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View Full Version : IK isn't always follow the goal object motion path (annoying)


dickma
06-13-2003, 03:20 AM
I would like to animate a cat which is walking...but I got a very annoying problem that the IK chain doesn't follow the goal's object's motion path.

It cause flickering in animation and everytime I need to lift up the cat's legs by move up the associated goals at very high position in order to make it "walk". I can't make a precision 'catwalk'.

Annoying!

Chewey
06-13-2003, 03:30 AM
Did you want help with the rig? If so, next time post some detailed info about it along with your post.

dickma
06-13-2003, 03:38 AM
I would like to post the scene but the size is over 20K...

Let me try to simpilied the question.

Let say I make an IK chain and all the IK settings is all restricted to P controllers,

but the IK chain doesn't always snap to the motion path of the goal object, sometimes the IK Chain only go nearest to the motion path, or it doesn't follow at all.

dickma
06-13-2003, 04:08 AM
There is an attachment of my crappy animation scene file attached in Lightwave3d.com---> Discussion Forum ---> LW Tips & Tricks.

Please have a look.

Chewey
06-13-2003, 04:10 AM
Try reducing the size of your layout file by removing all nonessential elements such as texture images and extra geometry. All you need in the scene file is the skeletal rig with the ik setup.

So replace your cat object with a null instead and see if you can get the file size to below 20k in size and post it.

dickma
06-13-2003, 04:22 AM
here:

Chewey
06-13-2003, 05:03 AM
For starters turn on Unaffected by IK of Descendants for the bone Spine5

If it were my rig I would stay away from trying to implement too many ik elements beyond the basic leg IK as spline IK just tends to be a bit messier to deal with even for a biped rig.

Try reconfiguring your rig approach with a focus on just a single null for the translation of the cat's body. Ignore the tail element until you get a stable quadraped setup and then add the tail IK chain afterwards once you get a handle on the basics.

dickma
06-13-2003, 06:12 AM
Chewey, do you hanv any suggestion on how to setup the tail?

Kvaalen
06-13-2003, 09:08 AM
Originally posted by Dick Ma
Chewey, do you hanv any suggestion on how to setup the tail?

For rigging the tail, you can use this plugin:

http://mapage.noos.fr/samuelLK/Plugins/RopeRig/Tutorial.html

A little tip: after creating the bones, you can select all of the tail bones and rotate them at the same time to create an arch, and then apply the IK. It just gives better resaults sometimes.
You should also read the tip at the end of the page if you want a couple controlers.

dickma
06-13-2003, 10:45 AM
Thanks Samuel for the tips.

Looking into your tutorial....

I think if the web-text a little bit darker will be better. thx...

dickma
06-13-2003, 11:20 AM
Hey Samuel:

you plugin may be got a little error on Step 2 & 3.

The target bone cannot made at the last bone of the IK chain...
it makes it in the first bone....

So I cannot enable the "Run RR IK Chain" in step 1.

Kvaalen
06-13-2003, 02:13 PM
You can run the RR_IKChain seperatly if you want to, just don't check the "Run RopeRig IKChain".

The bone that gets selected at the end of the RR_Bones plugin is the bone you selected before running it, so if you run RR_IKChain right a way, you have to make sure you have "Create IK Chain By Selection" unchecked, and then it will create the chain from the selected bone till its last child bone.

Hope that helps, don't hesitate to ask if you have any other questions. :thumbsup:

dickma
06-13-2003, 02:39 PM
What about the setting of the "Make first bone Unaffected by IK"

it's so weird when the conversion process is done

cannot see the IK chain instantly until I uncheck the "Unaffected by IK" of the bone

Kvaalen
06-13-2003, 02:53 PM
I've never had such a problem. What that function does is makes the parent bone of the whole IK chain unaffected by the IK chain.

I just tried it and it worked fine. :shrug:

kretin
06-14-2003, 12:14 AM
One of the reasons it's not working too well is because you have only setup the legs to rotate on a single axis (P). This means that the feet can't move left or right at all. With your current bone setup you can set Heading to IK for the thigh bones which will help. You can then use the Bank of the same bone to point the knees.

I prefer including a small bone at the root of each leg which has IK for Bank (enabling rotating out to the sides) and Keyframe for Heading (enabling me to point the knee) and leaving the thigh bone with just Pitch IK rotation.

Watch your rotational limits, they will stop the chain from following the goal properly too.

You should also turn on "Unaffected by IK of Descendants" only for the Parent of any IK chains. This means "spine1" and "spine5" in your case.

SplineGod
06-14-2003, 12:27 AM
Originally posted by Dick Ma
Chewey, do you hanv any suggestion on how to setup the tail?
I wouldnt use IK on the tail. Set up selection sets on sections of it and then rotate them additively. I have a rig that uses the same principle HERE (http://www.splinegod.com/rigs.htm) (The tentacle rig).

SplineGod
06-14-2003, 12:29 AM
Originally posted by kretin
One of the reasons it's not working too well is because you have only setup the legs to rotate on a single axis (P). This means that the feet can't move left or right at all. With your current bone setup you can set Heading to IK for the thigh bones which will help. You can then use the Bank of the same bone to point the knees.

I prefer including a small bone at the root of each leg which has IK for Bank (enabling rotating out to the sides) and Keyframe for Heading (enabling me to point the knee) and leaving the thigh bone with just Pitch IK rotation.

Watch your rotational limits, they will stop the chain from following the goal properly too.

You should also turn on "Unaffected by IK of Descendants" only for the Parent of any IK chains. This means "spine1" and "spine5" in your case.
The small root bone also just makes the IK faster and more stable. Turning off unused channels will also make it more responsive too. I also dont set rotational limites unless forced to.

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