View Full Version : Full Body IK Roll Joints?

01 January 2006, 12:37 PM
Anyone know how the roll joints in full body IK works?

I looked at the biped sample and when I rotate the wrist e.g. 20 degrees, what happens is that the ForeArm joint gets the full rotation - the ForeArmRoll doesn't get any. I would have expected the roll joint to get half the rotation and the ForeArm not to get any, but maybe I've misunderstood something.


01 January 2006, 11:20 PM
posted the same thing here:
just discovered this problem and it's frustratingly undocumented. all there is about FBIK in Maya's docs is very light... they don't say anything about the roll (apart from the fact that it exists and you activate it by simply typing the correct stuff), like it's just supposed to work well automatically. but it doesn't - not on my skeleton, not on the FBIK example. I can't understand what's wrong with the roll in FBIK but I really need to find out about this asap. does anybody know???

02 February 2006, 06:19 PM

just wondering if there had been any progress on this.

I have just started using the FB rig in maya... I have 'played' with the referance rig and have also created my own from scratch however I am having some horrible elbow rotation when rotating forearm/wrist. The arm almost twists into nothing around the elbow at only a small 30degree angle.

I have tried painting weights to solve the problem, but to no avail. It looks more like a problem to do with the actual FB controll in Maya 7.

Does anyone know of a fix or workaround to this problem!

Really could use any help.

Thanks in advanced.


02 February 2006, 07:20 PM
Let me apologize in advance if this doesn't help you. But in Motionbuilder there is a setting called Roll Extraction Mode... which I think has the attributes to say what percentage is being used on the roll joints. Perhaps Maya's version of fbik has the same setting.

...I just did a search for hikHandle in maya docs and came across Roll Attributes. Perhaps in these docs you can find your answer. Also try a maya doc search for Roll Extraction Mode.

02 February 2006, 07:45 PM
My suggestion is to bind your mesh to a 'bind' skeleton, NOT the FBIK rig. It's never a good idea to have the 'rig' skeleton as a deformation skeleton as well. Use the FBIK as a control skeleton and all your deformations on the 'bind' skeleton. That way you can set up custom controllers and deformers without having to deal with whatever the rig is doing.

02 February 2006, 09:08 PM
Thanks for the different suggestions ;)

I agree that using a separate bind skeleton is probably the best. I just noticed that there actually were roll joints in the biped sample, and was confused to see the way they worked (or rather didn't work).

I also saw that this months downloadable DVD on the Alias silver community is about Full Body IK ... maybe that would be worth a look.


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02 February 2006, 09:08 PM
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