Fk Controllers - Scaling

[bashesen]

okay, say I got a (non-straight) joint chain (joint1, joint2 and jointEnd)

Then I have 2 controllers outside the chain (controller1 and controller2)

I want the controllers to stay attached to the chain and controll the chain. The method I used sofar would be that I first group the controllers (controller1 would be grouped under controller1_GRP and controller2 would be grouped under controller2_GRP)

so the hierarchy is as follows:

CODE
joint1
-joint2
  -jointEnd

controller1_GRP
-controller1
controller2_GRP
-controller2

next I add 2 pointConstraints
joint1 > controller1_GRP
joint2 > controller2_GRP

these make sure the controllers stick to their joints.

then I add 1 orientConstraint
joint1 > controller2_GRP
to make sure the controller is aimed in the right direction.

last, to drive the joints, 2 orientConstraints:
controller1 > joint1
controller2 > joint2

Now here`s my problem. Everyting works fine when I rotate the controllers, but when I try to scale joint1, joint2 bends a little.

I can`t figure out why exactly it is doing this or how to fix it. Hope someone can help me make sense of this.

thanks

[uiron]

some links to help you out/understand the problem
http://www.highend3d.com/boards/index.php?showtopic=255463
http://forums.cgsociety.org/showthread.php...617#post5798617 (thread originaly on another topic, but some usefull info on constraints+scale, some workarounds as well)

[joojaa]

Actually now that i have tought a bit on this its clear:

Yes see joints dont work with scale. They represent sort of vertical struts that have a given length if you scale a joint it scales that section but not the next. Whereas a transform scales BOTH, in a ways this is not a big problem you can allways use a trasform instead of a joint, youd loose teh ability for maya to show a nice joint tough. In all other respects trasforms would do the same thing, yes you can even have ik on them just no labels.

This si the same reason why you cant just grab the base joint of a sceleton and scale it all up, but need a extra group in between. So they bend because the bone actually is bending even tough its matrix is not. *

You could also use aim constraints that aims along the bone isntead of orient constraints orient just reads the matrix values as siad but that is not what the bone is doing.

Are you guys trying to do this rig where you actually have 2 bones for the forearm by any chance? Theres a even easier thrik for that. You can eliminate 1/2 of your constraints form just eating up computation time and causing all sorts of interpolation issues.

• by the way this works differently in older mayas.

[bashesen]

thank you for you quick replies. I`ve quickly tested using aimConstraints in stead of orient and that seems to work fine. guess it was that matrix thing that the orient uses to calculate the output. Still, because joints omit some part of the total transformations (by scale compensate) while still feeding the data through to constraints makes it a bit untransparant...

[joojaa]

Its not actually omitting anything. The constraint node ASSUMES something about the transform, without this assumption it wouldnt work at all. Its just not a universal thing you can not assume constraints work under all possible circumstances all things have boundary conditions in this case that its actually ot within that boundary.

So you can assume constraints work under normal transforms, all else kind of sidesteps what they were meant to do. They MIGHT work in all other types. Any custom trasform type and all deals are off.