Maya
Skeleton Setup
Setting up a skeleton for your character and binding
it to the skin.
My name is
Larry Neuberger and I am a professor at Alfred State College in Alfred NY. I
created these handouts to use in my classes and most of my students found them
to be helpful. I now decided to submit them to be published on the web hoping
they can help others as well.
This lecture will go over creating a skeleton for your
character and attaching it to the skeleton using the bind command. We will also
be discussing the options for each of the bind tools and the sub-tools that
allow you to perfect it. Some of you will be creating characters with two legs,
four legs, no legs, etc. The easiest way for me to go over all of this is with
a basic human character.
First, when modeling your character, you want to be sure
that you pose him in a “T” shape before you even attempt to create a skeleton
for it (See fig 1.). By doing this there will be fewer alterations when binding
and your CV’s will not get intertwined.
Fig 1.
Once your character is set up you can begin to build the
skeleton. Before you start creating the skeleton you want to setup the options
for the joint tool. Go to Skeleton > Joint Tool . When the option box is open, set auto
joint orient to none (Fig 2.).
Fig 2.
This setting makes sure that joints constrain properly when
binding to the skin. Once this
is set we can begin creating the skeleton.
Creating the Legs
Now we can begin the actual skeleton. Depending on what kind
of character you have, your results will vary. I usually start with one of the
legs. Simply click once to start the skeleton, then click each time you want to
place a joint and at the completion press enter to finalize it.. See example below for my character’s leg skeleton (Fig
3.).
Fig 3.
You will notice I did not use the reverse foot method like
described in the “primitive man” tutorial in the Learning Maya book. If you
wish to use the reverse foot, refer to pages 314 – 320. The reverse foot has you
create a second bone structure, connect it to the foot, and add an attribute to
control the foots roll. I personally like to keep the
skeleton rather simple, animate it, then once my walk
is done, go back and animate the foot’s roll by hand. You should do whichever
you feel more comfortable with when creating your skeleton. It is also a good
idea to name all of your joints when you are done. This makes for easier
editing. Use the channel box to name your joints like we learned in earlier
lessons.
Once you have your leg set up we will want to add an IK
handle to it. An IK Handle is a manipulator which makes animating the leg
easier. Before we add the IK Handle though, we need to have the leg have a
slight bend in it so the handle knows how to control the leg. Simply select the
knee joint and rotate it a little to create a slight bend in the leg (Fig. 4).
Fig. 4.
Once the bend is completed you will need to set the
preferred angle. Setting the preferred angle tells Maya how to control the leg’s
movement. In this case we are saying to bend at the knee. Select the whole leg
skeleton, then go to Skeleton > Set Preferred
Angle. (Fig. 5)
Fig. 5.
Now that the angle is set, we are ready to add an IK Handle
to the chain. Simply go to Skeleton > IK Handle Tool. (Fig. 6) Then
click on the top joint, then on the joint where you want to end the bending
(the ankle joint). Once that is done you will see a thin line going from the
Hip joint to the Ankle joint. This is what you will Use to control the animation
of the entire leg. Select the handle and move it to see how the leg reacts
(Fig. 7).
Fig. 6. Fig. 7.
We now have an IK Handle set up on the leg and we are
almost ready to animate with it. We just need to rig it now. Before we go into
rigging it we will just go over what and where a few things are. (Fig. 8)
The pole
vector starts at the start joint, and with the handle vector defines
the reference plane. Because
moving the pole vector changes the orientation of the reference plane,
moving the pole vector can also change the orientation of the joint chain
directly, just as manipulating the twist disc can change the orientation of
the joint chain. This is because the joint chain's degree of orientation,
or twist, is defined as the difference in orientation between the reference
plane and the joint chain plane. The twist
disc is located at the end joint. The twist disc is a manipulator for
twisting the joint chain by rotating the joint chain plane.
Fig. 8.
The
pole vector effects the skeletons rotation around a certain plain. At it’s default settings, the pole vector faces forward and
creates an invisible plain that it will rotate around. See figures 9 and 10
below for a better explanation.
Fig. 9. Fig. 10.
Fig.
5 above shows the IK Handle pulled up and the leg deforming properly. You can see it is almost at the plane of the pole vector. Fig.
6 shows the IK Handle moved above the plane of the pole vector. Once it moves above the pole vector the leg is flipped and not properly aligned.
What we want to do is change the direction the pole vector
is in which will allow the leg to rotate freely and unchanged. To do this, select
the IK handle and press the show manipulator button (Keyboard shortcut T). (Fig. 11.) Then move the pole vector so it is pointing
inwards facing the body’s center (Fig. 12.).
Fig. 11. Fig. 12.
Now the rotation plane is going perpendicular through the
leg. So now when we move the IK handle to rotate the leg we will have no
undesirable changes. The only problem is now the leg is facing inward and kind
of pigeon toed. This is where the twist disc comes into play. While the
manipulator is showing, use your left mouse button and click and drag to rotate
the twist disc so the leg is facing forward (Fig. 13).
Fig. 13.
Notice
how the Pole Vector is now facing inwards. Now if we grab the IK handle and
move it, the leg will rotate properly with no negative effect on the skeleton.
(Fig. 14 – 15)
Fig. 14. Fig. 15.
Now
that the pole vector is going perpendicular through the skeleton, it will allow
it to rotate a full 360 degrees without and deformations or tweaking as
compared to before when it was facing forwards.
Setting Limits on a joints
rotation.
Now
that the leg is all set with an IK handle and ready to animate, it is a good
idea to set limits on certain joints so it cannot bend to
much an over extend itself. Right now, with no limits set, the knee is able to
bend more than it should as well as over extend itself (Fig. 16 – 17.).
Fig. 16. Fig. 17.
In
Fig. 16 you can see the knee bends too much in the reverse directions. In Fig. 17 the knee hyper extends when pulled forward.
We
can now set limits on the knee joint so this does not happen and we get a more
realistic movement on it. Select the knee joint and open the attribute editor
for it by going to window > attribute editor. (Fig.
18.) Once the attribute editor is open, go to the section labeled limit
information (Fig. 19.).
Fig. 18. Fig. 19.
You
can see in the limit information section in the attribute editor, you have
minimum and maximum values for the joint.
Select the IK handle and move the leg to the maximum rotation in the
reverse direction (Fig. 20.). Then select the knee joint and go back to the
limit information in the attribute editor. Press the arrow next to max and then
check the box next to it (Fig. 21.).
Fig. 20. Fig. 21.
You
have now set the maximum rotation for that joint. Repeat the steps above for
the minimum rotation. Select
the IK handle and move the leg in the opposite direction (Fig.
22.). Then select the joint, go to the attribute editor,
and using the same steps as above, set the minimum limit (Fig. 23.).
Fig. 22. Fig. 23.
That
is all there is to it. We now have a leg with an IK chain set up on it which rotates
with no tweaks and has limits set to avoid over bending and hyper extension. So
if you try to bend the knee backwards by moving the IK handle, you will see it
will stop at the maximum limit we just set (Fig. 24 - 25.).
Fig. 24. Fig. 25.
NOTE: Now all you would have to do is repeat the same steps for the arms and your skeleton will be ready to go. None of this is necessary nor required when rigging a skeleton, but by spending the extra time to do this, animating will be that much easier for you in the long run.
Now that the one leg is complete, we will duplicate it to
the other side. There is no reason we need to go do all this work again. Select
the entire leg by clicking the main joint (Fig. 26), then go to Skeleton
> Mirror Joint . (Fig.
27) Once the option box is open, select the appropriate mirror across
selection. If you are not sure, try one at a time until you get the right one.
Fig. 26. Fig. 27.
Once you have the appropriate mirror across selection, press apply and the entire joint (along with the limits, IK,
Twist Disc, and Pole Vector) will duplicate and mirror to the other leg (Fig.
28).
Fig. 28.
Creating the Torso / Spinal Column
Now that the legs are set we can work on the torso area. Use the joint tool again to create the spinal column / torso (Fig. 29).
Fig. 29
Once you have the torso done, notice all the space to the
left and right of the spinal column. Later on when we bind the skin to the skeleton
this could cause problems. To help reduce the space from the column to the edge
of the skin it is helpful to add a rib cage. This is not required, but once
again, extremely helpful and will make animating that much easier and flawless
later on.
To do this, use the joint tool and select a joint on the spinal column to start with, then click away from it to create the rib bone (Fig. 30). Repeat this until you have a full rib cage (Fig. 31).
Fig. 30. Fig. 31.
Creating the
Legs and Hands
Now we are ready to create the bone structure for the arms and hands. In order to do this we will repeat the steps we used to create the legs which I will go over briefly again.
Using the Joint tool (Skeleton
> Joint Tool), click joint by joint to create the skeletal structure
for the arms and hands. Don’t forget to name the
joints using the channel box when you are done. Once the arms is complete,
bend the elbow a slight bit using the rotate tool. Then go to Skeleton > Set Preferred Angle.
Fig. 32
Fig. 33
Fig. 34
Next, go to Skeleton > IK Handle Tool. Then click on the main joint (the shoulder), then the
wrist joint as the end effector. You should now see a thin line connecting
the shoulder to the wrist (the IK Handle). Select the IK Handle, then press the show manipulator
tool and drag the pole vector outwards towards the hand. Remember, the pole
vector acts like the top bar on a swing set. By doing this, when you rotate
the arm, you will not get any unwanted twists or tweaks.
Fig. 35
Fig. 36
Fig. 37.
Now set the limits on the arm. Select the elbow
joint, open the attribute editor and set the minimum limit. Then select the IK Handle, bend the arm inwards, select
the elbow joint again and set the maximum limit for that. Now we can mirror the arm to the other side. Select the
Arm’s root joint, then go to Skeleton > Mirror Joint
.
Fig. 38.
Fig. 39.
Fig. 40
Select the appropriate mirror across selection and
press apply. Now the arm is mirrored across to the other side.
Fig. 41.
Fig. 42.
Connecting the Joints
Almost finished!!!!! We now have a skeleton, but the arms
and legs are not attached to the rest of the skeleton. To do this, start by
selecting the leg’s root joint, then shift click on the torso’s root joint
(Fig. 43)
Fig. 43
Next, go to Skeleton > Connect Joint to open
the option box (Fig. 44). Once it is open, select parent and select apply to
connect the two.(Fig. 45)
Fig. 44. Fig. 45.
The difference between Parent and Connect is as follows:
Connect Joint
Connects the selected
joints and moves the joint chain of the first joint to the position of the
second joint. After connecting the joints, use Remove Joint to delete the extra
joint.
Parent Joint
Connects the selected joints by inserting a new bone between them.
Repeat these steps for the other leg and arms to complete the
skeleton (Fig. 46).
Fig. 46.
Constraining a Pole Vector
This is a very simple and effective tool for use
with animating. Sometimes when you move an IK Handle on a joint the structure
rotate a bit out of proportion. In order to fix it you would have to select the
IK Handle, then show the manipulator, then use the
twist disc to fix it. This will happen, so it is better to put more work
in the skeleton setup and rigging so animation will go smoother, faster, and
easier.
Go to Create > Locator. Position the locator behind the joint where you want it
placed. Select the locator, then the IK Handle (It most be in this order. If you select them out of order this
will not work.).
Fig. 47
Fig. 48
Fig. 49
Next go to Constrain > Pole Vector. Now select the locator and move it to test the results.
You will see that when the locator is moved the arm rotates. This will help
later when animating if your joints rotate out of position. (Something like
this will happen, so it is best to do this and be prepared.) Your finished product should look something like the
image to the left.
Fig. 50
Fig. 51
Fig. 52
Now your skeleton is setup, rigged, and ready to be bound to
the skin. In the following handouts we will go over the different binding
methods. Remember, this may look like a lot of work, but it is well worth it.
The time and work you put into the setup and rigging of the skeleton, the less
problems you will have when animating. The smoother the rig, the smoother than
animation process will be.