A Mechanical Earth-Moon-Sun Model Built From a Salvaged 3D Printer

Sniderj was walking their grandson home from school when the boy asked why the moon was visible during the daytime. If you’re familiar with our solar system and orbital mechanics, you probably intuitively understand why. But, could you explain it to a child without a visual aid? Sniderj had trouble with that, so they built a mechanical Earth-Moon-Sun model from a salvaged 3D printer to illustrate their orbits.

At first, that may seem like a trivial model to construct — just spin the Moon around the Earth, and the Earth around the Sun. But, for the model to be accurate, it needs to be far more complex than that. It has to account for the relative axial tilts of the Earth and Moon, which means the model needs to move on multiple non-parallel axes. Sniderj had recently purchased a used 3D printer, which was perfect for upcycling to replicate that astronomical movement.

The first step was to completely rearrange the layout of the 3D printer’s linear drives into a suitable mechanism for the model. The linear rods and lead screw were used to control the Moon’s vertical position, relative to the Earth. 3D-printed helical gears were used to move the Moon around the Earth. Finally, the Earth itself spins with a tilt-offset from a driven rod located in the center of the assembly. The Sun is represented by a stationary flashlight.

Of course, the hardware was only half the battle. To control the model, Sniderj used Marlin firmware running on RAMPS. A Raspberry Pi sends G-code commands via a Python serial interface. The real-time position data is taken from the open source Skyfield software, which gathers that data from NASA’s JPL. The result is a real-time representation of the Earth and Moon, and can be accelerated to illustrate to kids how their orbits actually work — and why the Moon is sometimes visible during the day.