.ModelicaAdditions.MultiBody.CutJoints.ConnectingRod2

Information

A ConnectingRod2 instance is a rod which has a spherical joint on each of its two ends.
It has 5 degrees of freedom. It has no mass and no inertia and is used as cut
joint to break a kinematic loop of a multibody system. It is highly recommended
to use this cut-joint whenever possible, because this enhances the efficiency
considerably.

The third cut frame_c is a frame fixed in the rod at the origin of frame_a
(definition of frame_c: x-axis = rod-axis from frame_a to frame_b;
y-axis = orthogonal to x-axis and to vector na which is fixed in frame_a).
At frame_c body objects can be connected to describe the mass and inertia
proporties of the rod. Since there are spherical joints at each end of the
rod, there is an isolated degree of freedom which allows the rotation of the
rod along the rod axis. This movement usually has no influence on the rest of
the multibody system and is of no technical interest. Mathematically, this
degree of freedom is removed by the additional constraint equation that
the y-axis of frame_c is always orthogonal to the pre-defined vector
na which is fixed in frame_a.

Parameters:
  L : Length of the rod in [m]
  na: Vector fixed in frame_a (i.e., fixed in the body which is
      connected at frame_a) and resolved with respect to the
      inertial frame in the home position. The y-axis of the rod-fixed
      frame_c is defined to be orthogonal to the x-axis and to
      vector na.

The single constraint equation on position level states, that the
distance between the origins of frame_a and frame_b is equal
to the length of the rod. As constraint force fRod (= Lagrange multiplier)
of the joint the force along the rod axis is used.