CAPSTONE BLOG #7: 3/23/24

        Between the work period of March 9 - March 23, the team has wrapped up any reprints that needed to be made to fully construct the prototype device. Particularly, the function of the clamp's mouth was finished. Additionally, the team has assembled the prototype device that consists of the ratchet system, the rotational clamp, and the retractable hook mechanisms as shown in Figure 1. The figure also shows an "in use" snapshot of how the device is aimed to work. Components were acquired from 3D printing services like ASME-UH and available suppliers such as Home Depot, Lowes, and McMaster Carr. 



Figure 1: Device Assembly with Size Reference Trash Can

Figure 2 shows the previous outer cam which was being used on the left and the updated outer cam that will be used for validation. The cam has been updated by introducing a larger cam geometry, allowing the clamp to open farther. This was accomplished by taking measurements of the cam length from the previous design and accounting for the open-mouth angle. From there, the team used those measurements to create a ratio which resulted in the maximum length that the updated cam needed to be. The previous outer cam was only yielding an open mouth angle of approximately 12˚. The team is hoping that the updated outer cam will yield a larger open-mouth angle that is expected to be at a minimum of 30˚ and maximum of 35˚. 

Figure 2: Updated CAM design

Currently, the team has begun validation testing to verify the functionality and reliability of the device. The team is currently using a single trash can to achieve functionality, and afterwards will introduce other trash cans as validation progresses.

        For the work period of March 24 - April 6, validation testing of the device will be conducted. The first task in validation is getting the device to actually form a knot. This involves verifying if the clamp grabs ("bites") the trash bag drawstrings as intended and the placement of the bite. In this time period, the team hopes to accomplish a significant portion of Milestone 5, which primarily consists of validating the initial device. At the time of project demos, the team discovered room for improvement with all mechanisms involved, especially with the setup regarding the rotational clamp and retractable hook. 

Since the device mechanisms work individually as intended, the plan moving forward in validation is to try several variations of placement and clamp shape to attain a more reliable device. The data collected in this time will used to show why certain set ups work better than others.

        The biggest obstacle the team currently foresees is getting the clamp to set up a bread knot in an efficient and reliable manner. Some minor issues are the side profiles of the clamp being too slippery and the depression angle contributing negatively as a result of that. One idea the team has to mitigate this issue is extending the side of the lower clamp to form a hook as seen in Figure 3. 


Figure 3: Potential Lower Clamp Update

Another obstacle that the team foresees while working on the project for the next two weeks is the rigid vertical adjustability of the ratchet system. The team found it difficult to smoothly adjust the height of the initial device. This issue is planned to be addressed after the clamp becomes more reliable, as it is less important to the scope of the project. A few ideas being considered are to reduce friction in the t slot with grease and reshaping the handle.

The team also foresees a minor obstacle involving "left vs right handed" usability of the device. The device can already be structured with a "left" or "right" hand orientation, but to make it even simpler, the team will print a single version of the handle that accustoms to both. The design is to have a handle on both sides of the ratchet piece, a "two sided" handle. This way, simply rotating the device will change the hand orientation, rather than needed to break it down and rebuild.

Figure 4: Current Handle (1 sided, right orientation)

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