I would create a circle with 2 keyframes for scale, the max and min sizes. Then alt+click the scale parameter and add the following expression:

`loopOut("pingpong")`

That expressions tells AE to go from the first keyframe to the last and when it gets that go back to first, forever.

Then if you want to adjust the speed of the circles all you need to do is drag one of the keyframes and the expression will automatically update. Another thing, you can set up all your circles with keyframes, apply the expression to one circle, select the scale parementer and then use the Edit > Copy Expression Only to put the expression in the clipboard. Then you can just select all the other layers and paste the expression.

I made a quick example project for you to illustrate the technique:

6454_pingpongcs5.5.aep.zip
Johnny Cuevas, Editor

Thinkck.com

"I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work."

---THOMAS EDISON on inventing the light bulb.