View Full Version : Use Bones From Object

01-11-2016, 11:16 AM
This has got to be so simple, thus why the following question cannot be found using this forum's search or google.

How do I get the parented motion of a bone in one object to affect the verts in another object using the 'Use Bones from Object' option?

Here's the set up... a single bone in Object 1 is placed such that the pitch rotation of Object 1 moves the bone in an arc. The bone properties uses the weight map only option, where Object 2 has a weight map on a few verts (the end of a cable). Object 2 is set to "Use Bones from Object 1". If the bone itself is translated, the verts of Object 2 are dragged along as desired and expected, BUT when Object 1 is rotated, the verts of Object 2 DO NOT move with the bone. I understand the reason why (you don't want the bone's parent object motion to be added to that of the bones themselves for obvious rigging reasons), but there has to be some sort of workaround of doing this sort of animation -- of attaching the end of a cable to a control horn such that when the control horn is rotated/moved, the end of the cable remains exactly and precisely fixed to its mounting hole in the horn? (Yes, it is desired that the cable stretches in length and is NOT pulled in its entirety, because the amount of "travel" is minimal and there won't be any textures to give the illusion away that the cable isn't actually moving through a pulley system).

01-11-2016, 11:27 AM
Well rotating Object 1 won't affect Object 2. What you could do is add a bone in Object 2 and constrain it to the bone in Object 1 and set it to world coordinates. That should then line up with the bone in Object 1, even if you rotate Object 1.

01-11-2016, 11:34 AM
I suspect the answer lies in the realm of "Same As Item" rotations and possibly a duplicate bone. Hmmmmm.. if Obj#1 is translated also, you'd need to add it's motion to the duplicate bone (I think). This is starting to smell very nodal. How about this: the #1bone and #1obj rotations are added together, nodally, and applied to the duplicate bone?

Or, after re-reading, parent a bone in Obj#2 to Obj#1, and set the pivot point of the bone to the cntr of Obj#1.

EDIT: rats, ernpchan beat me to it. :thumbsup:

01-11-2016, 01:02 PM
How about this:

Add a bone to Object 2 (the cable).
Move it to coincide with the pivot point of Object 1 (control horn).
Set strength = 0.
Add a child bone set to weight map only.
Offset from parent so it lines up with cable mounting hole in the control horn.
Add a 'Bone Target' Null and parent to Cable (obj 2) where the cable bends around a pulley.
Target child bone to this target null so that bone always points at far end of cable (bend around pulley) during arc rotation produced by parent bone pitch rotation.
Add Follower to parent bone, set to follow control horn's pitch (object 1) and uncheck 'After IK' option.
Animate Object 1.

Weeee! End of cable follows hole in horn, making the animator very happy.

Only took 4 hours of my day to R&D this.

01-11-2016, 04:25 PM
What's a control horn?

01-11-2016, 09:51 PM
How about this:
Screen grabs, please. One of deformation, one of schematic.

01-13-2016, 10:35 AM
Here ya go...


Oops... text in middle panel should read "while pivoting "in" obj1's control horn hole," not obj2.

01-13-2016, 07:34 PM
Thanks, I'll try to digest that later.

01-14-2016, 02:56 PM
Fixed version of the screen grabs.