I was approached to produce another icosahedron, with a few small alterations. This one was to be larger – just under 2m tall at the top nodes – than the prototype, but the same in as many other ways as possible.
This greater size meant the weight of the icosahedron was going to be greater, by about 15%, and the critical buckling load of the rods was going to be lower, reducing to around 63% of the previous iterations – therefore I expected the rods to be around twice as close to their buckling load as found previously. This required for robustness a move to 12mm diameter rods for the bottom members of the icosahedron, which has a minimal visual impact. The icosahedron stands fairly robustly with ‘all 9mm diameter’ rods but the softening due to axial loading leads to significant vibration when it is touched – hardly ideal for long exposure photography!
Aside from the size of the rods a couple of other changes were made: smaller magnets were used in nodes – the prototype demonstrated the larger magnets weren’t needed. The smaller magnets helped to reduce the congestion on the interior of the nodes, and allowed for a better quality of drill-hole without a pilot hole. The benefits of the reduced congestion were particularly apparent in the nodes mounted on the vertical legs, where room needs to be left for a rod to pass through as well. A further alteration on the prototype was that every magnet was glued in place, rather than allowing those that could to use friction – the prototype had occasionally ‘shed’ magnets as the wooden rods changed shape slightly stopping the friction grip, so magnets that were unremovable at manufacture because loose over time.
A final change was placing the nodes at the top of the vertical elements on the rods rather than using a magnetic connection. This increased robustness of the icosahedron but also had a key manufacturing benefit – I didn’t need to drill an end hole in a very long rod, reducing the risk of spoiling rods and also removing the need to rejig. The large holes in the top nodes were using the same setup as the ones that lie along the vertical rods.
The icosahedron was delivered on time and budget, and looks good! See below:
A final improvement was for the icosahedron was finding a new way to construct it with two people, to start, as many rods as possible were laid out on the floor:
Then one person provides support at the top of the icosahedron, holding the top rod in place, the other person builds the rest of the structure along, but has the benefit of two more ‘anchored points’ at the top of the icosahedron to hold everything in place, so this is quite easy.
I am looking to develop the design again – maybe experimenting with 3D printing or CNC manufacture to increase the build quality beyond what I can do by hand, so if you would like me to make you an icosahedron – let me know on firstname.lastname@example.org.