Control Rig (UE5.7) quaternion flipping when scaled

[Jence_42]

I am trying to make an IK setup with a twist bone between the hand and the elbow that allows for a better blended transition as the hand rotates (i.e. the roll of the hand should roll the forearm as well). The problem is, when I try to get the Rotation from “Get Transform - Control” and then use “To Swing and Twist” to isolate just the X (roll), and then “Interpolate” that so it scales it to .25 and apply it to the twist bone, when I rotate the hand around past 180 it flips to -180 and the scaled rotation flips as well.

Here is my basic control rig node graph to handle this:

And the output can be seen in this video where I am also printing the raw quaternion values. You can see when the control rotates >180 in x it flips and so does the quat X value.

Video: https://youtu.be/Vfp49QquOzA

Is there a work around for this? I have played around with a euler approach as well as a rotator. All of them seem to flip at 180 unfortunately. Any help would be appreciated!

Edit: I should note that in the Details panel for this control I can see the X (roll) rotate higher than 180 without flipping, it’s just the values that get sent to the graph that are the issue.

[Jence_42]

So I played around with it a bit more and also looked at an example of how the Mannequin_CR is setup in the Epic Games control rig mannequin pack. They have a forearm twist bone setup as well and their graph looks like this:

Unfortunately, that too produces the same rotational flip so it appears to be semi broken.

I ended up coming up with a workaround solution that accumulates the rotation each frame based on the delta, you can see that here. It seems to work well even if it’s a little messier than I would like. Hopefully Epic can fix this or provide a new feature on the Get Transform - Control node to allow for unclamped values (similar to what is seen in the Details panel as you rotate).

This works: