Closing Thoughts

2.008_FA20_Final_A2.MP4

Summary of Final Design

The Navig(.00)8 compass yo-yo has five distinct elements: the yo-yo body, compass star, spinning needle, snap ring, and decorative needle. The compass design was chosen with the unique circumstances of the semester in mind: we are all scattered across the world, but we all have a common “home” — MIT — which our compass can point us to.

The yo-yo body and ring are colored a deep black and joined by a snap fit. The body and snap ring are aligned with a locating notch, circled in red on the yo-yo body (see following page), which streamlines the assembly process and also prevents the user from rotating the snap ring around the body. The locating notch of the snap ring is on its underside and not visible from the photos below. The face of the snap ring has a raised NSEW detailing as well as recessed triangle features. The body was made from a single cavity mold that had two gates and the snap ring had four gates. The body had two gates to help with the filling process while the snap ring had four because we accidentally placed the ejector pin holes on the shut-off surface the first time around, so to fix it we created a circular runner/gate system around the part where the ejector pins could push off instead.

The compass star is colored gold and press-fits into the yo-yo body, where it rests on small ledges that prevent it from sliding down. There is nothing that constrains the star from lifting up because we expected that the press fit would be tight enough to keep the star in place. The compass star also has a locating notch that matches with another notch within the yo-yo body, again making assembly easier by streamlining the alignment process. The locating notches also create uniformity among the yo-yos by aligning the star with the snap ring text. The compass star had a one-gate mold.

The spinning arrow is colored red, rests lightly on top of the star, and is held in place by the brass decorative needle which presses into the star’s central hole. The decorative needle head gives the spinning arrow enough clearance so that it can spin while the yo-yo is in use. If desired, you could prevent the arrow from spinning by pushing down the head of the decorative needle until the arrow is firmly pressed to the face of the star. The arrows were made using a multi-cavity mold that produced ten arrows per IM cycle.

The Navig(.00)8 yo-yo is accompanied by a thermoform mountain stand that has a slot for the yo-yo to rest in (a little precariously, but it is a mountain after all!). The mountain stand was designed using the actual topographic data of Denali, the highest mountain peak in North America. The thermoform die was 3D printed using an SLA printer with durable resin. The thermoform piece is white because the Mimaki printer was down and there were not any other colors of thermoform plastic than white or yellow.

The final yo-yo prototype weighs 47g but it has a nice feel and a good response when in use. We could have probably increased the weight by adding some shims to the body interior, but due to time constraints, we were satisfied with the weight.

Final Report

Final Report

Key Features

  • Snap fit between body and snap ring, guided by locating notches

  • Press fit between compass star and body inner diameter, guided by locating notches

  • Spinning arrow element

  • Fine detailing on snap ring surface

Successes

  • The locating notches on the snap ring, body, and compass star streamlined assembly and created a uniformity of parts

  • The detailing of the snap ring came out very clean

  • The yo-yo survives a drop test

Opportunities for Improvement

  • Iterating on the thermoform mountain to find a design that securely holds the yo-yo

  • Iterating on the body and snap ring molds to fix the alignment between the two parts

Changing the Design for Mass Manufacturing

  • Widen the central hole of the compass star a tad to make press fitting the decorative needle (by hand) into the star easier

  • Narrow the central hole of the arrow to make less of a gap between the decorative needle diameter and the hole diameter

      • Experiment with different size holes for the ideal slip fit

  • Consider adding a constraint to the compass star by adding a notch to the snap ring that presses down on the star and prevents it from lifting up

  • Make multi-cavity molds for all parts

  • Redesign the thermoform mold to create a stand that securely holds the yo-yo