Revolute
========

A revolute joint creates a frame that is rotated relative to an existing frame about a motion axis defined in a specified reference frame. An optional rotational stiffness, damping, and equilibrium angle can be used to include rotational spring-damper physics in the joint.

**Keyword Arguments**

:param str name: Name given to the joint, default is uppercase characters in alphabetical order (A, B, C, ...)

:param str ref_point_key: Point at which the joint is displayed

:param str ref_frame_key: Reference frame in which the components of the rotation axis are defined

:param str motion_axis: Axis in which the rotational motion is defined

**Initial States**

:param numeric value: Initial value for the generalized coordinate 

:param numeric rate: Initial value for the generalized speed 

**Spring Parameters**

:param numeric k: Spring constant

:param numeric c: Damping constant

:param numeric equilibrium: Equilibrium angle