible which would make it reliable, cheap and easy to build. My first idea was to delay the marble long enough for it to trigger the switch itself. We drew little sketches to convey our ideas to the other group members. Our group was thinking of building a series of ramps to achieve the goal. I knew this would not work very well because there is a lot of room for variation thus it would be hard to lock down 30 seconds. For instance, table level would play a great role in the time it takes the marble to travel through the ramps and this project will need to be moved around. It would also be hard to make small time changes on ramps. My group members agreed. I left class that day trying to think of a better way to achieve a 30-second delay. When at home sitting on the john I came up with an ingenious idea. I could use sand as a timer. The marble would sit on a platform on the sand that would be in a 20oz bottle. I would set the marble on the platform and pull a pin that would release the sand and lower the marble down through a hole placed lower in the bottle. Then it would go down a ramp and trigger the switch. I came to class with this idea but Mr. Katuna said the marble must trigger the beginning of the movement. I thought the rules were that there could not be any human contact after the marble is set in motion. But the idea of using sand was still good.
My partner then suggested an idea that many other groups were using. Have a teeter-totter with a weight on one side and a cup on the other. Above the cup would be a 20oz bottle with a hole cut in the cap. A marble would land on a mousetrap, which would pull a pin out of the cap. The sand would be release at a given rate and tip the teeter-totter that could complete the circuit. Over the next couple of days we implemented this idea. We made many mistakes, the project was too big making it hard to control. The sand also had many impurities that would deviate the rate of flow. It soon became apparent that we would need to try something else. The idea would have worked if we implemented it better but we didnt.
My partner then suggested using the conductivity of water to complete the circuit. A 20 oz soda bottle would be suspended over a bowl with a hole cut in the cap. A mousetrap would pull out a paper clip with tape wrapped around it, which would be wedged in the hole of the cap to start the water. One alligator clip would be resting on the bottom of the bowl and the other clipped on the side. The water would fill up the bowl until it reached the alligator clip on the side of the bowl. The water would complete the circuit and set off the buzzer. It was just a matter of timing how fast the water would fill up the bowl and complete the circuit. I liked this idea because it was a unique and relatively simple solution.
One major dilemma we encountered was retaining the water. The plug we built would stick if put in too tight and leak if put in too loose. We aided this but did not solve it by putting an eye hook by the bowl so the string would be pulled in a more vertical motion rather than horizontal. The leak was not completely fixed but was minimized. Another problem we had was when we glued a stick standing vertical in the bottom of the bowl. When the stick got wet it would set off the buzzer before the water hit the clip. We fixed this by wrapping masking tape around the stick to shield it from the absorbent wet wood. This worked pretty well but the tape had to be dry. Also you had to be very careful on how you placed the clip. If it was slanted the wrong way it acutely changed the delayed time.
On the testing day our project was a great disappointment getting 24 and 26 seconds. One enigma was that the buzzer turned on gradually with a slight hum going to full loudness as the water seeped over the clip. The timers timed it at the slight hum which rather than the full buzz. This problem we did not experience in our testing. The other big problem was the leakage factor; we put the plug in very loose to be sure it would not stick but it leaked generously.
If I were to do this project again I would change many things. First and foremost I would create a leak free, reliable plug for the cap. Maybe some sort of valve that would open up and leak through a hole under it. Also I would not use alligator clips in the water because they can be very unpredictable. I think bare wire wrapped around the dowel would work best. Also I would have liked to get many more trials and liberate our switch of any other bugs and lock down the 30-second time. All this may have been accomplished if our group used our time more wisely and built the prototype quick and fixed all the bugs. Our group spent too much time on the discarded project and did not spend enough time in testing the new project.
At first our group dynamic was great, we shared our ideas and explored their effectiveness, but later when we started fabricating the project our individual ideas on how we should execute it clashed. For instance, on our first project, which failed, I thought we were making it too big and they thought it was just right. We fought for awhile on the size of it, and we compromised by cutting the teeter-totter down smaller. My group members thought I should do all the drawings and the handouts because I am the junior. I suggested we should share the work. In the end we shared the work evenly and it worked out very well. Overall, there were not too many disputes and we worked together very well. My role in the group was more of an idea man rather than a builder because I could not use the power tools. The decision making was done collectively as a group which worked out very well.
I believe this project taught me a great deal about basic engineering ideas and how to have an idea in your head and bring it to reality. I learned how to make scale drawings correctly and how to take the drawing and bring them to life. This project helped me with developing my creativity, the criteria was so open that it let us explore our creativeness. I also improved my teamwork skill including compromising my ideas to fit with others, which will be a huge asset in future projects. Many of our ideas came from other projects, we saw a good idea and adjusted it to fit our project. I think it is a valuable skill for an engineer to see what is around him and get ideas from it. We made many mistakes in our project, which tells me I learned a lot. I think the best way to learn is through your own mistakes.
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