Maybe I’ll have to script their underlying geometric constraint library? SolveSpace is a very nice lil’ CAD tool, but (as far as I can tell) lacks variables and other parametric / programmatic support. With a fair bit of pointing and clicking, I can coax my CAD software to visualize geometric modes:īut I’d love to find a free and open source solution upon which I can build a long-term foundation for programmatic workflows. However, I’m not quite sure how to go about it in practice. Iterate based on optimization criteria (e.g., maximize stiffness in undesired motion directions and the gap between the desired modal frequency and all the others).Generate instances and run finite element analyses (FEA) to find their modal frequencies.Develop parameterized geometric model (sheet thickness, number of springs, their width and position, etc.).I know that this process is doable in theory: How does the thickness affect the part motions?.How will using other plastics (or laser/waterjet-cut aluminum) affect the motion?.How do the angles of the springs affect undesired motions (pitch/yaw out of the plane or translations within the plane)?.To increase axial stiffness (for satisfying feel), is it better to use more thin springs or fewer thick springs?.In contrast, my flexure geometric optimization problem has a lot of well-defined dimensions to explore even within the constraints of a cuttable-by-2D-laser design space: This is refreshingly different from popular “generative-design” approaches which iteratively remove unstressed material from parts so you can save 5g of aluminum in exchange for an extra $100k of manufacturing costs and weeks of H.R. Given that I already have a the butterfly flexure in mind, how do I go about optimizing the geometry to get a robust, skookum-feeling rotational mechanism? Of course, this schematic/conceptual design is only half the story. (See lecture 1 for an intro, skip the math of 2 and 3, then watch lecture 4 for the big concepts and sweet pictures.) Until I (thank God) found the author’s far more comprehensible YouTube lecture series. This involved a lot of staring at what I presume are some of the trippier figures which’ve appeared in the journal Precision Engineering: To understand why the butterfly flexure moves the way it does, I read up on FACT, a theoretical framework for designing flexures. I quickly put down my original project to the side to further investigate flexures. I roughly drew a similar design up in CAD:Īnd spent a weekend cutting acrylic and tweaking angles/thicknesses to try and find a satisfying feel: In particular, I figured I’d try this “butterfly” flexure from a wonderful video overview, which is fixed only at the bottom but rotates around the center: Since I have weekend access to a 50W CO2 laser cutter, I figured this would be a perfect opportunity to explore flexures (AKA compliant mechanisms), which are fabricated from a single material with geometry designed to bend only in certain degrees of freedom. However, in my case I need an attachment point that is separate from axis of rotation. Normally one might turn to bearings, basically two concentric rings that can rotate with respect to each other. I’ve spent the last month doing the opposite of back-of-the-envelope estimation: Actually trying to make something work well.įor a yet-to-be-disclosed project, I need a satisfying-feeling axis of rotation - think “ knob feel” from a 1970’s stereo. Thanks to those of you who pointed out to me plant respiration, where carbon is lost as CO2 due to various plant metabolic processes (especially those occurring at night, when the CO2 cannot be recaptured by the plant via photosynthesis). Last newsletter we asked “ how fast can plants grow?” and I was unsatisfied with the 20x gap between my rough estimate and reality.
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