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Character Tutorial
Part 2 – Foot Setup For a
Chicken
by Kris Kapp
Last
time I talked about modeling the chicken. This time I’ll go into
how I set up the foot controls. I decided to use a "reverse
foot" to drive the leg IK. The advantage of the reverse foot is
that it gives you a solid heel that you can plant just like a real foot.
Normally you would build a skeleton and do a test bind on the geometry
before building fancy controls.
Start by creating the basic leg structure. When
creating the legs I like to set the Auto Joint Orient option to None.
Start with the pelvis, hip, knee, and ankle. The chicken foot is a
little more complicated than a regular foot so I added the back toe
joints, and front toe joints (I named them back_Toe01, back_Toe02,
Mid_toe01, Mid_Toe02, Mid_Toe03).
Side view of leg joints
Top view of leg joints
Duplicate the toe joints and move them over.
Rotate the first joint of the duplicated toe joint to match the toe
geometry. Do this for both the outside and inside toe. Rename the toe
joints prefix Out and In for the outside and inside positions.
Duplicated toe joints moved into place
Rotated toe joints.
Create an IK Handle for the leg that spans from
the Hip to the Ankle. Make a pole vector object from a curve using the
command: curve -d 1 -p
9.26493 1.180816 1.180816 -p 9.26493 1.180816 -1.180816 -p 6.903298
1.180816 -1.180816 -p 6.903298 1.180816 1.180816 -p 9.26493 1.180816
1.180816 -p 9.26493 -1.180816 1.180816 -p 6.903298 -1.180816 1.180816 -p
6.903298 1.180816 1.180816 -p 6.903298 1.180816 -1.180816 -p 6.903298
-1.180816 -1.180816 -p 6.903298 -1.180816 1.180816 -p 9.26493 -1.180816
1.180816 -p 9.26493 -1.180816 -1.180816 -p 6.903298 -1.180816 -1.180816
-p 6.903298 1.180816 -1.180816 -p 9.26493 1.180816 -1.180816 -p 9.26493
-1.180816 -1.180816 -k 0 -k 1 -k 2 -k 3 -k 4 -k 5 -k 6 -k 7 -k 8 -k 9 -k
10 -k 11 -k 12 -k 13 -k 14 -k 15 -k 16 ; xform
-cp;
IK Handle
This makes a cube "curve". I got this
trick from Chris Clay’s tutorial on setups. Scale the cube to a
suitable size and center its pivot. You can also just create a locator
instead but I’ve gotten to like the look of the cube pole vector.
Using the move tool snap it to the knee joint then move it forward along
the Z axis. Orient Constrain the IK Handle to the pole vector object.
Pole Vector Constraint
Next we will create the general structure for the
Reverse Foot. Place the root joint of the reverse foot where the heel of
the chicken’s foot would strike the ground. Snap the RF_Toe to the
MidToe03 joint of the original foot. Snap the next joint to the MidToe02
and the next to the Ankle joint. Name these joints RF_ToeMid and RF_Ball.
Reverse Foot Setup
Using constraints, we’ll wire the original foot
to the reverse foot. Point constrain the IK Handle to the RF_Ankle
joint. Do this by selecting the RF_Ankle joint and then the IK_Handle
then Constrain>Point. Orient constrain the original Ankle Joint to
the RF_Ball joint (select the ball joint first then the ankle joint and
then Constrain>Orient.) Orient constrain the MidToe01 to the
RF_ToeMid joint. Finally orient constrain the MidToe02 to the RF_ToeEnd.
IK Handle point constraint
Joints orient constrained
Select all the joints in the reverse foot except
for the RF_Ankle. Display the selection handles for all the joints and
in the component mode, move them away form the joints so you can select
them easier. By moving the RF_Root, you can control the leg. By rotating
the various joints of the reverse foot you should get proper rotation of
the original foot. We will take care of the inside and outside toes in a
moment.
Reverse foot with selection handles moved
Continued
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