Can't control curve While in "custom tweening"


I have a part that makes a 90 degree rotation along the Z-axis between keyframes A and B. A bit later on the timeline, I want it to return back to the original state (rotate 90 degrees back) between keyframes C and D, with the same time spacing between A and B, and C and D. Basically, C and D are a mirror image of A and B.

What I’ve done, is copy keyframe A to D and B to C.

However, the speed of the rotations is different, and I can’t see why.

In the image you can see the difference of the curve for the rotations.

So first thing I’d like to find out, is why the curves splines aren’t exact mirror images.

No, I’ve tried fiddling with the curve handles to try and match them, by selecting “custom” tweening for keyframe D. The curves remain locked for some reason. I can move them, but not edit the control handles. Why is this??


Hi again Arman,

Tweening is a rather complex mathematical thing. The speed of the animated changes (the shape of the curves) is the result of the many factors. I suggest you to have a look at some pages on our website

An answer to your specific questions:
a. The curves aren’t exactly mirrored ‘thanks’ to the Automatic Easing as explained in the video in a previous topic. There is Automatic Easing at work inbetween keyframes 0 and 312, but there is NO keyframe after keyframe 438 to ease with. The result of Tweening and Easing stretches over the keyframe. I.e. it takes the previous and the next one into account.

Simply deleting the zero keyframe makes the curve go symmetrical. Or you can add a symmetrical ending keyframe by copying the zero keyframe to tick 750 to get a situation like in the Duck video. The curves are not the same in both cases though.

By the way … you can see an other (positive) effect of the Automatic Easing in your model. The fact that the object stays still in between keyframes 312 and 438 is a benefit of Automatic Easing. Try switching it off and see how Cardinal spline tweening smoots the curve and adds some kind of inertia in the rotation.

b. In the CurveEditor the initial handle for costum tweening is drawn at the length of only 1 tick. Since your work stretches over a large range of ticks the handle is very tiny. You have to zoom in very closely to see the distinction between the control point itself and the curve handle.


Ok, thanks Luc, that works with some fiddling around.

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