The following pages contain the story of how I built an Orrery, which is a working model of our solar system. There are detailed videos showing each step of the process including making the gears, machining the idler and planet support arms, diamond engraving the calendars and assembling the model.

The model contains 30 gears and is driven by the small crank at the bottom. One full turn of the crank advances the Orrery by 14 days. The moon and all of the planets will then revolve around the sun in proportion to the way they move in our solar system. The gears are epycycloidal and Modulus 1, designed to provide a maximum error of 0.5% or less.

The orrery design consists of 4 interconnected gear trains that control the relative motions of the earth, moon, and sun, and a fifth gear train that ticks forward a dial marking 100 years.

Start by designing gears. The gears are the heart of the orrery. The gears need to have specific teeth ratios to ensure the planets move that the proper speed relative to one another. For each gear, you’ll need to know the number of teeth (which is proportional to its diameter) and the size of the shaft in the center of the gear.

You’ll have an input shaft (either hand-crank or motorized) rotating at a constant speed, and each planet will have a set of gears that translates that to its own orbital speed. Let’s run through a simple Mercury, Venus, Earth example:

Some of the gears are compound gears (2 gears in one part). They will also need to be positioned correctly. With a couple of exceptions I printed all of the parts at 50% fill.

For centuries, as both an educational tool and as technical skill demonstration of a business or clockmaker, people have constructed mechanical astronomical models under a variety of names (orreries, planetariums, tellurians, and more).

Sep 8, 2009 · What I present in this guide is a list of parts, especially the gears, and a description of how they fit together. It's enough to produce the innards of the orrery, but what exact size and shape you want is up to you. Description. This is a Copernican Orrery, which means it has the planets from Mercury out to Saturn.

An orrery is a mechanical model of the Solar System that illustrates or predicts the relative positions and motions of the planets and moons, usually according to the heliocentric model.

Feb 15, 2018 · The gear ratios for the orrery are very interesting. The bottom gear train (T39:T8:T39), rotates the Earth around its own axis once per year. The ratio is 1:1 and has the effect that the Earth is not tidally locked with the Sun (as the Moon is with the Earth).