Weekly Progress
Week One
The first week of testing was about getting experience using the Plumber's Catapult. This is a very simple catapult made with PVC pipe and gets its throwing power from rubber bands. After testing with three different operators it was discovered that this catapult has many flaws. It is neither precise nor accurate. As the data shows that each operator got many different distances for each of their tests as well as getting different distances when compared to the other two operators. So, the results from this week of testing made it obvious that the Plumber's Catapult would be a terrible setup for out competition because of its unpredictability. However, the Plumber's Catapult does serve as a good basis to observe how a catapult operates and possible ways to improve it. Below are 15 total trials testing the catapult with three different operators (5 launches per operator) and the statistical data for how precise the catapult was:
Data
| Entry: | Operator 1 Distance: | Operator 2 Distance: | Operator 3 Distance: |
| (#) | (in) | (in) | (in) |
| 1 | 77 | 83.5 | 134 |
| 2 | 78.5 | 87.75 | 147 |
| 3 | 75.25 | 75 | 150.38 |
| 4 | 69.5 | 62.5 | 139.38 |
| 5 | 88.5 | 86.5 | 146.13 |
| Mean: | 77.75 | 79.05 | 143.378 |
| Standard Deviation: | 6.910137481 | 10.50357082 | 6.588840566 |
| 75% Conf. Interval: | (84.66-70.84) | (89.55-68.55) | (150.0-136.8) |
| Operator's Name: | Shanewaz | Brandon | Chance |
Week Two
For the second week, the group experimented with the Plumber's Catapult again, but with different variables. This week, we tested out the projection by changing the band-strength and the height piece length. The band-strength corresponds to the number of bands used in the structure. the difference between each trial corresponds to the number of smaller rubber bands added, the first trial having none, the second having one, and the third trial having two smaller bands added. Based on our calculations, the greater the band-strength or the more bands added, the further the projectile reaches. The mainly has to do with the increase in potential elastic energy stored in the rubber bands and that energy is used to fling the balls further. The height pieces correspond to the length of the pieces connected to the axle at which the lever arm makes contact when launching. Three different trials for the height pieces were conducted, one with 2.5 inches, the second with 4 inches, and the third trial with height pieces of 5.5 inches. Based on our experiment, the longer the pieces, the further the projectile reaches when launched. This is because the longer pieces allow the lever arm to fully extend when launching while the smaller pieces limit the movement of the arm. Below are the statistical data for the experiments:
| Entry | Band Strength 1 | Band Strength 2 | Band Strength 3 | Height - 2.5" | Height - 4" | Height - 5.5" |
| (#) | (in) | (in) | (in) | (in) | (in) | (in) |
| 1 | 78.25 | 144 | 174 | 41.5 | 144 | 195 |
| 2 | 82.5 | 116.5 | 176 | 38.25 | 116.5 | 167.5 |
| 3 | 92 | 139.5 | 171.75 | 42.5 | 139.5 | 185.5 |
| 4 | 93.5 | 121.75 | 185 | 24.5 | 121.75 | 184 |
| 5 | 94.5 | 114 | 169.5 | 19 | 114 | 208.75 |
| Mean: | 87.55 | 127.15 | 179.25 | 33.15 | 127.15 | 188.15 |
| Standard Deviation: | 7.03 | 13.75 | 7.62 | 10.7 | 13.71 | 15.18 |
Week Three
For the third week, the group synthesized several different foams. The purpose of this was to determine the mass ratio of the two unknown chemicals that were used in the reaction that results in the foam that is the least dense. Six foams were synthesized ranging from a mass ratio of .4 to a ratio of 1.4, this is the mass of chemical A over chemical B. To keep the foams the same general size, the total mass of the combined chemicals was always 17 grams.
| Targeted Mass | Experimental Mass | |||||
| Foam | A (g) | B (g) | Total (g) | Ratio | A (g) | B (g) |
| 1 | 5 | 12 | 17 | 0.4 | 5 | 12 |
| 2 | 6 | 11 | 17 | 0.5 | 6 | 11 |
| 3 | 7 | 10 | 17 | 0.7 | 7 | 10 |
| 4 | 8 | 9 | 17 | 0.9 | 8 | 9 |
| 5 | 9 | 8 | 17 | 1.1 | 9 | 8 |
| 6 | 10 | 7 | 17 | 1.4 | 10 | 7 |
Week Four
For week four, the group created different blueprints for possible designs of the trebuchet. Each design focuses on a different aspect of the trebuchet. Also during week 4, the group calculated and compared the densities for the uniquely synthesized foams. Each mass ratio had a different corresponding density as presumed, and the denser the foam was, the more firm it was. The group decided that foam 3 was soft enough so that the projectile as padding to land on, but it is also dense enough so that the projectile does not fall through the foam and have a direct impact with the ground.
Foam Weight Ratio (Mass A/ Mass B) Density (g/in^3)
Week Five
For week five, the group looked over the possible designs for the trebuchet in order to come up with a final plan. Once this was decided on the group started building a prototype trebuchet. The prototype is to have all the same main components that the actual one will have; however, they will be scaled down. This will give the group experience with how to trebuchet so that when building begins on the real one it will be easier than if the group started with no idea of how to attach and support the different parts of the trebuchet. The prototype should also give a good idea of how much bigger the real project needs to be. The group plans to finish the prototype and test how it operates in order to see if any changes should be made to the design for the real trebuchet.
For week six, the group designed and modified the sling system for the trebuchet catapult. The group members utilized an old t-shirt and string for the system by cutting the t-shirt into a flexible shape that can enclose the racquetball tightly without slowing the launch system. The shirt was then punctured with holes to allow the string through. The final string system will be able to hold the racquetball during the launch until a certain elevation in the rotation of the launch where it will then be released through an opening of the pocket and will project through the air. The string will not be elastic so that the structure will be contained and the launch rotation will be almost consistent every trial.
For week four, the group created different blueprints for possible designs of the trebuchet. Each design focuses on a different aspect of the trebuchet. Also during week 4, the group calculated and compared the densities for the uniquely synthesized foams. Each mass ratio had a different corresponding density as presumed, and the denser the foam was, the more firm it was. The group decided that foam 3 was soft enough so that the projectile as padding to land on, but it is also dense enough so that the projectile does not fall through the foam and have a direct impact with the ground.
Foam Weight Ratio (Mass A/ Mass B) Density (g/in^3)
1 0.4 1.231
2 0.5 1.125
3 0.7 1.105
4 0.9 1.252
5 1.1 1.191
6 1.4 1.271
Week Five
For week five, the group looked over the possible designs for the trebuchet in order to come up with a final plan. Once this was decided on the group started building a prototype trebuchet. The prototype is to have all the same main components that the actual one will have; however, they will be scaled down. This will give the group experience with how to trebuchet so that when building begins on the real one it will be easier than if the group started with no idea of how to attach and support the different parts of the trebuchet. The prototype should also give a good idea of how much bigger the real project needs to be. The group plans to finish the prototype and test how it operates in order to see if any changes should be made to the design for the real trebuchet.
Week Six
For week six, the group designed and modified the sling system for the trebuchet catapult. The group members utilized an old t-shirt and string for the system by cutting the t-shirt into a flexible shape that can enclose the racquetball tightly without slowing the launch system. The shirt was then punctured with holes to allow the string through. The final string system will be able to hold the racquetball during the launch until a certain elevation in the rotation of the launch where it will then be released through an opening of the pocket and will project through the air. The string will not be elastic so that the structure will be contained and the launch rotation will be almost consistent every trial.
Week Seven
For week seven, the group started to build the final trebuchet design. The group members utilized 2 x 2 x 8 planks of wood and common screws to attach the wood together. The first part of the design that was built was the base, which consisted of three 3ft pieces attached to two 1ft pieces at the ends. From the base, two 2.5ft sidearm pieces were attached and these sidearm pieces will hold the axle and launch arm piece. To support these sidearms, two 2ft pieces were attached on each side of the sidearm at a 45 degree angle.
Week Eight
For week eight, the group made more progress on building the final trebuchet. The lever arm was attached between the sidearms with a 5/16 inch thick threaded metal rod. In order to make sure the lever arm swings smoothly and consistently, bearings were set into the arm and the rod goes through them. Then the lever arm is held in the middle of the metal rod with a locking nut on each side. Then regular nuts with locking washers are on both side of each sidearm to hold the metal rod in place. Then the sling that will carry the projectile was attached. Two hooks were attached to the end of the lever arm. One hook holds the string throughout the rotation of the arm, the second hook will release the one string so that the sling will release the projectile. Then two screws were added to the back of the lever arm so that the counterweight can be hung from the screws, but can be easily changed with different weight counterweights.
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