shoulder rig, whose movement is divided into 3 joints

[vladvitov78]

• Hello! I'm making a rig for a humanoid robot (mech), and the shoulder of this 3D model is divided in such a way that instead of using 1 joint, I needed to divide it into 3 joints. One for bending the shoulder, another for raising the shoulder sideways, and the third allows the shoulder to rotate around its own axis. Is there any reliable way to control this setup using IKHandle?

[FelipeFierro]

Hi!

You could avoid unwanted movements by splitting the setup into multiple IK chains. For example, use one IK just for the shoulder assembly and another separate IK for the arm itself, like in the example image. That way, the shoulder joints can handle the mechanical shoulder motion independently, while the arm IK controls the arm without causing unwanted rotations or offsets in the shoulder system.

This approach is usually much more stable for mech rigs compared to trying to drive all 3 shoulder joints from a single IKHandle.

[vladvitov78]

Hi!

Thanks for the response, but I don't think it will work in my case. I'll attach a couple of images of what I'm dealing with to make the situation clearer.

Z_rotate_jnt

 

Y_rotate_jnt

 

X_rotate_jnt

 

 

 

 

[FelipeFierro]

Oh I see, in that case, you can create a fourth helper joint that's gonna be the parent of the others, setup that joint as parent using a parentConstraint with rotation turned off. Then use that helper joint as the start of the IK chain.

That way, the other joints follows the ik shoulder position correctly, while the actual shoulder joints remain free to rotate independently. The child joints will still move accordingly because they inherit the translation, but you avoid the unwanted rotational behavior.

[lauri_barnhart]

@vladvitov78 - Welcome! Thanks for your question.

Did the information provided by FelipeFierro help?

If yes, please mark the reply as the accepted solution.

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In case you still need help, please provide an update here so we can help you best moving forward.

Best,

[vladvitov78]

Well, I've tried various methods, and the most effective approach is to create a separate IK chain of joints, then split the IK shoulder rotation into three components for the corresponding joints. However, I encounter a gimbal lock for Zrotate_shoulder_jnt, regardless of the rotation order I choose. Therefore, I believe that IK control is not possible for this setup, or I need to use some unknown methods.