Popsicle Stick Tower
It’s always been exciting to me when my school projects overlap with my hobbies and allow me to do my best work. Some, like the popsicle-stick-tower project that I completed in my freshman year of college, were so enjoyable that they consumed nearly all of my time until I had them completely finished. My water-pump project during my sophomore year of college fit into this category as well but took far longer and required many more trials to complete, making it far more stressful in the long run, so I got more enjoyment out of building and perfecting my popsicle stick tower.
Freshman engineering students were required to take a course called Engineering Problem Solving 1 in which we learned basic tools and methods that would be needed in our future classes. The EPS class was divided into two sections, each taught by different professors, with one geared toward the actual learning of engineering techniques and thinking, while the other put those concepts into practice.
The first major assignment that we participated in within the experimental portion of the class was a design challenge asking for an eight-inch-tall tower made from popsicle sticks. Students were given design criterion and constraints for the tower, with performance ratings given based on the students’ ability to keep the tower within the design constraints and on the tower being able to support the largest vertical load possible before failure. During class, I spent time with a straight edge, pencil and engineering paper conceptualizing and designing a structurally stable wall for each side of my tower, which was to be essentially a triangular pyramid. I used the 1/5-inch line divisions on the sheet to keep track of the dimensions of my section and make its structure consistent so that later on, I could use it as a visual reference when assembling the real thing.
In one night, over the course of I believe about six hours based on the image metadata of photos that I took at the time, I constructed my first iteration of the tower. The beauty in this assignment was that it gave students an opportunity to improve our designs based on the failures of our first models and then build a second tower from those new designs to test later. During our next class we tested each tower to find the maximum loads that they could support. The majority of the towers tested that day were able to support between 100 and 350 pounds before failing, which is impressive considering they were required to weigh less than 65 grams and were made entirely from popsicle sticks held together with hot glue.
I was quite surprised when my tower was able to withstand a compressive force of 790 pounds before one of the corners sheared and the hot glue separated. This ended up being the largest load that any of the first-iteration towers withstood in any Engineering Problem solving class that year, with second place holding ~500 pounds before failing. My second model fell short of my first despite my attempts to improve the design, but still held 560 pounds before failing. In another class, somebody’s second tower held 650 pounds, the maximum of any in the second round, which exceeded my second model. I was still quite proud of both models, especially the phenomenal performance of my first tower. I kept both as a reminder of the time and effort that I put into that project and how much it paid off.
Using what I thought I had learned from the failure of my first tower, I tried to improve my design in any way that I could. I only made small tweaks to reinforce the locations that had failed on the first tower, but I mostly stuck to the original design that I had used. Both towers ended up weighing about a half-gram less than the 65-gram weight limit. If I remember correctly, the constraints required that the tower be within a small margin of error of eight inches tall, have a triangular base with a maximum of five-inch and minimum of four-inch leg lengths, and fit through a circle of a given diameter at a certain height up the tower.
I expected from the given constraints that our professor wanted us to imagine triangular pyramids and base our designs around them, but there were some groups who chose to focus entirely on the vertical component and barely had any horizontal support. I felt that my design balanced the two, giving horizontal support in areas that would constrain the vertically loaded columns and keep them from separating under load, and also giving a large footprint below the structure to keep it standing vertically.
I used angled supports to try and create a triangular lattice, hoping that it would help to balance the forces between all of the members, but at the time I truly had barely a rudimentary knowledge of static lattice members, and most of them were useless. If I had the chance to redo it again after being thoroughly educated in mechanics, I would add rigid tensile supports to the small overlapped joints between sticks that relied on hot glue for their bending-moment support.
My first design did have sticks in place to better brace joints between other sticks, but I wasn’t nearly as focused on that task as I should have been when I conceptualized it. I also would have added more bracing across said joints to essentially try and eliminate them, minimizing the shear that would occur at the interface between sticks. I focused more of the allotted mass of my tower into the corner structure and had no “vertically” oriented sticks up through the center of each triangular face which might have ended up being a mistake.
One of the largest adjustments that I made was attempting to symmetrize the triangle supports to provide equal support to the legs of the pyramid in the same locations on each leg, which I believe now was a waste of wood that would have served better elsewhere. Reinforcing the joints was the priority, but I failed to do that sufficiently in my second design due to a lack of knowledge of material failure modes. This was most likely the cause of failure of my second tower at a lower compressive force than my first tower, combined with possible weak glue connections.
My first model sheared at the joint between vertically oriented sticks on one of the legs of the triangular pyramid. Each stick was about 4.5 inches long, so in order to reach the total tower height of eight inches, I had to stack two sticks to form each leg on each face and overlap them by only about a half of an inch in the middle of the tower where they were then glued together. Upon connecting the three triangular faces to each other at their edges, the vertical edges of the pyramid were each made up of two sticks stacked above two more sticks, but for added support and resistance to separation I glued a third stick to the bottom half of each edge.
Once I reached what I thought was a sufficient tower structure with supporting beams in all of the necessary places, I measured the tower’s weight to see if I could fit anything else into the structure. It was nearly at the limit of 65 grams, so I added a few internal supports to prevent the faces from caving in or flexing out, then used the remainder of my allotted mass to add extra glue to ensure that every joint was solid. I thoroughly believe that the attention to detail that I gave in this project is what led my tower to support nearly 1000 pounds, and I enjoyed every step of the design and manufacturing process. Enthusiasm about the work ahead always helps in dreaming up good design ideas. I aim to do this kind of work to support myself, so I can be proud of the effort going into the things that I create.