Introduction

After brainstorming ideas for our mechanical model, Madison and I decided to build a rotating globe. Although we thought this would be rather simple, it turned out to be much more intricate.

Low Fidelity Prototype

We began by researching laser cut globes to determine how we would create a spherical shape out of flat wood. With Dr. Wettergreen’s help, we acquired a pre-made illustrator file for the globe we wanted to build. We selected the portions of this file that were crucial for our low fidelity prototype, and laser cut those out of cardboard. We also used a gear-making website to get the correct sizes for our system of gears, and the correct spacing for the dowels. Finally, we used makercase.com to build the octagonal base of our globe. Here is what our low fidelity prototype looked like.

Medium Fidelity Prototype

In beginning our medium fidelity prototype, we encountered quite a few issues with the globe file. This model had many pieces and no information on how to assemble them, so a great deal of our time was spent trying to understand the model and adjusting it to our needs and materials. 

For example, in order to make the file compatible with the thickness of the wood we were given, we needed to scale everything up (since the model contained slots). However, this created a globe that was approximately 25 inches in diameter–far larger than what we wanted. So to correct this issue, I spent many hours painstakingly recreating the slots, so that each slot would match the thickness of the wood while the rest of the model remained a smaller, more reasonable size. 

At some point, we realized that this was taking up far too much time, and we needed to reevaluate the complexity of our method. So for the medium fidelity prototype, we focused on the gears, where we honed in the size and placement, and the base, where we added finger joints and engraved the seven wonders of the modern world. Here is our medium fidelity prototype.

Final Model

We had a lot of work cut out for us in the final weeks. After deciding that our original method of constructing the globe would be far too time consuming and complex (it involved gluing 144 wooden trapezoids), we pursued a dymaxion globe instead. A dymaxion globe consists of 20 equilateral triangles laid out in a specific placement, then “folded” together to create a somewhat spherical shape.

We laser cut these triangles with the world map engraved, then carefully sanded each of them to remove the laser burn. This made the whole model instantly look so much better! Here’s a before and after.

We recut the base with smaller engravings and shorter sides, then sanded away the laser burn on these pieces as well. We laid out the triangles in the specified order, then pieced them together by holding them in place with tape, gluing the edges, then peeling away the tape. We had to do this in three different sections: the top (5 triangles), the middle (10 triangles), and the bottom (5 triangles).

While waiting for the globe to dry, we used the water jet cutter to make the central part of the crank. 

Once the globe dried, we put everything together, with dowels (that extended through the base) attached to the gears, a crank attached to the outermost gear, and a dowel attached to the innermost gear to support the globe. At this point, everything worked fairly well, but we realized that the weight of the globe and the slightly imprecise fit of the dowels caused the gears to tilt slightly out of alignment after repeated use. So we decided to laser cut makeshift tunnels for the dowels and glue them inside the base directly underneath the gears. This would, in theory, stabilize the gears and keep the dowels from moving inside the base. Aligning the tunnels proved to be very difficult, though, and for the innermost gear, we decided to instead prevent the gear from tilting by adding small supporting dowels directly underneath the gear. Here is our final model!

Cost Breakdown

¼” 48 x 96 sheet of plywood: $29.88

⅛” 12 x 6 sheet of aluminum: $4.08

Labor (~30 hours x $10/hour x 2 people): $300