Can someone tell me why a oll like constraint cannot be applied to a bone that already has a spherical limits constraint?
I will attempt to answer this. You CAN put a roll like constraint on a bone with a spherical limit constraint on it. What you are trying to do is to make a parent bone (the forearm) roll like the child bone (the hand) The hand bone position is dependent on its parent bone, and yet you want to make the parent bone’s position dependent upon the child bone’s position at the same time. Is this starting to sound like a circle? What I did when I was learning each constraint was to make a very simple cylinder model, and start applying different constraints on the 2 bones I added to the cylinder. I typed in the constraint values at their extremes and played with the bones in an action window until I understood the effect each constraint had. Maybe this would help you?
