Scissors That Don’t Cut
Every investigation starts with a bit of background information. As simple or complicated as this knowledge may be, it is important to set the stage for the rest of your investigation. In my case, I started my investigation into this research project with a review of a couple of related research papers and code before I was able to build a working simulation of the concept for my project.
Before I could start working on coding the Hoberman sphere, I needed to read about the properties that determine the shape and properties of foldable structures like the sphere. Thanks to the aid of an undergraduate student I was collaborating with at the ASU Oasis Lab, I was able to view other’s research into the current and potential uses for foldable structures such as this one. One truly doesn’t realize the effort that the base mechanisms go to maintain the structure of stadium roofs and trellises, that being scissor mechanisms that allow for the wide range of internal motion required by these structures. One of the important discoveries I made from the research that I read was regarding the autonomous deployment of satellites using foldable structures. Specifically, the exponential growth of pressure on joints attached to the scissor mechanisms in circular-shaped foldable structures as the angle from its collapsed form increases. This does raise the concern that such a large change in pressure in such a short amount of time may cause the entire structure to collapse which I hope to address through the complete design of the the bumper.
As for the actual construction of the sphere, there are important factors that the research papers I read covered regarding the expansion ratio of a 2D version of the sphere. While it may not be the same as the 3-dimensional sphere, the properties remain similar. For starters, the thickness of the links composed of interlocking scissor joints in the sphere must not be overlooked. Since the expansion ratio of the sphere will decrease at a logarithmic-like rate as the thickness of the sphere increases, optimization between the two is necessary. The results from the research also model the behavior between the number of edges in the foldable polygon rising to a maximum and beginning a steady decrease. In other words, I will need to optimize the number of edges and thickness of each link to determine an effective Hoberman sphere expansion ratio.
With this important information in mind, I was able to start working with the team to start coding the Hoberman sphere. While the team currently works on the code for the sphere, we have been able to source the code for a Hoberman ring capable of expanding and compressing. With this code, I could develop the footage seen below of the basic concept of what my project hopes to achieve. Being able to edit the parameters within the code easily certainly made this task easier. For clarity purposes, the dashed line represents the shell of the bumper meant to surround half of the sphere(represented by the ring below). As a force is applied to it, the sphere should compress allowing the shell to move inward dissipating the force in the process. After the force has subsided, the bumper should be able to expand back to its original shape. Ideally, I will be able to improve this code so the left edge of the ring remains fixed demonstrating the bumper collapsing in on the sphere. While this footage does get the basic gist across, more work must be done to improve this. As we continue to work on coding the complete sphere(unlike the ring shown in the footage below), I hope to continue and refine this conceptualization in the process.
Figure 1: A rudimentary demonstration of how the bumper should work
How does this relate to my senior project you may be asking. Since my project centered around determining whether or not Hoberman spheres can be used to withstand the impact of collisions, coming up with a basic design for a bumper is necessary. These models will serve as the groundwork for testing the updated designs in the future through simulations. Stay tuned in next week as I update the bumper design and begin planning to put the bumper through simulations.
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