Question: Hinge-type animation? Eyes following head?

Allrighty–I’ve fished through tutorials, posts, &c., but have yet to find the answer to this . . . .

I’m working on my first (simple) solo model/armature–a robot (chosen so I don’t yet have to conquer Mt. Mesh Deformation) blatantly ripped off of Sky Captain. Model’s done, armature’s in-progress. How, though, do I configure robotic, hinge-type joints so they only rotate on one plane? I can’t do it simply manually in pose mode, because if the upper waist is twisted the elbows, &c. will no longer smoothly fit on one plane. Is there a constraint that curbs joint movement?

Also, I want to use emitters and/or lights for the eyes, which means they’ll have to be separate from the head mesh. If I place them, on the model, where they should be relative to the rest of the head, and do a “copy location” constraint, will that make them stay put in the head even when the head is rotating? Will they still be able to rotate/pivot/look at things?

I apologize if I’ve just overlooked this somewhere–I’m a can’t find-the-milk-in-the-fridge type guy. Thanks for any help!


Currently there are no bone-rotation constraints in Blender. (But I think the new animation system will address that…)

What I would do is: for each bone that must rotate rigidly: make an action that does the rotation. You can then control the rotation using an action constraint (shameless plug) or through the NLA Editor.

That way, no matter how you twist and bend the waist, the elbows will always spin their gimbles without derailing, as it were.

Hope this helps.

HERE’s a blend file showing how seperate eyes can be attached to a head and follow things using constraints:

In a nutshell:

Make eyes and parent to head
Create empty (I call it EyeFocus) some distance in front of, and parent it to head also (So that eyes will move with head if not looking at anything specific)
Create track-to constraints so that eyes look at EyeFocus
Create follow constraints for each object to be looked at and use IPOs to control when during the scene the eyes look at them.

Does that make sense?

Thank you both! Haven’t had a chance to give these a spin yet, but they make sense, which is a great first step!