Custom Mass-Manufactured Yo-yos

As a team of 5, we designed, produced, inspected and assembled 130 yo-yos, bringing assembly time down to 4.5 minutes per yo-yo. All measured parts had a successful fit with an interference of 0.0095 in.

This project was done as part of 2.008 Manufacturing at MIT.

Results

In total, over 130 yo-yos were made at an average of 4.5 min each. 4 parts were injection molded and 1 part was thermoformed, then everything was assembled together.

I am proud of my design of the core and the molds I CNC'd for injection molding. In 6 hours in the lab, five of us manufactured and assembled 80 yo-yos at 4.5 min per yo-yo, the second-best result in the class.

If I were to approach this design now, I would focus on:

• adding more mass to improve spin duration
• moving the interface between parts so the string never catches on the yo-yo
• experimenting with the shape to make it more appealing (rounder, for example)

Design

First iteration of the yo-yo core

In my initial design, I aimed to keep the part as simple as possible. After discussing it with the team and experienced machinists, I found several defects that made it unmanufacturable with our CAM and injection molding setup:

• no draft angles (the part won't come out of the mold)
• a very thin lip (impossible to injection mold)
• a small interference-fit area (won't produce a high-quality assembly)

Final design of the yo-yo core

After several iterations, I settled on a core that could be made easily and consistently. Improvements include:

• 2° draft angles, chosen to match the available 2° CNC tool and speed up mold making
• smoothed edges (90° corners are hard to fill in injection molding and to machine)
• symmetrical pieces for better weight distribution and better molded parts