Arm rigging (Radius, Ulna - suplination, pronation)

(AleksanderA.) #1

Hi all!
I would like to create an anatomical arm animation similar to the one on this video at 8.43:

Would also like to add muscles and so on. However at the moment i’m stuck with rigging.

Can anyone help me out?
Thank you in advance…


(Clockmender) #2

Well I guess this depends on how anatomically correct you need to be! So here is my first guess at this: :eyebrowlift:

There are a number of bones in there, including the important “control” bones.

To move the shoulder - rotate the “clavicle” about its X or Z axes - key R XX etc.

To twist the scapula - rotate the “scapula-pivot” bone about its Z axis - its locked so you can only do this.

To move the arm, e.g. flexing, extending - move the “hand-IK” bone - its distance from the shoulder is limited.

To rotate the wrist - rotate the “wrist” bone about its Y axis - its locked so you can only do this.

To reposition the elbow - move the “elbow-pole” bone along the global Y axis - again it is locked.

To rotate the hand - rotate the “hand” bone about its X or Z axes - again its locked.

To move or rotate the whole thing, manipulate the “root” bone.

Let me know what you think - you just have to add the fingers and thumb bones - these should be parented to the “hand” bone - you can do then as IK or FK, that’s up to you.

When you are happy with the rig, just “bone” parent “dem bones, dem bones, dem… dry bones” to the appropriate armature bone. To “bone” parent - select the mesh, SHIFT select the bone in the armature, key CTRL+P => “Bone”.

The “forearm” bone is just a control bone for positioning the radius and ulna IK targets.

You might like to add some more Limits - but remember you set limits for an IK chain in the bones’ IK properties in the Bone panel, not with constraints. :yes:

Cheers, Clock.

Here’s the blend file: arm.blend (480 KB)

EDIT: I spelled Ulna incorrectly D’Oh!

(AleksanderA.) #3

Thank you clockmender! :eek:
I love it!
Is there an option for the Ulna bone to stay still while the radius bone is rotating. I think this guy in this
video is trying to explain that:

Thank you again for your quick reply! :slight_smile:

(Clockmender) #4

Yes, just move the two IK bones up so the “ulna-IK” is coincident with the “wrist” bone and the “radius-IK” is further away. Its a good idea to keep these two bones spaced the same at all times. You can simply move the two bones in Pose Mode as below:

Cheers, Clock.

EDIT: Just looked at my arm again, when I twist it both radius and ulna move about a theoretical centre line between them…

(AleksanderA.) #5

Ok, thank you again. Here is the arm so far. I didn’t get the rotations right yet.
Will take a look tomorrow again… :o

(Clockmender) #6

I had a play - I think this is closer to where you want to be:

arm-clock.blend (675 KB)

I have changed the hand to “Bone” parent - you should consider this for all the bones - it was not working right when you moved the hand bone. Also consider making the wrist bone mesh a separate object to the hand and bone parenting this to the “wrist” bone. Or just parent the whole lot to the wrist bone if you don’t want to move the hand (fingers & thumb) separately to the wrist.

Cheers, Clock. :wink:

(AleksanderA.) #7

Thank you!
…and I have made a mess out of it again:

Press alt+a
What is missing is the Radius bone rotation caused by the muscle Biceps brachii (long head) pulling it upwards.
I have solved it here with a shapekey. Is it possible to make the armature rotate?
O and abaut the model, It is time for me to make my own better one…
Will post it here.

Thank you again…

(Clockmender) #8

Just quickly as I am of the the airport, I think you can just rotate the radius bone… I will check later.

Cheers, Clock.

(AleksanderA.) #9

Ups, you’re right! :eek: