How to integrate previous rotation values.

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Joined: March 28th, 2019, 9:16 pm

I have a simple composition made in Quartz Composer that spins a rotor on a wind turbine. The idea is the the speed of the rotation chances over the course of an hour or whatever. It's for a TV bug in the bottom corner of the screen and I'd like to make it in AE rather than render out to ProRes444 and overlay in Premier Pro (or whatever editing app).

The problem with using and random value in a

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Time * (random value)
type of expression is that when the random value changes, the rotational value for the rotor jumps to some random value. THat's not what we want.

In QC the trick is the Integrator patch, which like the mathematical term takes the value history into account when determining the new rotational value. It's as simple as joining this set of five patches and entering your Min. Max values into the random patch and 0º and 360º into interpolation patch.
Screen Shot 2019-03-29 at 12.24.32 pm.png
Screen Shot 2019-03-29 at 12.24.32 pm.png (98.74 KiB) Viewed 7424 times
I know the expression in AE for Random and for Slider. I guess I can make keyframes for the Slider Value and do away with the need for a random expression to change the rotational speed at different points in time but how do I stop the rotor jumping around when I change the speed?

I could write an expression for a sin wave for the speed or a parabola but it seems like overkill and not really the desired level of "randomness" I'm looking for either.
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Joined: December 10th, 2006, 10:23 pm


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