how can I set this expression up to stop when it lands on a surface.

[Kalleheikki Kannisto]

So, do you want to know how to gracefully stop it when it hits a certain y position?

[Chris Behl]

Yes please.

[Kalleheikki Kannisto]

Here’s my approach:

Add a layer named “control” with two sliders, “ground” and “ease”. Set ground to the desired y coordinate for the ground plane and ease to how many pixels above the ground plane you want to start the transition.

Then use this for the Position value expression

yVelocity = 200; //pixels per second
oscFreq = 1.5; //oscillations per second
oscDepth = 35; //oscillation depth (pixels)
drift = 25; // drift (pixels per second: - = left, + = right)
ground = thisComp.layer("control").effect("ground")("Slider");
ease = thisComp.layer("control").effect("ease")("Slider");

y_origin = transform.position.valueAtTime(0)[1];
x_position = transform.position[0];
y_position = y_origin+yVelocity*time;
z_position = transform.position[2];

if (y_position>ground-ease && y_positionground){
y_position=ground;
oscDepth = 0;
}

y_distance = y_position-y_origin;

pos = [x_position+oscDepth*Math.sin(oscFreq*Math.PI*2*time) + drift*y_distance/100, y_position, z_position];
pos

and this for the Y Rotation


yVelocity = 200; //pixels per second
oscFreq = 1.5;
maxTilt = 15; //degrees
ground = thisComp.layer("control").effect("ground")("Slider");
ease = thisComp.layer("control").effect("ease")("Slider");

y_origin = transform.position.valueAtTime(0)[1];
y_position = y_origin+yVelocity*time;

if (y_position>ground-ease && y_positionground){
maxTilt = 0;
}

tilt=maxTilt*Math.cos(oscFreq*Math.PI*2*time);
tilt


Now the animation will smoothly stop at the ground place regardless of starting position.

If you duplicate this to multiple layers the oscillation and motion will be synchronized, so you’ll want to add other random values for some of the variables. Or change the settings for each layer.