Final Yo-Yo Design

The Design

Our yo-yo displays a lotus flower on top of a lily pad and floating in a blue basin. The lotus flower is comprised of three injection molded parts: two layers of petals that were designed in Fusion’s sculpt environment and one stigma that is placed through the holes in the petal layers. The stigma both holds the flower in place on the yo-yo body and orients the petal layers so that the individual petals are offset between the two layers. The flower sits on top of a thermoformed veined lily pad that is captured by the snap ring. Notable distinctions between our yo-yo and others include a shortened yo-yo body length, veined lily pad, unique sculpted petal design, and the captured pin design for the flower as a whole.


From this view, the lily pad piece can be seen as being held between the snap ring and the body (cross section in blue). There are snap fit interferences between the snap ring and the body, and the stigma base and the body. These snap fits hold our entire yo-yo together. These 2 snap fits along with the triangular profile of stima and petals should constrain all degrees of freedom and prevent any parts from spinning freely. The snap fit interference is nominally 0.010” but we expect to adjust this as we prototype and test the shrinkage of each part.

C1 Yoyo Drawings.pdf

Our yoyo has many parts that are organically shaped and hard to measure reliably. We will rely on CAM to create the molds for these parts, therefore in the engineering drawings we have noted only the critical, measurable dimensions (such as petal ring diameter and z height) and left other dimensions unmarked because they are purely cosmetic (such the curvature of the petals).

Within these critical dimensions, some are harder to measure than others. We will be able to easily measure diameters, depths, and lengths with calipers. However the radius dimensions may not be able to be measured accurately without an optical measuring machine (OMM). We expect to measure a sample of the parts to assess whether or not the critical dimensions are within spec.


Center of Mass

We chose to estimate the performance of our yo-yo, by setting the appropriate mass properties than calculating the center of mass point for both one half of our design and both halves put together. It is important for the center of mass of the yo-yo to be in the geometric center of the yo-yo assembly (where the string will interface) in order for it to achieve good performance.


Printed Prototype

We designed all of the components in Fusion 360 and printed our first prototype. Completing this print allowed us to see and hold the yo-yo and give team members a physical representation of our product.

From seeing this print, we have decided that the lotus flower, because of its small size, is a sufficient design without the additional stamen details. Including the stamen would overly complicate the design and ultimately detract from the yo-yo’s presentation.

We also decided to test out varying sizes of lotus flowers. We printed our current lotus design scaled in various directions. The three printed options allowed us to decide which lotus size looked best visually. The chosen size of lotus flower is shown to the far left.

All individual components for one 3D printed yo-yo half. Printed for visual and physical aid in design decisions.

The Assembly Process

The assembly process for each side of the yo-yo will follow a set of logical steps.

  1. Press the upper lotus petal layer onto the stigma until the petals hit the stigma’s chamfer.
  2. Press the lower lotus petal layer onto the stigma until the two petal layers are touching. Put this assembly aside.
  3. Snap the thermoformed lily pad into the blue snap ring.
  4. Snap the lily pad and snap ring assembly onto the blue body.
  5. Fit the exposed stem of the stigma and petal assembly through the center hole in the thermoformed lily pad and press the exposed stem into the blue body.
  6. Check that all parts are sufficiently pressed and that no components are loose.

We have designed our yo-yo parts so that many of them fit together in unique ways to aid in the assembly process. For the lily pad, it is retained between the snap ring and the body, but also is kept from rotating by the triangle indent in the snap ring. We incorporated clocking into our stigma, so that the petals will be locked rather than free to rotate. Because we chose a triangle shape for our clocking design, there are three possible directions in which the petals can be placed relative to each other. We have decided that this potential variation of petal orientations during assembly will be a positive difference between each individual yo-yo that will add to our overall aesthetic.


Design for Manufacturing

Shrinkage Compensation

To account for shrinkage in our injection molded parts, we went into the LMP shop to measure mold and part dimensions of similar geometry parts and will scale our parts up according to these dimensions.

The chart to the right describes the shrinkage observed in each critical dimension of the parts we measured. Based on final part tolerances from the Succulent team, we can also predict an approximate shrinkage of the triangle cut out in our lotus petals to be around 1%. Based on our measurements in lab and the data we were able to use from the succulent team, we will assume 2% shrinkage in general and then 1% shrinkage on the triangle cutout in our petals.

Assisting in the Manufacturability of Components (against shrinkage)

Utilizing drafted surfaces and identifying parting lines.

Yo-Yo Body

Snap Ring

Lotus Stigma

Thermoforming the Lily Pad

Our initial design for the thermoformed lily pad involved cutting a corner out with scissors during assembly, which could lead to more variation in the parts as well as longer assembly times. In order to design for easier manufacturing, we made an injection molded snap ring that will sit on top of the thermoformed lily, holding it in place.

Blog post written on March 19th, 2019