Rigging animal limbs

[Pancho]

Just a few simple questions:

How do I rig animal limbs?

While the legs seem to be made for a fk (femur) + ik (tibia+metacarpals) solution, the front limbs with the moving scapula seem to be a bit more difficult. How would I split all the limbs into ik or fk groups to make it easy to deal with the movement. Is is a good idea to create an IK chain for the humerus/scapula? Would it be possible with GEAR to solve this chain in a manner that 80% of the movement is done with the humerus, while the scapula stays pretty stiff (and limit the movement more or less to one axis)?

Another concern: The animal's carpal bones actually split the rotation of the wrist joint rather in two seperate joints, than in one. If you bend the joint, this effect is highly visible. Can I create an IK chain in GEAR with two joints (3 bone IK) which simulates this effect? A simple two bone IK chain might be working in a distance, but for close ups it sounds like a very bad idea. The animals wrist (bend) looks rather like a block, than a pointed angle.

Any help and ideas are highly appreciated.

Best wishes
Thomas

[EricTRocks]

In 'rigging_01.jpg' the diagram on the right is the correct setup. Same with 'rigging_02.jpg'.

For the meta carpal issue you're talking about, most of the time it is faked with blend shapes that drive a fixer shape to maintain the volume. Otherwise it can become quite complicated to setup and maintain. One trick I've seen is to have the mid bone length shrink down as the joint straightens and then lengthen as it bends to fake the effect of the bones sliding against each other.

[Pancho]

Thanks, Eric.

The rigging you propose is similar to the one for a human character. I just thought because the carpal joint is the one with the biggest movement in a quadruped, that the IK would be best suited for this joint.

As there is 3 bone IK out there, what would be the problem to use it for the arm's carpal joint? Wouldn't it make things pretty easy, as long as the movement is distributed to both joints in the same fashion? Each 50% of the overall rotation?

[EricTRocks]

Ask your animators what they would prefer. The one I suggested is typically what they want / gives you the most realistic movement without having to counter animate a lot.

[minilogoguy18]

Is there a tutorial anywhere on building custom dog legs?

I could use the dog leg rig guide but I only need the legs and I want something a little more custom.

[andyboe]

Maybe this could be helpful:
http://www.riggingdojo.com/rigging-101- ... y-rigging/
It's Maya, but all stuff should be transferable to SI.

[minilogoguy18]

I'll look through it though I've never used Maya so how easily I'll be able to translate may be a challenge, would very much like to find a Softimage based tutorial on dog leg rigs.

[Hirazi Blue]

In the SDK there is a command named "MakeDogLeg" (and an example script), for which you have to "only" provide a list of 9 guide objects - Nulls - and some other parameters. This creates a dog leg only (i.e. with nothing attached). Maybe that's a start...
;)

[minilogoguy18]

The script wont run for me, not sure why, maybe cause I'm using Mod Tool 7.5?

The other thing is that only part of the leg will really work for what I'm doing, it's an AT-ST from Star Wars. I'd really just would like something showing how to do a reverse foot roll on a dog leg. Whenever I use the preset rigs like Biped Dog Leg Rig I try to open the Schematic view to look at how everything is constrained but for some reason it doesn't show any relationships other than parent-child. I can't even dissect the preset rig to see how it's made.

[Hirazi Blue]

The script wont run for me, not sure why, maybe cause I'm using Mod Tool 7.5?

That's weird. I checked it on my own Mod Tool install just now and it worked just fine. Did you switch the Script Language to JScript in the Scripting Preferences?

[minilogoguy18]

Yeah, I'm a dummy, not used to running any scripts and missed that.

Was able to dissect the MakeFoot script to be able to make something that fit my model perfectly. Thanks.

[Hirazi Blue]

Looks like a solid rig to me (but I am no rigger myself).
Care to elaborate (a bit) on what you did to the MakeFoot? ;)

[EricTRocks]

You're a brave soul manipulating a rig with constraint compensation on in that video...

[minilogoguy18]

Yeah, forgot about that, neutral poses saved me. I essentially just looked at the local transforms of my null skeleton since it's a shadow rig and typed them into the script manually for the guide nulls in the script. Would have liked to make something to call my own but thus will do until I learn how to make a 3 bone foot.