View Full Version : Basic Bone IK FK Blend problem. IK Handle is following the Bone?

08 August 2007, 06:36 PM
Now i am having a bit of trouble. So far everything in this DT Character Setup DVD has made sense, and my migration from XSI is going well (same concepts, etc), however i cannot seem to make my IK FK Blend work the same as the DT one. Im not sure if its a difference of Maya versions.. but to the best i can tell im following exactly what he does.

The problem, is simply getting IK/FK blending working on bones. The way it seems on the DT DVD, is that he basically takes two bones, puts an RP IK handle on them, and then point constraint the IK Handle to a Control of some sort.

Now up to this point i follow exactly, however, when he turns FK on (by disabling IK in the IK Handle), and rotates the joints, it appears as if the IK Handle stays with the Control, so that when you blend back to IK, you go where the IK Handle is. That is not the way it is for me.. For me, when i turn FK on, and rotate the bones, the IK Handle follows, and when i turn IK back on, hoping for it to "blend", it just sort of snaps weirdly but doesn't move, because the IK Handle followed the FK Bones.

Anyone have any idea whats causing this? Or what i am doing wrong?

Just to make it more clear, here are my steps to make the IK/FK Blend:
1.) Draw three joints in a small arc.
2.) Activate the IK Handle, hit Reset to make sure theres no weird settings, then Draw it from the first to the last joint.
3.) Create a Polygon Cube and snap it to the last joint.
4.) Select the Cube, then the IK Handle, and apply a point constraint. And for fun, test it to make sure it works.
5.) Now select the IK Handle, and under its IK Blend attribute, change it to zero.
6.) Now the bones are green (FK mode correct?), grab the 2nd joint and rotate it.

Here is where i think i screwed up, because the IK Handle follows the joint i just rotated. I can go in further, and drag the IK Blend attribute back up to "1", and it does not blend anywhere, it does not even move. Remember, its still point constrained. It only moved now, when i select the Cube and slightly move it, then the IK Handle Snaps back to the Cube.


08 August 2007, 03:13 PM
No one?
I had a little bit of success if i turn off "Snap" (Even though my Digital Tutors example file does not have snap off..), so now i can almost have it working. The problem is, now it flickers while blending IK/FK.. this is driving me nuts.

08 August 2007, 04:11 PM
Hah! I don't want to speak too soon, but i believe i figured it out. So for any future searchers:

1.) The problem of the IK Handle staying behind, is simply the Snap function. The documentation says it allows the IK Handle to follow the bones, exactly opposite of what you want in the IK/FK Setup.

2.) The problem of the blend popping, is some weird solving problem. No idea why, but if you use the IK Blend attrib, inside the attrib panel (not the channel box), and adjust the slider very slowly you get IK Popping. This must have something to do with the depth of the float values being used. ie, its using 0.119, 0.556, 0.887, etc. Instead, if you use the channel box, you don't get as smooth of anim (less room to slide), but you don't get the popping. So if you set a 0-10 value attrib to drive the IK Blend value, you then get buttery smooth IK Blending.

Hope this helps someone in the future.. and i hope im right about what i said above.. heh

08 August 2007, 02:09 PM
hi Zeusbwr,

In maya, if u do not key, constrain or parent ik or the joints to any of the controllers then the ik will always follow fk and fk follows ik ( its the initial stage where we create a bone chain and put ik handle, the minute we key or constrain or parent something - the thing will not work the way we want it) - but this is not what we want, we would like to have controllers controlling the handle and joints...

We need a fk ik rig which has the facility to switch between each other when ever we need (like the way we have it for max biped - in fact in max biped the fk follows the ik and ik follows the fk all the time, so switching between them is just a button click away, but biped has a few demerits too )

TTBOMK - ( pls correct me if i m wrong ) there is this ik blend issue and is there since a long time and if there is a solution to that problem by now autodesk might have addressed it and they would have reassured that its made userfriendly and documented well too... I have not tested this in 8.0 and + ! I guess it was originally done to work with joints direcly and some move fk to ik and move ik to fk tools were given by maya in later versions (7+) ... But normally riggers use curve controls and a 2d kind off scripted set of buttons to select those curves controls and the ik blend attribute does not suit our workflow or most of the custom workflows ... :(

One can get away with some work arounds, well almost none of us actually need a "blend" attr cause in any cause the interpolation might not be similar to what we want through the frame range - so snap is used and preffered 99% .... ( u can write expressions, scriptjobs, mel buttons etc to do this )

there are so many scripts available on highend3d for this and they would get u started ...

If u ck out some of the autodesk learning dvd's last year, they have not used blend attr (if i remember correctly) - even jason used a script to fix that pop which he was getting when he tried swiching between kinematics... Maybe we can ask someone to be sure, you can contact autodesk for this issue and ask - why have ikblend attr, what was it originally designed for, how does it help in production rigs, what method should i follow to use it, etc. If all of it is answered well - pls share it here, lets formulate a workflow which suits ik blend which also sounds production ready...

The minute ik blend works, no need to put three bone chain, no need to have a expression ( or scriptjob or mel button ) for switching between them. If they have stretch and squash in ik with different options then even setting up those things can be avoided... the rigs are alot liter and its from autodesk maya itself, so we can brag about it and use it....

there are some issues with constrains as well - when it comes to animators - the workflow is not easy with - so many things has to be done even with so many scripts .... lets dicuss this in a differnet thread if ur interested....

reg, sriram

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