Double Hinge

I have a solid base, that has an axle hooked to a set of arms and as it rotates, the arms move a link that moves the primary arm (it is hooked up to a can, but I have it hidden for the picture) lifts a can, who in turn is also moving the upper arm. This mechanical linkage keeps the can vertical. I've gone through youtube tutorials on adjusting the pivot points and locking axis for rotation, and parenting, but that only works with single linked objects and I'm failing to figure out how to make this work. This will be exported for Unity later.

Rigging Here is an example of some rigging I've tried. Even parenting Root2 to Root2.002 but that didn't work either.

Here is an example of the rotated locked track in pose/Object mode (it follows the arm in edit mode) and do you have the details for the locked track constraint? that is one I'm not familiar with. other then that, it works flawlessly so far.

lockedTrack error

  • $\begingroup$ to clarify, the round handle is what will be rotated to make the mechanism work. still stumped $\endgroup$ Commented Sep 8, 2023 at 12:36
  • $\begingroup$ You probably want to control the rotation from that bone, but not the location, right? It's easy enough if that's not true; it's easy enough with some choices of controls. But using that bone for rotation and some other bone for location is complicated, and I'd rather you confirmed that's what you want before going into details. $\endgroup$
    – Nathan
    Commented Sep 8, 2023 at 17:10
  • $\begingroup$ Well, there is another way, but only if your rotation doesn't have to exactly match your control. $\endgroup$
    – Nathan
    Commented Sep 8, 2023 at 17:26
  • $\begingroup$ Its most likely I have the bones wrong in general, or the IK methods are incorrect. The general idea is someone grabs the handle inside the round housing, and rotates it. WHich in turn due to the arm links lifts the can up. $\endgroup$ Commented Sep 8, 2023 at 18:04
  • $\begingroup$ If you want to lift the can up, it's easy enough, you just have to think about your IK slightly differently. I'll show in an answer. $\endgroup$
    – Nathan
    Commented Sep 8, 2023 at 18:57

1 Answer 1


Rest pose on left, hierarchy in outliner. Bones should have reasonable enough names.

enter image description here

We have a two bone IK chain, parented to the control bone; its target is parented to the root bone.

The cylinder/can bone is parented to the second bone in the IK chain, and then copies world space rotation from the IK target, which has the same rest axes as it, to remain parallel.

Finally, the top arm is relatively simple, I just have an cylinder-parented arm that's locked tracking a bone that's parented to the root.

  • $\begingroup$ I would have never thought of that. I'm out tonight and will try it when I get back. $\endgroup$ Commented Sep 8, 2023 at 21:01
  • $\begingroup$ OK I've spent the last 2 days working on/off this. bones easy. did the IK of ik1/2 (target: Armature; Bone: ikt) works. Added the Cylinder, added the copy rotation (target: Armature; Bone: ikt) works. (caveat: if I had the cylinder bone added before the IK, it would b0rk b/w edit/pose mode) now the issues I'm having is the "LockedTrack" bone. "Extending"/Duplicating then parenting to Cylinder will always rotate the new Tracking bone 90deg from Cylinder. $\endgroup$ Commented Sep 11, 2023 at 18:35
  • $\begingroup$ Bone creation order doesn't matter at all; if you're having problems, it's from something else. If you're having trouble with a locked track, you can just use a 1-chain IK instead, it doesn't really matter. Probably, your problems there are with the rest pose bone axes. $\endgroup$
    – Nathan
    Commented Sep 11, 2023 at 20:58
  • $\begingroup$ the 2nd IK worked. Sorry, I don't have the reputation yet to upvote your answer $\endgroup$ Commented Sep 12, 2023 at 14:57

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