Annular Dodecahedron
Geomag Annular Dodecahedron (side 3)
Side 3 version
Rods 1350 × Geomag rod icon
Spheres 700 × Geomag ball icon
Author --Karl Horton 11:34, 29 October 2007 (UTC)

A Geomag classic: pentagonal torii stitched together into a dodecahedron.

Steric Interference

There is a technical problem with this construction: all of the rods along the red edges of the outer dodecahedron are too crowded: they cannot all remain with full contact on the 1/2" spheres. Nontheless, after the model is complete there is no tendency for the joints to slip.


Each module has 105 center rods, and 15 edge rods. So, there are 12*105 + 30*3 = 1350 rods in total.

Each module has 40 balls: 25 center, 10 edge and 5 vertex. So there are 12*25 + 30*10 + 20*5 = 700 balls.

The model weighs 27lb (12.4kg) but can, with care, be moved.

Rod to Ball ratio: 2:1

Building Instructions

  1. Build a Pentagonal Torus module: it is helpful to build an extra module out of a different color and leave it nearby, because its really easy to get lost whilst building.
  2. Build another torus
  3. Strip the edge of one torus to join the two together
  4. Rest the linked modules on the hinge, and erect scaffolding poles to support the modules at the right angle.
  5. Now, resist the temptation to proceed onwards with modules. Instead, learn how to build the diamond-shaped tube in-place on the model. Use a contrasting color for the true edges of the dodecahedron to keep yourself orientated.
  6. It helps to use pentagonal panels to stabilise the build.
  7. Let the structure grow at first like a bowl, then like a dome. Keep the build balanced and keep evolving the model with an eye to the symmetry.

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