View Full Version : Stretchy Spline Help!

04 April 2010, 03:50 PM
stretchy spine is not stretching!!

i dont understand why, i set the local rotation axis correctly on the joint chain, made all the seemingly right constraints, and wrote out the proper expression


// Veritcal Scale

$vScale = div_sp01.arc_scale/globalScale01.scaleY;

bn_spA01.scaleX = bn_spB01.scaleX = bn_spC01.scaleX = $vScale;


i didnt get any errors after writing the expression but when i try and move the chest control, the spine does not stretch with it. instead the chest joints move along with the spline curve, leaving the spline joints and spline ik behind

i dont know if it has anything to do with it but when i made the info node for the curve my arc length value was greyed out and was not selectable.

if anybody can help out or have any suggestions, it would be very appreciated :wavey:

also i attached some extras screens showcasing some more relevant information

thank you in advanced

p.s. stretchy limbs seem to be working okey! :thumbsup:

04 April 2010, 03:53 PM
i added 3 more attachments to better get an idea of the problem

04 April 2010, 03:58 PM
Without seeing the file, I can only offer places to look and suggestions on what may be causing the issue.

Chances are that you have a bad constraint (control object moving the bone instead of the cluster, or a cluster moving a bone instead of a CV) This is usually the culprit. But without seeing the file I can't say for certain.

I would however warn you off from using expressions to do this. Its terribly ineffecient, that's not to say that you can't it is perfectly do-able.

As for the curve info Length you should just be able to select the Curve in the Outliner, then in the MEL Command Line enter arclen -ch 1; This turns on the construction history for the curve. More importantly it allows you to see the length of the cruve, measured in the current units.

I am not sure if you have seen the stretchy spine tutorial or not, which is only using Nodes.

04 April 2010, 04:46 PM
oh mah gooosh! thanks for the tutorial my man!!!

i'll definitely give it a shot if i cant get this expression to run proper :bowdown:

04 April 2010, 07:44 PM
i tried the node tutorial and it worked pretty good. :buttrock:

still fighting with the expression though, i wanna figure this one out before i try a new technique

im attaching the file incase anybody wants to take a peek at it and offer any suggestions.


05 May 2010, 07:30 PM
I am not sure if you have seen the stretchy spine tutorial or not, which is only using Nodes.

i used your stretchy spine tutorial on my character and its working like a charm but the joints aren't scaling with the rest of the character. it translates and rotates just fine but when you scale it up the joints stretch out in the Y, but only with the stretch attribute set to 1. when the attribute is set to 0 it scales perfectly but obviously no stretch.

i cant figure out how to make it scale with the rest of the joints and controls :banghead:

i attached a copy of the file in case that helps

p.s. the stretch attribute is on the cc_back01 control curve.

05 May 2010, 07:41 PM
will take a look at this later tonight once I get home. In central Time zone. So it will be 3 hours or so from now.

05 May 2010, 08:37 PM
mighty fine of you good sir :bowdown:

thank you X's 1,000,000!!!

05 May 2010, 05:38 AM
whew.. OK where to start....

First... your making this rig waaaaay more complicated than it needs to be. You have several issues that you may not quite yet see that your having, that will come back to bite you later.

Some of these are typical student errors. I used to see them all the time when teaching. You have a ton of joints that are not doing you any good at all in the scene. Stacking joints leads to a lot of hidden issues that will cause problems down the road. Use Groups inplace of another joint. It saves you time, energy and fustration.

I put your rig and my revamped portions in the same file so you could see what I was doing. Typically I parent the clavicals to the chest/ribcage however this is an instance of breaking a rule but knowing why. The reason I am breaking this rule and parenting to the sternum to take to clavicals out of the stretching heirarchy. This makes things cleaner and easier to deal with in the long run.

I cleaned up the Feet, again you should not stack joints unless there is a very specific reason to do so.

You should be able to take a look at what I have done, use the Hypershader and reverse engineer those things. Also pay attenetion to the Heirarchy and what is going on there.

05 May 2010, 07:22 PM
You should be able to take a look at what I have done, use the Hypershader and reverse engineer those things. Also pay attenetion to the Heirarchy and what is going on there.

thanks for the pointers meng, you really simplified things nice and proper like!
its really interesting how you used the ik handles to rig the foot controls. i been picking apart pieces of the rig all day. :cool:
really appreciate the bit of learning reference

one thing i still cant figure out for the life of me, is how to uniformly scale the rig,

and it seems to not be rotating on the Y axis either.

i think i need the rigging dojo :argh:

thanks again for you help though

peace and blessings!

05 May 2010, 07:36 PM
Once everything is grouped correctly you should be able to scale the rig up cleanly via the global control.

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