Design:

It took us a while to decide on our gear train project. First we looked though Dr. Wettergreens books on wooden mechanical devices, and I (Marie) was personally fascinated by the worm gear, but we were not quite sure how to meaningfully incorporate it into a gear train. We finally decided on creating an orrery using the first three planets of the solar system.

We watched many Youtube videos about how to make an orrery, and decided on a slightly simplified version. The design works by using nested shafts which would be linked to a gear tree so that each planet would have a different orbit. We also looked up the ratios of the orbits of Mercury, Venus, and Earth so the ratios would reflect their real orbits.

Here are some notes and calculations on planet orbits, gear ratios, and proposed ideas:

Proposal 1: 3 different gears

Distance between gear tree axis and main axis is 1.5.

Proposal 2: 5 different gears

Distance between gear tree axis and main axis is 1.6.

The planets will all align every 36 Earth orbits (or 45 Venus orbits or 80 Mercury orbits)

All numbers listed above are ratios and can be scaled up.

Number of gear teeth is proportional to the gear diameters.

To make the gear tree mesh:

Mgear + Mtree = 2*Vgear = Egear + Etree

-since we can reuse the Venus gear for the corresponding tree gear

in IronCAD:

Edge bevel = 0.03

Depth of groove = 0.005

fabrication and assembly:

Gears: We designed all the gears in IronCAD using the star-shaped pre-made shape. By adjusting the number of points on the star and the thickness of each star “arm,” we were able to make pretty accurate gear-like shapes in IronCAD that would mesh together quite nicely. We then set these gears to 3D-print on the Fordus. After gears were printed we used OOMOO to make the negatives. We mixed the OOMOO in one container, made sure there weren’t any bubbles, and moved it to a wider, flatter container, and placed the gears in. During this process, we were extra cautious about bubbles, poking them with a safety pin. We then Removed the 3-D printed gears from the cured OOMOO and used 300 to create our final gear products for the orrery. One problem we encountered was the OOMOO sticking to the 300 after everything had cured. We tried many things to get the OOMOO to come off. We tried pipecleaners as scrub brushes, which worked to some extent, but took forever. Then we pressure-washed them which proved more effective. We also sanded the gears in assembly to decrease friction.

Base + Stand: The stand and base were designed using Adobe Illustrator and then laser cut using both acrylic and wood. We based the top part on a fibonacci spiral that at the time looked to Mikaela like the Milky Way, but when it actually printed it kind of just resembled a triangular spiral. We also had a couple of issues with the gear crank: we had originally intended to re-cast one of the six gears that we had already cast for the gear trees for the actual orrery; however, we found that these gears do not rotate very well perpendicularly. Instead, we also designed another pair of gears to be cut out of acrylic, which we did using the rotate function on Adobe Illustrator. Adding in the second set of gears proved to be problematic, as we needed to incorporate them onto the gear tree dowel without having them impede the rotation of the gear tree. As such, we added a second tier of base, beneath which the acrylic gear for the crank would rotate. We made this circle slightly larger for artistic effect. Cutting  this proved to solve most of our problems with the gear tree, although the acrylic gears did experience some friction. We found that placing the gears a little further back so that they were not entirely flush decreased this friction pretty well, so we inserted wooden washers on the crank shaft to preserve this spacing.

We also designed “arms” for the planets in Adobe Illustrator, at appropriately staged lengths according to the orbital radii calculated above.

Planets: For the planets we first thought to paint spheres like planets. We did this, but unfortunately there was a lack of communication and the painted spheres were actually too big for the arms we’d already laser-cut (but they were beautiful and gorgeous and Marie is amazing anyway). Instead, we decided to use marbles and a foam ball which we painted gold then put gold glitter on for the sun.

Assembly: After laser-cutting and casting all of the pieces, we began assembly. We used laser-cut pins on the sides to hold all the pieces in place. The laser-cut elements did not cause us much issue in assembly, but we found that the gear trees had lots of friction between each other. We used a pipe-cutter to trim the nested metal shafts to appropriate lengths, and we used a wooden dowel to hold the secondary gear tree together, as the secondary gear tree required that the three gears rotate at the same angular velocity. After assembling the gear trees, we began assembling the base. We took the largest circle first and attached circular washers/spacers on the sides, which accounted for the space taken up by the acrylic crank-shaft gears. We also glued the base for the crank shaft into place.

After we assembled the base, we began experimenting with different ways to make the gear trees rotate more freely with each other. First, we tried sanding all of the gear trees and the tops of each gear. We found that we (mostly Mikaela, who seemed to have failed kindergarten gluing) had used too much epoxy when assembling the gear trees, which made the movements of each quite sticky. After sanding off the excess epoxy residue, we found that the gear trees spun fairly freely, although they still stuck inexplicably. After adding a generous layer of tallow to the gears, we found that this rotation became much more easy.

After we had debugged the gear trees, we glued the acrylic swirl on top to hold the shafts in the upright position. We trimmed off the excess dowels, added on the planets and their planetary arms, and finally attached the sun. The orrery was complete!

link to the video: click for video!