expression help with position movement0

[Dan Ebberts]

A dandelion seed simulation is an interesting idea. It’s not really random though. The position would respond to the wind which would vary somewhat, but the rotation would be a kind of spring/pendulum effect based on the acceleration imparted by the wind and gravity. Kind of like somebody hanging from a parachute. I don’t have a canned solution, but you’ve got me thinking….

Dan

[Ischille]

I was toying with an expression you wrote for leaves falling. I couldn’t get it to work for the dandelion stems. I couldn’t get the stems to animate across the screen on the x axis.

To be honest, I’m quite new to expressions.

[Colin Braley]

Ive got some expressions for you that work okay, but not great. If I have some time tomorrow or the next day, I might tweak them to make it look better. These are a bit complicated and have alot of references to pick-whipped properties in the expressions, so if you want me to post the .aep file (After Effects 7) I can do that. Well anyway, here you go:

try this one for position:
//begin expression
wind = thisComp.layer(“Controls”).effect(“wind”)(“Slider”);
//you can keyframe the wind parameter, negative values
//will make the petals blow in the opposite direction
minMass = thisComp.layer(“Controls”).effect(“min_petal_mass”)(“Slider”);
//don’t keyframe this, it is theminimum mass for each petal
maxMass = thisComp.layer(“Controls”).effect(“max_petal_mass”)(“Slider”);
//this is the maximum mass for each petal, dont keyframe me
gravity = thisComp.layer(“Controls”).effect(“gravity”)(“Slider”);
//this is the strength of the gravitational force on the petals
//dont keyframe this
minBlowAway = thisComp.layer(“Controls”).effect(“min_blow_away_time”)(“Slider”);
//this value is the earliest time a petal can blow away
//dont keyframe this
maxBlowAway = thisComp.layer(“Controls”).effect(“max_blow_away_time”)(“Slider”);
//this value is the latest time a petal can blow away
//dont keyframe this
//———

//——————————————–
seedRandom( index, true );
mass = random( minMass, maxMass );
blowAwayTime = random( minBlowAway, maxBlowAway);
if( time < blowAwayTime){ value }else{ adjustedTime = time - blowAwayTime; accelY = gravity/mass; posX = position[0] + wind * adjustedTime; posY = position[1] + accelY * Math.pow(adjustedTime,2); [posX, posY] } //end expression then, try this one for rotation //begin expression //if you are going to add more petals, decrase the value of the variable gap //use the following formula for determining what gap should be // gap = 360/ numberOfPetals gap = 10; rotationTendency = 1; //make this higher, petals will spin faster wind = thisComp.layer("Controls").effect("wind")("Slider"); //---------------------- startRot = index * gap; totalRot = startRot; for(i = 0; i < framesToTime( time); i++) { totalRot += wind/rotationTendency; } totalRot //end expression Both of these expressions have some explanation of what each variable does. For these to work right, you will need a layer named "Controls" with a few sliders on it. These should be called wind, min_petal_mass, max_petal_mass, gravity, min_blow_away_time, max_blow_away_time and should have the values of about 3.75, 20, 25, 45, 2, and 5, respecttively. I wis I had more time to explain, but I have to go. ~Colim