Last year I had done a virtually mechanical device (using concepts invented by the ancient Greeks) capable of calculating moon phases as well as solar and lunar eclipses:
https://www.thomasweibel.ch/meton/
And as to my mechanical lunar phase calculator: The assembly is pretty much self-explanatory once you have printed out the ten or so parts; this gif might give you an idea.
PS: Congrats for you work on FlightGear - I simply love the project!
Paul Förster :verified_blue: (npub1244…dcty)