Hi fellow Houdini users,

I'm looking to get started on a character animation project and I have a rough idea of how to capture geometry, set up bones etc … - but I do have some general questions. I have seen in various places (magazines, on screen …) that some set ups have a multi-boned spine - is this IK or FK? Are there any general rules to getting a good character set up? How can you get eye lids to follow an eyeball's surface and not intersect? (I also have a lot of trouble with colapsing elbows and knees - characters, not mine - especially at extreme bending of joints - any suggestions?) There must be methods for doing this - can anyone help? I have looked through all the tutorials which have been a great help but I'm looking for something a bit more advanced. Thanks

Matt

Houdini bones are simple parenting heirarchies that pass TRANSFORMS down the line. You can insert nulls anywhere in the chain, including inbetween two bones in an IK solution (but it is up to you to control the chaos).

You can wire as many bone chains that you want between two end effectors. You just have to go in to CHOPs each time you add a new chain and pass in the proper end effectors.

I have seen some bones with twist effectors just used to orient other bones in the chain.

In H6, you can blend out if IK to rotates and back again with great control.

There are the blend objects which allow you to pull any component of a TRANSFORM from any input to this blend OP. The blend takes as many inputs as you can feed it. For example, in a spine parented to a hip, you can insert a blend OP between the hip rotate controller and the spine root. Just unmask the Rotates and you have now cut off the rotates passed up. You can now wire in another null object in to the blend just to control the rotates of the spine. Just turn off the translate and scale inheritence from this second input.

Go crazy. It is a free network. The constraints are in the network itself if that makes sense to you. Not in the solvers. Although we do have an IK solver that has constraints but they are real constraints, rotational limits on the IK bones.

The only thing to worry about is infinite recursion loops in the IK solvers. Poke around in CHOPs as you create the bones. Have fun. Break them then fix them. Sky's the limit.

For the eyelids you could creep a curve over your eyeballs followed by a trail sop and skin sop, which should prevent the surface intersecting with your eyeballs.

Hi

There are no hard and fast standards here but these are just a few general guidelines :

I have seen in various places (magazines, on screen …) that some set ups have a multi-boned spine - is this IK or FK?

A multi-bone spine usualy implies “Follow Curve IK” or an IK chain thats controlled by a curve
Common on more realistic or rather Hi-Res characters that require fine control of the spine(Smoother deformation of the body too)

I've used Multi-Chain spines to, for example make a Winged character fly and smoothly transition to a walk. In this case the Root of the heirarchy had to move from near the wings(flying) to the Pelvis(walking)

How can you get eye lids to follow an eyeball's surface and not intersect?

you could try “soft” grouping the points you want to animate and Rotate them around the centre of the eyeball , ie place the transforms pivot at the eyeball's center- for instance

I also have a lot of trouble with colapsing elbows and knees - characters, not mine - especially at extreme bending of joints - any suggestions?

Insert another small(er) bone where the real joint would be
for example instead of ——-*——– try ——-*–*——-
check out the video called “Realistc Arm Setup” for a neat example. You may even layer Blend deformations that are driven by boneangles on top of your capture to tweak those pesky joints

Are there any general rules to getting a good character set up?

One I swear by: Test Test and Test again before laying down a single keyframe
Coming from a Maya background this rule was the Holy Grail. Houdini offers much more flexibility in that you can tweak the rig almost anytime you want.

What's most important to remember is that a rig needs to be clear and simple to animate with.
so when it comes to animating - Keep It Simple

You may want to go through rigging tutorials from other softwares too, since the principles are the same. Highend3d or 3dbuzz are good places to start

Hope this helps

cheers

tallkien