Joint where frame_b rotates around axis n which is fixed in frame_a and
where this joint is used in a planar loop providing 2 constraint equations
on position level.
If a planar loop is present, e.g., consisting of 4 revolute joints
where the joint axes are all parallel to each other, then there is no
unique mathematical solution if all revolute joints are modelled with
Joints.Revolute and the symbolic algorithms will
fail. The reason is that, e.g., the cut-forces in the revolute joints perpendicular
to the planar loop are not uniquely defined when 3-dim. descriptions of revolute
joints are used. Usually, an error message will be printed pointing out this
situation. In this case, one revolute joint in the loop has to be replaced by
model Joints.RevolutePlanarLoopCutJoint. The
effect is that from the 5 constraints of a 3-dim. revolute joint,
3 constraints are removed and replaced by appropriate known
variables (e.g., the force in the direction of the axis of rotation is
treated as known with value equal to zero; for standard revolute joints,
this force is an unknown quantity).
CONNECTORS
