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Case Study 1: The Xpult Challenge
EM451 Section 1, 10/6/16
The Dream Team (’92 Bulls)
Clint Hobbs
Zach Peck
Jared Carson

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a. Introduction
Utilizing an Xpult catapult, our team was tasked with launching a projectile 90 inches, into a plastic basin.
We are given the opportunity to adjust the catapult and the basin in order to maximize our successful
attempts. The number of successfulattempts to gain extra credit is 10 consecutive shots made.The
problems presented by the case study are as follows:
(1) Determine the set of specifications of the four design variables that result in launching a ball
into the bucket. (Xpult Challenge, pg1)
(2) Identify the sources of variation that affects the catapult launching performance with the aid
of a cause-and-effect diagram. (Xpult Challenge, pg1)
(3) Identify and (ideally) implement for the most significant sources ofvariation a
countermeasure that helps to reduce the launching process variability with the aid of an
affinity diagram. (Xpult Challenge, pg1)
(4) Videotape your best attempt of successfulshots and document the results. (Xpult Challenge,
pg1)
b. Description of the initial experimental approach
i. Team members’ roles (shooter,retriever, measurement recorder, scriber, etc.)
Jared Carson: Shooter, modifier
Clint Hobbs: Videographer, Editor, Scriber
Zach Peck: Retriever, measurement recorder
These roles were switched through, so everyone would get a chance to improve the shot and
understand what modifications would need to be made to make 10 shots successfully.The above
roles were the winning combination.
ii. Initial factors and levels selected (answer questions 1 and 2 from Section IV)
1) There are a lot of parameters that can affect the Xpult catapult, which can drastically alter the
shot and consistency.We compiled a list of all the things that did happen,and could happened
during this process,which can be seen in our Cause-and-effect diagram in Appendix 1a.
2) For a visual aid on the description below please see Affinity diagram, see Appendix 1b. We tried
3 methods, of which we altered pullback angle and the amount of rubber bands,seen in Appendix

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1c. To alter the pullback angle we used a combination of a recycling bin, a notebook,the Xpult
box, and a calculator. For our finalized pullback angle, we used a calculator instead of the Xpult
box. This set up and can be seen in Figure 1. We also did not use water in our bucket; instead we
taped this down with duck tape. This gave us an advantage because ourball did not get
inconsistently soaked with water, which can be seen in Figure 2.
Figure 1 Figure 2
iii. Lesson learned (describe any difficulty you had during the initial experiment and identify which factors
and levels will be considered for the designed experiment – you should consider only two levels per factor
selected).
In measurements on the affinity diagram (see Appendix 1b), we initially noted that shots tended to
skew to the right and undershot.This challenge presented the opportunity get some sort of basic metric on
where the ball might land, so we could make adjustments. We began to mark where every shot landed to
understand howcertain adjustment affected the overall performance of the Xpult. With the shots marked,
we began to make decisions based off the general trajectory of each volley and get closer to a uniform,
well-placed shot. Initially we did not keep this kind of metric, but due to excessive time spent on failed
attempts, it seemed like the next step.The lesson learned is that it is never too early to include data
gathering in an experiment.
c. Experiment
i. In executing our experiment we focused primarily on a trial-and-error process.We wasted no time in
setting up our catapult and getting launches off right away. At first we started small with just two rubber
bands and a launch angle of 60 degrees and a pullback angle of 70 degrees.After 5 launches we quickly
noted the distance wasn’t close to where it needed to be and to compensate we added a third rubber band
and decreased the pullback angle to 60 degrees.After 10-15 launches we knew we were close and only in

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need of a minor tweak. We increased the pullback angle to 65 degrees and were able to achieve the perfect
distance.At this point we were then faced with anotherobstacle. All of our shots were fading off to the
right of the target. After some deliberation, we noted that the catapult itself was shifting after each shot.
Our clamp at the time was at the end of the catapult, and to solve our problem of the catapult shifting we
simply moved the clamp more towards the center of the base of the catapult. From here it was smooth
sailing as we hit our next 14 shots in a row. An important thing to note is that all three group members took
turns launching the catapult,but in the end Jared proved to have the magic touch. Clint took on the role of
videographer, while Zach was in charge of recording measurements and retrieving the balls. In all, the
entire execution of our experiment took roughly 15 minutes.
ii. 1) Refer to attached cause and effect diagram.
2) Refer to attached affinity diagram
3) Our design variables in this case were the launch angle, pullback angle, amount of rubber bands used,
and the type of ball used.I would say based on our experiment that our design variables were ideal for
hitting our target 10 times. Having said that,we did achieve this feat in only 15 minutes, and therefore it is
safe to assume that with more time we could have found even betterdesign variables and hit the target
maybe 20 times rather than our 14 times.
iii. Video Link: https://www.youtube.com/watch?v=3LU_0TK7GD8&feature=youtu.be
d. Final remarks
i. The challenge could have been difficult or time consuming without good teamwork and a good sense of
trajectory/modifications that could potentially be made. Before even working on the Xpult, we all had ideas
of how to tweak the shots and adjust the catapult. Everyone on the team contributed evenly to the case
study as well.
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e. References
1) Martinez, C. (2016, January 26). Case Study1: The Xpult Challenge. Retrieved October 6, 2016,
From https://moodle.clarkson.edu/pluginfile.php/430642/mod_resource/content/1/Case study report
formatting guidelines.pdf
f. Appendix
1a.

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1b.

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1c.