A three-joint IK/FK chain with a pole vector and pin: the base building block for any bending limb.
What it does
FK and IK on a 3-joint chain, with a blend
SimpleIK takes a 3-joint chain (shoulder-elbow-wrist or hip-knee-ankle) and gives it FK and IK control with a switch to blend between them.
You get, per chain:
FK control per joint
IK control at the end joint
Pole vector for the elbow's bend direction
Switch control carrying the blend slider
When to use it
A generic bending limb, no limb-specific extras
Use SimpleIK for any generic 3-joint bending limb that needs an IK/FK switch and pole vector, without limb-specific extras.
SimpleIK
Generic bending limb. Also the foundation the others build on.
IK Arm
Built on SimpleIK, with arm-specific extras.
IK Leg
Built on SimpleIK, with foot-specific extras.
Stretchy is optional
The chain can extend past rest length in IK mode: stretch only, no squash.
Pole vector pin
The pole vector control has a pin slider that locks the elbow exactly under it.
Match, don't pop
Match to IK / Match to FK hold the pose through the switch; plain Switch can pop.
One unbroken chain
The 3 joints must be one unbroken parent chain, no branching.