View Full Version : PLG Ik question

03-22-2007, 02:35 AM
I'm busy playing with the PLG Ik plugins that can be found here (http://homepage2.nifty.com/nif-hp/index2_english.htm)

I just can't get this to work...not even with a simple 2 bone setup.

Here is what I do. I have 3 bones (Hip, Upper Leg and Lower Leg). On the Upper leg bone I add the plg_IK_Top plugin. On the Lower leg bone I add the plg_IK plugin and choose the Target Null as the goal object with Full-time IK on.

The bones point at the Target null, but does not bend at the knee.

Can anyone please give me some insight into these plugins?

03-22-2007, 03:35 AM
you can turn fulltime IK off.
And i think to fix your problem you just need to rest your bones before turning on the Plg plugins. It uses that information to setup bend angles.

Also you want to add one more Null near the knee. and under the Plg_top plugin set that null to be your twist target. This will be your up vector for the joint. So you con control the direction of your knee.

03-22-2007, 03:42 AM
Argh! I feel really stupid. Thanks Castius, I did not rest the bones before adding the plugins.

Thanks again.

03-22-2007, 03:08 PM
This is really weird! I managed to get the plg IK stuff working, but the left arm on this character refuse to work. I checked everything over and again. It's set up exactly as the right arm. The elbow just does not want to bend.

I really want to get this to work...any ideas?

03-23-2007, 12:46 AM
Is there no who uses the plg plugins? Would it help if I posted the rig?

03-23-2007, 01:01 AM
sorry didn't see your other post. Yes it would.

03-23-2007, 01:04 AM
I'm using PLG every time I need an IK rig in LW. I've built very complex character rigs using them. It's not easy to understand what's wrong in your case, but if you post your scene, I think I can fix the problem.

03-23-2007, 01:50 AM
Here is the rig. The right arm (in red) works wonderfully, but the left (in green) is the problem area. The spine uses the plg_ik_cirve plugin, and that seems to be working 100% as well. I've converted both legs to plg in another version and they also worked well. The left arm is driving me nuts. I even deleted the problem arm and mirrored the right hierarchy over, but still no go.

thanks guys.

03-23-2007, 04:10 AM
My advice is to align the pitch of all the bones composing the arm.

Try to rebuild the bone chain.

I never use the plug to convert from LW IK to PLG...it's better to do it by hand, you gain more control this way.

Using PLG you don't need the extra bone for IK (as in standard LW IK).

Two bones are enough to build a working chain (of course you may need extra bones for the shoulder roll and whrist twist).

Hope it helps.

03-23-2007, 04:51 AM
I would if I could, but I get an instant crash when I delete bones from the hierarchy. Someone already logged it in the bug tracker.

I'm really fed up with the half-***, bug-overloaded rigging tools in LW. I'm trying this on a clean scene with no plg plugins added. Wish it was easier to make changes to rigs on the fly.

03-23-2007, 05:25 AM
I would if I could, but I get an instant crash when I delete bones from the hierarchy. Someone already logged it in the bug tracker.

I'm really fed up with the half-***, bug-overloaded rigging tools in LW. I'm trying this on a clean scene with no plg plugins added. Wish it was easier to make changes to rigs on the fly.

My system crash only if I delete a hierarchy and I have more than a bone selected. I can delete bones from your scene with no problem.

I've deleted the arms...here is the scene.

03-23-2007, 06:31 AM
Thanks for the effort lino.grandi. I appreciate it.

Busy re-building the rig from scratch, and found that the plg IK plugin does not work when I bring skelegons in from Modeler. After doing a couple of bones in Layout, everything works well. Now I have to redraw the arm and leg bones in layout, but still sit with the delete bug. I cant delete any bone from this rig without a LW crash. :bangwall:

If all goes well , I might be moving over to XSI in a couple of weeks. I can't wait.

Thanks again buddy!

03-23-2007, 06:51 AM
hmmm, correction! The plg_IK plugin does not work if I reset the rotational values of the bones. Now I can bring skelegons in from Modeler without a problem. It's good this way...saves a bit of time not going into each bone to reset rotational values.

03-23-2007, 07:38 AM
I was looking at your rig. I've run into issues like this with bone creation order causing the plg ik to target from the wrong joints.
I noticed that your lower arm bone is out of order as I arrow down through the chain. Even with bone order problems, PLG ik will tend to work on one side but not the other,.. usually the left for me.
The only way I know of to fix this problem is to rebuild the bones in the ik chain in correct order.
A pretty easy fix is to mirror the right hiearchy from the other side to the left and lightwave will correctly re-order the bones. Then re-apply the plg ik plugs. You can then mirror the left back again if you want to fix bone order on the right side.
I have some plg rigs posted here if you want to look at them.


03-23-2007, 08:27 AM
Thanks nemac4! Thanks for the info. Will keep that in mind the next time I rig anything.

I actually tried your method of mirroring the hierarchy, but that did not work either. Usually I draw the bones in Modeler, and reset the rotational values in Layout. Every time I do that, the plg plugin does not work. Now I just bring in the skelegons and use the plg plugin without resetting the rot values...works now.

One other thing though. I can seem to get nice distributed rotation on the forearm. Follower does not work when used on the plg IK bones. Any ideas?

03-23-2007, 08:53 AM
If in the motion plugin order Follower comes after plg_IK, it works.

03-23-2007, 08:59 AM
I'm glad that you got it working. :thumbsup:
I don't use skelegons much so I've not run into those problems.
for the forearms,.. you could try to mix in plg_ik curve in a short hiearchy and use the twist control. I've used so many versions of the forearm/wrist that I don't remember what worked best for me. I'll look into it.

I do remember using multiple bones with some expressions to fade off the rotation from the wrist.
Concerning follower, I tried to get around that with some expressions. It worked fairly well but was inaccurate during ik/fk blend transitions. I used a null and some dynamic parenting with expressions.
I'm curious about the new Mix with FK option. It could open up some follower methods.
I'll try to work on it some when I have some free time.

03-23-2007, 09:13 AM
If in the motion plugin order Follower comes after plg_IK, it works.
I was thinking he meant an item outside the PLG chain but that method does seem to let transitional data pass to the following item... so a nested control might work like that.:thumbsup:
I'll have to play with that some.

03-23-2007, 10:16 AM
One question, why do you need to use the plg plug-ins?, seems like it makes more trouble than relief, but then again I'm not a professional rigger or animator.

03-23-2007, 11:19 AM
There is no real problem with Skelegons but you still need to get the pitch correct. It doesn't matter if you do it in layout or if you do it in Modeler. Skelegon editor from Dstorm is good for this.

Ztreem the PLG plugin adds some really usefull IK features that are geared towards Character animation.

03-25-2007, 09:17 AM
I have one more question for you guys. Just downloaded the latest version of the plg plugins. I see there is a "mix with FK" tick box. What exactly does this do? I just don't understand what the developer means in the docs. Does this have anything to do with IK/FK blending?

What would be the best way to do IK/FK blending while using the plg plugins

03-25-2007, 10:33 AM
I've recorded a video tutorial on the plg_ik stuff and I'll post it as soon as it is done encoding.

The mix with ik option allows you to keyframe the bank angle of the bones below the plg ik top while still using plg IK. Without it, plg would override the keyframes. Great for fixing twisting in the wrist. It works with Follower too.

03-25-2007, 11:20 AM
Brilliant nemac4! can't wait to see the vid! :beerchug:

03-25-2007, 05:46 PM
Here you go:

oh,.. btw ~100MB

03-26-2007, 02:06 AM
I just watched the clip and wanted to thank you for taking the time to make this. It really helped to understand the plg plugins...especialy FK/IK switching.

Thanks again David...you :jam: