scale & move chain of solids with lowest one anchored

[Filip Vandueren]

If I understand correctly, you can do this:

have the “first” layer on top (the one you keyframe)
have the “last” layer on the bottom don’t keyframe it, so it stays stationary

inbetween sandwich layers with these expressions:
(no parenting)

position:

first=thisComp.layer("first");
last=thisComp.layer("last");
i=index-first.index+1;
lag=0.2;

linear(i,first.index,last.index,first.position.valueAtTime(time-lag*i),last.position);


and very similarly: for scale

first=thisComp.layer("first");
last=thisComp.layer("last");
i=index-first.index+1;
lag=0.2;

linear(i,first.index,last.index,first.scale.valueAtTime(time-lag*i),last.scale);


[Greg Digenti]

Perfect! It’s genius, thank you so much!

[Anthony Hairgrow]

Hi Filip,

I’ve discovered your expression some years later and I believe this is getting me closer to my solution for a character rig that I’m creating.

When I implemented this expression for the position on several solid layers, I noticed that when I moved the “first” layer all the in between layers were moving at the same amount/rate.

Is there a way to alter this so that the layers that are closer to the bottom move at a slower rate than the ones towards the top?

Essentially, I’m creating a squash and stretch rig. My first implementation utilized several null points that were parented to a master null. The parent was located at the bottom of the character, sort of like a global position controller. The parent null was then scaled non uniformly, like 64,140 or 140, 64, which caused the children to move appropriately. When I did this, I noticed that the children closer to the bottom where the parent was located was moved at a slightly lower rate than the ones towards the top of the character.

This works out fine, but I wanted to improve the rig, but implementing the same look without having to parent the children and using the scale to move them.

Essentially I’d like to have a controller that I can move up and down, that would cause the other “non parented” children to move appropriately.

I’m familiar with working with expressions, but unfortunately I’m just an animator, with no programming skills, so I couldn’t begin to figure out the math equation to implement this.

I hope I was able to clearly explain what I’m looking for.