Variable frequency for a sinusoidal movement

[Dan Ebberts]

It’s not a simple problem. This should help though:

https://www.motionscript.com/articles/speed-control.html

If you’re wiggling the frequency, you’ll probably need the frame-by-frame method.

Dan

[Sam Beckett]

Thanks a lot Dan, this si exactly what I needed.
You couldn’t give me a better analysis.

Do you have any clue why my initial wiggle that shouldn’t overpass the [9;10] interval does it anyway ? It looks like there is a kind of 10% overpassing but I don’t know why.

[Dan Ebberts]

In my experience, wiggle() can give you an extra plus or minus 20% or so. You can either factor that in, or sometimes just changing the random seed will give you a more well-behaved wiggle.

Dan

[Sam Beckett]

Understood, thanks a lot for your so quick help.

Now I am sorry but if I follow the document there isn’t any solution given for my precise case :
Controlling the frequency with a wiggle expression.

So I try to follow the principle with the following code :

Freq_Min = 1 ;
Freq_Max = 2 ;
Freq_Offset = Freq_Min ;
Freq_Delta = (Freq_Max - Freq_Min) / 2 ;

freq = Freq_Offset + wiggle(0.1, Freq_Delta) + Freq_Delta ;
amp = 100;
n = freq.numKeys;
if (n > 0 && freq.key(1).time < time){
accum = freq.key(1).value*(freq.key(1).time - inPoint);
for (i = 2; i <= n; i++){
if (freq.key(i).time > time) break;
k1 = freq.key(i-1);
k2 = freq.key(i);
accum += (k1.value + k2.value)*(k2.time - k1.time)/2;
}
accum += (freq.value + freq.key(i-1).value)*(time - freq.key(i-1).time)/2;
}else{
accum = freq.value*(time - inPoint);
}
value + amp*Math.sin(accum*Math.PI*2)

But the expression returns an error.
As the wiggle into the “freq” variable breaks the rest of the code, I put the frequency wiggled into a Slider Control :
Frequency Slider :
Freq_Min = 1 ;
Freq_Max = 2 ;

Freq_Offset = Freq_Min ;
Freq_Delta = (Freq_Max - Freq_Min) / 2 ;

Freq_Offset + wiggle(0.1, Freq_Delta) + Freq_Delta ;

Y Rotation parameter :
freq = thisComp.layer("Prarmètres généraux").effect("Frequency")("Slider") ;

amp = 100;
n = freq.numKeys;
if (n > 0 && freq.key(1).time < time){
accum = freq.key(1).value*(freq.key(1).time - inPoint);
for (i = 2; i <= n; i++){
if (freq.key(i).time > time) break;
k1 = freq.key(i-1);
k2 = freq.key(i);
accum += (k1.value + k2.value)*(k2.time - k1.time)/2;
}
accum += (freq.value + freq.key(i-1).value)*(time - freq.key(i-1).time)/2;
}else{
accum = freq.value*(time - inPoint);
}
value + amp*Math.sin(accum*Math.PI*2)

Now the program doesn’t contain any error but the graph behaves wrongly.
So It turns that we have to work with an integrator expression, like your document explained but in my case we control the frequency of the sinwave by a wiggle expression. That is where I’m stuck.

[Dan Ebberts]

It would help to know the error message you’re getting with the first version.

Dan

[Kalleheikki Kannisto]

You might consider wiggling the Time Remapping Effect for the wing animation. If you have the butterfly wing animation in a precomp it should speed up and slow down the wing motion only, not the overall motion of the butterfly.

Kalleheikki Kannisto
Senior Graphic Designer

[Sam Beckett]

Thank you very much, this may be very helpful to sort this out very easily.
With all these responds I might close this thread as answered.

Thank you all for your help.