Bottle Opener

Brainstorm

When we first received the task of designing a bottle opener, I had mixed feelings. The good news is that we have a general idea of what a bottle opener should look like and how it works. On the other hand, since it is such a common object, I thought it would be hard to brainstorm on different ideas! In about ten to twenty minutes, we tried altering different ways of opening the bottle, considering people with different strength and perhaps disability, and altering shapes of certain parts of the bottle opener. We certainly felt silly at times, but eventually, we were able to narrow down to ten designs we liked or thought interesting!

Img 1 Final ten brainstorms (not to scale)

Theses designs most certainly have overlapping qualities (or some of them came out of no where). I (or I shall say my brain automatically) summarized the ideas based on a few categories.

First is the way to open a cap. The pressure could be applied in a downward motion (3, 5, 6), pulling the cap up from the top.  The pressure could also be applied in an upward motion (1, 2, 5, 6, 8), lifting the cap from the bottom. We also came up with more innovative ways to open the bottle, including twisting it (hoping that it will be displaced and then come off, 4, 7, 10) and poking a hole through it (9).

Now it is rather obvious that we want to stay with the first two ways to open the cap, and there are two basic shapes.

Img 2 A hooked design (left) and a flat ring design (right)

We narrowed down the design to the second flat ring design which lies horizontally, because it seems easier to measure. Then we had three different ideas for the edges: a straight line, a curve, and a line of teeth. We decided that we will make the top edge (which we wanted on top of the cap) tooth-like, because we wanted a little more friction to keep the top stable. On the other hand, we made the bottom edge (which goes below the cap) an arc, so that there will be more surface contact between the opener and the cap.

[Aesthetics] As we were sketching our final design, making adjustments here and there, we most certainly saw a chubby monster face, and thus we added eyes and ears to the design, changing the handle into a chubby body. And voila! Our baby monster is now born. We (or at least I) had much fun personifying the monster, imagining the color of its fur and silly things it would do trying to be scary.

Engineering Analysis

Our bottle opener resembles a classic cantilever as shown in the picture.

It follows the following equation:

deflection = FL^3/3EI,

where F is the force, L is length, E indicates the material stiffness (Young's Modulus), and I indicates the stiffness of cross-sectional area (area moment of inertia).

With the conditions provided by the assignment, we can only control the L and the I in the equation. In general, we want a bigger leverage for our hand, but a smaller leverage for the bottle cap. A longer handle will certainly provide more leverage, but the Delrin that we use is much more flimsy than regular metal, so we want to make sure that the handle is not too thin, otherwise it will bend instead of transferring the force to the cap.

Measurement and Foam Core Making

We took a rough measurement of the radius of the cap, since we did not have to be extremely precise. As mentioned before, we initially did not want a big opening so that we can reduce the leverage that the cap has on the cantilever. As the picture suggests, we made the vertical opening to be same as the radius of the cap, 1.3 cm.

Pic. 4 Here is a rough sketch of the "mouth"of our Monster Cutie 1.0

However, the first foam core model made us think twice about the vertical width of the mouth. The foam core was about 1/4", and when we were testing the model on a bottle to see its fit, we realized that we may not be able to fit the bottle opener below the bottle cap. We then found the Delrin sheets available to us, and decided that we would use the 1/8" sheet, as it is the most likely to fit beneath the cap. At this point, we had two thoughts. One is that we should perhaps change the design completely, and use the vertical hook shape as shown in Pic. 2. However, we realized that the measuring may be too complicated and the tip may break easily, as it takes most of the pressure from the cap. Besides, we grew much attached to our baby monster, so we decided to amend the original design, as opposed to start a new one.

Pic. 5 The top of the bottom edge of the bottle opener barely touches the edge of the cap

After some testing with a 1/8" Delrin sheet, we figured that we may want a larger mouth to help the bottom edge stay below the cap and put enough pressure on the cap. We thus extended the vertical measurement to 2cm. We also adjusted the radius of the head and the body of the monster accordingly, to provide a bigger cross-sectional area and make the shape more aesthetically pleasing. The second model seems to have a good fit to the bottle, and we thus moved onto Solid work.

Pic. 6 The second model and its sketch on paper

Solid Work and Testings

A monster is most certainly not the easiest thing to draw on solid works. Certain parts require combinations of multiple circles and arcs, and we had to trim off many reference lines and solid lines. The measurements from paper also do not completely match up with what we were drawing in Solid Work, since many curves and arcs are random free-hand drawings (since they do not have to be precise to function).

Pic. 7 Half of the monster cutie

With the help of Larry, we only had to draw half of the graph and we could mirror the image. Although we finished the first drawing, feeling the triumph, our first plastic iteration was a failure. Somewhere along the process of doing the complicated drawing, the opening of the mouth became 3 cm wide as opposed to 2 cm wide, and thus the bottle went straight through the mouth of our monster. In addition, the way of saving the Solid Work into a dxf did not quite work for our design. There were a few edges that appeared thicker than normal on the graph, and the laser cutter ended up going through these lines about 30 times, causing the back of our monster to burn relatively badly.

It was undoubtedly disappointing, but we went back to the computer and tried to fix it. It was certainly not a quick task to do, since creating the new edge requires quite a few reference lines and arcs. The second model was not perfect when it came out, but it certainly worked! We did a few adjustments. We had to file down the bottom edge a little for it to fit underneath the cap, and we had to hold the head in our palm for it to work as opposed to using the handle.

Pic. 8 The first iteration in plastic (left) and the final version (right)

Final Comments

Overall, we are happy with our monster cutie, since it successfully opened the soda bottle in class. However, here are two things that I would have changed if we had more time. 

I would have made the gap smaller than 2 cm, since we could have filed down the bottom edge to have it fit under the cap, though I would make it bigger than the 1.3 cm that we had for the first foam core, because it only caught a small part of the cap. We would have needed some more experimenting with foam core.

I would also get rid of the long body and have a bigger head, since it turned out that we only used the head part. Keeping the part that takes the pressure in our palm definitely helped compensate for the relatively weaker stiffness of the Delrin compared to metal. Aesthetically, this change also makes the monster even cuter.

All above being said, the biggest lesson we learned is always to give ourselves more time. We would have made the changes had we had enough time.

Last but not least, I would like to thank my partners, Maggie and Sebiha, who are extremely brilliant and fun to work with. I hope that we will get to work together some time in the future outside of this class!