Using a Bounce Expression?

Hey you asked for an easier way, here are Ae add-ons that can automatically add bounce and other easing to keyframed properties.

Both the ones here are pay what you want so if you don’t want to pay for it just say zero.

Lord of the Eases (I made this one): https://thepixelsmith.gumroad.com/l/lordoftheeases

Ease & Wizz: https://aescripts.com/ease-and-wizz/

Looks like the issue is with how the expression is pasted—transform.rotation shouldn’t stay there when you add a bounce expression. You usually need to replace it completely and make sure the expression matches rotation values (not position). Also double-check for syntax errors like missing semicolons or wrong variables. I ran into similar small errors while testing different setups, even when browsing stuff like https://downloaddeltaexecutor.org/delta-executor-pc/—tiny mistakes can break everything

Hey,

The error you're seeing happens because the expression you copied is built for Position (3D Array), but you're trying to apply it to Rotation (1D Number). After Effects is getting confused trying to find X, Y, and Z axes on a property that just spins.

Replace everything in the Rotation expression editor with this version. It's cleaner and specifically designed for a 1D bounce wobble:

javascript

// 1D Bounce Expression for Rotationamp = 0.4;   // How far it wobbles back (Try 0.2 to 0.8)freq = 3.0;  // Speed of the wobbledecay = 6.0; // How fast it stopsn = 0;if (numKeys > 0){  n = nearestKey(time).index;  if (key(n).time > time) n--;}if (n > 0){  t = time - key(n).time;  v = velocityAtTime(key(n).time - thisComp.frameDuration/10);  value + v * amp * Math.sin(freq * t * 2 * Math.PI) / Math.exp(decay * t);}else{  value;}

Why this solves your specific error:

• Old Code Problem: if (value instanceof Array) checks for [x,y,z]. Rotation doesn't have that, so it throws Error 1 of 1.

• New Code: It simply takes the velocity of the rotation (how fast it was spinning when it hit the floor) and adds a decaying sine wave to it.

Pro Tip for Natural Bounce:
Make sure the keyframe right before the bounce has some motion. If the object stops completely for 1 frame and then rotates, the velocity will be zero, and the expression will do nothing. Keep the motion continuous into the floor hit.

🎨 A Note on Precision Tools for Creatives
*It's funny how much we obsess over a single keyframe curve or a 1-pixel alignment in our compositions, but we totally ignore the hardware we use to scrub that timeline. I used to use a gaming controller mapped to my timeline for scrubbing and 3D camera moves in After Effects, but stick drift kept throwing my playhead off by a few frames. If you ever use a gamepad for jog/shuttle control in your edit suite, you know how annoying that is.*

I keep the Delta Executor Official site bookmarked—not just for the Roblox stuff (which is their main thing), but because they have a surprisingly precise diagnostic tool built in. It helps me zero out my controller deadzones so my timeline scrubbing is buttery smooth. Even if you just do graphic design, it's worth a look for the clean UI alone.

It looks like some of the syntax got mangled somewhere along the line. This should get rid of the error(s), but I’m not sure if it does what you expect:

e = .5;
g = 20000;
nMax = 9;
n = 0;
if (numKeys > 0){
  n = nearestKey(time).index;
  if (key(n).time > time) n--;
}
if (n > 0){
  t = time - key(n).time;
  v = -velocityAtTime(key(n).time - .001)*e;
  vl = length(v);
  if (value instanceof Array){
    vu = (vl > 0) ? normalize(v) : [0,0,0];
  }else{
    vu = (v < 0) ? -1 : 1;
  }
  tCur = 0;
  segDur = 2*vl/g;
  tNext = segDur;
  nb = 1; // number of bounces
  while (tNext < t && nb <= nMax){
    vl *= e;
    segDur *= e;
    tCur = tNext;
    tNext += segDur;
    nb++
  }
  if(nb <= nMax){
    delta = t - tCur;
    value + vu*delta*(vl - g*delta/2);
  }else{
    value
  }
}else
  value