8

IK Solvers 423
to define a direction for rotation, so the elbow
or knees bend correctly.
•
HD (History-Dependent) Solver (page 2–442)
The HD Solver is a solver well-suited to use
for animat ing machines, especially ones with
sliding parts that require I K animation. It lets
you set up joint limits and precedence. It has
performance problems on long sequences, so
ideally use it on short animation sequences. It
is good for animating machines, especially ones
with sliding parts.
Because this s olver’s algorithm is history
dependent,itworksbestforshortanimation
sequences. The later in the sequence it is
solving, the longer it takes to calculate a
solution. It allows you to bind the end effector
to a follow object, and it uses a system of
precedence and damping to define the joint
parameters. It allows for sliding joint limits
combined with IK animation, unlike the H I IK
solver, which only allows for sliding joint limits
when using FK movement.
•
IK Limb Solver (page 2–454)
The IK Limb s olver operates on only two bones
inachain.Itisananalyticalsolverthatisfastin
viewports, and can animate the arms and legs
of a character.
TheIKLimbsolvercanbeusedforexportto
game engines.
Becausethissolver’salgorithmis
history-independent, it is fast to use
regardless of how many frames of animation
areinvolved. Itsspeedisthesameonframe
2000 as it is on frame 10. It is stable and
jitter-free in viewp orts. This solver creates a
goal and an end effector (although the display
of end effector is off by default). It uses a
swivel
angle (page 2–430)
to adjust the solver plane to
position the elbow or the knee. You can target
the swivel angle to an another object to animate
it. IK Limb Solver also uses a pref erred angle
to define a direction for rotation, so the elb ow
or knees bend correctly. It also allows you to
switch between IK and FK by keyframing IK
Enabling, and it has a special IK for FK pose
function so you can use IK to set FK keys.
•
Spline IK Solver (p age 2–455)
TheSplineIKsolverusesasplinetodetermine
the curvature of a series of bones or other
linked objects.
Vertices on a Spline IK spline are called
nodes .
Like ver tices, the nodes can be moved and
animated to change the curv ature of the spline.
Thenumberofsplinenodescanbefewerthan
the number of bones. This provides the ease
of pos ing or animating a long multiple-bone
structure with just a few nodes, as opposed to
animating each bone individually.
SplineIKprovidesamoreflexibleanimation
system than other IK solvers. Nodes can be
move d anywhere in 3D sp ace, so the lin ked
structure can be intricately shaped.
A helper object is automatically placed at each
node when Spline IK is assigned. Each node is
linked to its corresponding helper, so a node
can be moved by mov ing the helper. Unlike the
HI Solver, the Spline IK system does not use
a goal. The positions of nodes in 3D space is
the only factor that determines the shape of the
linked structure. Rotating or scaling nodes has
noeffectonthesplineorstructure.
Note: 3ds Max also provides two other methods
of inverse kinematic manipulation of hierarchies,
which don’t depend on a solver:
Interactive IK
(page 2–462)
and Applied IK (page 2–464) .
IK with Bones
While you can apply an IK solver to any hierarchy
of objects, a system of
Bones (page 1–381)
combined with an IK solver is a good way to
animate a character.