How to control a ball joint

asked 2017-06-08 07:27:38 -0500

felix gravatar image

Hi,

I'm trying to simulate a simplified version of the human body. Up to know, I was giving only one degree of freedom (DoF) to each joint, and it works quite well.

However, I realized that I need to have all 3 DoFs at the shoulder (ie having a ball joint = spherical joint) in order to perform some of the movements I want to simulate. I replaced the rotation joint by a ball joint in the SDF file without problems.

The problem is that I have no Idea how to control the 3 degrees of freedom (3 rotation) : how are the 3 rotation axis defined? How do I get the 3 angles? And how can I put a torque on one of this axis?

Or do I have to use 3 revolution (hinge) joints instead? If so, how shall I connect them (I tried rapidly with 2 links of no length, no collision, and a near zero mass and inertia (not exactly 0 but a mass of 0.0001 and inertia of 0.00000000000000000000000001), but the robot exploded after a few moments.

Thank you very much in advance Felix

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