• Adobe After Effects Expressions

  Oscilate y based on x velocity

  Posted by Andres Torres on September 16, 2012 at 8:27 pm

  I’d like to create an expression that will move y pos up and down based on x velocity. So the faster the object moves in x, the faster and larger the oscillations. The object would look like it was on a floor so the y pos wouldn’t go below zero.

  Thanks.

  Andres Torres replied 13 years, 10 months ago 2 Members · 2 Replies
• 2 Replies

• 

  Dan Ebberts

  September 16, 2012 at 11:44 pm

  It gets tricky any time you try to control speed or frequency. If you’re using linear keyframes, you can use a modified linear keyframe integrator:

  
amp = 50;
freqMult = .05;

  n = numKeys;
i = 0;
if (n > 0 && key(1).time < time){
accum = velocityAtTime(key(1).time)[0]*(key(1).time - inPoint);
for (i = 2; i <= n; i++){
if (key(i).time > time) break;
k1 = key(i-1);
k2 = key(i);
accum += (velocityAtTime(k1.time)[0] + velocityAtTime(k2.time - .001)[0])*(k2.time - k1.time)/2;
}
accum += (velocity[0] + velocityAtTime(key(i-1).time + .001)[0])*(time - key(i-1).time)/2;
}else{
accum = velocityAtTime(inPoint)[0]*(time - inPoint);
}
y = amp*Math.abs(Math.sin(accum*freqMult));
value - [0,y]


  Dan
• 

  Andres Torres

  September 17, 2012 at 2:01 am

  Works great, thanks.

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