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I have a four-bar linkage system in Blender and I need to animate it with bones and armatures. The meshes are in the initial position to start, I just need to create the constraints to keep all 4 linkages together. Normal bone structures are serial or tree linkages, with each child bone only having 1 parent bone. As I understand it, I need a way to make 4 bones all connect together. I do not know if there is a way to have multiple parents, or if there is a way of mimicking the parallel behavior with a serial manipulator. How do you create the bone setup and vertex groups for a parallel linkage? Does this make sense?

This is the wiki page for a four-bar linkage system, in case that helps.

Edit:

I see something similar here, but I don't quite get how they got to the answer. (Like a math question with an answer provided, but no work to show, as I understand it.)

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Generally speaking, you'd create that via IK, which controls angles while keeping lengths constant:

enter image description here

That's your basic parallelogram IK, used for a lot of mechanical rigging. Note that it doesn't have to be a parallelogram-- if you build it with different lengths for your bones, different angles, it still behaves properly.

The IK target (and the first bone of the IK chain) is parented to root, while the last bone, "4", has a 4-bone-long IK bone constraint targeting the IK target. No matter how you rotate the bones, the lengths will not change.

To adjust the structure, you rotate the IK controlled bones.

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  • $\begingroup$ 1. Yes, the lengths are all different 2. So it is the IK that makes the parallel structure work? 3. How did you create the IK chain? I am new to blender, so I am not sure how to replicate you have displayed in the figure aka. how to reproduce your answer. $\endgroup$ Oct 15 '20 at 12:29
  • $\begingroup$ How to make an IK chain is a different question, that I'm sure has been answered numerous times. If you're new to Blender, then you should be watching some general purpose tutorials to get the basic knowledge you need to achieve your own specific goals. $\endgroup$
    – Nathan
    Oct 15 '20 at 14:38
  • $\begingroup$ I am just trying to ask how to replicate your solution. If you could provide a series of steps, I can google each step individually. It is not clear to me what to research next, that is the problem. $\endgroup$ Oct 15 '20 at 16:20

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