Created by Sophie Leibowitz and Damian Gonzalez

This was our longest, most challenging project yet, and it took us almost 4 weeks start to finish! For this mechanical model, Damian and I were inspired by movement number 55 from 507 mechanical movements, with a large internal gear and two smaller spur gears inside of it:

We were quickly drawn to the theme of planets orbiting, so these two ideas combined led us to our initial sketch for our model:

From there we began creating the 2D models of our parts that we would need to print or cut. For the orbiting planets, we took inspiration from a previous year’s project:

Our plan was to replicate this using wood with far fewer rings and notches.

We created the svg files for our gears with the help of geargenerator.com, which was very helpful in allowing us to set and change pitch diameter and diametral pitch as desired. Our initial plan was for our large external gear to have a pitch diameter of 7 in, but when we took the files to the cutter, we discovered that for some reason it had scaled everything up by 2 times. Undeterred, we decided that we actually liked the look of the larger gears, and kept going with the print. This meant that our largest gear, the internal one, had a diameter of 14 in.

The laser cutter cutting the first iteration of our gears.

We also decided to test the fit of our planet pieces using cardboard, which we cut at the same time. From there, we assembled our first low-fidelity prototype using our gears and bearings. Damian had the idea to support our large internal gear using four bearing supports, as shown below. The gear would sit ontop of these and rotate as the user’s hand guided it around.

A bearing stand for our large internal gear.

Our low-fidelity prototype.

We took several lessons away from this prototype. First, we needed to use sturdier dowels to support the planets in the final product, as the flimsy low-fidelity ones kept bending as the bottom gears rotated. Second, the alignment for our top central gear and the smaller “planet” gears was off, to the point where the planet gears couldn’t be driven around the middle one. Lastly, we decided to cut holes in our internal gear to press fit the dowels into, instead of just relying on the epoxy to stick them down.

We initially planned to test the fit of our planet pieces using carboard, but found that it was too flimsy to truly replicate how the notches would fit together with wood. Due to this, I began the process of designing and iterating the perfect fit ratio for the wooden pieces. I began by selecting the desired diameters for our three inner rings, and then changing the fit of the outer “semicircular” pieces based on that. It took about three iterations to find a sizing that fit well. Between this and the double layered gears that we needed to print for our final product, I got to know the laser cutting room very well, as some of these cuts took ~30 minutes!

An iteration of our wooden planets. As you can see, the middle ring is too small to fit with the outer edges.

A well-fitting test planet, put together using hot glue. 

At our instructor and TAs’ recommendations, we decided to double layer all of our gears to allow them to fit together easier. We then glued the two halves together with wood glue and left a piece of acrylic on top of it overnight to allow it to set. We also printed some acrylic stars for decoration.

Our final gears, printed and ready to be glued.

The final print of our base, with holes for the supports and bearings.

We opted for  a multi-colored splashing color scheme, with different gradients on each gear and planet. With that, it was time to put together our final model. First we constructed the base and the bottom three gears:

The bottom of our model put together. You can see all of the gears fully colored.

When putting the upper large gear in place, we quickly realized that it would not be able to support itself and stay stationary with only one dowel beneath it, as the planet gears were not rotating around it effectively. Due to this, we drilled 4 holes into the upper gear and the gear below it, and inserted four dowels vertically for extra support.

This helped a lot, and we found that the top was now able to remain stationary as the planet gears spun. From here, it was just a matter of making everything fit as best we could. At one point we tried to install supports for the planet dowels, but found that they fell of too easily as the model underwent the stress of rotation. We also glued on our metal part, a model rocket, which we had cut on the waterjet in the prior weeks.

Our model drying, almost complete. You can see a support in between two of the dowels that later fell off.

We found that the model was able to spin, albeit really roughly. Due to this, we sanded the teeth of many of the gears, and covered most of the contact surfaces in charcoal lubricant, which helped. However, in the process our model got completely covered in the black powder, so we needed to take it outside for a final coat of paint.

Our model complete, repainted, with our nametag attached.

And we were done! Below you can see a video of our model spinning.

https://drive.google.com/file/d/1vKXIunCvQyZt0BdijWqoGR_QmE6VVRBF/view?usp=share_link

This project was a really great was for us to put together all the tools we’ve learned to use so far over the course of the semester. It was very rewarding to steadily move from a concept to a working finished product!

COSTS:

3 Sheets of 2″ x 4″ x 1/4″ wood (estimated) – $15 x 3 = $45 (Home Depot)

4 colors of spray paint – $6 x 4 = $24 (Home Depot)

1 sheet of steel – $10 (Lowes)

Acrylic sheet – $18 (Amazon)

Bearings – $8 (Amazon)

Dowels – $8 (Home Depot)

~3 hours laser cutter time – ~$1 per minute = $180

30 mins waterjet cutter time – 0.5 x $20 = $10

Labor – 2 people, ~24 hours, $12/hr = $576

TOTAL: $879