View Full Version : SplineIK - twisting bone - why ?? Help ..

01-30-2006, 09:05 AM
hello ppl,...

been working on this for a while - regular joint chain (+y, aiming down the child n +Z up), with spline IK on it, cluster the curve, have them parented to Ctrl_Curves. i have attached a sample file(.ma file).. in which i have a COG curve, shoulder, mid_neck & head curves. i know you must be familiar with this method..

my problem is, when i try rotate my COG in y, in either direction, my neck bones kinda twist ??! ggrrrrr..........#@$@()*()*&%^%%^&% .. grrr.....

i have the local rotation axis visible.. you check them..in the .ma file... in rotateX, its stable.. can anyone tell me why this happens ?

now i tried these too : i know my bone chains r having +Y aiming towards the child...but, i tried doing the same setup on a bone-chain, with +X aiming down the child.. it happens in that too.. but in this second case, i select the splineIK handle, in the advanced twist attributes, when i put it to scene UP > +Y , the flip is controlled ...

i noticed that in my chain with +Y aiming down, when my COG is rotated -90, and on the splineIK, i make the roll to 45, the bone's twist is nullified.. at COG > RY = 90, roll shud be -45 ... but at COG.ry = (- or +) 180, roll has to be 180 , and at COG.ry = (- or +) 360, roll shud be 0. i cud'nt deduce any relation or ratio kinda pattern from these values..

is this a problem with the splineIK or with my method itself ? or is it that splineIK needs the bone chains to be having +X aiming down, only ? is this anyway connected to limitation of the adv,twist attributes, which work only on the bone chains with +X aiming down ?

but the same setup , i have on my spine area, which works fine.. but same setup on the neck.. is giving me the problem. how many times i tried to reproduce it, it always, twists.. can any one guide me what could be happening wrong ?

01-30-2006, 09:00 PM
is there a reason not to just use x down and advanced twist controls to aim at an object that is parented to the control?

BTW, its flipping because you are changing the shape of the curve (with clusters) . NOT rotating it...
so they are just trying to point in the same direction, as you are not telling it to do otherwise...


01-31-2006, 07:30 AM

cant really say why. but by adding a joint on top of the Neck joint and parent constraining with the COG solves the problem.

01-31-2006, 08:31 AM
hello maverickkk,,....

hi man.. yes, ur trick worked.. thanx alot... but can u tell me why , this works ?

hi john_homer,

well, actually its that i used the +y pointing down.... in the rigs. i can change to +x and fix the neck.. rig.. but u know.. have to redo in a whole lot of files.. ( i'm not on referencing yet :-( )

so now this trick of maverickk works... but here, my splineIK 's curve is still outside my hirarchy right ? then its still like the curve is still being just manipulated with the clusters.. but it works ?

but i think i kinda got another solution to the problem, with out the constraints and the extra bone.. in the sample file, when i parent the neck_01 to the shoulder_ctrl, it is solved ! i did the same thing in my rig, and that seems to have solved it...

thanx for the replies guys, that solved it !

btw: maverickkk, which place u r in bangalore ? i'm also in bangalore ...

01-31-2006, 09:46 PM
heed the words of john when working with splineIK ash... advanced twist controls are about the only way to wrangle splineIK into any workable fashion..


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