Constant expression to non constant expression

[Dan Ebberts]

This is one of those speed-control things that turns out to be trickier than it seems like it should be. Although it doesn’t address this case exactly, this article has some good background info on calculating the “area under the curve”, which is what you need in this case:

https://www.motionscript.com/articles/speed-control.html

This expression does that–it will begin to slow down at 6 seconds, and will slow to a stop over a one-second period:


rate = 150;
beginStop = 6;
stopDur = 1;

if (time < beginStop){
time*rate;
}else if (time < beginStop + stopDur){
r = linear(time,beginStop,beginStop + stopDur,rate,0);
(beginStop + stopDur/2)*rate - (beginStop+stopDur - time)*r/2;
}else{
rate*(beginStop + stopDur/2);
}


Dan

[Olly Lawer]

Thanks Dan tho that just fried my brain. Is there an easy way to do it with an expression control maybe?

Olly Lawer

[Dan Ebberts]

Well, you could add a Slider Control to the layer, set a keyframe for 150 at 6 seconds and another for 0 at 7 seconds, then apply the Rotation expression in this section of the article:

https://www.motionscript.com/articles/speed-control.html#linear

It should give you the same result as the previous expression.

Dan