I found my preferred strut material for now, and got plenty of this as well as variations, so whenever I feel like working a new shape out I can go ahead. Well, I avoid the noisy bits during night time, that's when I can sit back, explore the different aches in various parts of my body, and reflect my experiences.
42 unfinished
I built my first structures using an online 3d animation for tensegrity objects, and there were still some objects that challenged me to handle with my own hands. I watched the animation of an octahedron unfolding into a tensegrity structure over and over, planning the stages of construction for an object with 12 struts.
Cutting the cord to length and knotting into loops and tendons posed the monotonous challenge before getting the octahedron together. I started ambitiously using elastic cord at first, but after some accidents changed over to nylon. An octahedron has six corners, which open into squares for the tensegrity. 12 tendons pull along the original vertexes. A zigzag line of force connects the opposing corners of opposing squares; all the squares show the same chirality.
Seeing a 3d animation on a two-dimensional monitor helps a lot, but it doesn't prevent me from mixing up left and right. It took me hours to develop a decent build strategy that worked without additional hands (i used some small clamps, thinking about some improvement of these little helpers).
The puzzle consists of 12 struts, 12 strings with knots at their ends as tendons, 6 strings knotted into a loop for the corner squares. Starting with the 'bottom' square, four struts connects in a clockwise (or counter-clockwise, if you wish so) to all squares but the opposing square. The struts coming from the 'bottom' and from the 'top' make up the 'left' and 'right' corners of the 'middle' row of squares, which are laterally connected with struts coming from 'bottom' of one square to the top of the adjacent square. All struts join their square with the same chirality. Simple, innit?
42 unfinished lying
Although I don't plan to rebuild '42' at any later stage, I salvaged this accidental creation later with some additional tendons. I guess my difficulties to build this structure at all might relate to the 'technical' error in its construction. 42 has 4 clockwise squares and 2 two counterclockwise squares. When pushed on the left turning corners, the structure nicely compresses, but there's little resistance when other corners get pushed in, all in all it resembles rather an egg than any Platonian Solid.
It took me late into the night to have the sculpture together, and I needed to re-attach some of the tendon to prevent struts from touching. Still, when no strut touched each other anymore, it still looked and behaved somehow wrong. The next day I noticed the mixed chirality, and yet another day later four stabilising tendons gave it its final shape.
42
I had the puzzle nearly finished, just a minor mixup in chirality, so it shouldn't be a problem to do it again, or so I thought. I tried to remember the successful build strategy from the night before to do a proper octahedron, yet it felt more like I repeated some of the typical mistakes of the day before. Usually sawing the grooves is the most unpleasant part of this projects, with familiar tensegrity objects I have figured working build strategies, but this time finding the right sequence took considerable time.
WIth a lot of breaks in between I finished the next miss in building an octahedron. It's not even a tensegrity, some of the struts touch, and its easy to tune into a floppy shape. I wonder whether to keep it, or to reuse the material for the 'real' thing.
Twisted X's
WIth the current abundance of material for struts, I started preparing 20-30 at the same time, 24 were gone now for the octahedron attempts, so I prepared the next bunch. Another chance to experiment with the easiest movements for my repetitive task, and to look out for body feedback during a new task. Precision makes life so much easier- although it's not too difficult to replace a strut in a larger model, in the build phase a failed component usually means back to the start.
At least I still I had an idea how to build this structure now, had analysed some of my prior mishaps, and started to understand more of the dynamics of the octahedron. I found a sequence for connecting struts and strings that needs only little external support and can take a bit of handling without disintegrating, cutting and knotting strings to well-known length happened nearly by itself.
Anti-Octa (counterclockwise stellated octahedron)
The third object with 12 struts, 12 tendons and 6 loops finally turned out as octahedron. Strike! Like with my first attempts with the x-module, I persisted through a series of failures until found a decent way of building. Connecting the tendons the right way meant as well that the structure started stabilizing itself to a certain degree before it was finished. Now I've got another model that can do with rough handling, the symmetry distributes impact easily, as an accidental 2 metre drop proved.
Once I connected struts and strings in the way I wanted to in order to build an octahedron, I had a better understanding about the difficulties of this process. The right sequence provided relative ease, so I wanted to do it again. I checked the clock before I prepared the strings, I still had enough struts, carefully studied Anti-Octa to build the clockwise turning equivalent.
Counterclockwise and clockwise stellated octahedrons
After 50 minutes without great difficulties the sculpture was finished. Another beast tamed. Left and right turning octa's connect nicely in the triangles created by three parallel struts. When I get bored I might be tempted to build a high-riser, although I surely need some extra tendons for vertical stability.
Different turning octahedron joined at a triangular face
I felt ready for the next challenge, using the experiences gained to tackle the cube. I had a first go just after I finished 42, but settled for building a real octahedron first before moving to the next structure. The cube has eight corner, that span into triangles for the tensegrity, and 12 connecting tendons. The model needed a bit of tuning, but this time I succeeded with the first attempt.
Even as tensegrity the inherent instability of the cubic shape becomes apparent. I might be able to balance it on one corner, which is much easier with an octahedron. However, it offers ample space in its center and looks very airy even when sitting on four corners.
Slice o'Dice (Stellated Cube)
12 struts seemed no longer a challenge, two new shapes belong now to my tensegrity alphabet, So why not have a go at the trigonal prism? Six triangular loops connecting nine strut and 9 tendons. I solved this puzzle as well on the first go. I averaged a bit the tendon length. The model doesn't balance on all corners, yet provides a wide basis when placed on three corners (for a beam). Now I need to make up my mind whether to go metal or bigger, hanging some of the structures on a string provides some good stability test and maybe some durabilty test as well.
69 (Trigonal prism, balanced on one corner)
No comments:
Post a Comment