Considering the plethora of geodesic domes I had constructed out of panels (cardboard, plywood) and struts and hubs (metal, wood) I decided to stick with a strut and hub model to present to the class. This model has a number of advantages – is small and easily transportable (though it weighs a little bit when bringing it to class on a train), is simple to erect and break down, has a built in doorway to illustrate innovations (changes) possible within the triangular 2-frequency dome, and is incredibly over-engineered (read strong!!!!)…
The proof of the level of engagement domes have was easily represented by the immense and immediate interest the class had with the structure, even though it was less than a metre high. Vennessa threw herself into helping me assemble the dome, and caught on to the construction technique extremely quickly – the base dome I brought is what is known as a two-frequency geodesic dome.
[This means simply that there are two types of struts – an A strut and a B strut. As can be seen from this diagram drawn by Dave Breakspear, the A strut is roughly 62% of the radius of the final structure, and the “B” strut is roughly 89% of the length of the “A” strut (or about 54% of the radius of the final structure):
Interestingly, when building large domes on concrete surfaces, even unmarked you can tell which is which by dropping the strut and listening to the sound it makes – each “A” and “B” strut, corresponding to a “chord factor” in the drawing has a distinctive note. Though hardly a mathematician and somewhat of a musical neophyte, I like that as each different strut’s “chord factor” (length) is different, this results in a different sound, though more likely more a note than a chord. Like I said, musical neophyte here… 🙂
That Vennessa, heretofore unversed in dome-building, was able to steam ahead with construction really proved the simplicity of the technology – there are virtually no tricky steps in constructing domes. The only trick came for us when I realised I had not brought one strut and had to tweak the open-door addition design to accommodate the missing strut.
As you can see by these pictures, much fun was had before the pitch, as Mark investigated the womb-like interior* (see the squarish doorway and small struts that create a more vertical plane – my innovation on the basic 2 frequency geodesic – note that this innovation is largely unnecessary with a dome on a riser as the removal of a base strut still allows comfortable ingress/egress through the created pentagonal portal):
Mark making himself at home/at dome with an acrobatic Catherine*:
Meanwhile, while I demonstrated the incredible strength of the structure by standing on it and trying (and failing) to look nonchalant and not at all like I was some guru of the nouveau*:
* special thanks to Vennessa Harney for these photographs and assisting in assembling the dome in record time for the pitch, and to Mark and Catherine, my dome-loving models.