This thing all things devours:
Birds, beasts, trees, flowers;
Gnaws iron, bites steel;
Grinds hard stone to meal;
Slays king, ruins town
And beats high mountain down
You probably guessed it, we were inspired by time! Our yo-yo takes the form of an unconventional clock. The three gears in the center represent the hours, minutes, and seconds hands on a conventional clock. See our design below:
Overall one side of the yo-yo has four different parts and six individual pieces. The base serves as external support to hold all of the parts. It includes three pegs for each of the gears and aesthetic design. The three gears press fit onto the base pegs and portray time. The clear cover goes over the entire assembly and the orange ring creates a press fit between the cover and the base. Below is an exploded view of the entire assembly.
Base: Injection molding
The injection molded base will connect to the other side of the yo-yo. The central solid circle will securely contain the nut and each peg will press fit with the gears.
Gear Assembly: Injection molding
The gears are all separate parts but will be injection molded with a single mold. The mold will include runners to each gear to decrease production time. The gear will be assembled according to the correct pitch diameter, however they will not be able to move because of the inner peg press fit.
Cover: Thermoforming
The thermoformed cover will be clear such that it can protect the yo-yo interior but maintain the overall aesthetic.
Ring: Injection molding
The injection molded ring will be purely for structural support. It creates a solid surface for a press fit between the cover and the yo-yo base.
Design for manufacturing:
The class requires that by the end of the semester we build a total of 50 yo-yos. That means a total of 4 molds, 50 yo-yos, 100 yo-yo sides, and in our case, 300 gears! Below we will explain some considerations that we took to finish on time.
Rate:
Most of our parts are made through injection molding which is dominated by cooling time. To cut down on cooling time, we used thin walls on our parts. The design of the base, which has the thickest components, was creatively made such that the overall part is thinner.The gears, while small in size, will be manufactured in the largest quantity. Therefore, we will design a mold that can hold all three and reduce number of injection molding cycles.
Press fit:
Another step in yo-yo creation which will not be automated is the assembly. The design was made for easy press fit between parts such that the yo-yo can be assembled by hand.
Table of Specifications:
| Component | Diameter (in) | Thickness (in) | Tolerance (in) | Mass (g) | Tolerance (g) | Measurement technique |
| Base | 2.5 | 1.27in | ±0.005 | 17.04 | ±0.05 | Calipers for inner and outer diameter and attempt press fit with gears for posts |
| Gear Large | 1.12 | 0.15 | ±0.005 | 1.66 | ±0.05 | Calipers for inner and outer diameter and attempt press fit with base part for the internal hole |
| Gear Medium | 0.83 | 0.15 | ±0.005 | 0.86 | ±0.05 | Calipers for inner and outer diameter and attempt press fit with base part for the internal hole |
| Gear Small | 0.64 | 0.15 | ±0.005 | 0.32 | ±0.05 | Calipers for inner and outer diameter and attempt press fit with base part for the internal hole |
| Thermoformed cover | 1.98 | 0.03 | (+0.005/-0.000) | 3.34 | ±0.1 | Calipers for inner and outer diameter and attempt press fit with base part for the internal hole |
| Ring | 1 | 0.13 | (+0.005/-0.000) | 3.73 | ±0.1 | Calipers for inner and outer diameter and attempt press fit with base part for the internal hole |
Gantt Chart:
Here is a google doc where we keep track of our progress: Gantt Chart
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