Our Mission: Executing the our ideas for the task was certainly a challenge for our team, but in the end we pulled through. Over the course of about five months, we had the task to design, build, and test an tennis ball air cannon that would be able to fire a tennis ball over a great distance. Initially, we were to program an Arduino for the firing control system but never got around to testing the coding for it. Nevertheless, working with the Arduino was a fruitful experience. The finished design consists of the base of the cannon (the box), the cannon itself(with the stabilizer), an angle elevations device and a horizontal rotation mechanism. Each team had the same design for the cannon itself, but the designs for the stabilizer, rotations, and angle elevations were unique. The design has to be clean, material efficient, and precise. In other words, the tennis ball should go exactly where we tell it to. Throughout this five month timeline, I, along with my fellow teammates learned how to use different tools and software. I've gained more experience with the ShopBot, with OnShape, the laser, Arduino, and various saws in the shop.
First we had to build the cannon piece that every team is required to have based off of the model provided by the instructor. Everyone had to follow the same steps, but how well it was put together differs between each team. We cut a 10 ft. PVC pipe down into two pipes; one for the tennis ball and one for the compressed air that will be used to fire the ball. Each of the pieces of the canon were held together and sealed with primer and clear cement, and the bike tube air valve was sealed with epoxy. The sprinkler valve would control when the air would be released.
Week one consisted of working on trying to size, cut and assemble our cannon. It was all a learning experience for me, as I have never worked with such power tools before and have never used priming chemicals and clear cement or other strong-fumed chemicals. Being able to build the cannon itself gave me new skills with working with certain tools and gave me more confidence with the tools and chemicals. It was also interesting to work with my team because we were able to tackle this cannon in almost no time. I also learned the importance of "measuring twice and cutting once" and sealing properly with the primer and cement. Making sure the measurements are correct and each piece fully sealed for this design was crucial because when the cannon is pressurized, an incorrect measurement could result in a cap blowing off or air leaking.
Successes of Building the Cannon:
We were very successful with the construction of the cannon itself.We followed the instructions like a recipe from a cookbook. All the places that needed to be cemented and sealed were cemented and sealed. Picture one shows our group cutting the 10 foot PVC pipes down to size for the Cannon. We needed to cut the 10 ft pipe with a 2 inch radius into two pipes, one at 4 feet and one at 3 feet. We also had to cut down a PVC pipe with a 1 inch radius into two smaller pipes, one at 1.5 inches and one at 3 inches. Picture three is picture of one of our pipes after we've drilled a hole into it for the bike tube value. This valve allows us to load the cannon with pressurized air. The valve is held in the pipe with epoxy. Photo four is a picture of me mixing the epoxy for the bike valve; it had a weird smell and it was interesting how the epoxy starts to get warm when it is stirred. The sprinkler value (picture 5) connects to a battery that allows the cannon to fire the tennis ball when we tell it to. When both wires from the sprinkler valve are touched with the positive and negative ends of the battery, it released the pressurized air, sending the ball out of the cannon and up into the air.
The Stabilizer and Its Design
For the stabilizer, it was a challenge to find an idea that would keep the PVC pipes of the cannon stable. This is important because we want the shots to be accurate, and it can't be if the pipes wobble as the cannon is fired. The difficulty with designing the stabilizer was getting the holes the perfect size for the cannon. We didn't want it to be too loose or too snug. The pieces with the holes will be cut out twice from a piece of thin laminate wood, and the longer pieces served as the brackets that connected the two pieces with the holes together. The triangular piece was cut out and arranged between the two stabilizer pieces for support. The triangular piece had three little grooves for the three bracket pieces to fit into. The pieces with the holes also had grooves for the longer bracket pieces. These pieces fit very snug, which wasn't exactly how we wanted it. It stabilized the cannon well; there was no wobbling but the pieces with the holes had to be forced onto the cannon because our measurements were a bit off.
Successes of Designing the Stabilizer:
It took a few tries to get the design we wanted with the correct dimensions and gauge sizes, but for the most part, we did it. We were the first of the teams to cut a prototype of our design The PVC pipes fit snug, and overall does what it is supposed to do. The stabilizer holds the two PVC pipes in place so that it is not wobbly when it fires.
Flaws In Design: The Stabilizer
Our original design was going to utilize a string, kind of like a draw bridge design to help elevate the cannon for the different firing angles. We didn't end up using these holes but we decided to make a more sturdy angle elevation device. The first image below is a picture of one of the pieces for our stabilizer. The two holes are sized perfectly for where the PVC pipes go into but the space between the two holes were on the longer end and we had to forced the second stabilizer piece in. The second image is the design for our brackets, which we cut out 3 of those. The last two images below are pictures of our cardboard prototypes. We used scissors to cut off the ends to check if the measurements for the distance between the two PVC pipes were accurate. With the cardboard, because it's so flimsy, it was hard for us to tell that the design wouldn't fit right. We thought that the holes were the right size because with the cardboard it fit, but with the laminate wood it was really snug. This is because the cardboard is not a solid material, and can morph into a different size if enough pressure if applies. Overall, my team and I felt that the design for the stabilizer was successful, and that it was the most successful piece of our whole design for this project.
Designing of the Base for Our Cannon
We had the idea of creating a box shaped base for our cannon. We figured that this would be stable and would be able to support the weight of the cannon. Some successes were the making the calculations of the elevation angles. The design over all was not successful because of how big the pieces were relative to the other cannons we saw. We ended up having to cut off quite a few inches of material, sanding a lot, and completely flipping our base on its side on the testing day because sitting upright, the ball would be launched really high into the sky. Angles for elevation were very limited. Image 4 shows our original idea for the rotation of the base but we noticed that the big box of a base would not be able to balance well on a thin wand-like rotation device.
Below is a picture of our finished cannon with the stabilizer attached!
These are aesthetic photos of one of our work days where we cut out our parts with the CNC ShopBot and cut/shaved down a few more pieces for fitting. The CNC bot was to make our designs more precise as far as cutting out shapes goes, but our measurements were very off for some reason. We had to do a lot of sanding because a lot of the piece did not fit. This is because when we made the tabs for where each piece would fit together like a puzzle, we didn't think about material thickness. The thickness of the plywood varied in different parts of the sheet.
Assembly Day: It came time for us to assemble all of our parts for the base of the cannon.
Our group had a fun time assembling the box for our base piece, as every member of the group was working hard at the same time. While two people sanded, one would make the extra cuts, and one would start assembly and gluing. Some failures was the design as we had to change our idea quickly and on the spot due to some timing issues and the breaking down of the ShopBot.