Keshia Agazuma
Elias Askins, IV
Stephen Bridges
Kevin Stilwell
EF 151, B1
Our Rube Stamper: “The Construction Zone”
Objective:
Create a Rube-Goldberg device that, once activated, runs through a series of steps
to stamp a 5” 8” piece of paper without any outside interaction. Using a budget of $20,
the team had to construct a device that accomplished this task within a .3m  .5m  .3m
constraint.
Description:
Construction Zone is a device that incorporates projectile motion, conservation of
energy, and conservation of momentum all into a few short, yet effective, steps. A
marble is launched out of a shooter into a stationary, weighted tennis ball. The tennis ball
is knocked onto a spring-loaded platform that is pushed down under the weight of the
tennis ball, stamping the paper in the process.
Design Process:
We initially set out to design a Rube’s Stamper inspired by pinball machines, but
quickly ran into complications with the projectile motion aspects of pinball. Our device
was originally designed to shoot the “pinball” vertically, but we could not create enough
energy within the system we designed to propel an object upward. We then decided to
create a “shooter” that would launch horizontally instead of vertically, giving us an
opportunity to create the required energy. After settling on how to incorporate projectile
motion, we then had to decide on how to display conservation of energy and momentum.
We knew that the easiest way to show COM was to use the shooter we designed
to propel an object into another one that was initially at rest and that COE would be
easily illustrated by showing something falling from a predetermined height. We decided
that given what we had already put together, it would be easiest to shoot one ball into
another, knocking it over and somehow setting off the stamp.
We still wanted to incorporate our initial spring concepts so we chose to make a
spring-loaded platform that was connected to the stamp. The problem with this design
was rather or not the ball we dropped onto the platform would be heavy enough or fall far
enough to make a strong enough impact to overcome the force of the springs. We fixed
this problem by simply adding weight to the tennis ball. Even though we were still
displaying COE in this part of the project it was the momentum of the ball that would
need to change since we could not alter the height of the project.
Completed Project Picture:
Bill of Materials:
Note: All prices are stated based on approximate value of the item, i.e. we had to
buy a door hinge to get the spring, which is worth less than the total product purchased.
Also, the price of items not completely consumed is reduced based on their proportional
use in the project.
PVC Pipe: ~$3.00
Rubber Bands: ~$0.25
Tennis Ball: $0.50 (Filled with rocks which are free)
Wood: ~$8.00
Tape: ~$0.10
Glue: ~$0.10
Marble: ~$0.25
String: <$0.01
Springs: ~$0.50
Stamp: ~$1.00
Total: ~$13.71
Calculations:
Measured Values:
Length of the tennis balls fall: 3 inches
Length of marbles travel: 3 inches
Length of the stamps travel: 1/8 inch
Marble mass: 22 grams
Tennis ball mass: 180 grams
Rubber band’s spring constant: 17N/ inch (Measure in the lab)
Spring’s spring constant: 9.8N/inch (This was found by putting a 334 g block on the
spring, which compressed it ¼ of an inch. Then by finding the weight of the spring – 334
grams X 9.81 meters per second squared yields 3.27 kilograms, followed by multiplying
it by 4 to get it to a whole number of inches.)
Equations:
FRubberband  kx  (17 N / inch)(3inches)  51N
FSprings  4(9.8 N / inch)(1/ 8inches)  4.9 N
Energy of marble after impact:
mmarble v 2  (22 g )vmarble 2 *
Energy of tennis ball after impact ( x-comp):
2
mtennis v 2  (180 g )vtennis
*
*Note: The velocities inside the launcher and after the impacts could not be determined,
so no exact Conservation of Energy or Conservation of Momentum equation can supplied
from what we know. Given that the force of the rubber band is constantly changing as it
springs back (F=kx), we were unable to determine the work done. With this value we
probably could have found the velocity of the marble, and thus the momentum of the
system initially.
Potential Energy of tennis ball before impact:
ft
kg  ft 2
mtennis hg  (.180kg )(.25 ft )(32.2 2 )  1.5
s
s2
Speed of tennis ball just before hitting platform: vtennis  gh  (32.2
ft
ft
)(.25 ft )  2.8
2
s
s
Momentum of tennis ball before impact with platform:
ft
kg  ft
mtennis v  (.180kg )(2.8 )  0.51
(vertically )
s
s
Description of what we built:
Our design reflected a similar design of a pinball machine. We wanted to shoot a ball out
of a shooter into a weighted ball. The shooter consisted of a smaller PVC pipe inside a
large PVC pipe. We pulled back on the small pipe, which was attached with a rubber
band, and this was what shot the ball out of the tube. The weighted ball then fell onto a
platform that was on springs. On the underside of this platform was our stamp, and the
weighted ball pushed the platform and stamp down onto a piece of paper. Our platform
was held in by four vertical support beams. The springs that were under the platform
rested on smaller vertical supports that were attached to the inside of each of the larger
supports.
Conclusion:
Overall our rube stamper was successful. We were able to successfully put a stamp on a
piece of paper. In building our stamper, we learned how to work together as a team,
putting our ideas together to build a stamper that was functional. Even though it was
complex, we learned how to build a machine that did a function that was not as complex.
We also learned how to incorporate potential and kinetic energy into our machine, as well
as conservation of momentum, to get the job done. However, we did run into a few
problems. One problem we ran into was getting our springs to compress far enough to
stamp the paper when the weighted ball fell on the platform. Also, we had problems at
first with our launcher. We wanted it to be spring loaded, but that was difficult and was
not working, which is why we switched to a shooter. The other problem we ran into was
finding a small enough, but heavy enough marble to shoot out at the weighted ball, and
getting the weighted ball to have enough weight to compress the platform.