Description:

The coordinate system is right hand rule. X cross Y gives Z and Roll is right hand rule about X, Pitch is right hand rule about Y, and Yaw is right hand rule about Z.

Vector Storage:

All linear three vectors (LinPos, LinVel) store their values as [X, Y, Z].
All angular three vectors (AngVel) store their values as [Roll, Pitch, Yaw].
The transformation matrix TM is stored:

Pre-multiplying a local vector by the TM will generate the vector in global coordinates.

Multibody Dynamics, Link Numbers and 60 and 20 Length Vectors:

Please refer to Multibody Dynamics and 60 Length Vectors for information on 60
length vectors.

Methodology:

The universal joint models two revolute joints and a body with Mass and angular Inertia. LocalJointAxis defines the axis along which the downstream body cannot rotate about the upstream body.

The LocalJointAxis is defined in the local coordinates of the upstream body's coordinate system.

The universal joint is modeled using a combination of two Revolute components and a MassMB component. The universal joint calculates the joint axes of the revolute joints such that they are perpendicular to each other and to the LocalJointAxes.

The multibody solver calculates the actual joint acceleration, which is integrated and output in
JointAng, JointAngRate, JointVel and JointPos.
 

SimRealVar Force1[60] - Global Force (N)
SimRealVar Moment1[60] - Global Moment (Nm)

Outputs:

SimRealVar LinAccel1[60] - Global Linear Acceleration (m/s/s)
SimRealVar LinVel1[3] - Global Linear Velocity (m/s)
SimRealVar LinPos1[3] - Global Linear Position (m)
SimRealVar AngAccel1[60] - Global Angular Acceleration (rad/s/s)
SimRealVar AngVel1[3] - Global Angular Velocity (rad/s)
SimRealVar TM1[9] - Transformation Matrix (ND)
SimRealVar LinkNumber1[20] - Link Number Output (ND)
 

SimRealVar Inertia[3] - Inertia of Body (kg-m-m)
SimRealVar Mass - Mass of Body (kg)
SimRealVar CGOffset[3] - CG Offset in Body Coordinates (m)
SimRealVar LocalJointAxis[3] - Local Joint Axis (ND)
 

SimRealVar LinAccel3[60] - Global Linear Acceleration (m/s/s)
SimRealVar LinVel3[3] - Global Linear Velocity (m/s)
SimRealVar LinPos3[3] - Global Linear Position (m)
SimRealVar AngAccel3[60] - Global Angular Acceleration (rad/s/s)
SimRealVar AngVel3[3] - Global Angular Velocity (rad/s)
SimRealVar TM3[9] - Transformation Matrix (ND)
SimRealVar LinkNumber3[20] - Link Number Output (ND)

Outputs:

SimRealVar Force3[60] - Global Force (N)
SimRealVar Moment3[60] - Global Moment (Nm)
 

Outputs:

SimRealVar JointAng[2] - Joint Angle (rad)
SimRealVar JointAngRate[2] - Joint Angular Rate (rad/s)
 

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