User Guide > Characters > Kinematics   

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.

Load Start File


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.


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.


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.


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.


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.


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.