Making the arm follow the spine

00:04

The next step is to now make sure the arm follows the spine.

00:08

You see, as we manipulate it, the arm just floats here and doesn't move,

00:12

which isn't natural.

00:14

First, we need the left arm group back.

00:17

So let's create it again

00:19

and move it into the rig systems group

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and rename it.

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Move the

00:26

IKK and world space group into it.

00:30

Now create two new groups.

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We want two so we can store both the IK and FK positions of where the arm should be,

00:41

rename them. So the first is shoulder left I care world space

00:46

and the second is shoulder left FK, world space.

00:51

Now match these to the arm root control.

00:55

So they are in exactly the same place.

00:58

Actually, this should be left FK. So I'll change that to L

01:04

parent the ICA group to the ICARE shoulder control. So it follows it

01:09

and the FK group to the spine three control.

01:13

Let's also clean the attribute values too.

01:16

Again, moving them down to the offset parent matrix section.

01:21

There we go.

01:23

And now back to the node editor,

01:27

I'll just clear this

01:29

bring in the new ICA and FK groups

01:32

and also the left arm group,

01:35

all we want is a left arm group to blend between these two shoulder groups.

01:41

So as the animator blends between IK and FK, the arm will move to the correct spine.

01:47

So to do this, we need another blend matrix node,

01:51

rename this to shoulder IKFK blend.

01:56

Connect world matrix zero from the IK group

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to the input matrix attribute on the blend matrix node,

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go to the attribute editor and add a new item to the blend matrix node.

02:09

Now connect the world matrix zero attribute from the FK group

02:14

to the target zero matrix attribute.

02:19

Now connect output matrix to the arm root group's offset parent matrix attribute.

02:26

Now if I rotate the FK spine,

02:29

the arm follows

02:31

I'll just move this.

02:34

If we switch to IK,

02:36

nothing happens.

02:37

But that's because we also need to tell the blend

02:39

matrix node to swap to the IK group too.

02:44

Add the co control to the node editor.

02:47

Let's find the IKFK switch attribute

02:51

and connect that to the envelope attribute on the blend matrix node.

02:56

Now the arm follows when using the IK spine,

03:01

we can also blend between the two

03:03

and the arm follows.

03:05

Let's test the main root control again. Now things have changed.

03:09

Ah Right.

03:11

So we have the double transform issue again.

03:14

So all we need to do is remove the root's influence again. Just like we did earlier,

03:19

let's make some room

03:21

and create a new malt matrix node

03:24

call this shoulder left IK malt

03:29

duplicate this

03:32

and update the name to FK instead of IK

03:36

and remove that one.

03:38

Let's add the root control to the node editor two

03:42

connect world matrix zero from the shoulder I

03:45

group

03:47

to the shoulder I

03:49

mult nodes matrix in attribute.

03:52

Now connect to the root controls. World inverse matrix attribute.

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Remember

03:58

we use inverse because we want to take these values away.

04:02

Connect this to matrix A one.

04:05

Now we repeat this for the FK side.

04:08

So world matrix zero to matrix N

04:12

and then world inverse matrix from the root control

04:17

two matrix in one,

04:19

we now need to connect these to the blend matrix node.

04:23

So matrix sum

04:25

to input matrix

04:28

and matrix sum from the FK mult matrix node goes to target matrix

04:33

under target zero. Just here

04:37

we can rotate the root now and the arm stays in position.

04:41

You will also notice that the arm isn't rotating with the spine.

04:45

It's just staying almost level.

04:48

This is because we have its world orient attribute set to stay in world space.

04:53

If I change this to zero,

04:57

the arm now stays orientated with the spine.