Inspiring

Question

rotate expression

Forum|Forum|7 years ago
October 16, 2018
7 replies
13395 views

I would like to rotate something back and forth, every 4 seconds. How do I add the 4 sec variable to a loop expression? I assume AE can do this, I'd prefer not to keyframe it. Thanks.

jcalcinaAuthor

Inspiring

Interesting answers and dialogue. Thanks...

angie_taylor

Legend

Ah, OK, I wondered if there was some “magic” for working that out. Thanks Dan :-)

Martin_Ritter

Legend

Even if the expression-solution is a great way, this can be done with a simple loopOut(“pingpong”); - Loop as suggested in the first place.

The trick to "hold" the loop is to add another - 3rd - keyframe with the last rotation value on it. To adjust the pause, you just drag the last keyframe around.

Cheers,

Martin

L

little fat girl

Inspiring

ProTip: Any time you have an expression question, google it with 'Ebberts' attached to it. Dan Ebberts is the man with expressions. His answers are always the right ones. And he has a site (motionscript.com) that is super helpful.

jcalcinaAuthor

Inspiring

Sorry for the quality. The crab on the left was my goal, here accomplished using a series of keyframes. The crab on the right is the pingpong method, key frames at 0 and 2 sec. I didn't see how to get it to pause.

Dan Ebberts

Community Expert

Without any keyframes, it might look something like this:

period = 2;

rotationDur = 0.25;

rotationAmt = 30;

t = time%period;

if (t < period/2){

ease(t,0,rotationDur,rotationAmt,0);

}else{

ease(t,period/2,period/2 + rotationDur,0,rotationAmt);

}

Dan

angie_taylor

Legend

You ARE the man Dan. I was wondering if there was a better way than my suggestions. One thing I can’t understand is why the rotation duration is .25 and not .75? Am I missing something obvious?

thanks Dan - King of Expressions

angie_taylor

Legend

You can use something like this to do it without keyframes. This only does the first 4 seconds but you can adapt it. Plus you can add expression controllers to control the speed.

if (time<4) time*50;

else

time*-50

angie_taylor

Legend

Alternatively you could really simplify it by using a Cosine wave to control rotation, something like;

Math.cos(time*.75)*100

The multiplier number outside the parentheses controls the amount of rotation. the multiplier number inside the parentheses controls the timing.

OussK

Community Expert

I think you don't get Rick answer, please take a look on this link so you can understand better how to use loopOut("pingpong")

https://www.schoolofmotion.com/blog/loop-expression-after-effects

R

Rick Gerard

Community Expert

The easiest thing to do is set one keyframe for rotation at 0 seconds then a second keyframe at 4 seconds. If you want the rotation to go back and forth then add this expression:

loopOut("pingpong")

If you want the rotation to loop then use this expression:

loopOut()

If you want the loop to be seamless then the first and last keyframe must put the layer in exactly the same position.

jcalcinaAuthor

Inspiring

Thanks. So I want to rotate to the left, pause 4 seconds and rotate back to the right (starting position), pause 4 seconds. I thought maybe there was a way to do it using a loop expression with a pause.

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