Stack to Space

Bill of Materials

Before fabricating the challenge materials, I made a Bill of Materials (BOM) to ensure I remained within budget. I needed to order wooden balls, PLA filament, and rods of some sort.

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I picked out 50 wooden balls with a diameter of 2". I chose them to be wooden so they would have a smooth surface without being too dense. Additionally, wooden balls are much cheaper than metal.

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I had already had pink, grey, and blue PLA filament. I ordered black and white PLA so I could make 5 different color cylinder sets so that each player has a unique color.

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Finally, I ordered 5 two ft long XXX rods with a .25" diameter. The claws could not be super thick, or else they would be difficult to stack delicate cylinders and 2" balls. Therefore, I chose the rods to have a .25" diameter since it was the largest standardized size that could attach to the claw. I also ordered super glue to adhere the rod to the claw.

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Bambu 3D Printer Error

As I began printing beginning iterations of the cylinders, I realized that they were leaning ever so slightly in the y-z direction (see image below). While this may not be an issue for many designs, it is a large issue for this one, for the challenge will be nearly impossible to complete if the cylinders are not perfectly straight.

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I calibrated my printer, lubricated the guard rails, and tightened any loose screws, yet this issue persisted. After further inspection, I realized that the base of the apparatus was not square. I took removed the bed assembly from the base and found that there was a loose zip-tie stuck in-between the intersection. The zip-tie was part of the packaging and must have gotten stuck during original assembly. After removing this zip-tie and putting the printer back together, I found that the apparatus was square again. I then printed the same file, and it printed out perfectly straight.​

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Cylinder and Claw Design

The tolerances for this challenge were very small, causing me to fabricate many iterations. Constraints for the cylinders and claws are shown below:

• Claw ID must not exceed wooden ball OD (2")

• Cylinder ring must exceed the OD of the claw

• Cylinder ID must not exceed wooden ball OD (2")

• Cylinder ID must be as large as possible to allow for wooden ball to fit securely inside

• Cylinder wall thickness must be strong, so cylinders don't break when the stack falls

• Cylinder must be long enough so that wooden balls do not touch, but not too long or challenge will be too difficult

• Claw must not fit too snugly on the cylinder OD, so it is easy to place items on the stack

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With all of quantitative constraints in mind, I calculated a range of values for the diameters and the lengths of the cylinder and the claw. With each iteration, I then tested and tweaked the dimensions ever so slightly to ensure the final design fulfilled all of the qualitative constraints.               

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Final Design

The image below shows the final design of the challenge. I had created enough materials to allow for allow for 7 cylinders and 7 balls to have flexibility with the level of difficulty for the challenge. After undergoing a series of testing within the Challenge Design Committee, it was found that stacking 5 cylinders and 4 balls is the perfect level of difficulty to ensure a 30min-45min challenge.

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