Fast dome

FastDome is a set of 3D printed hubs to build an opensource geodesic dome using tubes. 

A geodesic dome  is a geometric structure with rigid triangular elements. These triangular elements distribute stress throughout the surface structure. Geodesic domes are able to support heavy loads, and are usually used to build greenhouses for agriculture, winter gardens, support for growing plants, playing houses for kids, and also for learning mathematics. It gives us a good hand on practice way of learning how geometric structures fill the space and how scale is correlated with our perception of it. 

A geodesic dome is a geodesic polyhedron, a convex polyhedron made from triangles. Geodesic polyhedra are a good approximations to a sphere:  a sphere encloses the greatest volume for the least surface area. 
 

65cm radius dome

For this dome I've used 16cm (outer diameter) PVC tubes but any other type of tube will do. PVC tubes are inexpensive and lightweight, this makes it suitable for building a light weighted and large geometric structure. 

I've also shared the OpenSCAD  model so that you can adapt the hubs to your chosen struts.  

For this dome with 16cm PVC struts we will need:

• 30 struts: 40cm - 'A' struts
• 35 struts: 35cm - 'B' struts
• 6 five way 3d printed hubs
• 10 six way 3d printed hubs
• 10 four way 3d printed hubs (base of the dome)

Printing

I've used PLA, but ABS or PETG will do perfectly.

• infill: 20%
• layer height: 0.3mm
• walls: 3
• tops/bottoms: 6
• no supports

Note that if want to use it as an exterior dome be sure to use some UV resistant polymer, PLA is not UV resistant, neither all types of ABS or PETG will work for this. Check the specs of your filament before putting the dome outside. As an alternative you can paint the structure with outdoor enamel water based paint.  

For completeness here's some photos of the 3D printed hubs. Nothing fancy, really. 

Five way 3d printed hubs

Six way 3d printed hubs

Four way 3d printed hubs (base of the dome)

Assembly layout

Other parameters of this dome are:

• diameter: 1.30m
• surface area: 2.65m^2
• floor area: 1.31m^2
• circumference: 4.02m

Note on resizing: the length of the structs do not scale linearly with diameter size. There are various on-line calculators for determining  the size of the two structs. For a nice dome calculator (not affiliated) see e.g. https://geo-dome.co.uk/2v_tool.asp 

CAD/modelling

The modeling was done using OpenSCAD, and is available under a GPLv3 license. Use the SCAD file to fit the hubs to any diameter tube. 

Conclusion and future work

I've build this dome with students of various ages, it makes a nice extracurricular activity and a hands on demonstration how math and engineering are coupled. Marking each strut with colored tape, e.g. red for the ‘A’ struts and blue for the ‘B’ struts, helps the building procedure; a drawing of the dome with some basic explanation suffices to ensure a smooth and autonomous assembly by the participants.  

Of course you can glue all the struts to the hubs and make it a permanent version, but if you are planing not to make it permanent you should adjust the hubs diameter for a tight fit, no glue is needed, you can assembly it for demonstrations purposes, disassemble  it, and store it for the future.

If you choose to make a light installation with these domes note that the hubs and connectors have a center hole for electric wires. 

Happy hacking!