Just a Houston booooy, making a project shaped like a tooooy. Spent his nights in the OEDK, pulling ooout hiiis haaaaair.

Strap in, this one’s quite the Journey.

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For the midterm project, I was tasked with building a crankable, functional, and lovable version of my mechanism from the 2D drawings project. This mechanism was Mechanical Movement 68, the Geneva mechanism, and my corresponding 2D drawing from Homework 03 is shown to the right. Before doing anything else, I decided that my first course of action should be laser cutting my existing 2D drawing to see if it functioned properly. This iteration—my lowest-fidelity prototype—was a success, and can be seen in the brief video clip below.

 

Finding that my gears properly meshed, I then moved on to brainstorming different ways in which the core mechanism could be incorporated into an enticing, crank-driven system. I found this brainstorming session to be more difficult than most, however, because visually interesting applications of the Geneva mechanism aren’t immediately obvious. After wracking my brain for ideas (and coming up with everything from a drawbridge to a scurrying mouse), I finally found a source of divine inspiration from Pinterest (see below/here).

What style, what grace with which that compound Geneva mechanism moves! I instantly fell in love with how it gives the appearance of a simple gear train, but all three drivers come together to drive the center gear in unison with unparalleled elegance. Not only that, but all three drivers must work together simultaneously because the center gear hugs the raised portions of all three drivers. Thus, unless all three drivers cooperate, the center gear will be held in place. While this animation uses a different—and more common, from what I’ve found—version of the Geneva mechanism, I challenged myself to recreate this system with the Geneva gears I modeled after those on 507 Mechanical Movements.

This immediately posed a problem: for the three legs of the compound mechanism to be evenly spaced around the central gear, that gear’s number of teeth must be a multiple of three. However, my previously-designed driven gear had ten teeth. To solve this, I reflected the gear’s tooth twelve times instead of ten, and I used a larger radius of reflection than before so that the arclength between teeth was conserved.

Another conundrum immediately followed: how could three drivers be driven with a single crank? My first thought was a triangular linkage whose center would be the handle of the crank. I envisioned the crank body sitting atop this linkage, but I realized that the triangular linkage would collide with the crank’s axis of rotation. Frustrated, I explored several other ideas, such as an interface of regular gears on the reverse side of the system, but I finally realized that the linkage and crank body could simply swap positions in my initial idea. With the crank body under the linkage and the crank handle extending through the linkage, there would be no collision of axles. I decided that the linkage would be my requisite plasma-cut piece, as its necessary level of precision was relatively low, and using a metal part as the top layer of the design would provide an interesting aesthetic.

With this general concept in mind, I inspected the OEDK’s available dowels—as well as past ENGI 210 midterm projects—to determine what size of dowels would best suit my application. I finally decided on half-inch dowels, and I proceeded to laser cut test pieces with different hole sizes so as to determine the proper hole diameters for my 2D drawings. I found that 0.500-inch holes were perfect for objects intended to rotate freely of the dowel, and 0.487-inch holes were perfect for objects intended to rotate with the dowel.

Another decision that needed making was what the shape of the system’s backing should be. I considered making it a simple triangle, but that would waste large amounts of space along the edges. I ultimately decided to create a much more efficient and geometrically interesting shape, surrounding the multi-toothed gears with equally-sized circles and linking them with circular tangent curves around the outside of the shape. It didn’t occur to me until after I had created this shape in Illustrator that I had just reinvented the shape of a fidget spinner. Surprised and a little disappointed in myself, I decided to embrace my excursion into the slightly cringier side of popular culture and move on. I drew the entire system in Illustrator, as pictured below.

Satisfied with these drawings, I laser cut my different components, fit them together with half-inch dowels, and left them unglued so as to remain adjustable. When I finally put everything together at 1:00 am one night, the mechanism barely moved at all. Despite a bit of sanding, the gears simply ground against one another so badly that the system appeared beyond all help. Exhausted and frustrated, I finally got some sleep, and the next day Pedro suggested that I apply some beeswax as a lubricant. Sure enough, it worked like a charm, and the universe was filled with joy and brightness yet again. My newly functional prototype can be seen in the video clip here (complete with very satisfying clicking sounds as the gears interact).

With this prototype, I confirmed that the triangle linkage worked as I intended, allowing all three drivers to rotate in such a way that they interact with the central gear simultaneously. I also found that I really liked the tabletop orientation of the prototype, so I resolved to continue in that direction rather than designing some method of standing the device on its side. Additionally, I thought that the bulky edges of the triangular linkage obscured the user’s view of the central gear, so I decided to try and minimize the surface area of the linkage. Furthermore, looking at the large, flat gears and base, I decided that I wanted both the base and the gears to be double-layered because I thought the device would be more satisfying to operate if the components had more bulk to them. Finally, I considered how I wanted the device to ultimately be colored, and I decided I wanted the driving and driven gears to be color-coded, and the backing of the device should be a different color than either gear type. Since I had already found that my system was tight enough to require lubricant, however, I didn’t want to risk the added width created by paint, so I decided that this coloration would come in the form of other surface treatments, like stains.

The only problem I experienced with this prototype is that every now and then, the driven gears would rotate a little too far, grinding the points of their teeth against the drivers and stopping motion from progressing. This phenomenon is pictured on the left. To prevent such jamming, I measured the center-to-center distance between a pair of driver and driven gears to determine the distance that would result in the surfaces being flush. I then redid all of my drawings to account for this new distance.

However, this is where I began counting my chickens before they hatched. Just before midterm recess, I came to the OEDK to laser cut my new iteration, but I found that the laser cutter was already in use. Since the plasma cutter was available, I instead decided to try and plasma cut my linkage. My reconfigured, less obtrusive design came out relatively well, although the holes were not wide enough to fit onto a half-inch dowel without incredible amounts of filing. However, with a caliper, I determined that my plasma-cut piece should fit perfectly onto a dowel if I used a diameter of 0.515 inches in my 2D drawings.

Then midterm recess began, and I came to the OEDK to laser cut my new, more tightly-fit iteration of my design. However, none of the supposedly on-shift lab assistants were anywhere to be seen, so I couldn’t get into the laser cutting room. I realized that most of the lab assistants were probably not on campus, and it was unlikely that any of them would be on shift over the break. Sure enough, I checked back multiple times and found nobody. Disappointed, I spent an hour or so double-checking my 2D drawings and making the cut file pictured below. As you can see, I added a second layer for the gears and the base, as well as an etched label on the bottom of the base. I also added several thin rings (seen in the center) to hold things in place on the axles, as well as preventing the axles from being removed. After this brief Illustrator escapade, I finally gave up for the rest of the break. As much as I had hoped to get ahead on my project, I was sure that when I laser cut my design the following week, everything would work perfectly.

That’s where I was wrong. When I finally got a chance to laser cut my next iteration, everything fit so tightly together that no amount of sanding and beeswax could rescue it. Since the original prototype had worked better, I transferred the new gears back to the previous iteration’s base, but even though the gear designs hadn’t been changed, they still functioned very poorly on the old base. That’s when I began feverishly switching pieces back and forth between both bases, trying to figure out how unchanged components had inexplicably become less functional, but it seemed that no matter what parts I used, the system no longer worked as well as before.

That’s when Dr. Wettergreen found me giving my prototypes an intense, far-off stare, trying to figure out what specifically was preventing the system from moving smoothly, while also clinging to the hope that if I fiddled with the pieces long enough, they would somehow start working again. He told me that the central gear in my mechanism was the main problem since all three drivers interacting with it at the same time generated lots of friction, while also requiring ridiculous amounts of precision. Additionally, he informed me that the way in which all three drivers pointed in different directions as they rotated indicated that my system was working against itself. With these new considerations, I finally decided to let go of the complex system in which all three drivers acted on the central gear simultaneously. Instead, I boiled my design down to a smaller, more condensed version in which a single driver sat in the center of three driven gears. The Illustrator file I created for this new design is pictured below.

Now that this design no longer featured my triangular linkage, I needed to find a new part to plasma cut. I decided to plasma cut the new, smaller crank body, as it (like the linkage) required less precision than the gears, and I knew I wanted the base to still be made of wood. Before considering plasma cutting, however, I laser cut the base components of this new Illustrator design to ensure that it worked properly. Sure enough, it was successful, so I prepared to a cut of all of the components and, with any luck, post-process them all the way to completion.

When preparing for the final cut, I realized that I actually needed my base to be three layers: one with half-inch holes to serve as the top surface, one with larger holes to create room such that one of my axle rings could tighten each of the axles against the first face, and a final back face to cover and provide a base for the axles. After creating such layers, I cut the file pictured below.

Once these pieces had been cut, I began by meticulously lining up and gluing together the pairs of gear pieces, as well as the top two layers of the base. I then sanded down the pieces until they were smooth. I also glued the three outer axles to the bottom, hole-less layer of the base, as the outer gears should rotate independently of these axles. Next, I decided how exactly to stain the wood. I knew I wanted the gears to visually pop out against the base, so I gave the base the dark color of a mahogany gel stain. For the gears, I took advantage of the driver gear’s symmetry, flipping it over so that the darker “back” side was facing up. Thus, I could apply beeswax to all four gears (as I already knew how helpful of a lubricant it was) while still creating the color-coded effect between the two types of gears, as I had initially wanted.

While my stained gears dried, I redesigned and plasma cut the crank body for the device. In order to ensure that this piece was firmly attached to the central axle of the device, I added a notch extending into the bore for this axle, planning to drill an equally wide hole into the axle and press the notch firmly into the hole. This would give the crank added integrity and wouldn’t rely solely on the strength of glue. I realized, however, that this notch would prevent the piece from sliding onto the axle in the first place. As such, I elongated the bore for the central axle, allowing the piece to slide along the axle until it reached the point at which to be pressed into it. I took advantage of my previously-determined optimal bore of 0.515 inches, and sure enough, it fit the dowel perfectly. This piece, after being plasma cut, angle ground, belt sanded, and sprayed with a clear coat, is shown in the picture.

After my stained wood pieces were dry, I wiped off the stains, and I rubbed the beeswax-treated components with mineral oil. After these were dry, I sanded the gears and the base one last time with fine sandpaper. Afterwards, it was finally time to begin assembling parts. I began by drilling an eighth-inch hole near the top of the central axle, pressing the crank body’s eighth-inch notch into that hole, and supergluing axle rings to both the crank body and its associated dowels in order to hold everything in place. Next, I superglued the rest of the associated components onto the central axle, including the axle ring on the underside of the base’s top layer, thereby preventing the central axle from being removed. This was successful in allowing the central axle to rotate independently of the base, as shown in the following short video clip.

 

At this point, I could finally glue the bottom layer of the base onto the other two layers. Afterwards, I placed the three driven gears on the three outer dowels and found that the system was still a little tight, so I sanded particularly troublesome teeth of the outer gears. I then applied another layer of beeswax to the edges of each of the pieces, but I still wasn’t satisfied with the smoothness of rotation. To finally settle things, I got some Vaseline, spread it across the edges of all of the gears, and noticed significantly smoother movement when operating the device.

At last, I declared the Geneva Spinner complete. I’m still not completely satisfied with the device’s smoothness of movement, but there’s certainly some diminishing returns at work when it comes to minimizing friction between gears that literally grip the sides of one another. Even so, the smoothness of the device has certainly come a long way, as have its other characteristics. I’ve certainly created a prototype I can be proud of. One last, summarizing look at the Geneva Spinner can be seen in the video below.