initial DESIGNING THE Barrel support FOR THE CANNON
Before we could start building a cannon, the first step was to have a barrel support that would be able to hold the cannon securely and prevent any minor skews, shakes, or changes of position when it came to fire (1 degree change in position could result in missing the target by a few feet! A good support system was critical).
These pictures were the use of Mr. Twilley's information about inputing our dimensions into an online box maker and then cut it out via Onshape. (Onshape is a design tool that is used to sketch, adjust, and virtually assemble projects where the engineer is free to create all the pieces/parts they would print out on a 2D space, in order to create their 3D model)
Before this, I had never used Onshape before, but I got acquainted with the system with the help of my group members, independent notes, and practice.
Trials & Errors of the box's Holes
Since measurements in the engineering world are never actually what is given (a 4-foot board is, in reality, more like 3.8 feet), so we needed to create openings in our barrel support that would grasp our cannon firmly. Since we had no cannon of our own, we took measurements of Mr. Twilley's previously built air cannon from different orientations and took the average of this recorded data. Then we adjusted our Onshape design accordingly.
Using Onshape and the class laser, we began the trials of holes whose diameters we were testing on the barrel. The purpose was to find the precise and ideal opening size for the barrels of the cannon--Onshape designs allowed for more significant figures in the dimensions of the parts than were obtainable by the limits of human capability and measuring tools used.
The various holes on the bottom picture actually only differed by at most 5 thousandths of an inch! However, they had drastic physical differences. For example, the final diameter of the holes was 2.363 inches, but a 2.365 inch hole would be loose enough to freely spin around the barrel. Our 2.363" was the ideal measurement because it allowed for us to move the face of the box to our desired length, but was firm enough to prevent any wobbling, turning, or shifting once the cannon's barrels were through.
Scrapped connecting piece of barrel support
preparing and Assembling the Cannon pieces
For the reaction between the primer and cement to be immediate and permanent, we applied primer to both the "female" (the inner portions of a connecting piece) and the "male" (the outward-facing surfaces) parts of the connecting joints of the cannon.
These are pictures of us quickly putting the glued and primed pieces in their proper positions, and holding them firmly so that the joining could set, which was at least 30 seconds (but we held it for 45-60 seconds to make sure the bond was permanent since the reaction tends to move the materials from where you placed them--creating a "pushing back out" motion that would be detrimental if the seals between pieces were skewed).
Scrapped Designs for First Base
I think the flaw with these sketches were that they were not realistic for the materials we were given, the mechanics of how it would work, and the time we had to implement the ideas. With each explanation of "how would we do this?", a new problem would arise with "that doesn't make sense because...". Looking back, these ideas were complex but not impossible. With a larger window of time, we could have recreated the VEX robot gears that would allow the the pulling of the front of the cannon upwards, while the back of the cannon remained on ground level (best shown by the left picture). I believe these concepts were born when I came down to Mr. Twilley's other class and briefly collaborated with Charles. However, relaying the concept back to my team served to only find flaws in the theories.
Scrapped "Gravestone" Design
The concept was a vertical structure that would have holes on its sides in which the cannon arms would fit. These holes would be wide enough to hold the cannon (maintain its position at the different intervals) while also being curved enough to allow small adjustments once the cannon was mounted in the correct elevation. In the photo with the water bottle, that was our early demonstration of the idea: the bottle was meant to be the barrel of the cannon, while the hole was a hole in the "Gravestone" barrel support. The idea would be that each hole would control the initial height of the cannon. Then it would be up to the member to tilt the cannon to the desired angle. The many variables and flaws that arose with this concept led to the idea being scrapped.
The ideas that did make it into the final product were the circular and square bases. The circular base would allow full 360 degree rotation (and was fondly referred to as "Ol' Reliable"). The square base, had a circular indent in it where Ol' Reliable would be able to swivel without loosing position.
Designing "Gravestone" Base
This was the Onshape design of the first version of the base structure, but since the Shop Bot cannot print in 3D--not able to cut structures along the z axis (since that would be coming up and out of the material)--we instead had to modify how the base was held together by designing the triangle pieces.
These triangular pieces had tabs that were meant to be inserted into the surface of another material (effectively connecting them like a puzzle). They served to anchor vertical components to horizontal structures in the final base. Looking back, the holes in the barrel support should have tapered at a downward angle--creating an ellipse rather than a circle--so that the cannon's back (the end of the cannon that is the U shape/not the 2 arms) would remain stationary on the floor, while the arms could comfortably angle upwards.
Overall, other than the classic concepts (Ol Reliable, the square base and the connecting triangles), the vertical component of this design was scrapped--probably for the better.
Inspiration for New Base Design
This concept of the tri-pod did not make it to the final version of our cannon base structure, but it was an early attempt at the control of elevation. We liked the idea of the small wheels on the base, but soon removed that as a possibility (since the power of the cannon would have an equal and opposite force (thank you physics) on the structure, and thus shift the cannon backwards. If that were to happen, we would never hit any targets!). It would be up to us to critique how we'd control the movement of the vertical position of the cannon, but nonetheless, it was a promising early design.
This telescope, was a turning point in the project. This image spurred the crucial concept of the rotating "arc". It was able to put into reality what our brainstorming was trying to manifest: a structure that could rotate giving the elevation angle full freedom, while still maintaining a firm grip on the cannon. From here, it would be up to us to figure out how to maximize contacted surface area to the box in order to increase stability, and to find a means of stopping the elevation at the desired angle. This arc concept gladly made it/was central to the finished product.
Sketches for "Arc" Base
These sketches were the rough, but consistent, layouts for the final Arc Base Structure. We demonstrated that the larger the box, the more surface area would be able to be connected, and thus create a sturdier and more reliable structure. We also drew different angles of the view: the side view showed how the holes in the arc would line up with the holes in the base (the 2 parts that hold the entire cannon up). Those holes would be able to be manipulated so that each hole in the arc created its own angle of elevation for the cannon. At the desired angle, we would then place a pin through the aligned holes in order to keep the cannon stationary at that angle.
The way we decided to control the elevation--using the tripod--was to create a ramp where the angled feet of the tripod could slide. Then at our desired height, we cold place a pin across the horizontal ramp to determine the stopping position of the tripod feet--and ultimately the height of the cannon. Looking back, I would have loved to have developed this idea further and include it in the final product. It would have provided us a lot more elevation manipulation.
The triangle connectors were also introduced on the drawing board here. The sketches show that the triangle piece would have a tab that was unique to an opening/indent in an adjacent surface to connect pieces (at 90 degree angles).
These sketches show how we would have created gears to control the angle of the cannon (an idea that was ironically expanded and executed in other groups' designs), but it was not efficiently applicable to the box we had produced, nor was it a sturdy structure.
Designs for Arc Base
Initially, we were going to make one mass for the Arc Base. However, Mr. Twilley taught us how we could conserve material: By creating two interlocking arcs. This meant that we were to make a copy of the arc design, but remove the material between them by adding a top piece into which they could attach. In these pictures, we have the alignment of holes shown, and the creation of the lengths of the "teeth" or the tabs that are meant to interlock with the top piece.
In Onshape, we designed the indent in the square base so that the circular base--on which the entire cannon will be mounted--could turn. We included holes in the square base because after turning the circular base to our desired direction, we could align the holes and hold that position. The T'shaped cut outs were meant to be the matching surfaces to which a triangle connector would anchor adjacent pieces.
This was our 3D assembly in Onshape of the connecting triangle pieces. They had short tabs to fit into the vertical parts since we only needed a point of contact. The bottom of the triangles are completely extended downwards because we wanted a strong contact into the circular base of the support system.
Getting that Perfect Fit
Many. Many. Issues. When one problem was fixed, another popped up. This process was after we cut out the parts in the Shop Bot, sanded them down to be smooth, and the time-race was on! Since the Shop Bot cuts corners in a "T-bone" fashion (meaning that the laser goes past the points of the square corner), and the fact that it was also partially damaged, Shri and I learned how to chisel away unwanted wood material in order to even down the corners, edges, slots, and openings. My least favorite/particularly hard spots were INSIDE the openings that would hold the connecting triangles into the circular and vertical bases. These proved difficult because they could not be sanded down like the other surfaces and edges, and required manual shaving down with various files. *Also, shout out to Kris Burns for saving the day!! After all the sanding, eroding and chiseling was done, Kris used a hammer and small pieces of wood to wedge the triangles into the openings, effectively closing the gaps they had and proving to be one of the most reliable/sturdiest portions of the structure. Those triangles are not going anywhere--not because of the wood glue, but because of Kris. Shri and I would have never thought to do that.*
Success had been reached! Thanks to Kris and the act of chiseling various tabs and openings for over an hour, Shri and I finally got the tabs of the parts to interlock fully! (In the top right photo, it shows that the tab had not been fully submerged in the slot. However, in the bottom photo, we see that the tab was fully enclosed and aligned in the opening of the circular base surface.
Finally, all parts have been assembled, placed, and glued. Final touch ups were adding a bolt in the middle of the structure so that the circular base could spin, but would be spinning around an axis rather than in an indent in the square base (as thought it would in previous designs). Another addition was the use of a small metal rod that would serve to be a pin between the hole in the circular base and the openings in the square base. The Arc Base received 2 of its own metal rods that allowed angling motion as well as stopping action.
Shri noticed that we are loosing the ability to access the higher angles (found towards the back end of the Arc), which defeated the whole point if we couldn't aim upwards. So we sanded the back corner of the base to be curved so that the corner wouldn't hinder the tilting and angling of the cannon. We also cut metal rods to be the "pins" that held the aligned holes in place when it came time to fire.
These pictures are us using clamps overnight to keep the parts in perfect position and even tape was used to keep the glue from dripping away (it made a cool design when bottom left dried though!)
This is our group shooting the cannon outside. On our first firing, our cap popped off because we never really glued it down with primer and cement. After doing so, the remaining pictures show Keon pumping in the air to get the pressure of the cannon up to the right PSI value, me measuring the pressure with the gauge in order to make sure the proper angle and pressure was used to hit our targets, and Shri doing a combination of these jobs on the 2nd day.
When we were outside testing our air cannon in the Battle Ship game, our team placed 2nd with 25 points (acquired from hitting the square surrounding tarp and hitting the lid of the target).