Introduction

This is Liam McConnico-Blanchet and Mustafa Latif, and for our Midterm Project, we decided to do a marble run. Initially, we wanted to create a marble run like one we’d seen in many videos, including a long, winding track and a conveyor belt. However, initial planning showed this might be much more complicated than we thought. As it turns out, making a twisting and turning road in a 3D space merely out of laser-cut wood requires significantly too many measurements and calculations for a midterm project. We created our model using Mechanical Movement #24, having two interlocked gears to crank our marble from the bottom to the top of our project.

Gate 1:

When we embarked on Gate 1, we had to decided how exactly we were going to build our marble run. We quickly scrapped the long complex marble run, but still wanted to keep the conveyor belt. We wanted to use Mechanical Movement #1 to create this conveyor belt by using a pair of gears with a laser-cut living hinge on top, and some small wooden laser-cut U-brackets to help bring the marble up.

As for the spiral itself, we thought of having two tracks, an inner and an outer track, where the marble would rest on top of so that it could move downwards. This would be done by having a gap between 10-12mm, since the marble was 16.5mm wide.

Once the marble reached the end of the spiral, it would run straight into the conveyor belt. The conveyor belt’s U-brackets would be just smaller than the width between the two tracks, so that they may pick up the marble without hitting the tracks. The top gear would then be cranked so that the conveyor belt would bring the marble to the top of the track, where it would drop onto the top of the track, and resume its path across the spiral.

At this stage in the process, we didn’t know how we were going to build our supports for the marble run. In Gate 1, we went with an idea of dowels piercing through the tracks at various points along the spiral, and we would have dowels on either side of the conveyor belt to keep it supported.

Gate 2:

As we set out to build a low-fidelity version of our marble run out of cardboard, we quickly ran into a major issue: we didn’t know how we were going to keep our spiral up. At first, we thought about using dowels to pierce through the cardboard, which we could then glue together. However, this would have needed us to make 32 different dowels, and unfortunately, there were not enough similarly sized dowels in the OEDK for us to do so. Instead, we laser-cut holes into the cardboard spiral, and pierced all of the layers of the spiral with four dowels equally separated. At this point, we were still using the idea of having an inner and outer track upon which the marble would lay, meaning we would only need 8 dowels total. We also didn’t have a track between our spiral and the conveyor belt, as we were unsure how we were going to make such a track work.

Alas, we found a problem with this solution immediately. The wooden dowels caused the cardboard to twist too much, and was largely inaccurate. It turned out that getting two pieces of cardboard to consistently have a 9-10mm gap was almost impossible, and caused us to be unable to run the marble through. Add to that the fact that the dowels themselves had width, and even if the gap was 9-10mm, the marble wouldn’t fit.

We also had issues with the conveyor belt: quite simply, it didn’t work as intended. The gears failed to properly grab the wood it was using as teeth on the fabric, and was too complex to work as a standalone solution. Additionally, we weren’t sure how to actually keep the conveyor belt upright, leading to problems where the belt would fall out of its supports.

Overall, we figured that we probably needed to entirely overhaul this design. The spiral would need to be too precisely made across 3 dimensions, and we didn’t trust ourselves to be able to get this kind of math correct. The conveyor belt also wasn’t functional, and we decided to switch pick-up mechanics.

Gate 3:

For Gate 3, we needed to build a medium-fidelity prototype using laser-cut wood instead of cardboard. For this gate, we decided to implement the switches to our design. Instead of a two-track system, we decided to pivot to a one-track system where the marble would run on the spiral, and the spiral above it would keep the marble on the track through centripetal force. Therefore, when the marble entered the track with enough velocity, it would go down the spiral thanks to the guardrail and the downward-tilting wood.

We were able to create such a complex and intricate spiral thanks to a YouTube video which provided laser-cut files for wooden spirals.

However, this laser-cut file came with a key issue. It was scaled for marbles that were approximately 12mm wide. Since our marbles were larger, and we also wanted a bigger spiral, we would have to change the .ai file to make it functional for our sized marbles. Additionally, you may notice the top of the spiral has two extra components: a small hook at the very end of the track, and a piece meant to act as a support. We weren’t sure how the hook was going to work, but kept it for the time being to see if we could figure it out.

We also decided to alter our conveyor belt quite severely. Instead of a conveyor belt, we would use a Ferris-wheel-esque contraption where the marble would go through a hole in a support as seen on the right wheel, and then would come to rest in a hole in the left wheel. Then, the wheels would be turned by using a hand crank, where the marble would go counter-clockwise until it reached the very top of the wheel.

The marble would then be dropped onto the above track, where it would run across the top track and the bottom pair of tracks would keep it from escaping while also being close enough together to make sure it wouldn’t rattle too much on the track.

We also decided to change the support system by making small square holes in each layer of the spiral, and then having one large support that connects all of the spirals together. By staggering the heights of the support, we were able to make it so that the spiral had a height difference of 20mm between each layer, which subtracted by the width of the wood, led to a difference of 15.2mm. Initially, we thought that the height difference would work since it was smaller than the height of the marble. However, we failed to consider that the wood can warp a little as the marble runs through the track, and the track above the marble is not directly above it, but rather above it to the side. This made it so that, when using our own marbles, they frequently left the spiral by flying through the gap between the layers.

Below are videos of each section of the track working, though only the smaller marble worked on the wheel and outer tracks, and a bigger marble had to be used for the spiral.

 

Final product:

To make this project work, we had to do one of two things: either change the spiral and supports to fit the smaller marble, or change the wheel and outer tracks to fit the bigger marble. In the interest of time, we chose to change only the spiral and supports. This would later turn out to most likely be the wrong decision, but in the moment we felt it would be more efficient. We scaled our spiral down from 11 layers to 9, and decreased the difference between layers from 20mm to 15mm to accommodate the smaller marble. We also removed the complex top of the spiral and replaced it with an extension of the track so our downward track could lead straight into it.

While printing the spiral, we ran into numerous issues. We found that the laser-cutter could not cut the spiral without severely burning the wood. We could either cut the spiral at a higher power and sand the burn marks away, or choose to preserve the wood and cut out the spiral with a utility knife. We chose to go with the latter, which was also retrospectively an error, as we spent hours trying to cut different spirals out of wood, trying to make sure the wood splintered and broke as little as possible.

We also ran into a much bigger problem: the wood sheets all had slightly different thicknesses. The holes in our wood were cut out for wood with a thickness of 0.18″. However, we would end up working with different thickness of wood, from 0.17″-0.19″. This meant that a lot of our supports simply didn’t fit into the holes that we cut out for them. To solve this issue, we printed all of our holes to fit the 0.19″ wood, which meant that although all the wood fit, some of the supports were quite loose.

The loose fitting supports led to a major error as we finished assembly. One of our tracks leaned too far forward, and the mechanism to drop the marble onto the track wasn’t properly aligned anymore. So, we made to and improvised a solution to extend the track outwards and have the marble go onto the track properly, leading to our final design.

 

Cost Analysis:

Plywood (1/4 in. x 2ft x 2ft) * 4 = $30

5 sheets of sandpaper of various grits = $6

Wood glue = $4

Wood stain = $8

1 sq. ft. vinyl = $1

Total labor: (60 hr/person at $15/hr) = $1800

Total cost: $1849

 

What we learned

We learned a whole lot about laser cutting through this process. First and foremost, we learned that dealing with 3D curvature with wood is a much more precise endeavor than we at first thought. We also relearned that you absolutely, at all costs, have to measure twice before you cut, because we made several mistakes when cutting which cost us hours. When using the laser cutter, we should also prioritize cut-through over aesthetics, as we can always sand the wood down, but getting rid of splinters is a lot harder, and wood that snapped is unusable. We learned how to properly vinyl cut, and how to much more efficiently use Adobe Illustrator using various shortcuts.

Final design + cleaned workspace