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# Cylindrical

Related class: VxDynamics::Cylindrical

The cylindrical joint is a two-part constraint, which simulates a tubular block sliding on a cylindrical rod, thereby allowing both linear and angular movements between the attached parts. It acts like a prismatic and a hinge combined, thus removing four degrees of freedom between the two parts. The remaining two degrees of freedom, the Linear and Angular coordinates, can be controlled independently. This leaves four uncontrollable coordinates, two linear and two angular, which can optionally be relaxed via the Other Axes tab.

 Controllable coordinates Angular and Linear yielding rotation and displacement of the second part (P1) around the primary axis of the first part attachment (P0). Axes of i'th part attachment are indicated by the set of vectors {ui, vi, wi}.

The cylindrical joint is not symmetric as its two part attachments have different geometric roles:

• The first part attachment represents the rod, which can be understood as a line in 3D space. The rod line is defined by the position and primary axis of the first attachment.
The linear and angular motion of the two attached parts, quantified by the two controllable coordinates of this joint, will occur along and around this line.
As the position and axes of the first attachment are specified relative to the first part, the rod is also fixed relative to the first part.
Consequently, if one of the two attached parts is static, it should be the first one, as this ensures that the rod line is fixed in world frame.
• The second part attachment represents the block, which is is attached to the rod. The position of the second part attachment defines the location at which the block is attached to the rod, and slides along and around it.
Combined with relaxation of the two uncontrollable angular coordinates (see Other Axes tab), this point acts as a springy pivot.

Controllable Coordinates

Name Type Effect
Angular angular Rotation of second part around the primary axis of the first part attachment.
Linear linear Displacement of second part along the primary axis of the first part attachment.