.ModelicaTest.MultiBody.FourbarVariants.SphericalSpherical .ModelicaTest.MultiBody.FourbarVariants.SphericalSphericalThis is a third version of the "four-bar" mechanism. In this case the three revolute joints on the left top-side and the two revolute joints on the right top side have been replaced by the joint SphericalSpherical that is a rod with two spherical joints on each side. This joint is defined by 1 constraint stating that the distance between the two spherical joints is constant. Using this joint in a kinematic loop reduces the sizes of non-linear algebraic equations. For this loop, only one non-linear algebraic system of equations of order 1 remains.
The SphericalSpherical joint may be massless or may have a point mass in the middle of the rod to approximate in an convenient way the rod mass properties.
Another nice feature is that the length of the connecting rod can be automatically calculated during initialization. In order to do this, another initialization condition has to be given. In this example, the initial value of the distance of the prismatic joint j2 has been fixed (via the "Initialization" menu) and the length parameter of joint "SphericalSpherical" is computed during initialization since parameter computeLength = true is set in the joint parameter menu (this sets "fixed=false" on parameter "length").