Several beginner rigging questions

Issues concerning rigging & Face Robot...
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Ande
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Several beginner rigging questions

Post by Ande » 10 May 2014, 16:00

Note, I'm building the rig on top of a null-skeleton which is what will actually be exported to the game engine. Maybe that matters.

1. IK for an arm with roll bones.
The arm has two roll bones, for upper- and forearm (dark green in the picture). Now, the IK for the left chain will obviously not behave like an arm. I know I can just have two bones like on the right, but the question is how do I properly set up the constraints?
The roll (x rotation) of the upper bone (dark blue, right) should only affect the roll bone (dark green, left) and not the main bone (dark blue, left), whereas everything else (yz rotation and translation) should affect only the main bone.
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2. Move hips but have the feet stay where they are.
Let's say I have a standard 2-bone chain with default IK effector. The chain is a child of the hip bone. Is it possible to have the hip bone move with the leg end effector trying to stay at the same position? So that when I move the hip down the legs would bend instead of staying straight and just being translated down?

I hope the questions are clear, if you need any more clarification, just ask.
Thanks in advance.

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Re: Several beginner rigging questions

Post by EricTRocks » 10 May 2014, 17:31

Hi Ande,

1) For the roll bones, I'd suggest setting it up like you have on the right of the image. Then create 2 nulls per bone. One is the main "bicep" deformer, one is the "bicep_roll" deformer. Same for the forearm: "forearm" and "forearm_roll". You'll need to tinker a bit to figure out how this should work but that's the art of rigging the arm. As general information, you'll need to constraint the position of the "bicep" and "forearm" nulls to the associated bone. For the "bicep_roll" and "forearm_roll" you'll have to do a percentage between the associated bone and the next one. For the forearm, you'll use the forearm bone and the effector. Next you'll have to figure out how to get them to orient correctly. Try some variations of the direction constraints. Note: Apply the position constraints for the forearm_roll objects first, then do the direction constraints on top. Just for cleanliness.

With all of that said, you'll have quite a few helper null objects within the rig that you also have to figure out where to constrain them and parent them. Again this is the part of rigging where you do trial and error. With the info above you should have enough info to figure it out. Make sure to really understand all of the functionality of the direction constraints. They are very useful.

2) Position constrain the effector objects to controllers that aren't parented to the hips.
Eric Thivierge
Lead Kraken Developer, Fabric Engine
http://fabric-engine.github.io/Kraken

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Ande
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Re: Several beginner rigging questions

Post by Ande » 10 May 2014, 18:50

Alright, thanks a lot already!

Some more:
How much of the skeleton should have it's neutral pose set to the base pose? From what I read it's usually the control objects, but what about the bones themselves?
Is the effector usually constrained to a control object, too?

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Re: Several beginner rigging questions

Post by EricTRocks » 10 May 2014, 19:12

None of the skeleton and I don't do it to the controls either. For controls, I create a null object and match it's position to the control. Then I parent the control to that null. It's usually called a buffer null or a rest null. This allows you to do some cool things like constraining that buffer null to other objects to make a very simple version of parent switching. Additionally, the neutral pose can get reset by animators easily where using buffer nulls allows you to lock them to prevent animators from accidentally moving them.

Effectors are usually constrained to controls yes. You should never animate on the actual bones themselves. Bone chains should be used only to calculate the deformer transforms.
Eric Thivierge
Lead Kraken Developer, Fabric Engine
http://fabric-engine.github.io/Kraken

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grendizer
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Re: Several beginner rigging questions

Post by grendizer » 11 May 2014, 15:20

I would add: it's always better to store a neutral pose animation clip for when things get screwed up. Select all control objects then store.

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Re: Several beginner rigging questions

Post by EricTRocks » 11 May 2014, 19:05

You don't need that if you have the buffer nulls. Select all controls, Ctrl + Shift + R to reset local transforms and you're back to your default pose. However if you have custom parameters driving rig settings then yes an action is best.
Eric Thivierge
Lead Kraken Developer, Fabric Engine
http://fabric-engine.github.io/Kraken

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Ande
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Re: Several beginner rigging questions

Post by Ande » 22 May 2014, 16:13

So for animating I will be only be making keyframes on the control objects?
If I just wanted to have some rotation for a bone and not use IK, would I create control objects for the single bones, too? And animate via those?

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Re: Several beginner rigging questions

Post by grendizer » 27 May 2014, 11:32

Hello Ande,

Eric is right, with parent nulls that can zero out the rig object's transforms (buffer nulls), there is less need for a reset animation mixer source, as you can select all control objects then reset transforms.
However, myself I always add this reset clip sources. First I set it on the skeleton. Because when you have finished the skeleton and start to skin the character, you rotate the legs, move the wrist effector, etc. So it's safer to have a reset solution at that level. Then when the rig is finished I also set a reset animation mixer source because when you have a complicated setup in the animation mixer, you often need transitions from and to reset pose clips. For example in distributed rendering, it is often better to have the animation mixer start by a reset clip. Reset clips can affect a whole character or parts of it.

I have worked in several productions where we had to export animations from Softimage to a game engine. In that case, it's much better to separate the rig and the skeleton. In these productions, I took the habbit to have 3 hierarchies in my character's model : 1: geometry, 2: skeleton, and 3: rig. All animation were done only on the rig. At export time, I plotted the whole skeleton and then export only the skeleton animations.
For a clean work, I think it's best to separate the 2, but if there's no restrictive export need, it may be too much work to have a control object for EACH bone or effector. For example : the fingers: 15 control objects on a single hand? Too much work just for the sake of cleanliness.
So usually, for simple animation projects, I choose a mix of the 2. I'm sure others have the same approach.

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