Building a tensegrity cubotahedron
Now all the fun began to start for April 4th and April 5th, which was yesterday.
Reference is Geodesic Math and How to use it, Hugh Kenner, p21.
This is Cubotahedron which has six square rectangulars and eight triangles.
The book explains how to build a cubotahedron with 12 struts and many strings: the strut length is 12 inches long, long tendon is 18.2 cm, short tendon is 15.8 cm. 12 inches is equal to about 30 cm which looked too big for me. So I decided to use 6 inches length (scale down to half of the size.)
It was feeling great because the mini table saw worked exactly I expected. A 20 mm x 20 mm stick produced four small sticks about 4 mm x 4 mm. I made little over a hundred mini struts within few hours. After finishing dinner I started building 12 struts, drilling holes on each side of a strut and putting two hooks made out of a 2 mm wire, then painted black, red, and blue three sets. The diagram has four sets of strut. I worked till to midnight.
I got up at six in the morning, began to assemble the T-cubotahedron. I used a nylon or plastic string to tie down the struts. It took longer than I thought and was tedious job whenever I attach a strut. Because one misplacement of a tendon wouldn’t provide the right tension in final assembly. I managed to finish the assembly around one P.M. However it was lack of tension and I found several missing tendons on it. At that time I did not marked orientation of all the struts, it was hard to pin point which part was wrong, misplacement of short or long tendon. Spending a good hour I destroyed it. I packed everything in the bag and left the base camp. On the way home I dropped by a hardware store and bought a roll of string.
Spending a night at the base camp still made the body exhausted due to cold, inconvenient conditions there. When I work at the base camp, I mostly work long hours without long breaks and sleep five to six hours. In addition food consumption is minimal. I don’t carry full load of food or snacks. Outdoor environment and raw in nature strangely keeps the mind and body in high.
I went to bed early.
I got up six in the morning, cleaned the computer desk for the assembly of T-cubotahedron. The new string is flat, easy to tear down. One strip produces eight small ones width of 2 to 3 mm. The second trial once again failed. It was loose. Even though I did mark orientation of strut simply, it wasn’t much help to pin point misplaced tendons. Coloring and diagram were insufficient to troubleshoot (?) the wrong connections.
I started the third assembly around two P.M. This time I spent some time to prepare tendons for exact numbers and lengths. Total number of long tendons is 24 with 15 cm in length, and short one is 24 with 14 cm. Total number of tie string is 96 because one tendon needs two ties. And I marked orientation of the struts, which were I for the top row, II for the middle low, III for the bottom and (A, B), (B, C), (C, D) indicators. For example, the first strut has I, A, B as you see on the diagram. The green and red strut (I, B) is connected to the blue (II, B) with a long tendon. This time I made a one mistake, which was to swap a long and short tendon on the red strut (II, C). I figured it out.
I finally built a T-cubotahedron around 11:30 P.M. I spent almost twenty some hours to get it done just for the assembly. I’ll glue the joints probably today afternoon.
Photos of the T-cubotahedron were taken in the morning of April 6th.