First of all, when we reached the building stage to build our thrower we noticed that our older conceptual design would not work properly with the mechanism of our thrower, so we thought of doing some changes on the older design. The base of our thrower will have 2 wooden rectangular bases with a length of 48-inches each laying horizontally and parallel to each other with a 30-inch distance between them. On top of these, are 2 wooden plates. On top of those 2 wooden plates is a third wooden plate, with a length of 10.32 inches and a width of 5.88 inches, which was placed at a 45-degree angle. This plate held the piston in place. In addition to that, we decided to place 2 wooden rectangular arms, with a length of 49 inches each, at a 45-degree angle on another two 49-inch wooden rectangular blocks, which are placed on the wooden plates just above the base. We placed another two support rectangular wooden blocks with a vertical height of 74 inches each. These blocks will hold the other two 45-degree angled rectangular arms in place. Figure 8 shows how it would look.
Figure 8: A side view of the thrower.
The PVC pipe we are going to use has a length of 16.81 inches. The special part about this PVC cylinder is that it has a wider diameter in the beginning than the rest of it. The front of the PVC pipe has a diameter of 3.25 inches, which can hold the tennis ball. The diameter of the rest of the PVC pipe is 2.81 inches. On both sides of the pipe we are going to have 2 opening slots with a length of 9.81 inches and a width of 2.06 inches. The PVC pipe is going to be set on a wooden plate by a C-clamp that is set on the angled arms. The length of this wooden plate is 12.96 inches, and the width of it is 12 inches. Figure 9 shows the shape and dimensions used to build the PVC pipe.
Figure 9: Shows the PVC pipe used and its dimensions.
The plunger we are going to use has a wooden cylindrical shape with a 1.5-inch diameter and a length of 6 inches. 1 inch away from the beginning of the plunger we inserted a metal rod, which extends 2.5 inches on both sides. The elastic surgical tubes are going to be attached to this rod. At the end of this plunger we attached an eye-hook with a length of 6 inches. Therefore, the plunger’s length is 12 inches total. The mass of the plunger is 0.39 lbm. Figure
10 shows the shape and dimensions used to build the plunger.
Figure 10: Shows the Plunger parts and its dimensions.
Our trigger is made of wood. It has a length of 6.43 inches and a width of 0.75 inches. A metal hook with a length of 2 inches is screwed into the trigger, and another hole is drilled 1.06 inches away from the metal hook. A metal wire with a length of 17 inches is going to be attached to the hold drilled in the trigger and will connect the trigger to the piston. The trigger is going to be pulled by the piston and hit a wooden plate so it unhooks from the eye-screw attached to the plunger. This wooden plate is attached to the back of the angled arms and has a length of 6 inches and a width of 5.50 inches. Figure 11 shows how the trigger looks.
Figure 11: Shows the trigger parts and its dimensions.
A wooden block is placed perpendicularly on top of the 45-degree angled rectangular arms. This wooden block will have holes in it, which are on the same line with the PVC pipe and the piston. These holes will allow the elastic tubes to pass through and get tied to the metal rod in the plunger. Figure 12 shows an overall photo of how the thrower is built.
Figure 12: An overall photo of the thrower after being
Ball’s coefficient of restitution
We observed the ball’s coefficient of restitution (e) by getting the ball we were to use in our thrower and throwing it from an initial height. Then, we observed the height the ball reached after bouncing on the floor. We did this multiple times, and we calculated the average value for all the times it was thrown. Then we used Eq. 12 to calculate the ball’s coefficient of restitution.1 Sample calculations are shown in the appendix.
After calculating the coefficient of restitution using Eq. 16 we found out that the ball’s coefficient of restitution will be 0.68.
We can measure our total system efficiency by using Eq. 13.3
We launched the ball from the thrower 5 times. The first time it reached 23, the second time 24, the third time 24, the forth time 25, and the fifth time 24. The actual range is calculated by taking the average of the distances the ball reached. The theoretical range can be found in the optimization table found in the appendix.
After applying Eq. 12, we found that our thrower’s efficiency is equal to 0.64. Sample calculations are found in the appendix.
We explained earlier that we will be using impact force. This is made possible by using a plunger that would hit the ball. The plunger should have a certain mass that would make it possible to be launched at a certain power to hit the ball so it can reach the 25-foot target. To determine the plunger length, we should first measure the weight of the sample of plunger material to obtain the total mass. Then we should measure the length of the plunger sample. After that, we calculate the plunger’s density using Eq. 13.
After that we conduct an optimization evaluation to determine the optimized length (designed) plunger mass. Then we calculated the optimized (designed) length of the plunger using Eq. 14.1
After following the experimental method mentioned above we found out that the length of the cylindrical wooden part of the plunger is going to be 6 inches. The total length of the plunger with the eye-hook is going to be 12 inches. The mass of the plunger should be 0.39 lbm.1
We explained earlier that we will be using a rectangular wooden trigger that had a screw hook that will be attached to the ring attached to the plunger. At first, we used a rectangular block with a width of 3 inches and a length of 4 inches, but the trigger did not unhook from the ring, which did not allow the plunger to hit the ball. Then we tried increasing the length of the moment arm of the trigger to 6.5 inches and decreasing its width to 1 inch.1
By doing so, the trigger successfully unhooked from the ring which allowed the plunger to hit the ball.
After getting our trigger to work properly, applied the air pressure by an air tank and the ball reached a distance of 16 foot away from the thrower. We observed the problem and noticed that by shortening the elastic tube we can get a stronger shot by the plunger and thus, we might get our 25 feet target. Initially, the elastic tube’s length was 12 inches. We reduced its length to 9 inches per pair on both sides.
After applying this change, we launched the ball and it reached 25 feet. So we were able to determine the appropriate measurements for both our elastic tubes and trigger used.