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The Trebuchet
Over the course of this semester, you will build a trebuchet, which is
a type of catapult used in medieval times to destroy fortified castle
walls. You will be destroying the Administration Building... just
kidding. You will build a trebuchet to launch a projectile of your
choosing. Project rules
are provided below, but first let's learn a little about these things.
In the above animation (from Siano, Donald B., http://www.algobeautytreb.com/,
2003), a beam is supported asymmetrically by some structure that allows the it
to rotate at the point of suspension. From the short end of the beam a
counterweight
(the large ball above) is attached. A sling is attached to the other
end of the beam, in which the
projectile is placed. The sling/projectile slides, ideally, along a track
(rather than the ground) until the beam rotation causes them to pivot, at a high
rate of speed, around the trebuchet and hopefully be hurled in the right
direction (not straight up!). A
trebuchet transforms potential energy (stored in the suspended weight)
into kinetic energy (the flying missile). Here
is another description about how this particular type of trebuchet works.
Competition Rules
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There are two competition components: maximum distance and accuracy.
In the first, both maximum distance and trebuchet efficiency will be
scored. For accuracy, the goal is to land the projectile in a
five-gallon bucket from a distance of 75 feet. |
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The projectiles will be
tennis balls. |
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Counterweights can be no more than 25 pounds. More than one can be
used. |
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The
trebuchet must be triggered remotely (e.g., by pulling a string) from a distance
of 20 feet, or 10 feet beyond the length of the long arm of the beam plus
the sling length, whichever is longer. |
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Only
falling weight trebuchets are allowed (no springs, inner tubes, twisted
rope, etc.). Both fixed and floating-arm trebuchets are permissible.
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Trebuchets must be pre-constructed (no field assembly) and easy to
transport in a standard pickup truck. |
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The
total construction budget must be less than $20.00; save your receipts and
the CE department will reimburse your team. Free, legally
scavenged, and donated materials are acceptable. Monetary donations are not
allowed. |
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For both the distance and accuracy components, each
team will have 2 practice shots and 3 scored shots on the day of the
competition. No repairs allowed during the competition. |
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Each
team must have a Professional Engineer review and initial the construction
details before building the trebuchet. Un-approved designs
will not be allowed to compete. Note that most CE faculty at
UI are Professional Engineers. |
Design Process
This project is like many design projects you will encounter, in that it
requires that certain steps be taken to successfully complete the project.
Here are the steps (Hyman, 1998):
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Recognize
the need. In this case, you need to complete the design project, as
defined, to pass the class. In Civil Engineering practice, the need
is typically based on serving the public needs in some manner (need to
build a road, need to treat the water, need to construct a hospital,
etc.). This step is where the purpose is
established. |
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Define
the problem. Clearly identify the goals, objectives, and constraints. |
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Plan
the project. Break the project down into manageable tasks, and
establish starting and ending dates for each task. Note that in
order to start a particular task, it may be necessary to first complete a
different task! |
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Gather
information. There is usually information available from similar
projects, but each design situation is unique. |
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Develop
design alternatives. Based on the goals, objectives, and
constraints, a range of design alternatives are conceptualized. |
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Evaluate
alternatives. Each alternative must be evaluated with respect to the
goals, objectives, and constraints. For this project, your should
predict how accurate each alternative will be using analytical skills -
since you have not yet constructed the trebuchet at this point, you need
to somehow model how it will behave. Also, economic
considerations are critically important at this stage of design. |
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Select
the best alternative. Based on calculations made in the previous
step combined with engineering judgment, the best alternative is selected. |
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Communicate
the design. Civil Engineers must communicate the results of their
work clearly to clients, colleagues, government and regulatory agencies,
and the public. Effective oral and written communication skills are
essential. |
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Implement.
In this step, the preferred alternative is executed, tested, analyzed, and
modified if necessary. The "as-built" performance is compared to the
predicted/modeled performance. |
Project Evaluation
Each team's project will be evaluated based on the following criteria:
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Competition results/performance (20%) |
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Finished product: aesthetics, creativity, and lightness/mobility (20%) |
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Written project report (40%) |
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Oral
project presentation (20%). |
The written report will be evaluated for technical correctness, quality of
writing, quality of presentation (formatting, graphics, etc.), and
completeness. It shall contain the following components:
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Title Page. Includes title, team members' names, date.
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Summary. |
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Table of Contents. |
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Introduction.
Includes the problems statement and objectives. |
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Design.
Discuss design alternatives, performance predictions, calculation
summaries, limitations, and constraints. |
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Construction
details. Can someone else build your design given the information
you provide in this section? |
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Results.
How did it work? |
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Conclusions.
Based on the results, describe what could be done to make the design
better. Also discuss how the performance could have been better
predicted. |
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Appendixes.
For this report, there must be at least two: one for detailed
calculations, and another will be an itemized list of all components
indicating material source and cost. |
Schedule
Please see the Schedule page.
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