Well Windlass: The Build

Back in middle school, I was part of a Science Olympiad event called Tower.  We were required to build a tower about a foot high that could support as much weight as possible.  However, the tie breaker for the event was that the lightest tower would win.  Hence, this resulted in some very thin wooden sticks being used to build fragile towers that supported pounds of sand.  So when we were told to build a windlass that had a similar functionality (minus the weight limit), I was a bit excited to get my hands back into building something.

Sketches

At first it seemed like a logical step to make the base square and the sides trapazoids.  However, since we were only allowed to use 500 cm2 of material, my partner and I had to iterate our designs over and over again to find the perfect shape that would be able to bear the weight.  We finally decided upon hollowed out triangles for the sides to solve this problem.

A further but small problem was the fact that we wanted to speed up the process of pulling up the bottle without turning the crack a few hundred times.  However, designing a way to increase the surface area of the rod that the string wrapped around while allowing the sides to turn proved to be quite a challenge.  In the end, we decided up on a 2.5cm rectangle that would span across the middle of the rod to increase the surface area that each turn of the crank would pull in.

An addition challenge with our design was how to fasten each part.  In my previous post, I listed a few different methods on how I planned on attaching various things. However, after examining the physical prototypes and the sketched out designs on the paper, it appeared that most of my plans were either not feasible or excessive.

Designing

Although I was initially frustrated with Solidworks, I have to admit that the program is starting to grow on me as I gain a better control over the software.  I'm still somewhat jaded that I can't type in the commands and am forced to search for each one in the toolbar but once I learn what the shortcuts are, I predict that I'll be more favorable to it.  I think the hardest part of designing this time was simply creating all the notches and hinges since the measurements kept changing on us.  We went through so many iterations trying to adjust the widths and heights of everything to account for the differences in Delrin thicknesses.

Engineering Analysis

We were initially concerned that the structure would collapse within itself since the weight of the bottle will pull the structure down and ultimately cause it to push outwards.  Hence, we designed support beams in the middle of the triangles to keep them from moving apart from each other.  The triangle sides were also thoughtfully designed such that the force would not cause one side of the structure to fail (ie collapse inwards as a square might do).  The equation variable was the most under our control was most likely the force of the bottle on the structure.  The 2.5cm rectangle that the string wrapped itself around distributed the force a little more equally in relation to the structure since the force would then not be concentrated in a single spot and cause a structural failure. 

Final thoughts:

In the end, our structure was probably not the most structurally sound thing on the face of the earth.  I believe this is most likely due to our obsession with the material constraints.  If I could iterate the design again, I probably would have made the triangles solid instead of hollowed out to improve its sturdiness.  Additionally, I wish there could have been some way to make the notches better but this was a factor controlled by the laser cutter.