Follow
Curve
In some cases,
you want to set up bones along a curve where that curve acts as
the kinematic control for the bone chain. Using the Path
tool and its corresponding Path
CVs, along with the
Bones on Curve tool, you can quickly set up
a follow curve kinematic solution.
Click below
to load a model of a spoon that you will set up using this workflow.
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1.
Create the Path
Switch to a
right view and zoom out until you can see the spoon. Select tab
> Path then click three times from the bottom
of the spoon to the top to define the shape of the path as shown
below. RMB-click
to complete.

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2.
Adjust the Shape of the Path
With the Path
tool still active, click on the top Path CV. Press r to bring up
the Rotate handle and rotate the CV to aling it with the curve of
the spoon. Next press e
to bring up the Scale
handle then drag on the arrow to reshape the curve to better fit
the shape of the spoon. The ability to scale the Path CVs to define
the tangents lets you create a wider variety of curve shapes with
fewer control points. If desired, click on the other Path CVs and
manipulate them to further refine the curve.

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3.
Add Bones to the Path
Press tab
> Bones from Curve, click on the path curve
and RMB-click to accept. With the Bones from Curve tool still active,
go to the Operation Control bar and change the
Number of bones to 16
and the Kinematics
to Follow Curve.

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4.
Capture the Geometry
In the Network
pane, select the spoon object and press i
to go into its geometry network. Select the
subdivide operator and set the Depth
parameter to 2.
Press u to go
back up to the Object level.
Select
tab > Capture Geometry. Click on the spoon
and RMB-click to
accept then in the Network pane, click on the
chain_root and RMB-click
to accept. Switch to a perspective view and tumble to see how the
results of the capture. Any areas that are colored have been captured
while white areas are not. Currently most of the spoon has not been
captured.

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5.
Keyframe the Bind Pose
Before editing
the capture regions it is a good idea to keyframe the bind pose.
When kinematics are defined using the Bones
tool, keyframes are usually created at frame 0 for the posing parameters
to define a bind pose. With the Bones
from Curve tool, no keyframes are generated
and must be set manually.
Go to frame
0 in the timeline.
With the Pose
tool, shift-click on the three Path CV controls to select them all
then press k
to keyframe their parameters. |
6.
Edit the Capture Regions
The capture
regions for the bones need to be expanded to surround all of the
spoon's geometry. Select tab >
Edit Capture Regions,
select all the bones and RMB-click
to accept. Next, go to the Parameter pane and click on the Capture
tab. Because you are adjusting 16 bones at once, it is faster to
use the Parameter pane to edit common parameters than to click and
drag on all the handles one at a time.
Set the Top
and Bottom cap values
to to 0.2, 0.4, 0.4.
This will edit all of the selected nodes. Tumble around to see if
things have been improved. The handle is now colored and therefore
captured while the head of the spoon still has white areas.

Next, select
only the top few bones in the area of the spoon head. Change the
Top and Bottom
cap values to 0.5,
0.7, 0.4. Tumble around to make sure that the
whole surface has been captured.

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7.
Pose the Bone Chain using Path CVs
Go to Frame
1. Select the Pose
tool and click on the top path CV. You can use the default handle
to move and rotate the path CV and pose the bone chain. If you rotate
the handle you will twist the IK solution around the curve. The
follow path kinematics are designed to respect the rotation of the
path CVs.

You can also
press e to go
to scale along the Z axis of the handle to control the tangents.
At any point you can press k
to keyframe the path CV parameters.

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