Wobbling image back and forth.

[Qwert11334]

Hey guys, i'm looking for some help in animating an image of the inside of a train carriage so it slowly wobbles from left to right in a random manner. It would actually be back-and-forth via the z axis from the POV of the camera, which is facing the side window. 

[ShiveringCactus · Accepted solution]

The simplest approach here would be to use a wiggle expression.  If you hold down ALT and click on the train layer's position stopwatch and expression area opens and you can type:

wiggle(1,30)

This would move the whole layer once per second by up to 30 pixels from the original value.  Increasing the 1 to 10, would see 10 changes per second etc...

You say you only want the movement on the Z position, so assuming you have a 3D layer set up, we can actually wiggle in one axis only with a slightly different expression:

var rocking = wiggle(1,30);
X = value[0];
Y = value[1];
Z = rocking[2];
[X,Y,Z]

Value is the original value, rocking is the wiggle amount.  Wiggle is smart enough to know if it is wobbling in 1, 2 or 3 dimensions, so we use the [2] to only look at the Z axis.

[Ando0o0 · Accepted solution]

Wiggle is also based on the index value of the layer. It's good practice to set a "seedRandom(##)" before the wiggle expression. This way if you like a certain wiggle pattern, it will not change when you move the layer up or down, or when you add new layers. 

[Qwert11334]

Thank you 🙂

[Qwert11334]

Thank you very much, works perfectly 🙂