7.5 - Implementation - Bottle Opener
Fabrication and Assembly
We utilized three fabrication methods for our final prototype: 3D printing, laser cutting, and milling. Most of our parts are manufactured in Texas Inventionworks. However, we did have to order the output link from SendCutSend, where they were able to laser cut a custom sheet metal piece for us. We decided to choose stainless steel (304 series) for its durability and strength, which will be needed to pry open and deform an aluminum bottle cap. It was also advantageous for its excellent corrosion resistance in case it happens to come into contact with any of the contents of the bottle. The parts in orange and gray (the base and ground link) were 3D printed, the parts in teal (input and coupler links) were laser cut acrylic (6mm), and the output link in blue was a custom laser cut sheet metal, as seen in Figure 1.
 Figure 1: Final Prototype Assembly CAD | Figure 2: Final Protype Assembly
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For assembly we primarily used standard M3 screws and nuts at varying lengths. We also used M3x8x5 threaded inserts to more securely attach our base and ground link parts to one another as the Bambu P1P build plate volume ended up being too small for a single print. In the video below you will see the threaded insert being melted into the toleranced hole via a soldering iron. A chamfer was added at the top of the hole to act as a locating feature.
For milling 304 Stainless Steel, we used a 4 flute 1/4'' endmill at around 500 RPM. Below you can see the before and after of the milling operations. We effectively increased the distance from the hook tip to the fulcrum. Resultingly, we were able to achieve a fulcrum point close to the center of the cap.
Figure 4: Pre-Milled Placement of the Output Link | Figure 5: Post Milling Placement of Output Link
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Lastly due to the unforeseen amperage requirements (as stated in 7.3 - Design Process) our design oscillated quite violently. We tested a few design variations to attempt to dampen the motion. Below in Figure 6 you can see the spring combination in series. Ultimately, it prevented the mechanism from applying enough torque to open the bottle so chose not to use any damping in our final assembly.
Electronics, Circuitry, and Software Development
The electronics used are:
12V DC Motor 251rpm w/Encoder
DC Voltage Supply
Originally before discovering the pitfall of the amperage requirements, we planned on using a moto controller, a battery pack, Arduino Uno, and limit switches to control the system. We had even written PID controls for the built in motor encoder in arduino software. Once we discovered that the motor controller could only go up to 2A, we switched over to a portable power supply to supply 10A and overcome the stall torque. Resultingly, we could not use the control system we created and had to control power via the coarse and fine tuning knobs on the power supply itself.