Geodesic dome 7 April 2005

I have constructed a frequency 3, 5/8 geodesic dome from plastic straws and pipe cleaners. The diameter of the dome is 73cm and the highest point is at 46cm from the floor. The time required to build the dome was less than 4 hours. Hours of great fun. Since building such a model doesn't take a lot of time, it is a fun thing to do away from the television screen, it is mentally stimulating, and educational. The end result is fun to look at and wonder about. I am currently planning more complex and bigger domes.

Materials

Here is a list of the materials I have used

The picture below shows the tools used, and how many straws and pipe cleaners I had left over after construction. Not much.

In total, I paid 8.75euros for the materials, i.e. 2euros for the straws (at HEMA) and 6.75euros for the pipe cleaners (at Pipoo's, a handcraft store, I saw them later at HEMA too). The pipe cleaners were in a kit containing moving eyes and stuff to make buttons and keychains. This kit was cheaper than buying the pipe cleaners seperately.

Method

The bending parts of the straws were removed, and they were cut to size according to the building plan. The maximum length without bending parts was 15cm. I guessed that the central knot of the connection would leave a space of about 1cm inbetween two connected pipes. Eventually this indeed turned out to be a good guess. Taking note of the knot width, the longest struts (C on the building plans) were thus 16cm. I entered this length into the reverse strut length calculator which gave me the lengths 13.5cm for A struts and 15.65cm for B struts. Subtracting the 1cm interconnection space, I needed

You thus need at least 165 straws cut to their proper size. I have used the colors of the straws to color code the different strut lengths. Since I didn't have enough straws of each type, I colored the base of the dome (blue straws) differently from the rest, which meant having both B and C struts in a different color code than the rest of the construction.

I have made 15 4-way, 6 5-way and 40 6-way connectors out of pipe cleaners to fasten the straws to each other. The following depicts how the 6-way connectors are made

  1. I have cut the pipe cleaners to pieces of 10cm, of which 3 are required for a 6-way connector (2 for a 4-way, and 2 and a half for 5-way)
  2. Wrap one around the other two. I usually have one piece that is a bit longer because of guesstimating while cutting the pipe cleaners. I use the longer one to wrap around the others
  3. Halfway through every arm of the connector, bend the pipe cleaner over so the thickness of the connector is doubled. This allows the pipe cleaner to have better grip on the straws.

For the whole dome I needed 162 pieces of pipe cleaner of length 10cm and 6 pieces of 5cm. The dome thus contains 16 and a half meter of pipe cleaner. I bought 18 meters so I had a bit left over. I would use more pipe cleaner when I'm doing a new model. The grip of the pipe cleaners in the straws would be better than what I have now if the connecting arms would be longer and thicker (i.e. bend the arms not just once but maybe twice to give a better plug).

The building plan showed me how to connect the many struts into a geodesic dome, using the connectors. I have constructed the dome starting with the base, and slowly building up to the top of the dome, which seemed like a good choice.

Results

The dome looks cool, but isn't very sturdy. The pipe cleaners and straws don't stick well to each other. As a consequence, the model isn't able to widthstand any physical pressure. The construction is strong enough to be picked up and walking around with, so it's strong enough to carry its own weight.

Building a dome out of metal pipes and nuts and bolts would make it a lot sturdier, this was just a test to get familiar with the design of a geodesic dome. I would like to try a dome with a higher frequency now. I want to build a 6v dome, which would require 555 straws cut into 9 different lengths. I would also need to make 30 4-way, 6 5-way and 130 6-way connectors, which would require 462 pieces of pipe cleaner (probably best to have pieces of length 15cm, so the construction would require 231 pipe cleaners).

References


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