bezier warp expression - slowing amplitude and velocity with fast decay

[idude20]

I've been working with an expression from Dan Ebberts Vibrating strings which I have modified to create a bending effect on a solid shape

This part is applied to a slider expression of the solid

veloc = 14;
amplitude = -250;
decay = 4;
amplitude*Math.sin(veloc*time)/Math.exp(decay*time)

Then a bezier warp has been applied to the solid shape to the Bottom Right Tangent and Bottom Left Tangent

value + [0,effect("Slider Control").param("Slider")]

This works very well except that I would like to be able to have the amplitude of the bending shape slow down as it bends and then snap back quickly in the decay but  I'm not sure how to accomplish this.  I have tried playing with the settings that I have, but am unable to make this work.

Any help would be very much appreciated.

Ira

[Dan Ebberts]

I'm not sure what you're describing exactly. The expression you're using generates a damped sine wave. What would the new waveform look like? Would it be the same except eased so the the wave spends more time close to the extremes and less time transitioning, or something else entirely?

You could build your own, triple-eased periodic waveform like this, but I'm not sure it's what you're after:

veloc = 14;
amplitude = -250;
decay = 4;

period = (Math.PI*2)/veloc;
t = (time+period/4)%period;
if (t < period/2)
  v = ease(t,0,period/2,-1,1)
else
  v = ease(t,period/2,period,1,-1);

v = ease(v,-1,1,-1,1);
v = ease(v,-1,1,-1,1);

amplitude*v/Math.exp(decay*time)

Dan

[idude20]

Hi Dan,

Thank you for your reply.  Here is a link to my after effects file that I applied the expression to:

http://www.mediafire.com/?gllpoif7g1fy1fq

What I would like to do is create the effect much like a rubber band, where the bezier warp pulls back slowly and snacks back quickly, if that's possible.

In the meantime I will try the code your provided to see if that will do the trick.

Thank you for your help

Ira

[Dan Ebberts]

OK - I can see how it looks now, but it would be helpful if you could keframe an example of how you want it to look.

Dan

[idude20]

Hi Dan,

Here is a link to a keyframed version of what I would like to accomplish.  It's a bit rough, but hopefully will give you the right idea.

http://www.mediafire.com/?r3ppuywq3q7hq5b

All The Best

Ira

[Dan Ebberts]

I can't think of a good way to model that with a formula. If it was me, I think I'd keyframe it once on a template null and then link to that motion using valueAtTime() from the Bezier expessions. The exact expression would depend on what you're using to trigger the animation.

Dan

[idude20]

Thanks Dan,  I will give that a try.  I appreciate your help with this.  By the way your motionscript site has offered some great expression ideas and examples and I have made very good use of it.

Thanks again and all the best

Ira