View Full Version : Arm IK/FK switch -- It is important?

01 January 2003, 12:33 PM
Is important my rig setup contain IK/Fk switch for arm?
As I read around the forums its "standart" for rigging arm, but when I have only IK in my rig and there is no problem when I animate.
So, why it is? What it is important for?In what cases?

Thanks, diak

01 January 2003, 06:48 PM
Most people don't like animating the arms with IK. So they end up using FK most of the time.

The thing is that there are times that you need IK (grabing things, etc) so you want to have IK for those cases.

I would say that if you are comfortable with IK, then keep it that way. or if you use FK and you don't need to grab anything or do any of the IK things, then just have FK on the arms and that's it.

I like to have the option of changing from one to the other if I have needs for it on the fly, that's why I usually include both in my rigs


01 January 2003, 06:58 PM
Thanks a lot.
I seen a tutorial on your web, so one question. It seems to be unnecessary dificult. Why enable solver ON/Off is not enough?

... note... your tutorials are great and helped me a lot!


01 January 2003, 01:00 AM
Yes, i think it's very mportant if and only if it works well. I hate using the blending systems as your animating the blend on top of everything else. If there's a system thats seamless transition then cool, otherwise have two diferent rigs.


01 January 2003, 01:07 AM
the problem with turning the solver on and off is that your animation can and probably will pop.

If you can do a smooth transition over time, (say even a few frames) then you won't have the pop problem.

And yes.. like eek mentioned, most of the time it's better to have two different rigs, but there are times when you want to do the transition on the same shot and then it's when it's nice to have the option.


01 January 2003, 11:01 AM
Aha, thanks for explanation. Maybe I should make my arm ik fk switch a bit difficult -- I must go deep into your tutor and learn something more

01 January 2003, 12:12 PM
I just hate those, slidy weighted blend things! EEEKK! maybe I should start another research thread on this? no ones truly every had a seemless transition rig.


01 January 2003, 05:17 PM
u can switch this way:

create 3 arms (of bones). they are all going to be used for one arm.

one arm for IK
another for fk
and a last that can blend between the two others.

01 January 2003, 05:48 PM
We use IK/FK blendable arms on all our characters in Jimmy Neutron. Usually the animator will just turn IK or FK on for the entire shot, but sometimes blending within a shot is needed. In general, it's not THAT difficult to set up.

There are other areas where switchable controls are also desireable. IK/FK blendable legs and IK/FK blendable spines/tails are also sometimes desireable. Blending eyes between a local target and a world target is useful. Blending the head between FK positioning and tracking a target can be useful. Even having a rig where you have IK/FK blendable fingers could be useful at times. The thing you have to be careful of though is that each additional level of control you add in can slow the rig down.

If you are adept at scripting, another approach is to have a basic rig in place that you load into each shot, but then you have several scripts you can run to build additional layers of control on top of the basic rig. So if you needed IK/FK fingers for three fingers on the left hand to pull off a certain shot, you could load the IK/FK controls for just those fingers onto the rig for just that shot. The good part of this is that you don't have to store and update several slightly different versions of your rig. The bad part is that it can be a bit more difficult to write a script to set up the alternate controls than it is to just build another version of the rig from the base rig. Also this can introduce bugs into the rig setup because the alternate versions likely won't be tested as much as the base rig, or some additional controls could interfere with other additional controls.

Yet another option is to have a modular rig. It is easier to do this for objects that have joints or seams where you can hide the connections between the different loaded parts. So for example you could have a torso that has FK, a torso with IK, an FK left arm, an FK right arm, an IK left arm, an IK right arm, an FK/IK blendable left arm, etc. Then you would add the character to the scene a piece at a time, and probably use scripts to attach the various pieces together. This works really well with robots who have different attachments for arms, etc.

This technique can also be useful if you have characters that require clothing changes. Imagine that you have your base rig with the torso and arm bones and everything. This is what you animate. Then let's say you have a shirt rigged and weighted to its own set of torso and arm bones. Then to put that shirt on the character, you'd load in the shirt rig, and run a script that would constrain the shirt's bones to the rig's bones. Then the shirt would move with the rig. Hmmmm.... just thinking out loud here.... I think I'm going to have to explore that approach sometime.... :wip:

Ok, enough typing for now.... gotta go...

Michael Duffy

01 January 2003, 06:53 PM

Nice explanations. I've been thinking of doing the script thing for a while.. have the bones all weighted and then just run a script on top for the controllers that I need.

I like your idea of the clothes and constraining things on top.

Here with the game I'm working on, we had 4 characters doing the same thing, so we animated one, brought in the other, had a script that would constrain one to the other and the hide hide the original and that's done.. it was nice and easy.. ( a little bit messy on the hypergraph, but it's all good) :)


01 January 2003, 12:32 PM
oh, good comments and explanations.

So, if I well understand, theres no simple set up for switch them.
And if, it behave bad - pops and so... Could I set up it without difficult scripting?
Maybe do it according to your tut, goosh, would be good way for me.

Oh, and another question...
what poses are critical for gir setup? When I rig character, then I animate them with simple movements and poses, where it work correctly but then I can suddenly came across with critical pose and find out, that rig is setup in wrong way. And all remake again.
So, what poses I could try, when Im rigging skeleton?


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