Catapult Project

Catapult

By: Hasan Abdullah (OSIS#200100360)
Group: 1 Class: Introduction to Engineering (Mr.Cornish) Period: 9 Date: May 20, 2013

PROJECT OBJECTIVE
The project objective was to learn about basic projectile motion theory, the mathematical models applicable to various projectile motion situations (e.g. catapult launch), and construction techniques for specific raw building materials. In addition, a catapult was to be implemented and built based on an existing design; this design was to be documented prior to building, and used as the primary documentary source when constructing the contraption. Furthermore, an eggonaut was to be designed and then built for the sole purpose of protecting a raw chicken egg from breaking when launched from the catapult. Lastly, component designs and scientific/engineering principles at work were to be demonstrated by the model.

GOALS AND CONSTRAINTS
The following were the specifications, goals/requirements, and constraints for the catapult:

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A document on an existing catapult design (including sketches, dimensions, materials, Bill of Materials, and estimated build procedure) was to be created prior to construction This documentation was to then be used to replicate the existing design (original) using all the same parts and materials, within the documented specifications Individual documents were to be produced outlining the work undertaken Contraption was to be fabricated within the provided specifications:

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the physical device must:

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be complete and safe load a raw chicken eggonaut capsule easily work; must protect the egg from breaking upon dropping be fabricated at school be left at school be fabricated from supplied materials [similar to those in original design]

A strict timeline was to be adhered to (each day)

RESEARCH
After the project objective, goals, and constraints were established, research was undertaken to better understand how catapults work. They work by converting potential energy, or stored energy, to kinetic energy, or energy during motion. This is done by a releasing mechanism, commonly referred to as the “arm” of the catapult. Attached to the end of the arm is a projectile holder, such as an inverted circular plastic lid. The arm is attached to

the base of the catapult (which acts as the support platform and framework of the entire model) by means of an elastic material (referred to as the elastic releaser) like rubber band(s). The base/framework itself is constructed with sturdy materials, almost always being wood. This allows it to absorb the impact once the arm is released from its starting position (which stores potential energy) to its final position (when the object is launched and kinetic energy is released). The elastic material, such as rubber band(s), simply facilitates the conversion of potential energy to kinetic energy. The following are several examples of catapults that have already been made: 1. One example of a catapult is the “Table Top Troll Catapult.” This design involves the use of basic materials such as wood, screws, eye hooks, glue, a piece of cardboard/poster board, a metal bar, and a rubber band. The wood forms the framework of the catapult, and is the support system for the arm; the cardboard (or poster board) fulfills a similar role. The screws stabilize this and is the primary attachment unit for the device; the other attachment units are the eye hooks and glue. The rubber band connects the top of the arm to the bottom of the wood, allowing potential energy to be converted to kinetic energy. The metal bar acts as the pivot point for the arm of the catapult, which allows the desired projectile to be hurled.1 2. Another example of a catapult is the “Mouse Trap Catapult.” The materials involved in this design are a mousetrap, pliers, a spoon, and tape. The platform of the mouse trap is basically the chassis of the catapult. The spoon acts as the catapult’s arm, while the spring (pivot point), hammer (support for arm), and holding bar (release mechanism) allow the projectile to be hurled. Pliers are used to remove the trigger arm from the mousetrap, and the tape is used to secure the spoon to the hammer of the mouse trap.2 3. A last example of a catapult is the “Teeny­Tiny Popsicle Stick Catapult.” The building materials involved in this design are popsicle sticks, masking tape, a piece of rubber band, and a paper shaped into an open box. The popsicle sticks provide a platform for the catapult, and the tape connects them together in order to stabilize it. One popsicle stick acts as the arm, while a rubber band is attached to this so that it can be flicked. The paper box acts as the projectile compartment at the top of the catapult’s arm.3
1 2

Kalif, W.. N.p.. Web. 7 May 2013. . David, K.. N.p.. Web. 7 May 2013. . 3 John, D.. N.p.. Web. 7 May 2013. .

MULTI­STAGE BUILD DESCRIPTION
After research was conducted about the different types of catapult designs, and an existing design was documented, the members of Group 1 and I came up with final catapult design to be used in the production of our contraption. It involves the use of materials such as wood, screws, hinges, and rope, as present in the original design. Commentary on the mechanics/principles at play inside the device: As described in the Research section, the wood of the catapult acts as the base/framework for the design, as well as the supporting platform where everything else is attached to. A specific piece of wood is shaped as the arm of the catapult, while the end of it has a projectile holder, which is an inverted circular plastic lid. The other end of the arm, on the other hand, is attached to an intertwined rope, which acts as the elastic releaser that converts the potential energy of the arm to kinetic energy, allowing the projectile to be successfully launched. The mentioned parts of the catapult are stabilized by attachment materials such as screws and hinges. The following are various pieces of documentation done (as mentioned in the Goals and Constraints section) for the intended catapult contraption design:

TESTS AND EVALUATION ­ COMPETITION RESULTS
After all groups completed the production of the catapult contraptions, a competition was held to test and evaluate them. In the competition, a group’s catapult was to be held by a person while standing on a bridge. Then, an eggonaut capsule (containing an egg) was to be launched from the catapult, aiming away from the bridge and down onto the ground. Each group’s catapult would launch its eggonaut capsule after the previous one was finished launching, meaning that two or more catapults would not be used simultaneously. Once the eggonaut landed on the ground, the egg inside it would be checked for any damage. If the egg is perfectly (or almost perfectly) intact, then the group’s catapult would be considered a winner. If the egg breaks, cracks, or anything of that sort, then the group’s catapult has failed. Distance of the eggonaut would also be taken into account after the aforementioned factors have been determined. My group’s catapult did not successfully protect the egg inside the eggonaut. The egg was slightly cracked, and was actually almost in perfect condition. In conclusion, even though our catapult was successful at launching the eggonaut, the eggonaut was not efficient at protecting the egg. Nonetheless, most of the goals and requirements that were set were accomplished by our contraption. The following is a picture of my group’s final catapult:

FUTURE WORK
The catapult accomplished all the goals and requirements that were set. Unfortunately, the eggonaut was not able to protect the egg from breaking when launched from the catapult. For future work, the contraptions could be improved even further. For instance, the eggonaut

design could be changed, using sturdier materials to better protect the egg from breaking when being launched. Also, a more complicated catapult design could be made, which also follows engineering principles like potential energy and kinetic energy, as discussed in the Research section. Another option for future work would be to try out different construction materials used in the catapult­ for example, instead of using rope for the elastic releaser, a more flexible material like rubber bands could be used. Doing this would provide me with a more accurate understanding of how potential energy and kinetic energy are found in everyday things such as slingshots and other weapon­like items. It would also open a pathway to a more enriched learning experience so I can pursue a professional career in the field of engineering.