Our Yo-Yo

The Project

As part of our Design and Manufacturing II class, our team has to design and manufacture a yoyo made of injection molded and thermoformed parts. The project is meant as an opportunity for student groups to apply their knowledge of CAD/CAM when designing and manufacturing, not only the yo-yos, but also the tools needed to make them. The goal is to help us learn how to determine the manufacturing rate, cost, quality, and flexibility of our product (and any other product or project we are involved with in the future!) in order to optimize our parameters for successful production of 50 yo-yos.

Design Requirements and Guidelines

To give a better understanding of the project and of the design constraints, here are some of the design requirements:

• Yoyo should include 2 or 3 injection-molded parts and at least 1 thermoformed part.
• Volume of each injection-molded part should not exceed 2.7 in³.
• Clear High Impact polystyrene ‘HIPS’ sheet of 0.030” provided.
• Max outside diameter of the injection-molded parts cannot exceed 2.5”.
• Spec ranges must be specified for each of the critical dimensions of the components

Our Design

Our goal when choosing our design was for the product to be feasible to be manufactured, but at the same time we wanted a bit of a challenge. During our first meeting, we generated ideas that ranged from chicken, to Dave doing cartwheels, to Harry Potter themed yo-yos. We ended up with a design the entire team felt met our goal, but would also be aesthetically pleasing, had some flair, and would provide a bit of a challenge. These design characteristics were especially important, and we felt that it was necessary for us to make our design unique. For that reason, we decided to take the design for the Arc Reactor Mark V and tried to stay as true to the design as possible.

Each half of our yoyo is made of four parts we will machine and manufacture, not including the shim to weigh our yoyo for easier use or the circuitry needed for our yoyo to light up when spun. 

Exploded SolidWorks rendered view of the assembled yo-yo.

The injection-molded body is the largest and most critical part of our yoyo, as it serves as the housing and point of attachment for all of the other pieces. The ring is attached on an interference, or snap fit, and the window and circuit are press fitted into the body. It will also house a shim, which will possibly be ordered from McMaster-Carr, to add weight to the yoyo to improve its performance. Each yoyo will contain two body pieces that will be connected to one another at the center of each piece with a hex nut and bolt.

The ring is another critical component of the yoyo assembly. In addition to securing the inner parts through its snap fit with the body, it also houses the design of the arc-reactor, which is the inspiration for our yoyo. The ring will be made of plastic by injection-molding, and will attach to the body through an interference or snap fit. The relatively complex geometry will make the mold design a bit challenging, especially taking into consideration the fact that it is supposed to snap fit with the body. Therefore, paying close attention to required tolerances and amount of shrinkage during cooling is very important.

Ring piece geometry, front view.

The thermoformed window, as we like to call it, is a clear thermoformed piece that will fit into the negative space of the ring. It acts as a ‘window’ into the reactor and closes in all of the components of the yoyo. A high impact polystyrene sheet with thickness of .030” will be heated and formed onto a die that inversely mirrors the geometry of the ring piece and will then be press cut into the circular shape to fit into the body. An anticipated problem seen with this piece is achieving the sharp geometry needed to fit into the gaps of the ring, but that will be addressed if needed during the trail runs with different parameters. For the time being, the piece will be designed to line-fit with the ring piece.

The clear, thermoformed circuit component will be drape formed.  The clear material will allow the LEDs, battery, and switch to be seen through the assembly, adding to the Tony Stark-esque feel.  The components will need to be soldered and snapped into the thermoformed part after the part is made.  During assembly, the circuit assembly with holder will press fit into the bottom of the body, using the hex nut standoff as the main registration point.  Posts will also go from the bottom of the thermoformed part to the ring, adding a second level of security beyond the press fit.  The circuit assembly will then be pressed into the body, before the thermoformed window and snap ring.

Throughout the design process, our team made it a goal to make the product as streamlined to manufacture as possible in order to keep the rate of production high. The two parts of the yoyo that we foresee having the most difficulty with, the circuit piece and the clear window, were designed to be thermoformed. This will allow us much more flexibility further down the line to make quick design changes.  Additionally, we predict that the circuitry will be main bottleneck in our manufacturing and integration process, and as a result have designed it to be a subassembly. In contrast to that, the parts that will have the biggest effect on the aesthetics and feel of the yoyo were designed to be injection molded to ensure that the quality is high and consistent.

Arc Reactor Mark V Yo-Yo.

We are currently working on the mold drawings for our injection-molded pieces and die drawings for the thermo-formed parts. Stay tuned to learn more about our project and to see where it takes us!

You can view a full list of our design specifications here. 

View our proposed schedule here.