Bottle Opener

The class started our first engineering project on the first day of class (well, technically the second class due to the snow days!)  Our task was to create a working 2D bottle opener with a single piece of Delrin (1/8", 3/16", or 1/4") no more than 6" in any dimensions using the laser cutter.

• Brainstorming Process
• Choosing the Design
• Engineering Analysis
• SolidWorks and Testing
• Reflection

Brainstorming Process

Our goal for brainstorming was to spend about ten minutes coming up with as many ideas as possible, amazing or silly.  The idea behind this is that the more ideas you produce, you will eventually come up with some fantastic ideas.  We drew a simple sketch, wrote a short description, shared the idea with each other, and kept going.  When we got stuck, some strategies were to combine different ideas, adapt the part to something else, or modify each other's designs.  For example, we thought a lot about the part that actually opened the bottle, but later thought about the part the user holds.  We ended up with about twenty pieces of paper spread across the table, some with a couple of ideas on the same paper.

Here are our many brainstorming ideas. 

Choosing the Design

After we mass-produced our initial bottle opener ideas, we grouped all of them into categories, such as rectangular, rounded, etc.  We combined, modified, and eliminated ideas until we narrowed it down to only 10 design ideas:

These four ideas all included an outer shape with an inner shape cut out.  For the half-circle shapes, the straight edge would go under the cap and the round edge on top.  The oval idea would work by putting the large end over the bottle, sliding it to the small end and pulling up on the handle.

These three ideas all had one edge longer than the other. The second two designs are modifications of the first: one with flat edges and the other with teeth.  The bottle would be opened by pulling the bottle cap from beneath using mostly the longer edge.

These three designs all have a rectangular shape.  The first had a smooth rounded end that would fit around the bottle cap.  For the second, we thought adding teeth might help it get under the cap.  The third incorporated an idea to make the handle more comfortable for the user.  On all three, the handle would provide leverage to pop open the bottle cap.

After reviewing these ten sketches, we had to narrow it down to one idea.  We eliminated any ideas with teeth because we thought it would make the bottle harder to open.  We also eliminated the hand-shaped idea on the first image because of the complexity, the donut idea because we simply thought it would not work, and the oval idea because it would involve detailed measurements.  

At this point, we needed to decide on the overall shape:  rectangular or rounded.  We came to the conclusion that the longer, rectangular shapes might not be as sturdy as a smaller shape, and that they would bend under the force.  Therefore, we ended up choosing the simple design of a circle with a smaller half-circle cut out on the inside. (which we promptly named the "smiley face" one.  So scientific.) 

Engineering Analysis

We decided on this design because the straight edge lifts up underneath the cap and the rounded edge would be on top of the cap, and this would provide nice leverage.  This design would also be strong and easy to hold in your palm.  Our bottle openers also act as cantilevers, so we considered the equation for deflection:

         deflection = FL^3/3EI

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

The factors we could change in this situation were L, the length, and I, the moment of inertia (stiffness of cross-sectional area).  We don't want the deflection to be too large (or else the bottle opener would bend too much), so we had to incorporate the two variables we could change into our decision.  Our decision to use the circle shape instead of a rectangle was to minimize the length L.

We took measurements of the bottle cap, sketched to scale model on foam core, and cut it out.  The outer circle was to be roughly the size of someone's palm, so it would feel comfortable when you hold it.  And we wanted the half-circle to be slightly larger than the bottle cap size.


Measurements
Radius of outer circle: 30 mm
Radius of inner half-circle: 20 mm

SolidWorks and Testing

Our machinist, Larry, helped us with sketching our part in SolidWorks and taught us how to use the laser cut, so we could cut out our design.  We decided to use 3/16" Delrin because we didn't want it to be too thick to fit under the cap, but we thought that the 1/8" might be too thin.  Here is our final cut piece:

Then came the moment of truth!  We tested our opener on a soda bottle and ... it didn't work right away.  It took several times to get the hang of it, and after a while we were both able to get the bottle open in about two or three tries.  The next class, since we decided not to do another iteration, we spent time practicing opening the bottle.  One thing that worried us was that the plastic on the straight edge chipped each time we opened the bottle.  If this became a real bottle opener, though, it would probably be made of metal and prevent this problem. 

When we presented our project in class, our bottle opener worked fantastically!  We were able to open the soda bottle in two tries and enjoy our reward.  Also, later on in class, another classmate tried using our opener and opened a bottle very easily.

Reflection

Overall, I really enjoyed having this as a first engineering project.  This project taught us how to brainstorm, and was my first experience using SolidWorks and the laser cutter.  Our design definitely has some improvement opportunities, such as adjusting the size of the inner half-circle to make the bottle easier to open or using the 1/8" Delrin to make sure the straight edge is able to go under the cap easier (however we don't have years to perfect it!)  Sonja and I worked well and efficiently together and we are definitely happy with our working result.

The next project, which my new partner and I have already started, is constructing a well windlass, so stay tuned!