How does this rig work?

[mtbuck24]

Okay I am following a tutorial online http://www.youtube.com/watch?v=i9QrlFP0QB4 by Incredible Tutorials and for some reason cannot figure out how the reparent bone process works on this rig. I will do my best to explain. I have two examples of a rig.

1. With the bones connected with out a neck. I have the shoulder connected directly to the top back bone. I have two layers Arm and Torso I bound all the points on the torso layer to the lowest (parent) back bone. I then bound the top points of the torso layer to the top back bone. With the shoulder bone I bound 3 points of the left shoulder area to the torso layer. Arms: top of arm bound to all arm points, Fore arm: lower arm points. My question is - with out a neck after all bones are bound to a layer - when I go to manipulate the arm bones the whole body moves pivoting on the parent back bone. Why is that?




2. On this example all the bones are parented the same way and bound the same way as before but now I added a neck bone. And when I go to manipulate the arm bone all bones stay in place as I move the arm bone around.



It's probably really simple but I just needed a explanation to help me understand why it does this. Hopefully my info helped.

Thanks!

[neeters_guy]

In the first case, the IK chain is uninterrupted. Adding the neck bone breaks the IK by splitting into two chains.

[ddrake]

Not sure I understand exactly what's going on from how you described it, but lets give it a shot, eh?

My question is - with out a neck after all bones are bound to a layer - when I go to manipulate the arm bones the whole body moves pivoting on the parent back bone. Why is that?

Are you saying that it seems the bones are bound properly, but you're wondering why moving the arm bones also alters the body position? If so, you're using the "manipulate bone" tool, and it does that on purpose using inverse kinetics, to try and help you naturally pose the figure, and comes into play if you are using bone locking to find a position the rig can be in and maintain the position of one bone. If you're wanting to just move the arm only, or a single bone on it's pivot you can use the "rotate bone" tool which will only affect the angle of that particular bone.

. 2. On this example all the bones are parented the same way and bound the same way as before but now I added a neck bone. And when I go to manipulate the arm bone all bones stay in place as I move the arm bone around. ?

Now, if I'm on the right track with what you're asking, and again assuming things are bound correctly, I think all that's happening is with the added bone, it recalculates how much influence the arm has over the rest. Think of it like pulling on the top limb of a tree and how much and how far down that will sway the trunk and compare that pulling on limb that's farther down or in the middle of the tree.

Anyway, not sure if that is in ANY way what your question or concern is, but that's how I was reading it. Let me know if that's somewhat helpful, and if not maybe a little more info and I'll try again

***Edit*** Looks like Neeters was already on this one and came to a similar conclusion. (I was just way less concise )

[mtbuck24]

Thank you neeters_guy and ddrake. You guys hit it right on the nose. Thanks for your help!