
Ok so here is a better example, the flaps on a plane.
If I design the plan so it is facing into X axis as shown in Blender.
I want to (in game) rotate the flaps around the red line labeled hinge line. This is not on a direct X, Y or Z axis.
How do I know what axis to rotate the flaps around?
Do I have to figure it out in Blender, and then do math on it when the object is moved around in the game world?