For this project my group constructed a PVC air cannon. To do this we had to learn to weld as well as using the ShopBot, Laser Printer and the Arduino. In the end, our goal was to have a cannon with angles controlled by the Arduino that would be able to calculate the angles it needed based off of distance and pressure. The cannon also needed to have a way to change and lock in vertical angle and preferably a way to change horizontal angle without moving the base. Most groups also included a method to prevent barrel torquing.
For the next part of the project we began to work with Arduinos to learn how to make a solution for automated firing. We had created a circuit and program that when run would allow us to put in data for distance, horizontal offset and power and would output the azimuth our cannon needed to be at. This is a video showing off our use of the buzzer, which in the final design provided a warning tone when the cannon was arming. However, we weren't able to utilize the Arduino on the cannon due to the equations we used not giving accurate data, the Arduino physically not being able to be mounted securely and the servos provided to us not being strong enough to move the cannon.
Due to our project relying on bike parts to build the frame we had comparatively few parts that we had to CAD out. Above are the two parts which we had to made, both of which were multipurpose. The circular piece is our angle marker that we used to mark both horizontal and vertical angle. That piece had the angle markers laser cut into the wood. The second piece is our barrel support, which we cut out four of on the shopbot out of 3/4" OSB forming two supports made of 1 1/2" of OSB glued and bolted together on both sides.
For the next step we began to create the mounting and torquing solution for our cannon.
One of the advantages to our design was that the way we had to mount the cannon to the wheel was by the use of cut strips of OSB, which also eliminated the possibility of barrel torquing. We also made sure to mount the wheel so that the center of the wheel was the center of gravity for the cannon, since the weight in evenly distributed on the wheel, thus balancing our assembly.
The way we mounted the cannon way by making a crush fitting in the OSB, sliding it onto the air cannon body and then dropping two holes through the wheel on both sides to put bolts through.
The next step in our process was the welding and assembly of our base. Our plan was to weld the bike tube to the legs that held the wheel to make a tripod stand and then to drop in a through bolt through a threaded hole to lock in our horizontal rotation, because the bike tube allowed us very smooth rotation, so smooth, in fact, that it rotated on its own. The step involved a lot of waiting, waiting for the welder to be ready, waiting for the welders to come in and waiting for a tap and die set.
The final step in building our project was painting our cannon and adding certain other helpful additions that weren't necessary per se, but were still helpful nonetheless.
This shows a closer view of our horizontal angle readout, which is mounted to the head tube and the fork to keep in it place as the cannon above it rotates.
Two of our biggest and most helpful additions are visible on the left of this picture. One was the addition of a battery mount to make it so we didn't have to hold it to fire the cannon. The second was the switch which allowed us to toggle the valve to be open or closed.
This is a detail of the bike fork that controlled our horizontal rotation.
The drawback of these additions was that adding a five pound battery to an eight pound assembly tends to throw the weight off balance, so now our cannon tends to lean back if not locked in tightly enough.
This is the end result of our project, fully painted and assembled. We have control of horizontal motion via the handlebars at the bottom and control of vertical attitude by loosening the axle of the wheel and turning it.
This is the final, last result of the project. We test fired the cannon at 75 PSI at a range of angles to find our ranges and best angles. The data is viewable by clicking the button below.