Mini Project.docx

Mini-Project Final Technical MemoTiffany Lontoc, Andrew PlaIED Section: 6Date: September 19, 2013Introduction

The problem proposed was to create a machine capable of launching a small projectile a distance of at least 20, while also being able to hit a target anywhere between 5 and 20. This launcher was required to satisfy certain dimensional, weight, and safety requirements. These specifications and guidelines were set by the IED professors who were, essentially, the customers interested in the project. Looking at previous launchers made by students, the group, Andrew and Tiffany, decided to stick to something simple, yet powerful. After considering several contending options, a catapult was chosen as the design to move forward with. The catapults selection was based on several criteria, such as manufacturability, reliability, and practicality. Having little experience with building machines, the group thought the catapult was the best choice because it was something that could definitely be built. Testing was performed on the initial prototype and various alterations were made in order to increase power and accuracy. The groups final product was able to launch a marshmallow as far as 30, adjust by 1 increments, and have an average accuracy within 1 of the target. At the end of this process, the group will have hopefully developed a better understanding of the engineering design process and develop a strong bond with each other.Concepts and Benchmarking

After being presented with the problem, the group immediately brainstormed a few ideas. The three main ideas were a pipe launcher, a trebuchet and a catapult. As shown in Table 1, the team considered using rubber bands, bungee cord or springs to create the tension in the machine that would shoot the marshmallow. They were limited to height and width constraints and weight requirements. This limited the amount of material used to build the machine, but three basic materials were still proposed: wood, metal, and plastic. The machine would have to be adjustable in order to shoot the marshmallow at varying distances, so the team also considered ways to adjust the machine. The means of adjustability varied with each concept, as shown in Table 1. From these ideas, the group then researched the different concepts to see the benefits of each one.

Table 1: Concept Combination TableOverall DesignEnergy SourceMaterialsWays to Adjust

Pipe LauncherRubber BandsWoodSpring compression

TrebuchetBungee CordMetalDraw distance

CatapultSpringPlasticAmount of tension

A Gantt chart was first created to organize the process of creating the product. The chart distributed work over time between Andrew and Tiffany and helped keep development on track. This Gantt chart is shown in Figure 1. The group was able to stick to the schedule fairly well, but hit some minor obstacles in between due to schedule conflicts. Having this Gantt chart allowed the team to stick to a schedule to remind them of due dates and benchmarks. The chart proved to be an important asset to the overall project because without it, the project would not have experienced as much success as it did during the competition.

Figure 1: This is the Gantt chart used by the group to organize the various tasksThe first concept was a spring-powered pipe cannon. The group was inspired to try this idea knowing that designs like these have been attempted by DIY websites. Numerous marshmallow cannons had been built, but the group was interested in one design that specifically used PVC pipe (Jon, 2012). The cannon barrel would be made from PVC pipe with a spring in the base. The spring would be pulled back with a string, allowing it to compress. A marshmallow would then be placed on top and upon release of a trigger, the spring would expand and fire the marshmallow from the cannon. Adjustability could be achieved through multiple slots cut out of the pipe as shown in Figure 2. The group, however, did not know how to adjust the angle the pipe would be set at, as shown in the right diagram of Figure 2. Further research was done and it was decided that there would be supports on either side of the pipe that held it in place at a desired angle (How to Build a Catapult). As the spring compressed, it would be possible to lock it into any of these slots, achieving different degrees of compression; therefore varying distances the marshmallow would reach. .Figure 2: Sketch of Concept 1 - Pipe cannonFollowing investigation for the pipe cannon, another idea was brought forth: a trebuchet. Trebuchets function through use of a counterweight, which imparts force onto a swinging arm. A sling attached to the arm flings the payload. This concept posed problems for the group, who had no prior experience of building a trebuchet. Searching for previous trebuchet designs had proven to the team that the design was indeed a difficult task. For example, one of the designs was built using a specific counterweight that would be difficult to reproduce (How to Build a Trebuchet). Aside from this, the process needed to construct a trebuchet would take a great deal of effort to make in such a short time period. This option was briefly considered, but eventually discarded because of its complexity.

Figure 3: Sketch of Concept 2 TrebuchetCatapults have similar structure to trebuchets, however their energy comes not from a counterweight but from a force pulling the throwing arm forwards. This force can be provided by an elastic band, spring, or pulley, but all have the same effect. Upon release, the arm is pulled forward until it encounters a crossbar. The arm stops, but the payload resting in the basket continues to fly forward towards its target. The team was inspired by Leonardo Da Vincis catapult design (Hucbald ap Urp, 2007). His design, however, was too intricate. Since Da Vincis design resembled that of a bow, the team then came up with the idea to use a pulley to create the force. The team researched for previous designs of catapults that used pulleys. They were unsuccessful in finding designs, therefore they moved onto the idea of using bungee cords (Catapult Crazy!). Bungee cords would provide a large amount of tension and surely launch the marshmallow 20. Rubber bands also presented the same benefits as bungee cords. Therefore, the team kept these two ideas in mind for when they finished the prototype. A catapult design appealed to them because of its relatively simplistic design. This was particularly attractive because if a part of the design failed, it would be relatively easy to solve the problem. For example, if rubber bands snapped, more could be added without dismantling a portion of the catapult.

Figure 4: Sketch of Concept 3 - Catapult After considering these first few ideas, the group decided to move on and create a concept selection matrix. The matrix helped with choosing which of the three concepts was the best based on certain criteria. These criteria were based on not only requirements for the project, but also the groups own requirements. For example, the launcher had to be less than 30 pounds. Therefore weight was an important aspect in choosing the final design. The catapult ended up with the highest ranking, as shown in Table 2. The catapult was a definite yes, however the trebuchet was also an option to continue with. The trebuchet was finally ruled out because it was more practical to make a catapult in the amount of time remaining before the competition.Table 2: Concept Selection Matrix

SolutionOnce it had been decided to proceed with a catapult, rough sketches were made and details determined. The catapult would be made of wood, with dimensions of 18x15x18. For power, the initial proposed source was bungee cords. The throwing arm, 24 long, would pivot around a wooden dowel fit into holes drilled through the base as shown in the top view in Figure 5. The basket could be made from a plastic bottle cap, where the marshmallow would rest just before the launch. As shown in the side view in Figure 5, an eye hook would be screwed into the underside of the arm. A gate hook would then be placed within this eye hook. This mechanism would serve as a trigger, because the gate hook, attached to a string, could be pulled from a distance away from the catapult.Adjustability could be provided by altering the distance the arm was pulled back. This would be done by increasing or decreasing the amount of string between the base and the trigger. The proposed method was to have the trigger at the base of the catapult, with a metal loop attached to the underside of the throwing arm. The string from the trigger would run through that loop, and down to the side of the base, where there would be wooden pegs that the string could be looped around. This system would allow the amount of string available, to pull back the throwing arm, to be adjusted while simultaneously increasing or decreasing the amount of force imparted to the marshmallow. Sketches were made of the design, as seen in Figure 5, with a picture displaying the final string adjustment mechanism shown in Figure 6.

Figure 5: Drawings of the final concept design

Figure 6: Shows how the string would be looped around screws (originally planned to be wooden pegs) to adjust how far the arm could be pulled backAs construction of the prototype proceeded, some alterations were made to the original design. Firstly, an issue was encountered with the bungee cords. They were too difficult to attach and provided either too much or too little power. The bungees were replaced with rubber bands that were attached to a metal u-nail on the crossbar. They were then attached to a hook on the throwing arm, as shown in Figure 7. Rubber bands provided a simple, effective power source with the benefit of easy adjustability: if more power was required, the addition of more rubber bands could quickly solve the problem.

Figure 7: Displays how the rubber bands attach from the crossbar to the arm.Additionally, the method of adjusting the amount of string available to pull back the throwing arm was altered as the product came together. The idea of putting wooden pegs along the base proved to be too difficult due to construction issues. The wooden pegs were replaced with metal screws, pictured in Figures 6 and 8. These screws were inserted into the base in a vertical line, each protruding 1. The gate hook trigger now latched to the throwing arm instead of the base. A string ran between the gate hook and these screws. Depending on which screw the string was tied around and how many times the string was looped around it, the overall amount of string between the base and the trigger could be adjusted to a precise distance.

Figure 8: Trigger and string-length adjustment mechanism.The last alteration made to the design was the addition of washers on either side of the throwing arm where it rotated about the dowel, shown in Figure 9. As a result of imprecise drilling, the arm shifted and wobbled as it was pulled back. This affected the accuracy and aim of the arm by a significant amount. For example, during testing, the marshmallow would consistently land further to the left of the target. To solve this problem, washers were added to each side of the arm on the dowel to hold it in place. This addition increased the accuracy of the arm and it no longer wobbled. The result of this construction was a rubber band-powered catapult with adjustable draw distance of the throwing arm that can be remotely fired. Overall views of the finished result can be seen in Figure 10. All that remained was formal testing and documentation of the machines capabilities.

Figure 9: Washers on either side of the throwing arm to increase stability

Figure 10: Pictures of top and side view of the finished product

Test Plan and Test Results

Once the initial prototype was constructed, testing began. The catapult was first tested for distance, and then for accuracy. The first few trials were disappointing because the catapult did not reach 20. There were a total of 5 trials attempting to reach 20 as shown in Table 3. At first, the arm was pulled back a small distance to see if it functioned properly. The arm was then pulled back the maximum distance it could go before any rubber bands were snapped. As a result, the farthest distance the marshmallow went was 16. In order to meet the requirements of 20, more rubber bands were added to the arm. The group decided that more tension was needed to create more power. The second round of trials were an improvement, however the marshmallow still did not reach 20. These results are shown in Table 4. After adding more rubber bands, the group was finally able to reach 20 and farther. These results are shown in Table 5. When the team was confident with these results, they worked on accuracy. They did so by selecting a target distance at random and would attempt to get a marshmallow to hit that target. Two of these trials are shown in Table 6, for targets at 12 and 18.During these trials, it was observed that the catapult was fairly accurate vertically, but not horizontally. This was attributed to be the arm wobbling about its pivot, as described in the Solution section. At this point, washers were added on either side of the arm to increase stability. Further trials were conducted and the results, shown in Table 7, proved the effectiveness of the washers. Satisfied with these results, the group decided that the product was ready for the competition.Table 3: The results from the first set of trials to test for distanceTrial #Distance (ft)

116

215

314

414

515

Table 4: The results of the second set of trials once more rubber bands were addedTrial #Distance (ft)

116

215

317

417

Table 5: The results from the last set of trials to test for distanceTrial #Distance (ft)

121

220

325

430

521

Table 6: The first set of trials testing the catapult for accuracy.Trial #Distance from Target (12)Distance from target (18)

12419

21626

33320

43016

51422

Table 7: The second set of trials after the arm mechanism was improvedTrial #Distance from Target (15)Distance from Target (14)

1113

2618

31316

489

5198

Conclusion

The final product that the team created was a wooden, rubber band-powered catapult with enough power to launch a marshmallow anywhere from 5 to 30. It also had an average degree of accuracy within 1 of a target. The development process leading up to this creation was lengthy, but organized in a manner that provided a clear path towards success. Just as the group had learned in lecture, the design process starts out by figuring out the problem, finding ideas to solve that problem and getting feedback from their customers. To begin with, the group created a Gantt chart to organize the process, and then brainstormed various ideas: cannons, trebuchets, and catapults. These concepts were fleshed out further and finally compared in a concept selection matrix. A catapult was chosen as the machine to move forward with. More detailed sketches were made, and a prototype was constructed from wood. Adjustability was achieved through limiting the draw distance of the throwing arm. The power provided, at first, was through bungees, but quickly changed to rubber bands. The trigger took the form of a gate hook, released at a distance by pulling a string. Dimensions fell under the maximum limits, measuring 19x18x21 at its largest points. Testing of the catapult was done to first establish the amount of rubber bands required to throw the maximum distance. Once this was determined, next was the catapults accuracy. Slight adjustments were made to increase performance until the group declared the launcher to be satisfactory. While further alterations may have been possible to marginally increase the accuracy, they would have involved significant overhauls of the design. In the end, it was decided that accuracy within 1 was acceptable. On the day of the competition, the catapult performed well, ultimately winning the competition. The data for these trials, for a target at 15, is shown in Table 8. A chart was also added to plot the points where the marshmallows landed on each trial in relation to the target, shown in Figure 11. Overall, while not perfect, the group was satisfied with the product. It met the customer requirements set forth to a relatively high degree and represented a tangible accomplishment for the group.

Figure 11: A chart mapping out where the marshmallows fell in relation to the targetTable 8: The distances, along the X and Y axes, the marshmallows landed in relation to the target XYPrecisionAccuracy

Distance From Goal lineDistance From CenterlineDistance from CentroidDistance from Target

(inches)(inches)(inches)(inches)

Test 1-5.00-6.7514.528.40

Test 2-3.753.509.625.13

Test 36.000.002.906.00

Test 414.757.7510.1416.66

Test 517.2510.0013.4319.94

5.852.9Average10.1211.23

Centroid XCentroid Ypts9.8838.77

Lessons Learned

Tiffany learned she needs to be more understanding of her partners schedule and also stick to the teams schedule. This whole process showed her that she needs to work on her time management skills and not be afraid to be more assertive with her opinions. Having previous bad experiences with group work, Tiffany also noticed she tended to keep to herself about what she was doing. She later learned to ask Andrew for help and also give out help when needed. Not only did she learn to confront her partner when she had an issue with something, but she also learned to take constructive criticism as a positive thing. Going into this class, she had no prior experience in a workshop, so she learned not to underestimate her skills or her partners skills. Overall, she recognized her flaws and learned to overcome those flaws by offering the best at what she was good at. The mini project was a whole new experience for Tiffany and she could not have had a better partner to help her during this process.Andrews typical experience when working on a group project was to collaborate a bit on the work but ultimately sit down at the end and make sure everything was just how he envisioned it. In this project however, full collaboration was the only option. Andrew learned to be more trusting in his partner, who in turn did just as good a job as he could have, if not better. Splitting and distributing the work load was a valuable skill that had to be developed. Moreover, Andrew went from having next to zero knowledge around a workshop to a passable proficiency. Careful observation, guesswork, and, at times, trial and error, helped the group figure out just how to put something together that actually works. Andrew took away from this project a new respect for the capabilities of each member of a team, as well as more respect for mechanical engineers. As a whole, the group was able to work together to construct a successful marshmallow launcher. They ran into time conflicts and design obstacles along the way, but they were able to overcome these hardships as a team. Looking at the engineering design process, the group learned that getting feedback from customers means a great deal to the engineer constructing the product. Without knowing the needs of the customer, the engineer would not know where to start and what the customer wants it to look like. Not only did the group learn that they need feedback from customers, they also learned that they need also need feedback from each other. Each of them was able to leave this project with a positive attitude and a better understanding of the work that goes into creating a project like this.

BibliographyCalvert, J. (2000, January). Cannons and Gunpowder. Retrieved from http://mysite.du.edu/~jcalvert/tech/cannon.htmCatapult Crazy! (n.d.). Retrieved from http://www.stormthecastle.com/catapult/index.htmHow to Build a Catapult. (n.d.). Retrieved from Storm the Castle: http://www.stormthecastle.com/catapult/how-to-build-a-catapult.htmHow to Build a Trebuchet. (n.d.). Retrieved from http://www.stormthecastle.com/trebuchet/how-to-build-a-trebuchet.htmHucbald ap Urp, H. (2007, April 14). A Leonardo da Vinci Leaf Spring Catapult. Retrieved from http://www.hucbald.ramst.ca/articles/leonardo_catapult.htmlJon. (2012, December 21). Weekend Project: Marshmallow Guns. Retrieved from Dad is Learning: http://www.dadislearning.com/2012/12/21/marshmallow-guns/