```{raw} latex \clearpage ``` # General info for all joints ## What a joint is A joint is a constraint between two rigid markers - `MarkerBodyRigid`, `MarkerNodeRigid`, a super element or kinematic tree marker - which fixes some of the relative motions of the two frames and leaves the others free: the revolute joint the rotation about one axis, the prismatic joint the translation along one axis. Everything the page of the constraints says - Lagrange multipliers, index 3 and index 2, `activeConnector`, redundant constraints - holds for the joints. ## Joint frames The free axes are those of a **joint frame** in each marker: `rotationMarker0` and `rotationMarker1` rotate the marker frames into the joint frames, and `ObjectJointRevoluteZ`, for example, turns about the local $z$-axis of the joint frame. `mbs.CreateRevoluteJoint`, `CreatePrismaticJoint`, `CreateSphericalJoint` and `CreateGenericJoint` take a global position and axis and compute the markers and the joint frames. ## Reaction forces The multipliers of a joint are its reaction forces and torques; the output variables give them - `ForceLocal` and `TorqueLocal` in the joint frame $J0$ of marker 0 for most joints, `Force` in the global frame for the spherical joint -, as the page of each joint lists them. (sec-drawing-objectsjoint)= ## Drawing A joint is drawn as a connector: if `connectors.show` and its own `show` are True, at the positions of its markers, in its `color` or `connectors.defaultColor`, a `drawSize` of -1 takes `connectors.defaultSize`, and `connectors.showNumbers` writes its number. The 3D joints draw their axes as cylinders (`general.cylinderTiling`) and, with `connectors.showJointAxes`, the frames of their markers (`connectors.jointAxesLength`, `connectors.jointAxesRadius`, `general.axesTiling`); the 2D joints draw circles. The settings: [`connectors.show`](#sec-vsettingsconnectors), [`connectors.showNumbers`](#sec-vsettingsconnectors), [`connectors.defaultColor`](#sec-vsettingsconnectors), [`connectors.defaultSize`](#sec-vsettingsconnectors).