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380 Chapter 5: Creating Geometry
contributes no force--either compression or
extension. For example, if the placement of the
binding objects stretches the spring to a length of
50 units but the Relaxed Len is set to 30, then an
extension force is in effect because the spring is
stretched fur ther than its relaxed length.
Co nstant k—The amount of force exerted per unit
change in length with respec t to the Relaxed Hg t
value. This could also b e described as the measure
of force-per-units-change in length as compared
to the Relaxed Leng th. For example, if your spring
is set to a Spring Constant of k=10 lb per in, and
you stretch it to be ten inches longer than the
Relaxed Hgt value, it will try to close with a force
of 100 pounds. If you compress it two inches
shorter than the Relaxed Hgt value, it will push
back with 20 pounds of force.
Spr ing constant is in—Lets you sp e cify the
measurement of force to use: Pounds per inch or
Newtons per meter.
Spring works in—Letsyouspecifythetypeofforce
youwantthespringtoexert.Whilemostsprings
actually provide both compression and extension
force, if your simulation requires only one, you can
save calculation time by using one instead of both.
•
Co mpression Only—This type of spring provides
only expansive force when its length is shorter
than the specified Free Leng th.
•
Ex tensi on O nly—Provides contractive force
when its length is greater than the specified
Free Length.
•
Both—Provides both expansive and contractive
force, depending on the variation from Relaxed
Hgt.
Enable Nonlinearity—When on, the compression
and extension of the spring are non-linear, based
on the assumption that a spring has physical
limits to the amount it can stretch or contract.
Thus, t he further t he spring gets from the Relaxed
Hgt setting, the less linear the feedback. The
non-linear compression is calculated using the
relationship between the coil dimensions, wire
diameter, and length. Extension compares the
relationship between the wire diameter and overall
spring diameter.
Creat ing Syst e m s
Create panel > Systems
Asystemcombinesobjects,linkages,and
controllers to produce an object set that has a
behavior, as well as geomet ry. Systems help you
create animations that would be much more
difficult or time-consuming to produce using
features independently. Systems can range from
simple object generators to full-scale subsystem
programs.
• Bones (page 1–381) creates a hierarchically
linked set of bones and joints.
You can transform and animate bones using
both forward and inverse kinematics. See
Animating with Forward Kinematics (page
2–408)
and Inverse Kinematics (IK) (page
2–417)
.
•
Ring Arr ay (page 1–392) creates a ring of boxes.
•
Sunlight (page 1–394) creates and animates a
directional light that follows the geographically
correct ang le and movement of the sun over the
earth at a given location.