Class 1/30/13

We had a brief overview of engineering, then tried to build the sturdiest cantilevers with one piece of paper and a binder clip.  My group was quite successful with our tightly-rolled design, but we only tested one other idea, so our brainstorming session was less effective.  After we briefly touched on the physics behind cantilevers, we discussed the general process of design:

• Identifying the problem
• Developing concepts
• System-level design
• Detail design
• Testing and refinement

We emphasized the iterative nature of this process, which seemed reminiscent of the scientific method.  Another way to think about this:

• Research--it's important to know some physics so you have some idea of how things could work (and what won't ever work)
• Brainstorming--15 minutes of chucking out creativity as fast as possible, without discouting any ideas yet; don't get stuck on the first good idea, but push through the "crazy idea" trough to get to the really brilliant breakthroughs
• Selection--throw out the utterly impractical ideas
• Analysis--make a Pugh chart to compare the best ideas; combine the best features
• Prototyping--make "looks-like" or "works-like" models, or even actual full-size things that are just not manufactured on a huge scale yet
• Experimentation--check to see if things work!
• Evaluation--note what needs to be changed, go back to the beginning and start over

Finally we divided into pairs to try to design a bottle opener (lab partner: Laura Liu).  Spurred on by the promise of real South American Fanta, we excitedly began scribbling down many ideas in our initial brainstorming.  We used the Pugh chart to whittle down our ideas into two good designs, then cut out "looks-like" models with foam board.  Next class, we will draw our designs in the CAD software SolidWorks and then use the laser cutter (!!!) to cut out the final product from 1/8, 3/16, or 1/4" Delrin (my group chose the 3/16" Delrin as it will be thick enough to be sturdy but thin enough to fit underneath the bottle cap).
Although we initially discounted the similarities between a bottle-opener and a cantilever, we came back to the physics to try to figure out which design would be most effective with the Pugh chart.  Deflection is directly proportional to the force and the cube of the length, and inversely proportional to Young's modulus and the area moment of inertia of the cantilever.  Length seemed the most important term here, since deflection is proportional to its cube, so we tried to make the lever length small to ensure a sturdy bottle-opener.  On the other hand, we know from physics that the amount of force needed to apply a given torque must be greater for a shorter lever--so a shorter handle on the bottle-opener will be more difficult for the user.  We discussed the benefits and drawbacks of lengthening the handle, and eventually decided on two very similar designs with no real handle at all:

Above: lots of different designs, with a Pugh chart comparing our four favorites.
Below: the two designs Laura and I finally picked (very different from our first 7 or so ideas)--traces of our foamboard "looks-like" models.

Laura and I both enjoyed our designs; while Laura's was more symmetrical and aesthetically pleasing, my opener was ergonomically designed to fit just between the fingers.  Either design could be used equally by right- or left-handed people (mine would flip upside-down).  We fiddled with the center hole for a while--we briefly toyed with the idea of giving the bottle opener teeth, but discarded that after realizing how easily they might break off.  We eventually decided on a smooth ellipse whose minor axis was the diameter of the bottle cap, with a slightly bigger major axis--we would rotate the bottle opener around the major axis to pull off the cap.
We were excited to draw our design on SolidWorks and print it on the laser cutter soon!