View Full Version : Hard object at end of bone chain?

12-28-2017, 01:30 AM
I have a cable that I want to distort with bones, but the plug at the end of the cable should move and orient with the bones, but stay rigid and undeformed. I added bones to the cable object, and then parented the plug to the last bone. The plug is getting distorted as well as moving with the bones.

How do I keep the plug solid, while moving and rotating with the bones?

(This is just for several stills, I don't have any IK or anything fancy, just want to FK pose the bones in a couple different positions, without squashing the plug...)

12-28-2017, 02:08 AM
Weight map can inform LW which bones modify object vertexes. If just one bone is modifying some object, it should not be distorted.
So set up weight map 100%, for one bone, and all the others to 0%.

12-28-2017, 06:29 AM
You could make the plug end a separate layer and just parent it to the last bone.

12-28-2017, 09:22 AM
You could make the plug end a separate layer and just parent it to the last bone.

That is how it is setup. The end is separate and parented, but it is getting wonky.

12-28-2017, 09:44 AM
I think it is because I tried to cheat the length of the cord by scaling one of the first bones to be .5 on Z, and then scaling one of the last bones to be 2.0 on Z. This works fine and keeps the plug the right size if the bones stay pretty straight, but if they get curvy the plug gets distorted - which is a bummer because I thought it was a good way to adjust the length of my cord.

Any other suggestions on adjusting my cord length? I'm hoping to duplicate the same hierarchy several times, and be able to make some cords longer than others (while all the plugs stay the same...)

12-29-2017, 01:03 AM
Yeah: if a parent or grandparent is being scaled up the bone chain, that's what you're interpreting as distortion, ie scaling.

Rather than parenting, use Motion Panel/Controllers and Limits/Position SAME AS ITEM constraints on your XYZ coordinates, in World mode I guess. Note that the plug will not rotate with the Bone at all, unless you do the same with Rotation etc etc blah blah blah.... if you only use Position, it will only "inherit" the Bone's position.

Or: Using Same As Item (SAI) on Position AND Rotation AND Scale is equivalent to Parenting/Childing. But using the Controllers (aka "constraints") allow you to turn off any/all channels of "inheritance"-- it's like Parenting on steroids.

BTW, note that since there is an envelope for Interpolation, you can smoothly slide constrained items from their own keyframed positions to their constrained positions etc etc blah blah blah.... So landing a birdy on a character's hand is easy.

12-29-2017, 03:52 AM

I'm doing something very similar and have the same issue. Instead of parenting the plug to the last bone, what I did was add the plug to the cable object in the same layer. When I add bones, I start the bones at the plug end of the cable and make the first bone the exact length of the plug, then add my first child bone. Adjust the size of that child bone to make it the size needed to properly distort the cable (usually making it smaller than the plug bone), then add as many child bones as needed.

When that first bone for the plug moves and bends, the plug geometry will move with it but not be distorted. I would then use Spline Control to move the rest of the bones to control the movement of the cable. This will mean working backwards from what you're doing I think, but I've used this method before and have gotten good results.

Good luck,