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Orrery

From Trammell Hudson's Projects

My six planet orrery was inspired by Hielke Rispens' laser cutable design, which was in turn inspired by MatthewS3's design. Rather than target a laser cutter or shopbot, I modeled the entire orrery in OpenSCAD with a goal of 3D printing the model. I tried to reduce the complexity of the outer planet reduction gear, but messed up the ratios for my first printing.

Orrery gears

The gear ratios from the input drive on the second version are better, although Saturn is very slow:

Planet Gear ratios Years Days Actual Error
Mercury 74:18 0.2432 years 88.78 days 87.97 days 0.9% slow
Venus 57:35 0.6140 years 224.11 days 224.70 days 0.27% fast
Earth 46:46 1.0000 years 364.24 days 364.24 days exact
Mars 32:60 1.8750 years 684.38 days 686.98 days 0.38% fast
Jupiter 16:32, 16:56, 36:61 11.8764 years 4334.88 days 4322.82 days 0.27% slow
Saturn 16:32, 16:56, 15:76 35.5871 years 12989.29 days 10,755.70 days 20.76% slow

Still todo is to add a month read-out to the moon ring and a year read-out to the Jupiter ring. It would also be nice to pose the configuration at a known date for printing so that the readouts accurately reflect the position in the orbits.

The orrery not printable on an FDM printer, so I'm trying it at Shapeways with the "Print it now!" option since their automated tests think there might be loose shells (pieces that have a risk of fusing together) as well as thin walls. This is my first involute gear designs, so I'm not sure how well it will turn out.