The Hill- Charterhouse Challenge 2005: A year in review
by Tom Hutchinson, instructor of physics
The Charterhouse Challenge was a great opportunity for students. Although it is easy to look at the win and loss as a sign of success, what went on behind the scenes is actually where the real learning took place.
Last spring, shortly after Steven Hearn posed the second Hill- Charterhouse Challenge to the Hill community, a small group of students, including some of the best physics students at Hill, started to brainstorm about possible ways to "beat the British."
Each school had to build a device that would produce the most light energy. The rules required that all the energy used to produce light come from 30 seconds of student input. The energy had to be stored in some form because the light wasn't allowed to be turned on until the 30 seconds of student input was completed. In addition to these rules, there was a strict limitation on the amount of money that could be spent, and a limitation on teacher input. The group quickly broke the problem down into four parts: 1) how to maximize the amount of energy input by the student; 2) how this input would be converted to electricity; 3) how to most efficiently store this energy; and 4) what light to use to get the most out of the electricity. With the complexity of the task, everyone knew that there was a realistic possibility that after a year's worth of work the group might not be able to produce light.
The group considered many options in terms of student energy input. The first of the ideas involved lifting some form of weight to a higher place in order to gain potential energy. Thoughts included leg pressing a large mass; lifting numerous heavy objects up to a platform; carrying water to a raised tub; and lifting a light weight to a very high place. Each scenario had its strengths and weaknesses. Part of the group actually built a device in which water was raised up, and then as a stream of water fell, it turned a wheel connected to a small generator which powered a light bulb. The raising of weights method forced the group to look into the gearing that would be required to slow the fall of a large mass.
Since the different parts of the project were interconnected, the students were simultaneously looking into options for producing electricity. They actually built a generator around a cardboard box and another model using K'nex for all the moving parts. Since a generator requires a magnet, a lot of time was spent looking for the most powerful magnet possible. After several attempts at building a generator, the group decided to spend most of the allotted money on buying a generator. Even the smallest ready-made generators were easily out performing the student models. This still left the question of how to input and store the energy?
After deciding that the gearing needed to make lifting heavy weights workable was too difficult and complex, the group settled on using a bike as the form of student input. In this area, they were fortunate in terms of the allowed expenses. Hill Security had an accumulation of bikes that had been left at the School through the years, and the group was able to take one of these at no expense. From there they built a bike stand that was sturdy enough to support a sprinting student. This actually required a great deal of thought and time. Mike McKibben let the group use the backstage of the CFTA. He had the metal working tools that were necessary and Michael Garrett '05, one of the students in the group, had the expertise in using the tools.
The group was now able to produce a lot of electrical energy; however, the problem of storing it hadn't been addressed. With the winter term almost over, some members of the group started searching the internet for ideas of what kind of battery could best store this energy. A great deal of time was spent on this task, but about three weeks before the group was to leave for England, Jason Evans '05 talked to an electrical engineer who suggested that capacitors would be a lot better tool for storing this amount of electricity. Capacitors are very tricky for most physics students and there were many variables that needed to be considered concerning how to handle these objects. With winter exams fast approaching, there wasn't much time for testing theories of how to best use the capacitors. As the group left for England for the first round of the Challenge, the group was still analyzing the capability of the capacitors.
With a variety of LEDs in tow, the decided light source, our group worked hard to in putting the capacitors together, but in the end The Hill team fell short. It was clear that our group was producing a lot more electrical energy than the Charterhouse group, but our group had a problem with storing the energy.
When our group returned to Hill, we knew we could win the second round of the Challenge if we could find a way to effectively store the energy. After several trials back at Hill, it seemed like Hill had found the right combination of capacitors. In an unfortunate turn of events, the success we had during the trials did not materialize during the actual competition which took place on Monday, April 11. After the fact, it's now easy to hypothesize about what went wrong and left our group wishing that there was a third trial.
In looking at the year's experience both Steve Hearn and I feel that this has been a very worthwhile learning experience for both groups. There is a huge difference between being a physicist and being an engineer. In physics class, there is usually a correct answer that can be calculated, and this correct answer brings closure to the problem. In engineering, there is always a better solution, and almost never with closure. There are an infinite number of solutions and perfection is never reached. Unlike with solving physics problems in class, the process of solving engineering is rarely clean and involved a lot of just plain trial and error. The group was able to get a true feel for the mentality of being an engineer.
The group also learned a lot about electricity. Capacitors, voltage, farads, and coulombs are usually not much more than abstract formulas or ideas in class. To this group these concepts took on new meaning. They had a chance to get a feel for the actual cause and effect of these ideas. Although everyone associated with the project would have liked to have won, we all had a worthwhile and enjoyable time going through the process. The English team did a fantastic job.