1
Beffrey et al
Leprechaun Trap
Alex Beffrey
Chris Riley
Nissa Smith
Laura Webster
EF151 B2
Spring 2006
April 28, 2006
1
Beffrey et al
Table of Contents
Table of Contents 2
Executive Summary 3
Design Process 3
Construction Process 3
Analysis 4
Calculations 4
Step 1: (0.188kg Leprechaun Falls 0.12m) 4
Step 2: (1N force is applied to pin over 0.01M) 4
Step 3: (Energy is conserved) 4
Step 4: [Spring (92.3 N/M)potential is released turning into Kinetic energy] 4
Sketches 5
Assumptions 5
Materials 6
Conclusions 6
1
Beffrey et al
Executive Summary
We were tasked with designing a “Rube Goldberg Device,” that would execute a minimum of three energy conversions, under a price of twenty five dollars. With that our team decided to construct a leprechaun trap. To capture the leprechaun several design schemes were analyzed, and in the end one was chosen. The basic design of the trap is such that upon walking up and across a platform the leprechaun falls into a box causing a cage to fall on top of him. The main goal with our device was to make it extremely reliable, and in doing so we have achieved a design that has not failed to work a single time.
Design Process
We decided to make a simple trap for a small creature such as a leprechaun. Our first idea was to pull a pin setting off a larger trap. One of our original ideas was to have a trip wire to set it off. We discarded that idea and decided that the leprechaun would instead climb up a ladder onto a box. He would walk across the box toward the Lucky Charms, causing the opposite side of the lid on the box to rotate 180 degrees. The lid rotates on an axel which is in turn attached to a string, attached to a pin. When the lid flips, the pin is pulled, which then releases a dowel rod causing a spring loaded cage to fall, totally encompassing the smaller box holding the leprechaun.
A similar idea we discarded was having the cage drop down on top of the leprechaun, but this would require a suspension device for the cage which we did not want. We instead attached the larger cage to a platform; the box was resting on, through a hinge.
The criteria for this design was to accomplish three energy conversions, have a design that works, and build it under twenty five dollars. Our design consists of four apparent energy conversions, works one hundred percent of the time, and cost less than twelve dollars.
Construction Process
Using a radial arm saw, six pieces of small paneling sections were cut for the box assembly, along with six small wood blocks to serve as supports inside the box. Finishing nails were then used to affix the five panel sections to the six wooden blocks to create a topless box. Two holes were drilled on opposite sides of the length of the box, near the top. A dowel rod was then cut, slid through the hole, and the lid of the box was attached at the center with finishing nails. Note that one side of the top has no support pieces, so that the lid could rotate about 170 degrees. With a table saw, a large base board was cut to size out of half inch plywood. A section on the back center of the plywood was chiseled out so that a hinge could be attached to the box, while retaining a smooth surface at that point. Eight sections of scrap cedar wood were then cut, and nailed together in the shape of a box. Sections of chicken wire were then cut to size with a cutting wheel, and stapled onto the frame. Safety wire was then used to affix all the sides together. A board made of pine wood was then used to attach the cage’s thin cedar to the plywood board’s hinge. A small eyehook was attacked the board, and a spring attached to the eyehook and the cage. Four metal pieces were machined, and two attacked to the front with holes thought them to lock the cage to the plywood base. The other two were attached to the top of the base in the bottom right corner. The pin attached to the string is then set between these pieces, and the dowel rod is propped against the pin holding the cage up.
Analysis
The device consists of four major energy conversions. However, when looking in detail we found an extremely large amount of conversions/transfers of energy that are too meticulous for us to bother getting into. Therefore only our four major conversions will be outlined.
Step one consists of the leprechaun exerting work on the lid of the box, as his weight forces it downward a distance. Step two consists of the platform rotating with an axel. As the axel rotates it pulls a pin a given distance. Step three is the pin coming free, releasing a stick held against it. Step four is the stick coming free, releasing the elastic potential in the spring attached to the cage. The cage then closes.
Note that the simple efficiency of the device is around two thousand percent. This is due to the fact that a very small amount of energy releases a large amount of spring potential energy. The spring already had an equal amount of kinetic energy applied to it, to convert it into potential energy. Therefore energy is conserved throughout the entire process and the device is not in any way a perpetual motion leprechaun machine.
Calculations
1
Beffrey et al
Step 1: (0.188kg Leprechaun Falls 0.12m)
W=MGH
W=(0.118KG)(9.81m/s/s)(0.12m)
W=0.0139J
Step 2: (1N force is applied to pin over 0.01M)
W=FD
W=(0.010M)(1.00N)
W=0.010J
Step 3: (Energy is conserved)
W=W
Step 4: [Spring (92.3 N/M) potential is released turning into Kinetic energy]
W=
W=3.12J
Sketches
Figure 1: Trap in ready position
Figure 2: Trap in closed position
Assumptions
1. A leprechaun can climb a ladder.
2. A leprechaun eats Lucky Charms.
3. A leprechaun has a mass of at least 0.118 kg.
4. No Friction
Materials
Paneling Scrap / $1.00Pine Wood Scrap / $0.50
Finishing Nails / $0.10
Dowel Rod / $0.50
Door Hinge / $1.50
Acrylic Paint / $2.00
Spray Paint / $2.00
Cedar Scrap Wood / $1.00
Plywood / $1.00
3” Spring / $0.50
Eye Hook / $0.01
Staples / $0.10
Chicken Wire / $1.00
Aluminum Pieces / $0.00
Screws / $0.10
Total / $11.31
Conclusions
In conclusion, our trap worked flawlessly catching a leprechaun every time it was tested. The hardest part of the entire system was designing a way to trigger the trap through the small force of a leprechaun, and then have a cage encompass him instantaneously. All members of the group contributed in their own way to the device, from writing to design and construction. Overall it was a good learning experience as far as scheduling time, and working in a team environment.