Hi VadimBernhardt!

In your TwoBoneIK setup, have you added a Spatial-based node to act as a pole? This can greatly increase the stability of TwoBoneIK, especially when close to fully extended. I think that is causing the issue you are seeing, though its hard to say for sure. Can you record a small video showing the problem?

As for the setup, it should be fairly easy: You need to have two Twisted_Bone3D nodes, a Twisted_Skeleton3D, a Twisted_ModifierStack3D, and finally a Twisted_ModifierTwoBoneIK3D. In the Twisted_ModifierTwoBoneIK3D node, you can look in the properties and assign the two Twisted_Bone3D nodes to the first and second bone slots. Then, you can set a target node and an optional pole node, then when the modifier stack is executing it should rotate the bones to point at the target.

One thing to look out for though is making sure the tip/second Twisted_Bone3D node has a proper length setup. If the second Twisted_Bone3D node does not have a child Twisted_Bone3D, you will likely need to set the bone length manually. You can do this by selected the Twisted_Bone3D node in the inspector, disabling "auto calculate bone length" and then manually inputting in the length of the bone in the bone length filed that should then be visible.

The example development project has a working example of TwoBoneIK in use that may also be helpful as a reference.

Thanks for reaching out and please let me know if you are still having problems! I'm sure we can figure out what is going on and find a solution :)