Got a chain of bones, how do i link the other side to my Armature?

I ran into an armature loop parenting error.

I have a simple chain of bones, with Inverse Kinematics constraints. One side moves around like I want it to. But I don’t know how to get the other end to stay attached to the rest of the rig (air hose between two moving joints).

Essentially this is the slinky problem. You hold a slinky with two hands, the other side isn’t supposed to by held in place by an invisible force, and certainly, if you start walking around, one end isn’t supposed to be locked to that point in space, stretching the slinky out as you move.

How do I unstick the other side of my bone link? How do I get that last bone to stick to some other part of my armature without getting one of those parent loop errors?

I’m simply not following you here, I don’t understand the problem or maybe you don’t have something right about your set up. I use IK all the time, well not all the time, but I use it when needed and I control both ends of the bone chain just fine. A normal biped character will usually have 4 IK bone chains, both arms and both legs.

A normal leg IK chain has 2 bones, upper leg and lower leg, and a foot controller. The upper leg’s parent is the hip controller, move the hip controller and that end of the bone chain moves. The lower leg has the IK constraint and it’s target is the foot contoller. Move the foot controller and the other end of the chain moves. The foot controller cannot be a child of any of those other bones mentioned, usually I make it a child of the character’s root bone. It’s when the IK controller bone is a child of the wrong bone that you get the parent loop error (cyclic dependencies).

So if this doesn’t help, please upload the .blend file so someone can take a look at it.

Randy

how do i upload a 13 meg file?

scissors.blend (451 KB)

OK so i created a crude pair of scissors to illustrate my dilemma (because i figured the smaller file would upload, and they did).

You reduce it to under 10 megs… I think 10 megs is the current file size limit for .blend files. Likewise, image formats have size limits as well. I think I saw this info in a link in the file upload window that opens when you upload a file…

There are ways to reduce file sizes, ask me if you want to know…

I looked at your scissors file. If you are looking to have the spring bone chain automatically controlled when the scissors open and close, I can show you how, it’s very easy.

I just don’t want to spend the time doing so, until I know what you are after. I have spent a lot of time helping others, only to find out that the problem I solved wasn’t the actual problem they had.

Randy

Ah, ok, I see what you are trying to do, rigging hydraulic lines on an excavator.

So I took your scissors file and rigged up the spring…

I added in 2 bones, Handle_ctrl_1 & Handle_ctrl_2, these are the bones that control the handles and will open and close the scissors. I added in another bone, called Spring_base, that’s at the first bone in the ik chain and made the first bone of the ik chain a child of it. Then I made the Handle_ctrl_2 bone a parent of Spring_base. Now when you rotate the Handle_ctrl_2 bone (the bone controlling the blue part), Spring_base bone moves, because it’s a child of the handle bone, and the ik chain moves because it’s a child of Spring_base.

On the purple hande, I added in a bone at the tip of the bone with the IK constraint. Named it Spring_IK_target and made it a child of the Handle_ctrl_1 bone. Now it moves as the purple handle is rotated. Then in the IK constraint, I named this bone as the target bone, and it works.

It’s not perfect, I don’t think the spring bends evenly on the left & right sides, but I don’t think that matters in your case. You’re just doing hoses which can move around unevenly.

Since those hoses are always run in pairs, I think I would try one bone chain, and weight paint both hoses to the chain and see what happens before I would rig each hose individually.

Two other methods to do the same thing would involve using curves. They offer more control and more work to set up…

Randy

Attachments


scissors.blend (413 KB)

Much thanks RR! While i never figured out how to duplicate what you did with the scissors, messing with it and adding more inbetween bones for parenting allowed me to solve my original problem with the excavator. The hydraulic lines bend and curve where and how they should now. I can finally move on to other lessons. :slight_smile: