Adding custom attributes and controllers - Part 3 Arms IK/FK blending


Last week in part 2 of the rigging process I have taken care of the spine of the model by adding custom controllers and constraints. This week I will be rigging the arms and clavicles.

I have started with the FK rigging first (as the rig created features both IK and FK arms bones) on the left arm. As in the previous posts, I first created three different geometric shapes and aligned them with the joints: shoulder, elbow and wrist. I have then linked and then constrained the orientation of each FK bone to that of its controller:
  • ·         Wrist bone orientation to the wrist controller
  • ·         Elbow bone orientation constrained to elbows’ controller
  • ·         Shoulders’ orientation to its controllers orientation



Now I was able to rotate the FK arm bones using the individual controllers. I have also locked the movement of the controllers on the three (XYZ) axis and the rotations as necessary. For example, the elbow shouldn’t be able to rotate on the X or Y axis, so I have locked them.



Next up I moved on to the IK bones of the left arm. Similarly, I first created one controller for the whole three bones long arm IK chain. That is because of the way an IK chain works – having one wrist controller allows me to move the whole arm freely, as opposed to the FK chain where the user is required to move each individual bone in the chain separately.
I have then created an IK chain between the shoulder and the wrist bones – exactly like the link between the thighs and the heels, for example. Aligned the controller to the wrist and linked the IK goal to the controller (so that the controller acts as a controller).



Ultimately, I have added a custom attribute (like in the previous posts) that controls the elbow swivel.
Now that the FK and IK chains were rigged, I had to blend the main bones between the IK and FK ones. In this situation, although the IK and FK bones are not attached to the mesh, they act as controllers for the main bones of the rig that are otherwise attached to the mesh. Essentially, both chains behave differently – so the main bones are blended between them so that the animator can use IK or FK selectively when animating, depending on his needs. The main bones will then mimic the movement of the chain the animator chooses to use.


To blend, I linked and constrained the orientation of each main bone in the chain to the IK and FK ones, in order. So the wrist bone was constrained to the IK wrist bone first, and then to the FK wrist bone. The elbow and shoulder bones to their counterparts as well, in the same order.




The last step was wiring the parameters between the constrained bones:



As explained a few lines back, I’ve created a custom attribute so that the animator can choose between using the IK or the FK chains:



The clavicle was rigged in a similar fashion, but no IK or FK chains, custom attributes or parameters wiring was necessary. Adding a simple controller that allows for the rotation of the clavicle was enough.

The next step will be to repeat the same procedure on the right arm of the character. However, this time I proposed myself to not have any guidance while doing so. This will test how much I have learned in the first process, although it will most likely take me a longer time to complete the task. Where necessary, I will consult the materials at my disposal.



References:

YouTube. (2012). Rigging a Character in 3ds Max - Part 9 - Arms FK Rigging. [online] Available at: https://www.youtube.com/watch?v=LtJimmET32o&list=PLnKw1txyYzRlxh1-BT4CifPXC5TBg2vUd&index=33 [Accessed 22 Feb. 2019].

YouTube. (2012). Rigging a Character in 3ds Max - Part 10 - Arms IK Rigging. [online] Available at: https://www.youtube.com/watch?v=QsrzQzyinr8&list=PLnKw1txyYzRlxh1-BT4CifPXC5TBg2vUd&index=34 [Accessed 22 Feb. 2019].

YouTube. (2012). Rigging a Character in 3ds Max - Part 12 - IK FK Blending for Arms. [online] Available at: https://www.youtube.com/watch?v=j8UVIsjskE0&list=PLnKw1txyYzRlxh1-BT4CifPXC5TBg2vUd&index=36 [Accessed 23 Feb. 2019].


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