Controlling the speed of a rotation

[Dan Ebberts]

Changing speeds is one of those things that can be pretty tricky with expressions. One way to do it is to do a frame-by-frame integration (accumulation) of your speed control. Here’s an example with a slider named “rpm”:

slider = effect(“rpm”)(“Slider”);
accum = 0;
f = timeToFrames(inPoint);
while (f < timeToFrames()){ accum += slider.valueAtTime(framesToTime(f)); f++; } accum*thisComp.frameDuration*60 Dan

[Nicolas Plaire]

Thanks… I’ll try to see how it work [because after that, I’ll try to link that rotation speed to an audio layer].

Very helpful, thanks!

[Greg Digenti]

This seems like it could have been what I was looking for in my attempts to slow a rotation, but there seems to be a lot wrong with it. There isn’t an opening curly bracket, or a closing parenthesis, and one line is “while (f” and just ends like that.

[Greg Digenti]

Wait, never mind! How strange, the first time I viewed this thread, there was a lot of things missing from your code, then when I re-loaded the page, the missing parts showed up! Must be a Cow bug. Works great, thanks!

[Paul Roper]

A response to a post lost in the mists of time…

I came across this while trying to fix the same problem the original post highlighted. So I used Dan’s expression, which worked perfectly…except there’s no motion blur!…(and yes, I do have the motion blur switch on!)

My layer rotates beautifully, but no matter how fast it goes, no blur occurs. To check things, I duplicated the layer, deleted the expression and did an old-fashioned keyframe rotate animation, and lo and behold we have motion blur, so it’s not a problem with my comp.

I’ve made a fix using Radial Blur linked to the speed slider which works fine.

Anyone else come across this possible bug? I guess it’s something to do with the cumulative nature of the rotation expression. Maybe.

[Jim Darski]

Thanks so much Dan! This works really well.
Just make sure Slider Effect is applied to the rotating layer and renamed it to rpm. (took me a few minutes to figure it out).

[Dave Currie]

Hello Dan,

I made a camera rig in CS5.5 using a similar expression to your solution here.

You can start from 0 and accelerate, then decelerate back to 0. Here is the position expression I used for that:

pSpeed = thisComp.layer("Easy Camera Controller").effect("XYZ Rig Speed")("3D Point");
pOffset = thisComp.layer("Easy Camera Controller").effect("Camera Rig Position")("3D Point");
accum = 0;
f = timeToFrames(inPoint);
while (f < timeToFrames()){
accum += pSpeed.valueAtTime(framesToTime(f));
f++;
}
accum*thisComp.frameDuration+pOffset

This works nicely in CS5.5, and I made a modified version for CS5 by splitting the 3D point controls into individual sliders.

Using the same expressions in CC works, but for some reason when I use Element 3D and add a light, it crashes After Effects every time with no error messages.

Here is the expression so far for the CC version but for some reason it always comes up with ‘valueAtTime is undefined’. I need to find the right solution so that AE doesn’t crash with Element, and I still have the same functionality on the rig.

pSpeed = thisComp.layer("Easy Camera Controller").effect("XYZ Rig Speed")("3D Point");
pOffset = thisComp.layer("Easy Camera Controller").effect("XYZ Rig Position")("3D Point");

accum = [0,0,0];

f = timeToFrames(inPoint);

while ( f <= timeToFrames()){
accum[0] += pSpeed[0].valueAtTime(framesToTime(f));
accum[1] += pSpeed[1].valueAtTime(framesToTime(f));
accum[2] += pSpeed[2].valueAtTime(framesToTime(f));
f++;
}

[accum[0]*thisComp.frameDuration+pOffset[0], accum[1]*thisComp.frameDuration+pOffset[1], accum[2]*thisComp.frameDuration+pOffset[2]]

If you’d like to see the whole rig just let me know and I can send you a copy.

Thank you for any help you can provide!

[Dan Ebberts]

You need to do the array indexing after valueAtTime(), so, for example, this:

pSpeed[0].valueAtTime(framesToTime(f))

should be like this:

pSpeed.valueAtTime(framesToTime(f))[0]

I don’t know if that’s the only thing wrong, but try fixing it

Dan

[Dave Currie]

Thank you for your help Dan!

This seems to work in CC:

pSpeed = thisComp.layer("Easy Camera Controller").effect("X Y Z Rig Speed")("3D Point");
pOffset = thisComp.layer("Easy Camera Controller").effect("Camera Rig Position")("3D Point");

accum = [0,0,0];
f = 0;
while ( f <= timeToFrames(time)){
accum[0] += pSpeed.valueAtTime(framesToTime(f))[0];
accum[1] += pSpeed.valueAtTime(framesToTime(f))[1];
accum[2] += pSpeed.valueAtTime(framesToTime(f))[2];
f++;
}

x = accum[0]*thisComp.frameDuration+pOffset[0];
y = accum[1]*thisComp.frameDuration+pOffset[1];
z = accum[2]*thisComp.frameDuration+pOffset[2];

[x,y,z]

So my rig is in the scene and I add a solid layer with Element 3D, everything works fine.

The second I add a light to the scene the whole thing crashes – could this have something to do with how CC caches in the background and the frame-by-frame integration in the expression?

I’m pulling my hair out trying to figure this one out!

Thanks again Dan and Happy Thanksgiving!

[Dan Ebberts]

Does it crash when you add the light if you don’t have Element applied to the solid?

Dan