8.2 - Design Process

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Contents:

• Iteration Documentation
• Final Prototype
• Bill of Materials

When we initially considered the problem at hand, the most prominent design concern regarded the amount of weight we were to move. To maintain simplicity, we opted for a simple mechanism which moved the cup along two planes.

Iteration Documentation

Prototype 1

This prototype was built based on our CAD design to test the necessary movement of moving the cup up to the user's mouth. Overall, the movement worked as expected, though there was some resistance in the linkages on the way down.

Figure 5: First laser cut prototype in motion.

Prototype 2

For this prototype, the main design change was the removal of the prismatic join, which had added stability but was ultimately redundant and added friction. We also attached the cup holder to the main design, stabilizing the two sides with regard to each other. Given the torque necessary to lift the cup, edits needed to be made for the final design for the motor to be able to lift a cup with water in it. In addition, we needed to add a mechanism that will cause the cup to tilt once it reaches the top, while remaining vertical on the way up and down.

Figure 6: Second laser cut prototype.

For the following video, weights were placed in the bottom of the cup to ensure the the cup would not tilt over the other way and fall out of the cup holder since the cup used for testing did not have the same dimensions as the cup that the cup holder was based on.

Figure 7: Second laser cut prototype in motion.

Prototype 3

We created a four bar mechanism that could be used alongside the main four bar that attaches to the bottom of the cup in order to cause the tilting motion. This, over the rotation of the mechanism, would slowly tilt the cup from upright to tilted enough to pour water.

Figure 8: Third laser cut prototype in motion. The red circle indicates the part representing the cup.

We also introduced the idea of using intermittent motion using a Geneva mechanism to tilt the cup so that no water would come out of the cup until it reached the apex.

Figure 9: Geneva mechanism prototype separated from the main motion.

Figure 10: Representation of the Geneva mechanism with reference to the rest of the mechanism and the smallest linkage still representing the cup.

The Geneva mechanism was not added to the final prototype due to friction concerns with both the mechanism itself and prismatic joint it introduced. This was also more of a quality of life inclusion rather than a necessary inclusion for our purpose.

Final Prototype

For the final prototype, we made our mechanism out of acrylic for friction reduction and aesthetics, and 1/4 inch, instead of 1/8 inch as our prototypes used, for stability. Most of the linkages from prototype 3 were also taken away in favor of just a linkage connecting from the existing long piece from prototype 2 to the base of the cup, where another cup holder with a smaller diameter was also introduced. This was because the other linkages, when added to the entire mechanism, were redundant and added weight. The slider was reintroduced despite the friction since we needed a way to reliably stop the motion of the cup from continuing forward past a certain point so that the linkages would not collapse the wrong way, making it impossible to reset properly without outside assistance. Rubber bands were also added between some of the linkages to solve torque issues that came with not using gears (since, after the initial proposal, we decided to stay away from gears).

Figure 11: Final laser cut prototype in an upward position.

Figure 12: Final laser cut prototype in motion, manually controlled.

Bill of Materials

Note: All other materials we already had or would be easily acquired from materials provided by the class or TIW.