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I'm trying to rig a robot leg that has 3 different pieces (thigh, knee & shin), but I would like to use the standard biped armature, so the leg has only 2 bones.

All fine, it moves nicely, but the knee piece is deforming when I move the bones, it gets squished the nearer the bones are:

Bone Squishing

The middle piece is 0.5 weight for each bone, maybe I shouldn't do like that, but I'm not sure how would be the best way to do that. I tried adding constrains instead of using the armature deform, but it is very mad lol.

Any tips? Thanks

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  • $\begingroup$ Can you upload your file please ? $\endgroup$ – Leander Oct 18 '16 at 17:42
  • $\begingroup$ How do you want the knee piece to behave when moving the bones? An example of what you want to achieve would be very helpful for us to guide you to the right direction. $\endgroup$ – Polosson Oct 18 '16 at 17:50
  • $\begingroup$ I want the knee to look like a solid metal piece, not deforming. The movement is exactly like it is, an angle in between both bones. And I added the .blend on the post. $\endgroup$ – Kinosei Oct 18 '16 at 20:39
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1. Armature Modifier Settings

Check Preserve Volume in the Amature Modifier.
preserve volume, armature modifier

2. Method using an additional knee bone

  1. Add a Knee bone. Shift+A
  2. Parent the Knee bone to the Thigh bone (connected). Ctrl+P
    enter image description here
  3. Go into pose mode.
  4. Add a Copy Rotation Constraint from the Thigh to the Knee bone.
  5. Add a Copy Rotation Constraint from the Shin to the Knee bone.
    enter image description here
  6. Set the Influence to 0.5 on the second Copy Rotation Constraint.
    enter image description here
  7. Create the correct Weight Groups for the knee with the new bone.
  8. The knee will be orientated wrong. Apply the current orientation as the rest pose. Ctrl+A
    enter image description here

The .blend file of the second method.

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  • $\begingroup$ Strange... I've seen this preserve volume option and had tried it before asking here, but it didn't work. Now I tried again and it works fine. I think it's the easiest way to do that. Thanks! $\endgroup$ – Kinosei Oct 19 '16 at 14:53
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Could be sufficient to add a small knee-bone between the others, which is the only one to move the knee?

enter image description here

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  • $\begingroup$ If I do that, I will not be able to use normal biped animations. $\endgroup$ – Kinosei Oct 19 '16 at 14:50

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