Rigify for robots?

Question

I created an armature with rigify and want to use it on a robot. All is working fine (I simply parented the limbs to the bones), but the rotations of the bones is not correct. For example: the elbow should only rotate around the x axis, since for a robot with a hinge it looks broken otherwise.

The same goes for the knee of course, but from what I’ve seen, the knee seems to be handled properly.

And when I rotate the upper arm around the y axis, I also get some strange secondary rotation in the lower arm.

Is there a way to configure rigify so all these joints are completely locked on specific axis?

(I think that adding constraints afterwards is not ideal, since I wouldn’t be able to regenerate the rig?)

Answer 1

Select the Metarig, in Edit Mode select the arm and forearm bones and set their bone roll so to have their X local axis aligned with the desired axis of rotation (in my example there's an empty which represents the desired rot for the forearm), you can use the N panel Bone Roll property or the shortcut Ctrl R.

Then go to pose mode, select the arm bone only, go to bone properties, "Rigify Type" panel, and change the rotation axis from "Automatic" to "X manual".

Set the "Limb Segments" to 1.

Repeat for Right side and for the legs.

Then generate the rig.

This method works also when fingers don't bend the way that's expected, just be aware that Rigify rigs are made of chains of bones, and the Rigify Type panel appears only in pose mode and only on the very first bone of every chain.