How to IK Rig a human arm with external controllers?

Question

So in the above image: Symbol Description

S - Shoulder

U - Upper Arm

L - Lower Arm

W - Wrist

F - Fingers

Now, I have to IK-rig it from upper arm to fingers and I was hoping for someone to explain how to go about this as I couldn't find a simple enough video to understand; I am relatively new rigging. You can just rig one of the fingers and adapt it to the rest and just explain what the differences are between rigging a finger and rigging a thumb. If you could do so by posting screenshots, I would be grateful.

Answer 1

As Josh said there are many ways to rig an arm, here is one basic:

• Add a Target bone and a Poletarget bone to your arm. The Target will be the arm controller, the Poletarget will determine the arm orientation.
• Parent these 2 bones to the Root bone of your armature.
• If don't have a Root bone yet, at least deparent these 2 bones.
• Disable their Deform option in Properties panel > Bone > Deform: When you'll parent the armature these 2 bones won't deform the mesh.
• Parent the Hand bone to the Target so that when you'll move the Target the Hand will also follow, which is very convenient.
• Give the Lowerarm an IK constraint, choose a Length of 2 so that it will move Loweram and Upperarm only, and choose the Target bone as the Target and the Poletarget bone as the Pole Target.
• If you want your Hand to stick to the Lowerarm, give it a Copy Location constraint with the Lowerarm as the Target and a Head/Tail value of 1.
• For the fingers: give the second phalanx a Copy Rotation constraint with the first phalanx as the Target, and give the third phalanx a Copy Rotation constraint with the second phalanx as the Target so that when you'll rotate the first phalanx the rest of the finger will follow.

A good thing would also be to choose a B-Bone Display for your armature (in the Properties panel > Data > Display), and to segment the Upperarm and Lowerarm so that they will bend smoothly (Go in the Properties panel > Bone > Bendy Bones > Segments and give 5 segments for example). In that case, give the Lowerarm an Copy Rotation constraint with the Hand as the Target and Space > Pose Space / Pose Space: when the Hand will rotate the Lowerarm and Upperarm will follow. Also, you could limit the rotation of these bones in the Properties panel > Bone > Inverse Kinematics, but it's a bit tricky and most of the time you won't need it.

Answer 2

There are many ways of IK rigging an arm, from a simple one to lots of sofisticated mechanism.

One simple classic way is: In edit mode: - select the wrist bone and unparent it (Alt P, clear parent) - select the first bone of a finger, shift select the first bone of all others 4 fingers, shift select (at last) the wirst bone, and parent them (Ctrl P, keep offset). Select the Lower arm bone, go to bone constraints tab and add an IK constraint, setting the armature as target, the wirst bone as target bone and 2 as chain lenght.

In this way, moving the wirst bone will solidly moving all the fingers (as it's set as parent) and will IK moving Upper and lower arm by the Ik constraint.

If you set chain lenght to 3, also the shoulder bone will be affected by the IK constraint.

The only difference between the thumb and the others fingers is that a thumb has 2 phalanges, while the others 3, so generally we use 2 bones for the thumb and 3 bones for the others fingers.