IKs and FKs

Inverse Kinematic's and Forward Kinematic's are both different methods of control and movement.

The definition I have gotten from class on IK's and FK's are

Inverse Kinematics (IK): A form motion manipulation that indirectly affects driver transform(s) based on the movement of a target effector(s)

Forward Kinematic (FK): A form of motion manipulation where a driver transform directly influences a driven transform.

It's good to setup both an IK and an FK system for your rig, rather than simply having just one, as they both have their strengths and uses. It can also be a matter of personal preference.

When dealing with an FK system, for example if you create one for a leg, it would allow you to move the leg limb by limb. Allowing you to adjust the knee separately from the thigh or from the ankle.

While with an IK system, you would only have on control, which would typically be located around the bottom of the foot, or possibly around the ankle, when dealing with a leg. It would allow you to move the entire leg by that one control.

I personally have come to prefer an FK system when it comes to legs and an IK system when it comes to Arms.

However, it isn't just limbs that can use IK's and FK's, as they can be used pretty much almost anywhere else.

When having both an IK and FK system, it's good to include a Switch Control. This way everything is not just out there in a jumbled confusing mess. This is done through SDK's, and allows you to switch the visibility between the two, so you can use whichever system you'd like whenever.