Rigging and Skinning - Animating with Blender: How to Create Short Animations from Start to Finish - page 140

single bone in the chain that would most benefi t from it, seeing how that affects the chain's overall motion
and proceeding from there. If you want to get this deep into the IK system, it's best to only change one thing
at a time, experiment, then go back and readjust.

In the end, the only way to tell if your settings pro-
duce the desired results are to attempt to place the
character into different poses. Carefully constructed
limits and locks in an IK chain will dramatically
increase the realism of your rig and reduce the time it
takes you to make your poses look good. On the other
hand, bad settings here can ruin an otherwise good rig.
Remember, you want your rig to work for you. You
don't want to have to fi ght it every step of the way.

The last IK parameter we'll discuss for now is called
Chain Length . The Chain Length property is found
on the constraint itself in the Constraints panel, as seen
in Figure 9.20. Chain Length tells the IK solver how
far up the bone chain to continue its effects. A length
of 1 will only affect the constrained bone itself. A
length of 2 affects the constrained bone and the
next one up the chain. The IK solution will go
as far as the highest bone in the entire parent—
child hierarchy if you let it, including the master
bone! Chain lengths need to be adjusted care-
fully so that the effects of your IK solver don't
extend too far.

Figure 9.20 The Chain Length parameter of an IK constraint

New IK constraints are created with the chain
length set to 0. The 0 length signals that the
IK effect should extend as far up the chain as
possible. Unless you have an animation death
wish, the fi rst thing you should do when you
create a new IK constraint is to change the
chain length to something reasonable. It is
usually best to stop the infl uence of IK on the
last connected bone of your chain.

LENGTH : 2 LENGTH : 4 LENGTH : 5

Figure 9.21 This shows the mother rig with three different values for
chain lengths of the leg IK chain. Obviously, some settings are better than
others

When multiple IK chains affect the same bones,
the result can be pleasing when manipulating and posing, but it can cause problems if not managed carefully
during keyframed animation. For example, if both leg chains in the mother rig are allowed to affect the base of
the spine, moving a single foot will affect the positioning of the entire rig, including the other leg. Unless you
are generating some extreme motion, it's probably better to keep IK effects isolated to their own limbs.