After Effects expressions - pendulum motion not working properly

[Karel Reina]

Hello, 

I am trying to make a triangle shape in After Effects swing in a pendulum motion which decays.  This is the expression I have used:

timeToStart = 8;

if (time > timeToStart)

{ Math.sin((time-timeToStart)*10)*50/Math.exp(time-timeToStart)

; } else {

; value

}

The problem that I am having is that after the 8 second mark, the triangle returns to the original position it was in, before I put the code in. To explain better, at the beginning of the animation the triangle does a circular rotation and then stops in a specific almost horizontal position. And what I want it to do after it does that circular motion, at the 8 second mark, is swing down from it's horizontal position to a top down position (meaning that the long pointed end of the triangle is pointing up). The anchor point is in the long point of the triangle which is pointing up. I hope that makes sense - I want it to swing down from it's anchor point in a pendulum motion which decays until it is still in a completely vertical position. 

However what is happening is that the expression I have used overrides the rotation and causes the triangle to jerk up into its original almost horizontal position, and then it does the pendulum-decay-animation. The animation is perfect, but the position is wrong. 

Any idea on how to fix this? Hopefully this wasn't too confusing to understand 😕

[Dan Ebberts]

Try changing the third line to:

{ value + Math.sin((time-timeToStart)*10)*50/Math.exp(time-timeToStart)

[Karel Reina]

Thanks for your answer! But the problem still persists. now the code is like this:

timeToStart = 8; 

if (time > timeToStart) 

{ value + Math.sin((time-timeToStart)*10)*50/Math.exp(time-timeToStart)} else { 

; value

}

the triangle still returns to it's original wrong position when it does the animation.
Any idea why it does that?

[Dan Ebberts]

It's hard to picture exactly how you have things set up, but see if this gets you closer:

timeToStart = 8; 
val = value;
if (time > timeToStart) 
  val = value*Math.cos((time-timeToStart)*10)/Math.exp(time-timeToStart);
val

[Karel Reina]

That seems to cancel out the animation and the triangle just sits still. Yeah I understand it's probably hard for you to help me without seeing the set up! But thank you anyway! I think I will just try going a different way with the animation. But thanks for all of your help!