View Full Version : Basic bone question

01-25-2008, 02:49 PM
I have a few bends that I have to animate in a 30-bone chain. Is there a way to rotate a joint down the chain first and then use the same joint to rotate up the chain? I've tried IK and IK boost, but it doesn't seem to be effective for this kind of move.

In the attached jpg, I want to use bone 3 to rotate bones on the left downward. Then somehow get the bones on the right to rotate WITHOUT moving the bones in position on the left. Thanks.

01-25-2008, 03:07 PM
you could do it like this, and many other ways.

01-25-2008, 03:15 PM
As far as I know, you can do this using Relativity Motion modifier, and you cannot use IK.

Using 2 nulls, you can set the first bone and the joint bone to use Relativity Motion modifier. In relativity, use the Dr. Target for these nulls. Make sure you activate "Explicit WC (World Coordinates)" and AFTERIK.

i've attached a small screenshot.

You also have to turn on Relativity and the Interactive Relativity to see it interactively.

Lightwave runs into problems since it doesn't save information from a motion modifier on object up the heirarchy chain. Makes me mad when I encounter this. Relativity does its own calculation. I once had to write a plugin to solve this problem using quaternions. This problem is one of the biggest limiting factors to Lightwave's Character Animation abilities, IMHO.

01-25-2008, 03:20 PM

So, with 30 or 40 bones, would I need to make a separate rig with interspersed nulls? And with some bones facing one way and some the other?


Does every other bone have to have this applied in order to get complex bends?

01-25-2008, 03:37 PM
Does every other bone have to have this applied in order to get complex bends?

Short answer: Yes.

Long Answer: This is why I am mad at Relativity. It's not UI elegant. It doesn't allow SDK. Thus problems, so I wrote my own plugin which has morphed into RigMaster (which is an even longer answer).

I believe the type of rig you want is an IK Spine.
You will have to become with the PLG_IK plugins i believe....


01-25-2008, 03:44 PM
Yeah, I thought what you were trying to achieve was as simple as your drawing. Thats what your post made it sound like. If you want to have long bone chain with the ability to bend any joint in both directions you will not want to do it that way! I will mess with it for a minute and see if I can come up with something. What exactly are you trying to do?

01-25-2008, 03:57 PM
MedArt dude, are you still trying to do this?? I used IK and two goals. the middle goal is 0.5 strength. My heading stiffness is 5.0.

01-25-2008, 09:21 PM
I hadn't thought of using bone strength. Do you have 2 goals for the first bone in your sample? Thanks.

dccpro: I'm trying to get loops to grow and bend in relation to some other objects in the scene. A few bones are linear then they make an S-curve and then a C-curve, etc. I've tried using a bunch of plugins but I'm now back to bone basics trying to get this done.

At this point it's like being the clown at the fair who twists long balloons into poodle shapes. I may have to manipulate the curves off camera and then snap them into place. I just don't know enough yet...

01-26-2008, 02:50 PM
I just tried to make a caterpillar walk using two goals, and it seems I get a lot of flipping using multiple goals. So maybe it's not an ideal solution.

If you have to do twisting and everything, and cannot cheat it using endomorphs or bend deformers, then I do suggest PLG_IK spine plugins to help. The above link to SpinQuad.com also has a video on how a fella did it.

p.s. i would say this topic is beyond "basic bone question" as the thread heading suggests :)

01-26-2008, 02:58 PM
"i would say this topic is beyond "basic bone question" as the thread heading suggests" (AdamRW)

Yep, I hoped it was a basic bone question. Thought I was just missing something.

I originally tried this chanin with 10 goals and IK and had the same results as you described. Thing moved smoothly but not accurately.

01-26-2008, 03:00 PM
you may be able to use a 2 point poly chain and socky monkey on each point then use the method that caveman used in this tutorial...http://www.newtek.com/forums/showthread.php?t=77259

01-26-2008, 03:51 PM
PLG-Ik spine tutorial was helpful to watch. SplineGod had recommended it before (in another thread) but I couldn't figure out how to use it properly. I don't fully see the advantage of it over IK boost at the moment--at least for what I'm doing. Looks like a load ofsettingsscattered between windows--not sure I'll be able to make good use of it.

2-point poly tuotorial was interesting, too. Thanks. I may go back to trying Trailer plug-in which seems to be similar.

01-27-2008, 10:24 AM
Does anyone know how I could replace my rig with a new one shown below? I've got one end of my bone chain shaped and moving, but it would be great to swap out my rig with the new one, which would facilitate adjusting the other end. Is there a good way to do that without losing what's done? Could I delete the bones and just redraw them in the new direction? (Turning off "allow deformation") I'm assuming there will be many problems, so I'm asking first. Thanks.

01-27-2008, 11:13 AM
Yes deleting and creating new bones should be fine. Imho, LW bones allow a very flexible and open workflow. If you know what your doing, you seldom have to redo anything, but can add to and tweak what you already got. You don't even have to turn off deformations. That is just a recommendation so the mesh stays still while you tweak the bones into place. Either way you still need to Record Bone Rest Position once you're happy with the bone placement. Turning Deformations on right before resting might be an eye-opener for those who still haven't fully understood why and when they need to rerest.

When it comes to bones in LW, I'd say "Just do it!".

Using the "Use bones from Object" option you could even test out several different bone setups. But might be complicating thing for now. :)

01-27-2008, 11:44 AM
Thanks, Evenflcw-- Will give it a try and see what happens....

01-27-2008, 05:50 PM
...Not working at all.

My rig has 40 bones in a straight line. On frame "0" I've looped them into an S-shape. The animation goes through a number of undulations until frame 300. I now find that it would be great to have 20 bones going in one direction and 20 going in the other direction, starting from the middle.

Evenflcw made it sound easy to swap out bones, but nothing works. Should I save transformed object first, so that the starting deformation at frame "0" is proper? Ideally I'd like to pop in the new rig at frame 300 which is where I really need it.

When I delete the old bones, the object goes nuts, so I've loaded a replacement object with a new set of skelegons. Not sure even how to delete the old bones. (LW crashed when I use the delete bone button.)

Is there an elegant solution to this? I pose the question again: What's a good way to change out bones. Many thanks.

01-27-2008, 09:48 PM
William Vaughan did a video showing a reverse bone parented within the chain. That seems to be working except I don't see a quick way to activate the reversed bones. (There's no envelope control for bone strength.) At the moment I'm setting the bone strength to zero for each overlapping bone, and setting it to 100 for the reversely oriented one. So I'm not actually swapping rigs.

01-28-2008, 02:03 AM
Well, this might help:

It's an IK/FK plugin that allows a slider to control the bones that deform. I don't know if it's helpful at all, or if you can adapt it to choose a different set of bones. The plugin is based on the idea that oyu have TWO extra sets of bones (one IK, one FK, and the original bones) and you use a % follower to influence your original bones.

Switching bones on the fly I don't believe is possible with Lightwave.
I know it can be hacked with a plugin, but you'd have too get someone that has a little time to write it. :)

01-28-2008, 04:22 AM
Sorry wasn't really sure whether you wanted to keep the old bones (and their animation) or not. I guess you do.

Attached files shows a quick and dirty way to switch bonesetups on the fly using Use Morphed Position. Simply put you have several bone setups placed at an offset from eachother (when resting them; later place and pose them so they overlap). These offsets are mirrored and controlled via a morph. So when you morph to another offset you also morph to another bone setup, thanks to bone influence. Limitations: you can't morph regularly, you probably shouldn't use weightmaps and it might be tricky to do this only for part of a mesh in a smooth fashion. Obviously you'll need bigger offsets than I used to get rid of all the influence from neighbouring setups.

The oldschool way is to just have two different objects with different rigs, fade one in the other out, or two different scenes altogether.

The big problem, whichever solution you'll end up using, is to align the two rigs at the handover.

EDIT: Turn on Bone XRay to see what bone setup is at work at any one time.

...Not working at all.

01-28-2008, 07:28 AM
Thanks for your help. Your suggestions make my 3D life possible!

01-28-2008, 08:40 AM
Thanks for your help.Your welcome.

Your suggestions make my 3D life possible!
I'm sure that's not the case, or were you being sarcastic!? Uncommon approaches are what keeps me going though, they are the most fun. Usually you dream up cool things you could do with them, unfortunatly often it doesn't quite work out because of the limitations imposed by using the odd approach. I think for this trick I also toyed around with animatable pivot and something else... don't remember.

01-28-2008, 08:48 AM
I'm not being sarcastic. Without the help of discussion boards I wouldn't have been able to get much of my 3D work done. I've spent hundreds of hours trying to do things, getting nowhere until someone suggests a tool or technique. I've still got a long way to go, too.

01-28-2008, 10:38 AM
Yes. That probably goes for most of us. Whether we are giving or receiving. Without any peers and like-minded this wouldn't be half as fun.