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Post date: Oct 13, 2017 6:00:07 PM
I began this project with no idea what to create. I browsed around many websites for ideas and found the trebuchet. I thought it would be too simple at first, but I realized that with some testing and research, I could turn it into something more sophisticated that could be optimized. I started with the cardstock prototype, which was potentially one of the most difficult things to create. I slaved over the flimsy cardstock and masking tape for a couple classes and couldn't even get it to fire. By the time I was ready to move on to the cardboard version, the top of the trebuchet was leaning so far to one side that it was almost touching the floor.
I started with the cardboard version. I really enjoyed optimizing the trebuchet with this version, and it was probably my favorite part of the project. I had to find the proper ratios for the weight of the projectile and counterweight, the length of the arm, and from where to release the arm to make it fire the farthest.
I was also able to master the use of the laser cutter when creating the cardboard version. Making this required many trips to the laser cutter to cut new parts to make it more efficient. I specifically learned about using the "set home" feature to save material and the importance of making sure it is in the correct place when I accidentally cut slots on the wrong part of my cardboard. After the cardboard prototype, I learned the importance of "measure twice, cut once." I had to make several new versions of parts because I did not think the calculations through before cutting or was rushing in Inkscape.
Also, throughout the cardboard prototype and into the final version, I struggled a lot with the sling. It either wouldn't release the marble I was using or it would release it too early, causing it to shoot straight up instead of forward. I couldn't find out why. After creating most of the final project, Mr. D. helped me do some research to overcome this challenge. We found that the payload arm needs a peg on the top that the string could rest on so that one side of the sling could release at launch. This allowed me to overcome the sling challenge quickly and move ahead. Mr. D. also helped me with a minor challenge in the final project as well. When gluing the final parts together, I didn't realize how long it took for wood glue to dry. I glued some parts together in the middle of class and thought that they half of class would be enough time to dry. At the end, I picked up the parts and they fell apart and onto the floor. Mr. D. showed me how to properly apply the glue and that it takes two hours to dry. I also learned from Mr. D. that I would need a bottom board to stabilize the trebuchet, which proved to be very useful later on.
With the end of the project approaching on the last day of work, I felt extremely proud when I shot the trebuchet for Mr. D. to see and the marble flew further than it ever had before. It was by far my finest moment in the class.
Day 1: 10/112/17
Today, I used my sketch to begin creating a paper prototype for my trebuchet project. This sketch gave a scale model drawing of the trebuchet, which I was able to create by finding the proper proportions for the various arms and supports on http://shortsleeveandtieclub.com/designing-a-trebuchet-optimizing-weight-and-length/.
The creation of the paper prototype began with the creation of scale parts made of cardstock. I decided to make the model half scale of the original design. I drew out all of the parts with proper measurements. Below is a photo of the parts before cutting them out.
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Original Sketch
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Outlined Cardboard Pieces
Day 2: 10/13/17
Today, I cut out the parts for the cardstock prototype and began assembling them using masking tape. I created the base, the vertical supports, and the diagonal supports on both sides. I was unable to complete the arm or the payload section today. I also created two extra copies of the payload arm to tape to the original copy. I decided that this was needed in order to stabilize it as it was a moving part that will be operation under heavy weight. It took me several tries to get the parts to stay with tape because of the flimsiness of the cardstock. I will complete the first prototype next class
Day 3: 10/17/17
Today, I completed the basic paper prototype. Coming into class, I found that the prototype had been broken on the shelf, so I began by reinforcing it with some tape. Afterwards, I used an X-Acto knife to cut circular holes in the main support beams. These holes on either side would support the center bar. I also cut a similar hole in the payload arm for this bar and assembled this mechanism with the use of a bit of tape. I then used a push-pin to attach the weight box to the short side of the payload arm. I filled the weight box with paperclips. Afterwards, I created the payload sling with a very wrinkled piece of cardstock and two pieces of string that I wrapped around the cardstock and attached to the arm with another push-pin. Next class, I am going to start by reinforcing the weight box, as it is a bit fragile when in motion. A picture of the nearly completed paper prototype is shown below:
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Cardstock Prototype
Day 4: 10/19/17
Today, I reinforced the paper prototype with a longer push-pin for the weight so that it does not fall apart with its own weight in motion. The prototype leans to one side, but I resolved that it wasn't necessary to make it completely stable, as it was made very flimsy by the cardstock. I also began to make the design for the parts of the actual design on Inkscape. I used the grid function on Inkscape to make it easier to measure the parts. I created two longer pieces for the length of the base and two shorter ones for the width of it. I made each of them 45 degrees at the end so they could be glued together cleanly. I also made two main column supports with a hole at the top for a dowel. I made two diagonal supports as well. I made the payload arm with a hole at the end to secure the weight as well. I have yet to finish all of the parts and will do this next class. A picture of the parts in Inkscape is below:
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Partial Inkscape Design
Day 5: 10/23/17
Today, I made some edits to the Inkscape design that would make the trebuchet operate more smoothly. Mr. D. recommended that I make the holes the same size as the dowels available in the Fab Lab, so I made them 5/16 of an inch. I also added an extra hole to hold the payload arm in place, as I forgot this earlier. I created the weight box as well as some supports for this. The weight box was a cube box that would hold a heavy object inside. It would be supported by two smaller pieces of cardboard that would have a hole the size of the wooden dowel. These pieces would be glued to the weight box, and the dowel holes would line up with a similar one in the payload arm so a dowel could hold them together. I made a hole near the end of the payload that I can feed the string through for the payload sling. Finally, I got the printer ready to print the pieces in cardboard but did not have enough time to complete this. I will print them next class
Day 6: 10/24/17
Today was not a full workday, so I was not able to complete as much as I would have like to do. I was able to set up my trebuchet design in Inkscape on one of the desktop computers to prepare to laser-cut it onto cardboard. After doing so by making the lines red and hairline width and making the setting correct, I began to cut. I had to use an almost completely new piece of cardboard as this prototype was to be full scale. I began to assemble the base for the trebuchet with hot glue but realized that I would not have enough time to complete it. I also noticed that it would be much more efficient for me to laser-cut two slots on either side of the base so that the main pillars can stay standing more easily. I will create a file with these new cuts in place with the proper measurements next class. Below is a picture of the newly cut cardboard with a little bit of assembly.
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Cardboard Parts
Day 7: 10/26/17
Today, as I was planning the assembly for the cardboard prototype, I realized it was be much easier if I could insert the supports with some slots in the base. I created an Inkscape design with these slots and the proper spacing and cut it into my cardboard base. I made all of them one inch only to realize that the secondary supports next to the main beam would need to be larger to fit the supports cut at 45 degree angles. I created another Inkscape design with the slots 1.41" each and cut it but didn't realize that the laser cutter's home was set at a different location. It cut in a different place from the original slots. Luckily, the entirety of the new cuts made it onto the base. I planned out the rest of the design and ended up making some of the supports shorter as they were too long to fit before. I will glue in the supports tomorrow. Here is a picture of the new base with two sets of slots accidentally cut:
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Cardboard Base
Day 8: 10/30/17
Today, I almost finished creating the cardboard prototype for the trebuchet. After cutting the rest of the secondary supports to the correct size, I hot glued them to the base along with the main beams. I found one of the wooden dowels and cut a large piece for the main cross section and a smaller piece for the weight box on the band saw. I used a screwdriver to lightly loosen the holes that hold the dowels in order to support better rotation. I attached the dowel and the payload arm to the trebuchet and hot glued the weight box together, making two of the four sides triangular instead of the original square plan. I attached the weight box to the payload arm with the dowel and two laser-cut cardboard arms. I also used a very thin but strong piece of string and some metallic tape to create the sling. I measured the string to be the same length as the payload arm and tied it around the tape and through the hole I cut for the string in the payload arm. I have yet to decide on a weight and a projectile and will figure this out next class. A picture of the nearly completed trebuchet is featured below:
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Cardboard Prototype
Day 9: 11/2/17
Today, I decided to make some modifications to the weight box, the base, and the sling on the prototype. I began with the weight box. The last time I tested it, it hit the side main beam that holds up the payload arm. I made a new design that was smaller but could still hold a decent-sized object. I printed it out and attached it.
Next, I printed a new base for the trebuchet. I measured the inside space and printed a new rectangle. This allows me to put the payload on the base without it getting caught during launch. I slid the rectangle into the frame, and it pressed in perfectly.
Finally, I did some testing on the sling, even though it's only the prototype. I tried using some tape like I did last time, but it proved to be too stiff. I experimented by making the sling more cupped or flatter, but the marble I was using either fell out at launch, went backwards, straight up, or straight down. I got a tip that I may need to use fabric instead of tape to make it more flexible, so I decided I would do some research later.
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Cardboard Weight Box
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Cardboard Prototype w/ New Base
Day 10: Saturday 11/4/17
Today, I used some time I had on Saturday to do some research on the sling and rope mechanism. I discovered from observing different examples on http://www.siege-engine.com/SlingsAndPouches.shtml that the sling should be shaped roughly like an ellipse, be made of some sort of cloth, and have only one piece of string on either side to attach it to the payload arm. I will make these adjustments the next time I am in the Fab Lab this coming week.
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Tape Sling
Day 11: 11/6/17
Today, I started class with a few minutes testing the sling. I cut away the second version of the sling and made a new one with some green felt I found in the Lab. I cut the felt into an ellipse shape and made two holes on either side. I used the same string as before as well. I attached it to the trebuchet and did a few tests, although the cardboard was too flimsy to hold the weight of the marble and the weight because a few new creases had been created in the supports. And even when I held the supports to stabilize them, the tape either held the marble too long and caused it to go straight down or released it too early to make it go straight up. The sling has been a big challenge throughout the project. I decided I would wait for the final wood copy to do more sling testing. I also finalized the Inskcape document for printing on wood for the final copy. I decided that I would use 1/4 inch wood to make it more stable. I fixed the base to make it one whole piece with six slots for the supports. I also copied some pieces to the main document and had to use a second document to fit all of the pieces. I consolidated everything to make it as small as possible on the document. I will be using the next class to print it out and begin to assemble it.
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Penultimate Inkscape Design
Day 12: 11/8/17
Today, I found some 1/4" wood to cut the final version on. I found out that the boards were 18" by 24", so I had to do some rearrangements on the Inkscape document to put it all in one file instead of spread over two, as I originally had two documents with 12" by 24" pages in them. I also experimented with some circular pieces that Mr. D. recommended that would act as spacers between the supports and the payload arm on the trebuchet. I designed them on Inkscape and found I would need 18 of them in between the supports and the payload arm to space them apart and two outside the supports but still on the wooden dowel to hold the supports in place. I decided I would glue these ones on. I created 19 copies of the original piece in the document and spaced them out for a total of 20 circular pieces. Before cutting all 20 of these pieces on 1/4" wood for the final, I cut a cardboard piece to make sure it fit quite snuggly around the dowel, which it did. I began to cut out the final parts on the laser cutter, not realizing how long the 1/4" settings would take to cut. Mr. D. was very nice and offered to supervise the cutting while I went to my next class. Next time, I will assemble the parts with wood glue.
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Final Inkscape Design
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Some of the Final Pieces
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Close-Up of the Circular Spacer Piece
Day 13: 11/10/17
Today, I began to assemble the final phase with 1/4" wood. I began to put it together but discovered that the ends of the diagonal supports were cut at too sharp of an angle to line up against the main vertical support and the slots for them in the base. I looked on the Inkscape file and found that this was true. They were not exactly 45 degrees on either end. I made some adjustments so they would be 45 degrees and cut out these four parts on the original piece of 1/4" wood. These fit perfectly into the slots and along the main vertical support. I began to use the wood glue to put the trebuchet together. I started with the main supports, not realizing that wood glue can take up to two hours to fully dry. I put some of the supports in and used some extra bottles of tacky glue to hold them up while I moved on to gluing other parts. Near the end of class, I removed the glue bottles to let the supports stand by themselves. They quickly fell over. I asked and learned how long the wood glue really takes to dry. In order to make up for some of this lost time, I decided to come in during my free block that same day.
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Drying Base w/ Supports
Free block: Day 13 and a half 11/10/17
I came back into the Fab Lab to glue the parts together again. I glued in the supports with the wood glue. I decided I would glue as much as I could take advantage of the weekend and let it all dry. Mr. D. also recommended that I cut out some small triangle pieces to hold up the main supports. I made two 1.5" isosceles triangles on Inkscape and cut them on the laser cutter. I glued these into place along with the rest of the basic parts. I also cut the dowel and put it in place between the main supports so I could space them correctly to dry over the weekend. I put on the circular parts to space out the arm from the supports. I also glued the weight box together that will go on the opposite end of the arm from the payload. I left on panel off the weight box so I can experiment with different weights in the box during the next class. I will work on testing the weights, fixing the final sling, and sealing up the weight box next class. Before leaving the Fab Lab at the end of the day, I made sure everything on the trebuchet was set perfectly so it would dry in the right place over the weekend. I will conduct tests and finish the assembly next class.
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Drying Assembled Version
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Close-Up of the Isosceles Triangle Supports
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Drying Weight Box
Day 14: 11/13/17
Today, I attached the weight box to the payload arm on the trebuchet. My original design for this section had the two pieces of wood that hold up the box attached to the top of the triangle. The other ends of these pieces would line up with the arm, and a wood dowel would be placed in the three holes to put it together. This worked with the cardboard version of the design because the cardboard was more flexible and could bend around the box to give more support. I could not bend the wood, and the wooden box was too heavy to be held up with only glue from the top of the triangle. To solve this problem, I rotated the box so that the flat faces of the box, as seen in the picture below, were facing the sides of the trebuchet. I then attached the pieces that hold up the box to these flat sides and used a longer dowel to feed through the holes in the support pieces and the arm. I still had to assemble the last face of the box, but I decided to wait in case I wanted to change the weight I used inside. But, instead of using the entire face, I cut a small part of it to use to hold in the weight but make it removable as well. I will do more testing next class.
Cardboard Version
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Final Wood Version
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Free block day 14 and a half: 11/15/17
Today, I began optimizing the nearly complete trebuchet. I started with finding the optimal weight. I needed something that was very heavy but small enough to fit in the counterweight box. I found a small hexagonal piece of metal that was quite heavy, but it stuck out a bit from the weight box and was not heavy enough to fire the marble that I had selected. I later found a rectangular piece of metal that was used as a weight for material on the laser cutter. It was very small and extremely heavy for its size. It fit perfectly in the weight box. I also needed to finish up the sling, which had been giving me trouble since near the beginning of the project. I asked Mr. D. for some help. After helping me with some research online, we discovered that the fabric, which was felt for me, had to be cupped enough around the marble that it would hold it in place. We also found that the string on one side of the sling would have to be detachable from the payload arm so that the marble could be released during launch. He helped me make a piece with a notch that the string could slip off of when I fired the trebuchet. After gluing this on, I assembled the sling. Mr. D. advised that I may want to secure the trebuchet to a larger panel of wood if I am using such a heavy weight with so much momentum. I will investigate this more next time.
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New Release Peg and Sling
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Close-Up Release Peg
Day 15: 11/15/17
I devoted today to testing the trebuchet. Within the first launch, the trebuchet fell over from the momentum. I realized how vital a panel on the bottom was to keeping it steady. I found a temporary piece and clamped it on. Also, the first test revealed that the new peg on top was a success! The string on one side of the sling released from the top of the arm, allowing the marble to slide out of the sling and fly farther than it ever had. I did some testing with the angle of the arm to find out where its starting position should be. I found that the best place to put it would be a bit past 45 degrees. I decided to create a locking mechanism to keep the arm at this angle next time.
Free Block day 15 and a half 11/16/17
We didn't have class today, so I came in during another free block. I went to the woodshop and found a nice slab of wood to secure the trebuchet to. I used drywall screws at Mr. D.'s recommendation and drilled them into the base of the trebuchet and attached it to the slab. I also decided to make a locking mechanism for the launching of the trebuchet. To do this, I cut to pieces of wood on the band saw and drilled a hole in each one for a hook. I screwed in the hooks by hand and glued the wood down onto the base of the trebuchet. I imagined that I could put a dowel on the hooks to hold down the payload arm and removed the dowel to release the arm. I decided to wait until tomorrow before testing it to let the glue dry before putting the mechanism under any stress.
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Screwed in Base
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Locking Mechanism
Day 16: 11/17/17
Today was the final day of Design class in the Fab Lab. I checked on the locking system and found that the glue dried nicely. I decided to take the trebuchet outside and test out the completed version with the locking mechanism. I tried sliding the dowel out from one side, but it got caught from friction on the payload arm, causing the arm to tilt to the side and the weight box to hit the support columns. I decided I would take advantage of the extension of the dowel outside of the hooks, as pictured above. I used my fingers to hit both side of the dowel down on the outside of the hooks. This allowed it to leave the hooks evenly and quickly enough that it wouldn't hit the sling and the projectile at launch as well. I took a photo of the final trebuchet and some footage of it firing below.
Final Design
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Open to see trebuchet fire: https://drive.google.com/open?id=1THIONCUlic62mRyTSufnoOz16gbMQcJC
Open to see Inkscape file for trebuchet parts: https://drive.google.com/open?id=1NDcCWRIW7zii7FBgaTHSZiikMPwT-mdN
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