Hmmm, where to even begin with this. Rigging is so complex to us noobies so I tend to personify technical terms a bit too much.
It appears for the arm bone to be of use to the control bones it has to be flexible, a little bit bent at times. From the controller’s point of view, an inflexible arm is not much use. Let’s look at it from the arm bone’s point of view for a second. Why does it need a pole target? Even the target its self, the arm is quite self-sufficient and can move in so many more directions without a ‘control’ bone’. I can’t speak for all bones but no bones in my character are afraid of the control bones. Not at all. Hold onto that for a sec.
I note also that the control bones have been made immune from deformation. However, the arm bones are not. Now we can’t consider this in isolation. The previous coding matters and must be taken into account. Let’s say the coders, because no one checks up on them, only earlier this year, used some particularly nasty code to force the arm bone to comply. And equally unnecessary, counterproductive techniques over say, the last decade. Now if the bones are not afraid, and you can be sure they are not, would not this kind of behaviour on the coders part just make them look like nasty people who should never be trusted? It certainly is not in the interest of getting a good animation happening. So is there a way forward?
I note there are three weight settings at the bottom of the IK bone constraint dialogue box. These vary the intensity and way in which the control bones exert control. So the bones can breathe. It is the attempt at total control that brings inflexibility. As any engineer / designer knows, over constraint is always a temptation and a big mistake. So use those checkboxes and associated sliders. Let the bones breathe, above all (to use a coding analogy) … don’t use threats! Implied or explicit. There are a thousand other, better ways to get a good animation without compromising the integrity of the game. Yes, force is the easy option, but is it the best? No, it is not.
I will continue to look for ways to make this animation work. But don’t forget there is the option to just move onto a different character. It may be easier to cut your losses and just begin again. Thay would be OK too. I’ll get back to work on convincing this arm to trust the control bones. Sheesh, that’s a big call, but we shall try.