Almudena Prieto Prieto and Taylor Junck
The first step in making our globe mechanism was coming up with an idea. We turned to Pinterest for inspiration and found a bunch of world globes. We decided that this would be a good theme for our project, and decided the best way to make the globe rotate would be through a series of gears that would allow the globe to rotate when the handle (or dial in our case) was rotated. We decided to use a three gear system for two reasons: first, it allowed us to separate the handle from the globe giving us more space, and second, it made it so the rotation of both gears was in the same direction. We also decided to use a 2:1 gear ratio because we wanted our mechanism to have two rotations of our dial to one rotation of the globe. To make it more visually appealing, we decided from the beginning that we would make the entire mechanism out of acrylic for the minimalistic and clear aesthetic.
Once we decided on the direction of the project, we created a very low fidelity prototype by cutting simple shapes from cardboard. This allowed us to visually estimate the size of our mechanism. We decided we would have a 8” globe rotating about a 0.25” dowel which was attached to a 4” gear. The dial gear would be ½ of the globe gear (2”). We generated the gears using geargenerator.com. After we determined the rough shape of our base and the size of our globe, we decided to generate the 2D drawings in illustrator that we would then laser cut in cardboard for our medium fidelity prototype. We initially had the gears of this medium fidelity prototype in cardboard, but quickly found that they were not very robust, so we replaced them with acrylic gears. During these low fidelity and cardboard models, we made some changes to the base. We originally were planning on having a closed box in a rectangle shape. However this left lots of empty space and made the base very large to encompass the gears in a linear arrangement.
We decided to size down the gears and cut the box corners into a trapezoid to cut down on the space and material of the base. When turning the globe on the cardboard model, we realized that the axis on which it turns would need to be reinforced by another layer underneath the gears to keep the axis straight, since the globe was heavy and subject to gravity pulling it off axis. At this point we realized we didn’t need to close off the box and would instead have 2 layers, no sides, and changed the direction of the gears to the side of the globe rather than above or below the globe. This allowed us to decrease the size of the gears, since we didn’t have to increase the space between the dial and the globe.
We also determined that we could simplify our original globe design to have less meridians which would also reduce our overall weight, since the globe cut from acrylic would be very top heavy. After some modifications to the illustrator files, we were ready to cut everything in acrylic. When we were assembling our original box, we were not able to obtain acrylic glue, so we decided to use an epoxy. This left undesirable results as it was very visible through the clear acrylic. We decided to spray paint the base to hide the epoxy, but since we couldn’t find any primer for acrylic, we ran into some problems. The first coat went on fine, but was somewhat transparent, so we spray painted another coat or two. This is when the first layer started peeling up underneath. We tried sanding it off and spray painting it again with the acrylic roughed up a bit, but the box looked horrible. We decided to recut our box, since it was relatively small and we really wanted to be happy with the finished look. We would only use acrylic glue to carefully glue the base together to avoid having to paint the acrylic. This is when we decided to redesign the base (big thanks to Dr. Wettergreen for his help) so we wouldn’t have to worry about the angles for the axis on the two layers that the gears turned on, since the gears were all at an angle to tilt the globe. Thinking about having flat edges to glue the layers together via triangle side supports made assembly much more seamless. We decided to paint the screws holding the gears, the globe axis dowel and the dial in a matte black (using a black spray paint and a matte spray finish) to create a more cohesive look.
For the vinyl component of our mechanism, we cut out a world map and placed it on our dial. Additionally, we opted for having our name tag be out of vinyl instead of etching acrylic. Again, we were going for a more minimal appearance. Overall, we are very satisfied with the result even though it caused us a lot of time, effort, and frustration at different parts of the process. Here is our final device:
Cost Analysis
2 cardboard boxes: $3
2 screws, nuts, and 3 washers: $5-10 for a hardware pack, but we didn’t use many so $.50
¼” wooden dowel: $0.25
⅛” acrylic sheet: $10
¼” acrylic sheet: $10
Acrylic glue: $20, didn’t use the whole bottle so $8
Black spray paint: $6, didn’t use the whole can so $2
Vinyl: $1
Labor at $15/hr, 44 hrs between the two of us: $660
Celebratory beers @ Valhalla when we finished: $2.50
Since we have open access to the laser cutters at the OEDK, we did not include this equipment rental in our cost analysis, however if we did not have access to this, the cost would be much higher.
Total Cost: $697.25
Material Cost: $37.25
