Purpose of 6-DOF Joint in Robotic Architectures

In MathWorks example robotic architectures, 6-DOF joint is used in Biped Robot and Quadruped Robot whereas it is not used in Humanoid Robot. So, what is the exact reason of usage of 6-DOF joint? What is its functionality? Is it inevitable to use 6-DOF joint for a moving architecture in 3D environment?

Answer 1

[Steve Miller]

The 6-DOF Joint is typically used to set the initial position of the robot body. The initial positions of the arms, legs, or other parts will be set in the individual joints.

In some cases, the joint limits will be enabled to prevent the robot body from going through the floor.

--Steve

[Kevin]

I’m struggling to get my robot to not slide or fly away when I don’t have it welded in place. I’m starting from an onshape assembly that I’ve imported to simscape. If I fix the torso to the origin in onshape then the assembly is stable in simscape and the legs can be given signals to move however, I want to simulate walking so I tried to use a 6dof joint and the thing either zooms off like it has a rocket engine strapped to its back or do some twirl into the air. I just don’t understand what it is that’s going on.