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Manipulating an expression's timing

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Richard Noble
Manipulating an expression's timing
on Dec 16, 2011 at 3:01:12 pm

Hello,

I'm fairly new to expressions and have a problem I'm pretty certain there is a simple solution for.

I'm using Dan Edbert's pendulum expression which works amazingly -

http://www.motionscript.com/expressions-lab-ae65/pendulum.html

I am applying the expression to the z axis of a piece of footage to simulate a swinging from a wire effect.

The expression starts at frame 0 by default, but I would like to be able to dictate when the expression starts and stops. For example if I want to start the expression at frame 300 and again at 350 in the same piece of footage, what control setup do I need?

I'm pretty sure I can use a slider control, but I'm stuck at how to construct the correct controls.

If someone has a simple solution I would be very grateful

Thanks
Richie

veloc = 7;
amplitude = 80;
decay = .7;

amplitude*Math.sin(veloc*time)/Math.exp(decay*time)


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Kevin Camp
Re: Manipulating an expression's timing
on Dec 16, 2011 at 4:37:41 pm

something like this would allow you to use layer markers to control the timing for the start of the 'wobble'.
veloc = 7;
amplitude = 80;
decay = .7;

n = 0;
if (marker.numKeys > 0)
n = marker.nearestKey(time).index;
if (marker.key(n).time > time) n--;

if (n > 0)
t = time - marker.key(n).time;
else
t = 0;

amplitude*Math.sin(veloc*t)/Math.exp(decay*t)

to control how long it wobbles, you'd need to adjust the veloc, amplitude and/or decay variables.

Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW


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Dan Ebberts
Re: Manipulating an expression's timing
on Dec 16, 2011 at 4:49:41 pm

Here's the same thing with a couple of syntax issues resolved:


veloc = 7;
amplitude = 80;
decay = .7;
n = 0;
if (marker.numKeys > 0){
n = marker.nearestKey(time).index;
if (marker.key(n).time > time) n--;
}

if (n > 0)
t = time - marker.key(n).time
else t = 0;

amplitude*Math.sin(veloc*t)/Math.exp(decay*t)



Dan



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Kevin Camp
Re: Manipulating an expression's timing
on Dec 16, 2011 at 6:03:11 pm

thanks dan.... sorry richard if there was any confusion.

Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW


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