• Adobe After Effects Expressions

  object on a string damping

  Posted by Göran Thorén on June 13, 2008 at 1:22 pm

  Hi all!
  I looking to create an anomation that looks like an object is droped from top and damps like it was attached to a string.
  I tried Dans “jack in a box” expression but it didn´t really work the way i would like.
  Any suggestions?

  Thank´s

  Husse

  Jerry Adams replied 14 years, 2 months ago 6 Members · 8 Replies
• 8 Replies

• 

  Dan Ebberts

  June 13, 2008 at 4:59 pm

  Try this:

  g = 3500; // gravity (pixels/second/second)
  floor = 400;
  e = .35; //elasticity

  b = floor – position[1];
  h = b;
  T = Math.sqrt(2*h/g);

  if (time < T){ y = - g*time*time/2 + b; }else{ Vy = g*T; while (true){ Vy *= e; t = T; T += 2*Vy/g; if (time < T){ t = time - t; y = Vy*t - g*t*t/2; break; }else if (T - t < thisComp.frameDuration){ y = 0; break; } } // end while } [value[0], floor - y] Dan
• 

  Göran Thorén

  June 15, 2008 at 9:00 pm

  What can I say.. Dan you´re the man!
  Thank´s a million!

  Husse
• 

  Adam Lukas

  February 22, 2009 at 2:48 am

  What exactly is this expression applied to? sorry this is such a noob question…
• 

  Adam Lukas

  February 22, 2009 at 3:47 am

  never mind, i figured out what i was doing wrong 🙂
• 

  Dan Ebberts

  February 22, 2009 at 4:12 am

  The Position property.

  Dan
• 

  Brad Hilton

  September 2, 2010 at 7:03 pm

  will this work in cs5?

  cause im getting an error message.

  After Effects warning: Timeout while waiting for the engine
  Expression disabled.

  Error occurred at line 16.
  Comp: ‘Cloud2’
  Layer: 1 (‘Vector Smart Object’)
  Property: ‘Position’

  g = 3500; // gravity (pixels/second/second)
floor = 400;
e = .35; //elasticity

  b = floor - position[1];
  h = b;
  T = Math.sqrt(2*h/g);

  if (time < T){
y = - g*time*time/2 + b;
}else{
Vy = g*T;
while (true){
Vy *= e;
t = T;
T += 2*Vy/g;
if (time < T){
t = time - t;
y = Vy*t - g*t*t/2;
break;
}else if (T - t < thisComp.frameDuration){
y = 0;
break;
}
} // end while
}
[value[0], floor - y]
• 

  Dan Ebberts

  September 2, 2010 at 7:52 pm

  You’ll get that error if you start your bouncing layer below the “floor” (y = 400 in this case).

  Dan
• 

  Jerry Adams

  March 15, 2012 at 11:53 pm

  well..this is too hard for me… can enyone do a tut for this effect…pls?

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