PDA

View Full Version : Realistic Helicopter Propeller Spin



alexjose
08-02-2013, 10:34 AM
Hey Everybody,
I'm trying to animate a good helicopter propeller spin. The way I have it now with motion blur it looks ok but if you look at a real helicopter propeller spinning you generally see the 3 blurred blades spinning kind of slowly. Mine looks like theres about 6 blades spinning. Anybody know the best way to achieve this? Thanks!

m.d.
08-02-2013, 01:36 PM
what you describe is an effect of temporal aliasing....cameras see this because when you run 24fps...or 60 fps ect....according to nyquist theorem, you can only accurately sample 1/2 the frequency....
hence why CD audio is 44khz when no human can hear beyond 22khz

so while a camera may be shooting 24fps...it can only accurately sample 12 fps in time....anything over 12hz becomes temporal aliasing.

Thats why you have the effect of heli blades spinning slowly, or even backwards....

Not sure how to achieve this in LW....maybe with the shutter integration time(shutter efficiency), and faster shutter speed i.e. 90 degrees or even 45...in the real world there is more temporal aliasing the faster the shutter speed

http://tessive.com/the-time-filter/
this video is pretty informative of the causes....they implemented an external shutter to fix the issue....now owned by Red camera to be integrated into a new mount