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Yet another bounce expression question – not falling, but pop-up with a spring effect.
Hey Guys,
I’ve been searching but haven’t found what I’m looking for yet. I’ll dive into it more fully later on, but for now I was hoping someone has already done this.
I want to animate a bunch of layers rising up from off screen (bottom), and then settling into their positions. I want to keyframe the offscreen position, and the final on screen resting position, but i was hoping an expression could take care of secondary bounce. ie, when the layer flies up to it’s final position, it should bounce up and down (with decay) a few times, like it’s on a spring.
Actually, almost exactly like a jackinthebox using only the Y dimension.Surely someone has done this before?
Thanks!
Scott. -
6 Replies
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heh, thanks, i would have checked jj gifford and dan’s site later on, i’m just swamped at the moment. perhaps this should be added to that sticky list of common questions, i searched for “bounce” and got a million responses (they were all drop-and-bounce though, not jackinthebox).
cheers,
scott. -
So the jackinabox pops up, and bounces with decay to a halt. but then imagine it went back into it’s box, it should have a small anticaptory bounce before going back down. i actually don’t think this is possible with the one expression on the one layer, as the beginning motion and the end motion are two different things, one a decaying spring, the other an anticipatory pseudo-squash-stretch motion. it’s not simply playing the first move in reverse…
any clues here guys? dan?
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hang on… is this expression from dan
veloc = 35;
amplitude = 30;
decay = 1.0;
y = amplitude*Math.cos(veloc*time)/Math.exp(decay*time);
value + [0,y]even work properly? it doesn’t for me. two keyframes, and… nothing. do the keyframes have to be at the start of the comp, ie, t=0?
i’ve been fiddling with veloc, amp, and decay, and i can’t seem to get it working. the decay time is always massive, the layer bounces and just keeps bouncing…and bouncing… and bouncing.i can’t get it working.
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Is your comp less than 5 sec? With the decay at 1, the bounce lasts about 5 sec.
Up the decay to about 4 and the bounce will last less than 1 sec.Yes, that expression is triggered from time 0. Dan’s page says he set the 2 keyframes at frame 0 (jack below the box) and frame 1 (Jack up above the box) so he pops out from frame 0 to frame 1. If you want the bounce to be triggered by a marker, try this:
n = 0;
if (marker.numKeys > 0){
n = marker.nearestKey(time).index;
if (marker.key(n).time > time){
n–;
}
}if (n == 0){
value;
}else{
t = time – marker.key(n).time;
veloc = 18;
amplitude = 55;
decay = 4;
y = amplitude*Math.cos(veloc*t)/Math.exp(decay*t);
value + [0,y];
}Set the marker where you want the bounce to start.
Note: this is a much smaller and shorter bounce, adjust velocity, amplitude and decay as needed.
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thanks for explaining that for me, yikesmikes.
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