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Expression to allow keyframing of RATE/SPEED of rotation.
Hi everyone!
First time posting on creative cow today. I asked this question already in the main forum, but realized this may be a better place to post this… here goes:This one’s got me and my colleagues stymied.
I’m trying to create an expression (keyframable using a slider control) that will animate the speed of rotation on an object.
The actual rotation value of the object is not as important to me as the RATE of rotation.
I started something using time multiplied by a slider but my quandary is that when I set my slider to zero, I don’t want my rotation to go back to zero.
I want it to stop rotating, to hold at that value.
I tried creating some sort of identity switch using a second slider but got nowhere. Something tells me I’m on the wrong path.Any help would be much appreciated!
Thanks!
-Gabe -
2 Replies
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Unfortunately, there isn’t an easy way to control speed.
You need to convert your speed control values to total degrees rotated. One way to do that is to integrate (as in calculus) your speed control over time. In practical terms, that means calculating the area under the graph of your speed control. It’s relatively straight-forward (but certainly not trivial) if you limit yourself to linear keyframes.
If you ease your keyframes, then you’re forced to use the brute-force method of calculating the area under the curve frame-by-frame, which amounts to adding together (for all previous frames) the slider value times the frame duration. The drawback there, of course, is that the farther you get into the comp, the longer the calculation takes at each frame (because you have to look at all previous frames).
Sorry if you were expecting a simple answer…
Dan
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Thanks Dan!
I was hoping for a simple answer, but not expecting one, seeing as I couldn’t find anything about it anywhere on the net!
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