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Specific question about the Speed Graph/ Easing

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Eduardo Ramos
Specific question about the Speed Graph/ Easing
on Apr 23, 2020 at 8:25:28 pm

Hello! Hope everyone's doing well in this crazy time.

I have a question about the speed graph -

Basically I have a camera that's moving through 3D Space. I want the camera to gradually speed up, maintain a constant speed for a few seconds, and then gradually slow back down. Below is what my speed graph looks like.

I'm having trouble figuring out how to have a linear path between the two keyframes in the center, and not this giant downwards curve that I currently have. What would be the best way to approach this? Hope this makes sense...Thank you!

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Graham Quince
Re: Specific question about the Speed Graph/ Easing
on Apr 26, 2020 at 8:59:34 am

I find speed graphs frustrating. They were a relatively late addition to key frames and are not as flexible as C4D’s similar looking timeline.

What I find is that it’s easiest to build key frames from start to end of an animation. That is to say if you got back and add a key frames at the mid point, sometimes it can get a little screwy. I also do easy ease after setting all my key frames, rather than as I go. - Free FX for amateur films - FX blog

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Darby Edelen
Re: Specific question about the Speed Graph/ Easing
on Apr 27, 2020 at 6:13:47 am

You'll either need to lower the speed at the two 'peak' keyframes or move those two keyframes closer together.

It looks like 500 px/sec might be about the right speed if you keep the keyframes where they are, but I'm just eyeballing it. You could calculate the distance between the two keyframes and divide that by the number of seconds between them to find a more precise speed.

The thing to keep in mind when modifying the speed graph is that you cannot change the value of the keyframes. You can change the spacing of the keyframes or the speed at the keyframes.

In the first case (changing the spacing) moving keyframes closer together means there is less time for the layer to move from position A to position B so it must move faster to get there in less time (same distance / less time = faster speed). Moving them farther apart means there's more time and so the layer moves slower.

In the second case (changing the speed at the keyframes) the distance to travel and the time to do it in remain constant. If you increase the speed on both sides of the travel then the speed must decrease in the center of the travel in order for the layer to go the same distance in the same time. Imagine 2 cars leaving San Francisco for LA at the same time and both taking exactly 6 hours to arrive. Car A could travel at a constant speed the entire trip and Car B could start off traveling at twice the speed. For Car B to arrive at the same time as Car A then it must have slowed down at some point.

If you change the speed or spacing of the keyframes in the speed graph the 'area under the curve' must remain constant as the same distance still needs to be covered in the same amount of time. To boil that down: if you raise the speed somewhere then it will have to go down somewhere else.

I personally really like the speed graph. I never use the value graph for positions as I find it much more convenient to adjust them by using the pen tool to modify the bezier handles of the motion path. In this way 'where' the layer goes and 'how fast' can be kept entirely separate. Modifying the value graph directly affects both of these (where & how fast) at the same time.

Darby Edelen

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