Rigging the Arm
While rigging the arms will be fairly easy, arms can be more complex. Usually, they’re also animated using IK, but because they’re not constantly touching a surface, you may prefer to use Forward Kinematics instead. For that situation, you can create what is called IK/FK Blend, which is basically a rig made of three different chains: the IK arm, the FK arm, and the deform arm, which blend using Copy Rotation constraints between the IK and the FK. As this is just an introduction to rigging, you’re only going to build the IK rig, but you should look into IK/FK Blending if you like rigging. In Figure 11.5, you can see the resulting rig for the arm.
Follow these steps to create the arm’s rig:
1. In Edit Mode, extrude a new bone from the elbow, clear its relationship with the arm bones (Alt + P), and move the new bone back (name it C_arm_pole). This bone will be the pole for the IK.
2. Duplicate the D_hand bone, disconnect it (Alt + P), and scale it down (name it C_hand). Now, using the 3D cursor (Shift + S), move the head of the new bone to the wrist joint. This bone will serve as the IK target for the arm and will also control the hand’s rotation. The reason why it’s scaled down is that it doesn’t completely overlap the D_hand bone because these bones are in exactly the same position: making C_hand smaller or larger will let you see it in Wireframe display mode (Z). Add an IK Constraint using the new bone for the hand (C_hand) as its target and C_arm_pole as the IK pole.
3. Select the D_hand bone and, on the Bone tab in the Properties Editor, deactivate the Inherit Rotation option in the Relations panel (just as you did for the head bone). Then, add a Copy Rotation constraint to the D_hand bone using C_hand as its target. Now, as you move C_hand, you’ll control the arm’s IK and, when you rotate C_hand, you’ll rotate the hand’s bone as well.