6.11.1 Curl a Finger
In this example we will create a simple finger by using a conical tube
tool and control it by using the INVERSE KINEMATIC and SKELETON
methods.
If you are already familiar with the conical tube tool, you know it
creates its objects by combining quadrics, such as cones, cylinders and
spheres. Because this tool is suitable for modelling robots, the
question "how to keep joints stuck to each other" is quite an
interesting one.
The idea of this example is the following: an object created by a tube
tool represents one finger. A SKELETON method is used for controlling
many finger objects and the skeleton curve is animated by defining the
path of its end point using INVERSE KINEMATICS. This is quite a common
way to use inverse kinematics with skeletons.
1. Create a polygonal line using the function Create/Controls/Open Line.
This line represents the bones of your finger, hence it consists of
four points. It will be used as a primary skeleton curve.
2. Create a tube representing your finger by selecting the menu
Create/Compound Tools/Conical. Because you use quadrics,
the skeleton must perfectly match the tube. So, use dragging when you
define center points for conical tube joints. Because inverse
kinematics allows you to define the position for the END point,
make sure that the direction of your tube is the same as the direction
of your skeleton.
Otherwise you would define the position for a finger-root, not for a
fingertip.
3. Make the tube object the current level and create a SKELETON method
to the same level with the component primitives of the tube.
4. Use Cut and Paste to move the skeleton curve under the method
object in the hierarchy.
5. Create the secondary skeleton by creating an axis primitive
perpendicular to the primary skeleton. Now the skeleton is ready,
so select the menu Animate/ Control/Refresh.
This instructs REAL 3D to fix the target objects to their current
positions on the skeleton.
6. Now, select the primary skeleton curve and the function
Modify/Special/Inverse Kinematics and modify the end point
of the skeleton. Then refresh the animation system and,
as you can see, the finger is pulled to the skeleton and all the
joints of the finger remain connected.
7. Create an INVERSE KINEMATICS method at the same level with the
skeleton curves; the skeletons will be targets for the
INVERSE KINEMATICS method.
8. The INVERSE KINEMATICS method requires only one parameter, which
defines the end point of the target curve. So, create a B-Spline
curve defining the route for the end
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