CONCRAPTION
William Bragg, Dominic DePaoli, Janson Harless, Brian Paul
December 1, 2009
Section B2
Team 2
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Abstract:
The objective of this project is to obtain a more complete understanding of the
concepts learned in Engineering Fundamentals 151 by collectively devising and
constructing a Rube Goldberg device which follows a series of complex steps before
ultimately raising a banner. In order to accomplish this feat, the group utilized
inexpensive materials and the concepts of conservation of energy, conservation of
momentum, torque, center of mass and projectile motion. After overcoming several
challenges, a unique contraption was created and tested for repeatability and
reliability. Thus, a further understanding of physical concepts and the importance of
collaborative efforts was achieved.
Introduction:
The purpose of this project is to create an inefficient, complicated and yet creative
Rube Goldberg device which raises a unique banner. The criteria included the
incorporation of at least four physical concepts that were learned over the course of
the semester and at least five steps. The requirements also stated that the device
should fit in a 0.5m x 0.5m x 0.8m box when unassembled, though the project could
exceed these limits when fully constructed. It was also deemed necessary that the
device set up should not exceed a minute and could run safely without external
interaction.
The device is an agglomeration of the concepts which were learned throughout the
semester. The contraption is initiated when the previous group bumps the bolt of our
spring loaded projectile launcher. When the projected object hits a structure, a
washer is knocked off its center of mass, thus falling through a funnel into a cup upon
a lever. Torque is created to raise the opposite end of the lever which in turn hits a
Hot Wheels car. After slowly rolling down a short length of track, the car encounters a
Hot Wheels booster which creates angular velocity. The car races down the remaining
track until an inelastic collision occurs with a structure. The damage causes a mass
with gravitational potential energy to fall, therefore releasing kinetic energy. The
falling mass also serves to initialize the subsequent group’s project. The released
energy then initiates a pulley system which raises our banner.
Device Design:
When the group began brainstorming the contraption, the primary objective was to
raise a banner. Thus, the group swiftly decided to raise the flag in a manner similar to
the popular video game Super Mario World. Therefore, the preliminary sketch and
design concepts were based around this idea. After devising a blueprint and layout for
the various steps of the project, responsibilities were divided and costs were
distributed. Upon approval of the preliminary device design, the group began
collecting various parts and bought the items which were needed such as PVC pipe
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and Hot Wheels track. After constructing several steps in the design it was decided
that several ideas were trivial and were altogether abandoned. This included a series
of dominoes, a loop, and the Mario theme. Though the group stayed true to several of
the original design ideas, construction demonstrated slight modifications were
needed. These modifications included the addition of a cup to one end of the lever, a
funnel to ensure the coin fell into the cup, and a collapsible platform for the pulley’s
counterweight. After constructing all the needed steps the device was ready for
testing.
Device Description:
The device begins with a spring loaded PVC cannon. This cannon fires a projectile at a
K'NEX structure which is supporting a washer balanced on its center of mass. The
force applied from the projectile is transferred to the structure which upsets the
balance of the washer. The washer then falls into a funnel attached to the structure
to provide repeatability within the project. The funnel directs the washer into a cup,
which is attached to the moment arm of a lever. The torque produced by the falling
washer rotates the lever with enough force to knock the Hot Wheels car into motion.
Ergo, the car rolls down the track into a Hot Wheels Booster, accelerating the car
further down the track. The car then collides into a weak structure holding a weight,
this collision causes the structure to collapse. The weight triggers a series of pulleys
which raises the teams banner. The weight is also the trigger for the next groups
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project.
Analysis:
1. Conservation of Energy and Projectile Motion
1/2(M)(V)^2=1/2(k)(x)^2+MGH
V = 6.77385 ft/s
2. Collision
The coefficient of restitution is 0 due to an inelastic collision
therefore
(m1+m2)v'=m1v+m2v
v'=.1600
3.Torque
T=F x R , F =.125lbs , R = .5 ft
T= (.125)*(.5) T= .0625 ft-lbs
4. Angular Velocity
linear velocity= ω/r, ω=.795 rad/s , r= .0833
assuming no friction or losses
.795/.0833=9.54 ft/s
5. Conservation of Energy
The general law of a simple pulley is that the weight is halved for every pulley in the
system that changes direction; therefor, the starting weight in our system can be
pulled with one forth of the actual weight of the object. Also the distance for the
other object will travel four times the distance of the starting weight. With this law
you can apply conservation of energy equations. (I think)
(M1)(g)(h)=1/2(M2)(v^2)
v=13.8996 ft/s
4v=55.5986 ft/s
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Bill of Materials
Material
3/4" x 1' PVC Pipe
3/4" PVC Cap
Brick
Bolt
Duct Tape
K'NEX Set
Washer
Cardboard
Funnel
Wood Triangle
Wood Slat
Small Cup
Hot Wheels Set
(Track, Booster, Car)
Rope
Fishing Weight
Price (Dollars) Quantity
Total Price (Dollars)
0.25
1
0.25
0.6
1
0.6
0.75
4
3
0.5
1
0.5
1
1
1
2
0.05
0.05
0.38
0.25
0.25
0.05
1
1
1
2
1
1
1
2
0.05
0.05
0.76
0.25
0.25
0.05
10
0.05
1
1
10
0.05
1
0.5
0.5
Overall
Cost
19.31
Results:
Project testing quickly became a priority due to multiple moveable parts throughout
the project. It was decided that the device would run to completion ten times before
it was deemed reliable and ready for presentation. The first series of runs
demonstrated the need for some minor adjustments and repositioning of parts. After
several more tests, it became evident that the projectile launcher would need more
work, especially a larger notch for the trigger. After fixing this problem the device ran
smoothly, but it needed to be replicated in the same fashion to avoid error.
Therefore, the group traced out the precise layout of the device on a large piece of
butcher paper. This reduced the possibility of failure and ensured a quick yet exact
set up. In the presentation, the layout was extraordinarily helpful and the device was
set up swiftly and ran flawlessly. The device was successfully triggered by the
previous group’s device and aided in the initialization of the subsequent group’s
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device. Overall, the thirty plus test runs were vital to the group’s success both
individually and collectively.
Conclusion:
In conclusion, this project has enabled us to utilize principles learned this
semester and visualize concepts learned off paper. This project also gives
us a taste of working as a group as we will in an actual job environment.
We found that each persons perspective and ideas applied to a central
project greatly increases its effectiveness. This project was long but very
enlightening and fun!
Sources
Engineering Fundamentals Website; http://ef.engr.utk.edu