It looks like Hannes has a good solution for some things I was trying to get to work.
I don't have any post-work software except Adobe Photoshop. So, this was my solution to animating a ducted fan on an airship.
I made four separate copies of my model. Then I rotated the fan a tad on each model and rendered every fourth frame with each model. Model 1 rendered frame 1,5,9 …; model 2 rendered fram 2, 6, 10…; model 3 renderd in frames 3, 7,11…; and model 4 rendered in frames 4, 8, 12, ….
Much of my movie thing was crap, but the fan looks like it turning to me!
Russ