Mid term examinations, essentially the hump-day of semesters for college students and professors alike. To kick off the season at the OEDK, the ENGI 210 class was tasked with picking out a mechanism from 507 Mechanical Movements to be used as the model for a functioning prototype. Each student was to pick a partner for a “team evaluation” of their mid-term grade.

My partner: Nick Escobar. My mechanism: number 92, the ordinary crank. The initial mission: to create a musical instrument powered by marbles striking metallic surfaces. The original idea came from a youtube video of a hand-cranked music machine which you can follow on the following link! https://www.youtube.com/watch?v=IvUU8joBb1Q

Nick and I decided to split the work up and make a simpler model to see if our engineering skills were at the appropriate level. My job was to get the marbles back up to the dropping position. The initial ideas included using a piston, a wheel with scoops, and an archimedes screw. After going around the designs from a manufacturing standpoint, I discarded the archimedes screw as it would become too difficult to manufacture. After doing some preliminary drawings, the more logical solution appeared to be using a crank-driven piston which led me to mechanism 92.

The modifications began using Adobe Illustrator at the OEDK, and something within drove me to switch over to drawing on SolidWorks. The drawings were looking great, with proper dimensioning and tolerances. I definitely condone the use of CAD software to get an idea of what the design will look like and how the parts will fit (if you are feeling extra ambitious you can even set up a working model to see if the design will work as intended). A word of caution though: CAD software can sink u into a comfort zone called Design Fixation, where you try to perfect the design before having made any part (this is obviously not the goal of the class). After the first deadline, I became design fixated as I wanted to decrease the number of iterations and get a working model from the first try. Falling into this trap takes away so much valuable time of building real prototypes. As an added downside, I managed to lose the USB where I had stored all of my CAD drawings, 2D drawings, process screenshots, and part screenshots. This was about four days before the second deadline (the one where you had to produce a low fidelity prototype).  Panic arose and I felt an urge to change the original design and even started to look for new mechanisms to create something else. After Dr. Wettergreen witnessed my delays, he asked me to build low fidelity hand-made prototypes to at least get an idea of where the design could go. After making the hand-made iterations, I got back on track and started re-drawing my design on Adobe Illustrator (so as to avoid design fixation).I integrated skills learned using makeabox.com and was able to come up with some decent drawings to for laser cutting.

The slot that goes outward was intended to make the dump bucket pivot forward to “dump” all of the items inside. What I did not account for when I made the drawing was the added dimensions of the tabs, these would end up hitting the frame in the back stopping the entire motion of the system. The finger joints should have been smaller to create a tighter fit on the assembly, or glue should have been used. Some parts were moving around quite a bit. I wanted to cut out the links using the plasma cutter, but for some reason the machine would stop traversing and would cut in the same spot until I turned off everything. The program did not even cancel the cut. The part I managed to salvage was the disk for the crank, which was cut from 3/16″ aluminum.

As you can predict from the caption, the holes were made using a 1/4″ drill bit on the drill press downstairs to fit dowels of the same size. After adding the metal disk to the assembly, I realized the wheel had a lot of play and was jamming the entire crank motion. I wanted to cut ribs out of a wooden disk of the same size to use as backing but I did not have access to the band saw as I was running out of time. So I decided to simply glue the wood part onto the disk as an extension.

I had a few hours before class so I started spray painting everything black and wanted to add yellow lines to make it look like a Tonka toy. I realized late that we did not have any yellow spray paint and I did not think to look for other paints. Time had run out, but at least my parts were painted. I proceeded to assemble the pieces and noticed that there was a lot of play and the mechanism did not work very well. This is the importance of iterating through multiple physical prototypes before building a final product.

The mid-term project was a great opportunity to bring a fun mechanism to life, had I dedicated more time, effort, and creativity to it the outcome would have been quite different. This was a great learning experience of what to avoid when building a device that involves hand-made moving parts. It is much easier to purchase multiple components and then assemble them on a design, making the components yourself has greater room for error. I have to be honest, I’m not proud of my project at all. It has also given me insight into a problem I had yet to accept about myself and have taken the initial steps to solving it.