Mechanical Planetarium

thingiverse

[Update, 12/16/2020: Thanks for all the kind comments. Some people have had trouble with gear meshing, and various improvements have been proposed and posted elsewhere. I appreciate the efforts others have made. Mine still works fine for me, but as with all designs your mileage may vary. I've just added a photo of the planetarium advanced to today's date, after not touching it for 2 months. Gratifyingly, it clearly shows the conjunction of Saturn and Jupiter, as well as how they are only visible near sunset given the low angle with respect to the sun. Mars is falling behind Earth as expected, from its position of minimum distance in October 2020.] *Original Text* A working planetarium*, modelling the orbits of the inner 6 planets and the Moon. One rotation of the dial equals 14 days of movement. https://youtu.be/AKBxbvwoRgs Accuracy (orbital period in Earth days, actual / model) Mercury 87.97 / 86.31 Venus 224.70 / 224.87 Earth 365.26 / 365.26 Mars 686.98 / 688.65 Jupiter 4332.80 / 4325.32 Saturn 10755.70 / 10787.85 This model is based on plans for a mechanical planetarium shared by Ken Condal (http://zeamon.com). I have adjusted the gear ratio for Venus for better gear meshing, at the cost of ~1.5 days accuracy in the orbit of Mercury. Watch the following video for how to assemble the gear train: https://youtu.be/gCyWxUscdN0 Mine printed well with 15% infill, 0.25mm layers, and a 0.4mm nozzle. In addition to the printed parts you will need M3 screws, 5 and 10mm, about 10 of each ought to do it. I painted the planets with dollar store nail polish. Success with this project will depend on organization (not mixing up parts), willingness to sand the many tightly-fitting parts, and your print quality. "Elephant foot" will ruin gear meshing, a problem that can be addressed either through printing on a raft or within your slicer's settings. The OpenSCAD files used to generate the parts are included here. To use it, you will need to download the gear generator file "Getriebe.scad" by Dr Jörg Janssen from Thingiverse (https://www.thingiverse.com/thing:1604369), and place it in the directory of your project file. If your gears are not meshing well, try changing the "idler_length_correction" a bit up or down. A word of caution, the planet peg lengths are a bit off, so I just eyeballed at assembly time and clipped off to height with nippers. *-- Yes, I'm aware of the 4th Earl of Orrery, who received a mechanical planetarium in 1704, and in one of the English language's many injustices, became the common name of all future mechanical planetaria. The Earl played zero part in the conception, design, or manufacture of his particular device, which was a copy by John Rowley of a model designed by George Graham and Thomas Tompion. Further, mechanical planetaria predate his by millennia.