Four Planet Orrery


Over the years several satellites and probes have been sent to the planet Mars. The Mars 2020 mission by NASA was a new milestone by sending the Perseverance Rover, which will search for signs of ancient microbial life. Strapped to the rover’s belly for the journey to Mars, a helicopter called Ingenuity, has achieved a “Wright Brothers moment “ by testing the first powered flight on the Red Planet on april 19, 2021.

Inspired by these latest developments I decided to modify my 3 planet orrery into a 4 planet orrery by adding the planet Mars and it’s moons Phobos and Deimos.

pic Four planet orrery including Mars and it’s moons

After some Internet search, I found an interesting website selling planets to scale. The planet Earth is a printed glasssphere and measures approx. 5cm in diameter. The other planets and the Moon are to scale, except for the moons Phobos and Deimos. The diameter of the later 2 would be less than the diameter of the pins they are mounted on. pic From left to right: Mars, Earth (with the Moon), Venus and Mercury

Mars orbital system

pic Mars orbital system with it’s moons Phobos and Deimos

The Mars moons have been 3D printed and can be downloaded here.

The white 65t gears and 20t pinions are 3D printed (ABS) gears, but they are available as original Meccano parts as well and can be obtained through various UK suppliers or as a 3D ABS print through the sale page of Meccano Kinematics. The geartrain is after a design by John Nuttall. I only changed the framework and because of this I had to choose other idlers in order to make the construction as compact as possible.

An important detail are the 2 ball bearings for each moonarm. Without these bearings there is quite a lot of clearance between axles and their corresponding holes with a possible misengangement between gears during operation. A video of the Mars orbit can be seen on Youtube.

Standard ball bearings 4-10-4 were used, but a Meccano axle doesn’t fit into the inner diameter. Therefore I made an instrument to ream the inner diameter of a 4-10-4 ball bearing. In case you need a couple of these modified bearings, just contact me.