How to set up the Isner spine properly?

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  09 September 2010
How to set up the Isner spine properly?

In the Digital Tutors video "Rigging quadrupeds" the instructor uses the SI spline for the horse. In order to work properly he sets it up on the y-axis and then rotates it into place by 90. In his horse rig the spine is completely straight. While it may work with this horse, in general animals don't have a straight back. How would you match the spine to the angled back of a giraffe, the bend one of a kangaroo or the curvy one of a cheetah? What would be the steps? Especially if I need to reach a goal (e.g. the center between the shoulder blades) it gets difficult. I would in general create the spine straight between two points on the y-axis. Then I would translate/rotate the spine's hip into place. But what then? I need to use the two vertebrae nulls to match the form of my animal's spine and then try to reach the goal between the shoulders with the spines last vertebrae. The question is what problems might arise in general with a deformed Isner spine while animating and how do I reach the goal between the shoulders with the spines end? Unfortunately the Vertebraes don't adapt to the "new" spine length and stay in the same distance to the hip like the one they inherited while setting up the spine. Would I need to do this over and over again by trial and error till I find the correct length for the spine and it matches more or less my animals dimensions? Please, how do I need to do this properly (which steps) so that I get a proper working spine (stretchy)?

Cheers
Pancho
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  09 September 2010
Originally Posted by Pancho: I would in general create the spine straight between two points on the y-axis. Then I would translate/rotate the spine's hip into place. But what then? I need to use the two vertebrae nulls to match the form of my animal's spine and then try to reach the goal between the shoulders with the spines last vertebrae.

I'm not sure I understand the problem. Is there a reason that you need to create the spine pointing straight up and then rotate it into place? Wouldn't be easier to create two nulls exactly where you need the base and the tip of the spine to be, create the spine using them, and then adjust the spine to match the form your want using the checkDepth and hipDepth nulls? If you do it this way then you shouldn't need to change the length of the spine and you don't have to reposition the vertebra directly.

Or is there more to it than that?
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  09 September 2010
I guess there is a problem with the rotation. If you just put the spine into the horse, from hip to chest, the bank rotation didn't work anymore. So the spine need to get created on the y-axis (a bone was use as a reference for the needed length of the spine) and then got rotated into place (z-axis). Then all rotations did work properly. But this example was pretty simple as there was no need for a deformation of the spine. Hip and chest where on the same height. In the animal I'm talking about the spine is angled, bend and curvy.

Is there a way to play around with the inital length in the spine%length to fit it into place?
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  09 September 2010
I see the problem now. I've just tested it out and you're absolutely correct. The rotations get all wonky if the spine is not created along the Y-axis.

You can make the vertebra spread out as you resize the spine by doing the following:


  1. Select the topmost vertebra (the one slightly bigger than the others).
  2. From the MCP, press the "Selection" button.
  3. Go to "Kinematics" -> "Constraints" -> "PathCns" -> "Path %age" node.
  4. There will be a node named "FixedLength" under "Path %age", select it and hit "delete."
Now the topmost vertebra will always be at the tip of the spine, and the others will spread out proportionally, hopefully with no ill-effects.

HTH


EDIT
Actually, it would probably be much simpler to measure the distance between the hips and the neck, create two nulls that are at the same distance but aligned on the Y-axis, create the spine between those, and then rotate the spline into place. It should fit right in. Of course unless there's some other issue I'm missing that wouldn't allow for that.
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Last edited by ShaderOp : 09 September 2010 at 09:23 PM.
 
  09 September 2010
That's something I did in the beginning (the two null with the propper distance). What you are missing: a) Just deleting the path%... makes the spine full time stretchy and b) that the two nulls which shape the spine will change its length after setting up the spine between the two null.

I just wonder if ICE would be a solution to the whole spine?

There is just one thing. In Lightwave you needed to "rest" the bones before animation can start (set the initial position and influence). How is this done in SI, if there is the need to do this in SI at all?
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  09 September 2010
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