By Catherine Wang & Sammie Mahung
When the midterm project was first assigned, we began to brainstorm ideas for potential mechanical models. Our first thought was to build a carousel or something that operates based on a similar mechanism, but after looking over some past projects, we were inspired by all the creative projects past students had made and wanted to create something more unique. After further discussion about our common interests, we thought of a scene in the movie “Kpop Demon Hunters” where Derpy (a tiger) continuously tries and fails to make a flower pot stand upright after knocking it down.
We knew instantly that this was the idea we had been looking for, and thus our prototyping journey began.
Our first step was to clarify the mechanical subsystems for our model, which included the mechanism for the circular paw motion, the mechanism for the flower pot movement, the crank mechanism, and a way for Derpy to stand upright. At this stage of prototyping, our focus was mainly on figuring out how to realize the paw and pot movements, as those were unique to our project and had far less general methods for implementation. To get a better idea of what kind of mechanical movements we would need to utilize, we started off with a rough sketch of what the general motion should look like.
From there, we went shopping on the 507 mechanical movements website, where we saw an interesting mechanism – mechanical movement 222 – that moved similarly to what we envisioned for Derpy’s paw.
For the pot movement, we devised a makeshift cam-and-follower mechanism that intermittently generates a rocking mechanism for the pot. The system consists of a rotating gear with a curved, knife-like object attached to its flat face. As the gear rotates, the “knife” hits a horizontal dowel attached to a slanted “lever” connected to the pot, which brings the lever closer to vertical position and therefore brings the pot upright. When the knife rotates past the point of contact on the dowel, the lever returns to its original slanted position, knocking the pot over once again.
With these preliminary ideas, we created a few sketches on Adobe Illustrator so that we could test them out. These sketches included the gears required to construct mechanism 222, the components required to construct the pot mechanism, and Derpy’s body parts.
With that, we were ready to begin laser cutting cardboard for our low fidelity prototype.
The first thing we did was to get proof of concept that mechanism 222 would work for our paw mechanism. We laser cut our cardboard pieces, used the bandsaw to cut a few dowels, and used hot glue to assemble our first paw mechanism. Through much trial and error, we were able to gain information about the necessary spacing between gears and which dowels had to be fixed versus freely-rotating. Most importantly, we were able to prove that this mechanism would work with some minor tweaks.
Unfortunately, it was difficult to verify the viability of the pot mechanism without a box for it to hang on. For the time being, we printed out a piece of cardboard with a small slit in it to simulate what it would eventually be. While the mechanism did function as expected, we learned that it would be very important to make sure that the width and height of the slit would be somewhat snug around the wooden “lever” (connector) so that it does not freely rotate. We also realized that the angle at which the lever is connected to the pot would be very important to the success of the mechanism.
With these proofs of concept, we went on to lay out how all the gears would be positioned for all the mechanisms to work and started drawing out how all the layers of construction would have to fit together with spacers. The arm mechanism offset the gears away from the plane of Derpy’s body, and the pot needed to be on a plane completely separate to either of those for the “knife” mechanism to move the pot. Thinking through this also helped us plan the box for Derpy to stand on.
All of this helped us design and finalize most of the remaining parts we needed to begin Gate 3, such as the support for the gears as they leave Derpy’s body and move into the box and the support for Derpy’s arm.
To begin our medium/high fidelity prototypes, we cut out all of our parts from wood, except for the top of the box that Derpy would stand on. We initially cut the box top out of cardboard so that we could figure out and troubleshoot where the holes would need to go to fit all the parts of our mechanism. Once we got everything working with the cardboard top, we measured all of the openings we made so that we could add them to our file for laser cutting.
While putting everything together, we decided where to add the crank, and then realized that we needed more spacers as well as some way to increase the stability of all of Derpy’s components since the gears kept lifting out of place. So, we decided to add a backboard to sandwich our mechanisms between it and Derpy’s body for extra security. It only seemed fitting for the backboard to continue with the Kpop Demon Hunters theme, so we made Gwi Ma, the king of demons from the movie who appears as a giant purple fire.
Once we secured all the gears with the backboard, we tested the mechanism to see if Derpy’s arm would move properly. We then discovered that the arm was too tense at a certain point in its rotation and couldn’t move smoothly. At first, we were completely puzzled as to why it wasn’t working as anticipated, but after much deliberation, we realized that we had put the additional hole for the variable movement too far from the center of the gear. After we moved that hole closer to the center of the gear, everything moved properly.
With all our wooden components nearing completion, we were still facing one major problem: the pot wouldn’t fall back easily after reaching its vertical position because of its uniform weight. After some brainstorming, we realized that introducing a small metal piece on the bottom side of the pot could provide the perfect solution. We used the waterjet cutter to cut out a circular metal piece, then laser cut a circle of the same size out of the bottom side of the wooden pot. We also cut out some additional plant/bush pieces that would sandwich and hide the metal to maintain the aesthetics of the pot. We left a little peephole as proof that metal was actually in the pot 😀
The last step before finalizing the assembly was to paint Derpy, the pot, and the backboard (Gwi Ma). While we were able to freehand the pot and backboard, Derpy was much more complex due to the patterns on his fur. Therefore, we decided to cut out a vinyl stencil with the Cricut to help us out. Using the Illustrator files of Derpy we had created at the very beginning of the projects, we created negative stencils to overlay on Derpy, painted over the exposed areas, and removed the vinyl to reveal the final result.
We also stained the box using walnut wood stain for a more elegant finish.
With all of our pieces finished, we were ready to permanently assemble the final product with wood glue. After letting the glue dry to form a secure bond, we tested the overall mechanism out and were very happy to see that the metal piece in the pot had solved our problem with the pot refusing to fall back down. We then synchronized the timing between Derpy’s paw movement and the pot movement by adjusting the position of the paw gear, and followed this by turning the crank multiple times to wear the gears down a bit and allow for smoother movement.
With that, we had our final product!
Overall, building this mechanical model was a huge learning experience for us. Looking back at where we started, it feels slightly unreal that we were able to turn an abstract idea into a real, working piece. Although this was very much a trial-and-error process and there are many things we could have done better (e.g. planning out gear spacings more meticulously), we’re both really proud of this project and overall very happy with how it turned out. If we were to build this again, I think we could improve on increasing the range of movement for Derpy’s paw and make the pot mechanism more dramatic, as it’s not immediately clear what Derpy is attempting to do. Regardless, we hopefully did enough to seal the Honmoon!
Cost:
Materials:
- 3/16” Thick Wood Sheet: $12.89 for a 2’x4’ sheet from Home Depot
- 4”x4” Aluminum Sheet: $32.93 for a 1’x1’ sheet from Metals Depot = $3.66
- 1’x1’ Vinyl Sheet: $1.66 from Michaels
- 4oz Paint: $0.79 for 2oz from Michaels = $1.58
- 5 Paintbrushes: $5.19 for 25 at Michaels = $1.04
- 8oz Walnut wood stain: $12.97 for one quart from Walmart = $3.24
- 8oz Wood glue: $4.37 from Walmart
- Dowels:
- $1.78 for one 36”x0.25” dowel from Home Depot
- $4.04 for one 36”x0.5” dowel from Home Depot = $0.67 for 6”
Tools/Equipment:
- Makerspace: $50 per month for two people = $100
Labor: 33.5 hours x 2 people x $7.25 = $485.75
Total = $616.64
