One of the most iconic aspects of ENGI 210 is the midterm project. Students and OEDK visitors always enjoy playing with the various mechanisms and seeing how they’re put together. These projects are sometimes the deciding factor when a students are considering adding the course to their already packed schedules. The creative freedom and technical challenge of the project made me excited for this class.

This project involved selecting a movement from 507 Mechanical Movements and creating a 3D replica. I wanted to create a project that was not just a movement, but was an entire themed device. After some brainstorming, I decided upon movement 346. 

I immediately sketched up the design in Illustrator. The members were not to scale, because I simply wanted to get a visual of how the device actually worked in 3D. Since I do not know Solidworks, I took the time to laser cut a cardboard miniature prototype and see which parts were translating, which parts were rotating, and which parts were just supportive members. I forgot to take a picture of the prototype (a common theme for this project), but it gave me a greater intuition to start sketching the actual designs.

I decided that my overall theme would be NASA. Why? Well, why not?

I designed the channel to be the center of the rocket and the piston to be flames that are exiting the rocket as it takes off. My initial plan was for the base to be a wooden box for the crank. The rocket would float above this box with a vertical back member for support. However, after some discussion with Dr. Wettergreen and my partner Tori, I ended up modifying the sketches to include an acrylic box. The acrylic would add stability to the device and allow the translating ‘flame’ member to be seen clearly. So with the new designs in hand, I began building the Illustrator laser-cutting templates. Though they are often underused, artboards in Illustrator are extremely helpful. I set up multiple artboards to organize the parts and designate what parts were complete from those still needing to be cut.

With the files complete, I began to assemble a medium-fidelity prototype. Looking at the past ENGI 210 projects, I noticed that many students used the technique of stacking 1/4″ plywood to achieve a desired thickness. I used the same technique in my design, making the channel separate from the rocket itself to create the needed protrusion for the internal components. I also stacked the hand crank and lever arm in order to add stability for the wooden down axles.

Now a sophomore and TA for ENGI 120, I have had a lot of experience with the prototyping and engineering design process. One of the biggest lessons I’ve learned is to not put excessive effort into lower fidelity prototypes, as their main purpose is functionality or proving a concept, not aesthetic. Thus, all of my prototypes up until the deadline were secured with orange painter’s tape and pipe cleaners. It may look stupid, but it’s even stupider to permanently fasten pieces together only to find multiple design errors  ¯\_(ツ)_/¯

*add image of taped components from med-fid prototype*

Before moving on to the next prototype, I reread the rubric. One of the requirements for the mechanism was for a moving part to be plasma cut. Knowing that the rocket would look better if made from wood, I decided to plasma cut the hand crank and lever arm. After using the belt sander and a file, I used medium grit sandpaper to achieve a metallic finish. My initial intent was to sandblast the pieces, but after dealing with some metal scratches during assembly I just sanded the pieces again.

 

Now, the rest of this project kinda devolved into a bunch of minor/major problems and my attempts to solve them. Since I was too focused on the project to take pictures, here are just a few of the issues I encountered and different approaches I took to get to the final prototype (as you can see, the majority of the issues revolved around the flame vertical member…)

1. Vertical member would not move within chamberSolution: tallow (i.e. animal fat) for wood-on-wood lubrication and a little bit of sanding.
2. Vertical member rocked side-to-side when it was supposed to move strictly up and down 
   Solution: Make the neck of the translating member the exact width of the channel (a la shape-builder tool). The laser cutter will already create a small gap and you can use tallow for smoother movement.
3. Vertical member rocked from the front to the back of the acrylic box 
   Solution: Add a “t” shape to the translating member that is flush with the box’s dimensions. As seen in the final prototype, this is a thin bar above the flames. It restricts the flame’s path to the box.
4. Wooden washers kept breaking when being press-fit to wooden axles
   Solution: Just cut them out of acrylic. They will fit better and not split every time you breathe on them.
5. Entire mechanism refuses to rotate
   Solution: Make sure rotating members are properly aligned on their respective dowels. Add washers for spacing. Be patient and USE TALLOW.
6. Making a functional prototype with an aesthetic theme
   Solution: Painstaking etch the rocket only to realize white paint will look more realistic than wood stain. Borrow Tori’s white paint only to discover it is clumpy and difficult to use. Find better white acrylic paint and spend hours painting the rocket, the flames, and all wooden axles. Watch the paint slowly chip away during assembly. Grit your teeth, finish the mechanism, and repaint at the end. Etch intricate designs into the acrylic box to try and detract from any painting flaws.

The past couple weeks have definitely been rough. I have without a doubt spent more time on this project than all my other midterms combined. And even though the motion is still not as fluid as I would like and there are some cosmetic flaws, I am satisfied with the end result. I originally thought I had bit off more than I could chew by choosing such a complex machine, but this project showed me that I’m capable of executing a difficult project. I just have to be willing to ask for help and put in the effort needed (even if that means spending 12 consecutive hours at the OEDK).

And without further ado, the final prototype. 3…2…1….lift off!

Click to see the rocket in action: IMG_4184-1gwxruo