A good rig should have both FK/IK
built in to the arms. Also a hand controller to switch
on and off the influence of the rotation from the lower
arm. And there should be a "twist" bone.
why we need a ON/OFF switch for the hand is to have
control over the hand if it's placed on a table or
grabbing somthing to hold on to.
Remeber to always
use the "lock_object.js" script on all ZERONULL's. It's
described in "spine" tutorial on how to use it.
use the mesh and spine setup I talked about in the Spine
tutorial. First I create a two jointed chain for the
left arm (create it in the top viewport).
Move it up
and to the correct placement. You might also have to
rotate the root a little.
To not bore you with me drawing all
the hand chains I'm just going to use the palm bone. So
draw the palm chain in the front viewport and then move
it to the correct position. Also in the front viewpost
draw a single chain from the spine to the root of the
arm chains. Move it into place. Name it
Make the end effector of the shoulder
chain the parent for the Arm root. And make the last
Spine chains end effector the parent for the shoulder
Now we need tp prepare for the ON/OFF
switch for the hand rotation. Create a null, rename it
"LH_NULL". Then postition constrain it to the end
effector of the arm. And then also orientation constrain
it to the end effector of the arm.
Then make the
"LH_NULL" the parent of the palm root.
If you now grab the upper arm's chain
and rotate it the "hand" should follow. Undo the
Now for the twist bone. Create a chain
that is half the lenght of the lower arm (draw the chain
in the top viewport). Position and Orientation
constraint the root to the lower arm, then remove the
Move the chain in local mode so that
it's placed at the lower half of the lower arm. Then
make the lower arm the parent for the twist arm
We now need an expression to control
the twist arm. And the controling chain should of course
be the palm chain. And we want half of the rotation to
be effected. Open up the kinematic properties for the
twist bone (select the bone and press CTRL-K). Right
click on the key button for the X rotation and chose
In the expression editor you need to
add the palm chain values of it's X rotation. In my case
the expression becames this:
0 + (bone5.kine.local.rotx / 2)
The "0" is added in front to make sure the
expression starts with that value and nothing else. Then
it adds the value of the palm chain and divide it by 2.
So if you now rotate your hand in X the "twist" arm
should follow with half the value.
Now is the
time to duplicate this to the right side. Branch Select
the "L_shoulder_Root" and also branch select the
"LH_NULL". Then use the symmetry option to duplicate
Also check the box "Share Parent" so
that you don't need to parent the new chains to the
- Edit-> Duplicate/Instance-> Duplicate
You should now have to working sides with
arms and twist bone.
The next step is to create the IK and
sliders for the extra controls. So to make the
controller we need a Custom Parameter Set. And also a
object to place it on. The easiest is to create a text
from curves. If you are on Linux® you don't have the
text option in XSI (in current version 3.01). So you
just have to be creative with the curves.
curves over the head and make the spine effector the
parent for that object (same as the
With the curve selected you now
create a Custom Parameter Set
Name the set Arm_Controls. Still
Selected you now add a Parameter
- Parameter-> New Custom Parameter Set
the control LeftHand_Influence. Set the default
value to 1, and also check the box UI Range and
the default values are already correct (see image
- Parameter-> New Custom Parameter
Now add three more parameter
exactly the same but with these names (in that
You should now have a
parameter set that looks like this one:
Lock the parameter set so that it's
always open (click the keyhole icon on the
Next is to create the IK. Use the Puppet
Master toolbar (that you should have downloaded from the
Spine tutorial). And create an object of your choice
which you name "LeftHand". Select the ZERO null and
position constrain it to the end effector of the left
arm. Then remove the constraint. Instead, constraint the
end effector to the Object you named "LeftHand". Do the
same with the right arm but name the object "RightHand"
(quite obvious eh?).
Now create a "Puppet Cube"
that you name "Left_UPV_ARM", and make the lenght 0.5 or
something you would feel is small. position constrain
the ZERONULL of the "Left_UPV_ARM" to the lower left
arm. Then remove the constraint. And move the ZERONULL
(branch selected) behind the character in a negative Z.
Make a similar one for the right arm, call it
Both UPV's ZERONULL should have the
same parent as the shoulders.
Now select the left upper arm and set
the "Left_UPV_ARM" object to be the upvector constraint
Do the same
for the right arm. And now a little trick. To avoid that
the arms snapp, or behaves strangely when you switch off
the IK for the first time we now set a keyframe on both
upper arms. So select both upper arms, make sure your
transform tool is set to rotation and press K to set a
keyframe on the first frame.
- Skeleton-> Chain Up Vector
Now for the more
tricky part of connecting. Select the left upper arm and
hit enter. Under the tab/section Kinematic
Chain you can find the slider "Blend FK/IK". If you
now have your Custom Parameter set still open you can
drag the "LeftArm_FK-IK" key button to the keybutton of
the "Blend FK/IK". See image below.
Do the same with the right arm. This
one will only disable the UP Vectors. So now we need to
do this with the end effectors as well. Select the left
arms end effector. On the right side of the UI click on
the botton "Selection", find the Position CNS
(located in the Constraints 'folder') and double click
With the properties open for the position
constraint do the same as you did with the "Blend
FK/IK". Drag the "LeftArm_FK-IK" key button to the
"Blend Weights" key button. Do the same for the right
Exacly the same thing we are now going to do
with the "Right/LeftHand_Influence". Select the
"LH_NULL" and find the orientation constraint. Do the
same and drag the "LeftHand_Influence" to the "Blend
Weight" key button. Then do the same for the right
You should now have a IK/FK rig with also
the possibility to change the influence for the hand
As the extra little trick we are also
going to turn visibility on and off for the arm chains,
depending on if we are in FK or IK mode.
upperleft arm, find the Visibility and double click on
it. There you'll see "View Visibility, Render Visibility
and Selectability". The only one we need to work with is
the "View Visibility". Right click on the key button and
chose "Set Expression". Then write this expression
cond( crvlist.Arm_Controls.LeftArm_FK-IK < 0.8, True, False )
depending on what you named your curve/text
above the characters name this one should work. Just
drag 'n drop one of the sliders down in the expression
editor window and you'll notice what name it has. This
expression turns the visibility value off when the
slider is below 0.8
This last this is just optional.
But play around with it and see how you like it. You can
download the finished scene here
I hope you enjoyed this tutorial.
"lock_object.js"©2003, Bradley Gabe, ILM