Why does this Copy Loc contraint not work with this IK bone?

Question

I'm working on a (toy) VR kayak simulator, but have limited rigging knowledge. I'm attempting to have two IK rigged arms holding onto a paddle, so they will animate with the paddle's movement, like this:

My basic strategy is to create an empty (visible by the hand), and then use a copy location and rotation on the hand bone targeted at the empty. Here's my constraints tab for my hand bone:

The IK works fine, the copy rotation makes the hand rotate with the empty, but moving the empty has no effect on the hand, despite the constraint. Wondering why this is, if I can fix it.. as I'm writing this, I've found this answer: Do some Bone Constraints only work with Root Bones?

...but I don't understand why I can't move this bone with a constraint, as I am clearly moving it when I pose it. I've also tried using an additional bone and a 'child of' constraint, with the exact same results, I get rotational tracking, but not location. I was also able to get a 'paddle bone' working as a child of one hand, but couldn't get it to affect the movement of the other hand...Thanks for your explanations! (how do I post the project?)

EDIT: Another method that I tried was creating two paddle bones meeting in the center, and then each separate paddle bone having a "paddle control bone" that was in the same location. I figured I could copy transforms for these control bones, and it would keep the hands a set distance apart.. but that didn't work either.

Answer 1

The issue you have is parenting. You would have the hand bone as a child of the lower arm bone, this parenting defines the position of the hand, preventing the location constraint from moving it. As the bone parenting doesn't effect the rotation, your rotation constraint can do it's thing.

You have the right idea with using IK, the IK constraint will set the location of the hand bone and move the arm bones to the right position to match it. What you need to do is remove the location constraint and set the empty as the target for the IK constraint.