Using transformation constraints and paths to create clockwork orbits

That’s not entirely accurate. I’m looking to copy the rotation of an Earth-like object–we’ll call it “Earth”–onto a Moon-type object while it is constrained to a path. But the moon doesn’t orbit the Earth every day. It takes a few days. Let’s call that a “month” for convenience sake. Any idea how to get the moon to move around the path of the Earth every 27 Earth rotations? I assume this could be done with the transformation constraints. Any ideas?

Actually I think I found a better solution. If anybody is interested, it’s easier to just set a unit of time to base the entire simulation, for instance using a frame for every hour and then use the frames function in the path animation panel for the Moon’s orbit. If you have the Earth rotating every twenty-four frames, then you set the frames for 656, which corresponds to twenty-seven days and eight hours, roughly the orbital period for the Moon. Then, using the F-curve editor, I extrapolated the rotation curve for the moon’s rotation, set at that same rate, and could then create an infinite Earth-Moon system simulation without having to use any track to constraints on the empties.

Here’s the blend file I created. Nothing is to scale but it’s good start to some kind of eclipse-predicting simulation, I guess.


EarthMoonRotateTest.blend (757 KB)

Looks good to me