Tag Archives: 3d

2017-02-02: Eagles/Kids

This would be a sculpture, along the lines of Swimmin’ Hole. The scene would be asking set with a couple of kids on the swings, another waiting his turn, and another flying through the air having just “bailed out”. The quirk is that kids in flight, or just taking off (and maybe landing) are shown as eagles, or transitioning between kid and eagle.


2016-01-29: Rhombic Dodecahedron

I’ve been interested in the rhombic dodecahedron (RD for short) ever since I learned that it is a space-filling polyhedron (i.e., they can be packed together with no wasted space), and that all faces are identical, like the rhombus below. Here’s a rotating 3d picture, and the relative dimensions of one face.

Rhombicdodecahedron . . . RDface

The angles of the rhombus are approximately 70.53 and 109.47 degrees.

My first thought was that a modular building, such as house, could be made from a collection of them, with suitable openings and infrastructure. I made a couple of them out of thin plywood. Later, when I started thinking about modular spacecraft for the Two Years at the Hot End story, I decided to make several of them and see how well they could be used. By this time, I was using Shapeways to 3D-print my designs, so I designed a rhombus with flanges to connect them at their edges, and clips toehold them together. I designed a large hole in the rhombus, to provide access to the interior, as if for a door or airlock.

The cost of ordering two faces was too high at the original size (10 cm along the long diagonal), so I reduced it to half-size. At this size, the thickness of the clips and the indentations to hold them didn’t meet Shapeways’s design rules, but they provide a “print it anyway” feature, which I used. The first two faces worked pretty well, so I ordered 10 more to make full RD. This worked fine, as in the figure below, but was too expensive to make very many.

Next I designed a set of twelve of the faces connected into a single “part” by way of two bars of clips. By printing as a single part, the cost was reduced by about 70%. The images below show the 3D model and the part as received. Apparently for packing, Shapeways separated the faces into pairs.

To have a reasonable number of RDs to try various arrangements, I next designed a complete RD only 2cm across, with clips to hold them together and again with holes for access. I made a grid of 25 of these, with thin wires strung between them, and rows of clips attached. This still counted as a single part for pricing purposes, and was affordable. The picture below shows five of the RDs and a couple of clips, and the rest still strung on their wires. Unfortunately, the size of the holes was a bit too small to allow tweezers inside to attach the clips. I might end up using water-soluble glue to arrange the RDs into various configurations.


2015-11-27: Two Years At The Hot End

On the Orbiter Forum (discussion of topics related to the Orbiter space flight simulator), someone mentioned that they were reading Two Years Before The Mast, by Richard Dana, and that the story might work if set in space. I re-read the book, and tend to agree. I envision it set in late 21C, with asteroid mining having recently become established as an economical activity. The narrator would serve on a ship making passes to/from the asteroid belt, with a nominal two-year tour of duty.

Some of the assumptions I would use:

  • Fusion power plants providing great amounts of power, based on the Bussard polywell ideas, and the boron-proton reaction. The reactors and radiators are at the rear of the ships: the “hot end”.
  • Ships based on a rhombic dodecahedron module, such that any size ship could be built by connecting an appropriate number of modules, or a large ship could be split into smaller units (limited by the number of power plants).
  • 3D printing capability (“makers”) on board to fabricate any material needed, from tanks of raw materials, refined by atom-sorters. Capacity to make panels for modules, if maker operates within an open module (one panel removed).
  • Module panels have flanges to construct modules; attachment points for exterior shielding, sensors, thrusters, structural support, landing gear, etc.; large opening for hatches; smaller opening and channels for liquids and gases; signal and electrical power channels.

Some observations that might influence the story:

  • Asteroid belt characteristics: semi-major axis range 2.1 to 3.3 AU; edges and Kirkwood gaps at 2.1 AU (4:1 resonance with Jupiter), 2.5 (3:1 resonance), 2.82 (5:2), 2.96 (7:3), 3.28 (2:1).
  • Volume of torus 2*pi*pi*r*r*R = 19.2 cubic AU.
  • Total mass ~3×10^21 kg; 1/3rd mass in Ceres; 1/2 mass in Ceres (mass 9×10^20 kg, dia. 950km), Vesta (2.6×10^20kg, 525km), Pallas (2.1×10^20kg, 512km), Hygiea (8.7×10^19kg, 431km); 200 have dia > 100km; 2 million have dia > 1km; eccentricity < 0.4.
  • Density of asteroids with dia > 1km = 2*10^6/19.2 ~10^5 per cubic AU, < 1 per 10^19 km; average distance of 10^6 km.
  • Average speed at a=2.1 AU = ~20km/s; at 3.3 AU = ~16km/s. Typical passing speed 4km/s. To detect potential collision within 24 hours, need detection range of ~4×10^5km.
  • Odds of a belt-crossing probe hitting asteroid is < 1 in a billion.
  • Chief engineers on all ships are called “Scotty” for obscure historical reasons.
  • Learning is in two phases: theory and practice. Theory is learned rapidly (a few days) by use of drugs and tech, but lost unless practiced (which takes much longer).

In addition to the story, I would develop modules and ships for Orbiter, and for printing as desktop models.


  • 2015-11-27: Vision only
  • 2015-02-01: Proof-of-concept 3d-printed rhombic dodecahedron faces/clips (5cm long)