Greetings from Ravi, Santiago, and Sid.
Over the past three weeks, my teammates ventured into a multifaceted project to create a crazy mechanical model from wood, bearings, and dowels. Here was the idea – connecting motion from planetary gears to multiple gearing. Both motions are in 507 mechanical movements. This was a large challenge for all of us because we had to think about how our toolchain would impact the final design. There were many differences in opinions, but one by one, we overcame them via teamwork and communication.
Ravi, with his experience in SolidWorks, took the lead and designed the planetary gear system digitally. Using CAD drawings, we were able to present an initial laser-cut prototype by Gate 1. With everything that naturally exists, our model had some key flaws. The internal spur gear – the outside shell – had 90 teeth and combined with the kerf removed from laser cutting, we noticed the teeth were weak and could break anytime. The feedback from Dr. W and the TAs was internalized and so we reduced our teeth count to 30. SolidWorks does not build gears well apparently, so we switched to another gear software discussed in later phases.
In our medium-fidelity prototype, we slightly scaled up our model to allow for larger teeth. After testing a few dowel fits, we sanded the internal gear hole to make the dowel a tight fit. We found that it was easier to largen gear holes rather than downsize dowel diameter. After constructing the planetary gears, we had a lot of trouble in transferring the motion to a multiple gearing system, so the latter idea was dropped quickly. Here, we were too ambitious. While this could have been done, we could not iterate due to both a lack of laser cutter and wood availability. Also, in this phase, we decided on a theme. Since the planetary gears spin independently on their axis, an idea sparked – a carousel of sorts. We decided to create the theme of bumper cars revolving around sun gear.
In our high-fidelity design, everything started to come together well. After constructing our planetary gear motion, we linked it to another gear which would be manually operated with a handle. Both gears were attached to a base via bearings and we printed spacers mounted on dowels to prevent the two levels from collapsing. The handle was waterjet cut from steel – also sandblasted (kind of) – and our final model was done.
Lastly, it was time for some post-processing. The top visible surface was lightly stained (walnut). Bumper cars were laser-cut, spray-painted, and attached to the planetary gears. A nameplate was etched, laser-cut, and attached. Images of gears were vinyl cut and were used to decorate the large visible gear where the handle was. Here’s our final result:
In this project, there were few places for improvement. First, we started out too ambitious. However, with the right planning and time management, we could’ve connected planetary gears to multiple gearing. A large issue we faced in the project was fit and tolerance. When programming diameters, we slightly under-sized or kept the original size to achieve a tight or loose fit, respectively, to account for kerf. This held true for both laser cutting and water jet. Additionally, it’s easier to have tight gear and largen the diameter instead of sanding the dowel down to size. Next, the planetary gears have no shield so they can easily be removed from motion – this is something we could’ve implemented. Lastly, a little of the post-processing was hasty due to time constraints. We noticed rough edges, dried glue, and uneven stain application – this is also something we could’ve worked on. While there are different areas of improvement, overall this project was a success. See you until the next midterm project!
Here are our final deliverables:
bumper planetary gear demonstration
Here’s our proposed cost table:
| Cost | Price ($) | Source | Quantity | Total |
| 24”x24” laser cut wood | 11.95 | maker stock | 5 (prototyping work included) | 59.75 |
| ¼ in x ¼ in x 48 in Pine Round Dowel | 5.68 | home depot | 1 | 5.68 |
| ¾ in x ¾ in v 48 in Pine Round Dowel | 3.37 | home depot | 1 | 3.37 |
| Cardboard Sheets | 13.99 | amazon | 1 | 13.39 |
| Spray-paint Cans | $6.48 | home depot | 3 different colors | 19.44 |
| Dark Wood Stain | 7.98 | home depot | 1 | 7.98 |
| ¾ in Bearings | 8.99 | amazon | 1 | 8.99 |
| ¼ in Bearings | 7.99 | amazon | 1 | 7.99 |
| Wood Glue | 3.68 | home depot | 1 | 3.68 |
| Stainless Steel Sheet | 20.93 | home depot | 1 | 20.93 |
| Adhesive Vinyl | 10.99 | amazon | 1 | 10.99 |
| Vinyl Transfer Paper | 15.99 | amazon | 1 | 15.99 |
| Labor | 19/hr | laser cutter operator | 30 | 570.00 |
| Operating Cost (Laser, Vinyl, Waterjet) | 22/hr | machine operator | 10 | 220.00 |
| TOTAL: | 968.18 |
