1.2 - Project Prototype

Prototype:

Open F1.1: Back of window washer	Open F1.2: Front of window washer	Open F1.3: Added cleaning pad

Open F1.1: Back of window washer	Open F1.2: Front of window washer	Open F1.3: Added cleaning pad

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Figure 2: Video of Prototype

Above is the mechanism we showed on demo day. In Figures 1.1 and 1.2, the front and back sides of the mechanism are shown, illustrating the overall geometry of the system. We had not yet added the belts, but this allowed us to test the Geneva mechanism itself. Figure 1.3 shows the fully assembled mechanism, where we added a cleaning pad at the end of the slider-crank to act as the wiper, made from a portion of a foam mat and a cloth. As demonstrated in the video, turning the main driver produces continuous reciprocating motion of the slider-crank and intermittent motion of the pulleys. Additionally, we show that the gears cannot be rotated from the back side when the Geneva is not engaged, and thus the Geneva mechanism prevents backdriving when not engaged, effectively holding the mechanism in place.

Kinematic Analysis:

Analysis

Code

Iteration Documentation:

Our first “iteration” was a simple cardboard cutout to get a feel for how the Geneva mechanism worked. While whiteboarding the design, we were initially planning to have a sort of ratcheting mechanism to hold the pulleys in place, but this iteration showed us that the Geneva mechanism itself acts as a lock while not engaged.

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Figure 3: Initial iteration of Geneva mechanism

Additionally, we still had the original slider-crank from Build Assignment 1 that was very effective, and thus we decided to reuse a very similar design for the wiper.

Next, we designed in CAD, which was pretty much a straight shot to the current physical prototype. Even though it was first fully designed in CAD to allow us to visualize the packaging, we first printed the Geneva mechanism (not pictured, though it is the same one on the final prototype). This allowed us to effectively verify that not only would the driver mesh with the follower when engaged, thus allowing for intermittent rotation, but also that the Geneva mechanism itself acts as a lock while not engaged. Afterwards, we 3D printed the parts, laser cut the acrylic base, and assembled the components (excluding electronics), building our demo prototype as shown above, which is representative of Figure 4, our first CAD prototype.

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Figure 4: First CAD Prototype

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Figure 5: V2 Added Idlers

 

Future Changes:

After assembling our prototype, we were satisfied that our window washer can be driven upwards intermittently while the wiper runs continuously. We did notice that the belts to the pulleys could slip, though this was not observed once we attached strings. However, to prevent any likelihood of slipping, we plan on adding idlers to help tension the string pulley belts, as shown in Figure 5. Additionally, we will make slight adjustments to the Geneva mechanism to reduce some of the play.

Current CAD:

Draft BOM: