Ik + Fk

Hi i am starting to rig my dude and i was wondering which was better. IK or FK…i have been reading the FK is better on hands and IK on legs or the walking…You guys think this is true? and reasons?

thanks for your thoughts

I would suggest making an IK/FK slider so you can use both. Though if you don’t like that method, I would agree with what you said. IK is better for the legs and FK for the hands.
When people walk, usually their legs move in the same way all the time and it resembles the motion of an Ik chain. However people are a lot more creative with their arms, they move them in a larger variety of ways.

Both are necessary of course… rather than arguing why I’d say : get one of the many rigs that are available for Blender and do some animation with them to get a sense of what is needed, why they work well and why they don’t.
If you can, download or buy Mancandy FAQ . Of course I have a bias because I had such a great impression of Bassam when I met him years ago but it is good, very good.


Neither is really better, they just work in different ways. Ideally, there is a way to switch between the two seamlessly.

FK produces arcs by default, and arcs are the way we move. That’s why arcs are a crucial ingredient in good animation. We are always weaving those important arcs into every action.

IK on the other hand, does not produce arcs by default. If you key an IK target in two different locations, you will see that the IK target follows the shortest path between the two keys, ie a straight line.

There are several factors that make IK useful however. When you need to fix the end of a chain in place, IK comes to the rescue. This is why we use IK on the legs. The feet need to be locked to the ground. But our feet still need to move in arcs, so we need to make those arcs manually, by creating keys in the right places. It takes a bit more work to get the arcs, but it’s a small price to pay for having our feet nicely locked in place.

Sometimes IK is also good for posing limbs quickly, especially when the position of the end of the chain is important, for example picking up a cup. The hand needs to line up with the cup before we can grab it. IK can be a quick way of getting the hand into the right place. With FK, you would have to rotate each bone in the chain.

There may be other important differences between IK/FK that I’m not aware of. I think these are the main ones though.

Evrything depend of what kind of movment you wanna reproduce, for fights for example, the ideal, is to have boths becaus if your dude does a front kick, it’s better to use FK system, but when he just have to move without jumping or anything else, the IK are the best…
The concept to have the both (i can’t give details cause i’m a newbie with Blender…), for ONE leg for example : You have three Armature legs, 1 with The IK system, 1 with the FK system, and 1 which wille be used for the skinning, on bones of this last, there is a Rotation_constraint to the IK system, and a Rotation_constraint to The FK system, then you have to set a swicth. It will be The IK and FK armatures which will be animated… here is the concept , godd luck :stuck_out_tongue: