Documentation

Revolute-Revolute

Constant-length joint connector with two spatially separated revolute axes

Library

Joints/Massless Connectors

Description

The Revolute-Revolute block represents a composite joint composed of two revolute joint primitives. The Body coordinate systems (CSs) on either side of the Joint are each connected to a revolute primitive. The primitives are separated spatially by a vector of constant length but variable direction connecting the two Body CS origins.

    Warning   This joint becomes singular if the two revolute primitive axes align with the vector separating the primitives. The simulation stops with an error in this case.

Massless Connector Between Revolute and Revolute Joints

Satisfying Joint Requirements

A Joint block represents the relative degrees of freedom between two bodies, not the bodies themselves.

You must connect any Joint block to two and only two Body blocks, the base and the follower. All Joints have a default of two connector ports for these connections, defining the direction of joint motion (base to follower). You connect each side of the Joint block to these Body blocks at a Body coordinate system (CS) point.

You specify the joint primitive axes, if any, in the Joint dialog.

You cannot connect an Actuator or Sensor to a Massless Connector.

Assembly Restrictions on Massless Connectors

Both joint primitives are assembled but spatially separated. That is, the connected Body CS origins must not be spatially collocated points.

The distance separating the two ends of the connector is computed automatically from the Body CS origins to which the Joint is connected. This distance (the magnitude of the vector between the Body CS origins) remains fixed at its initial value during the simulation. This initial value must be nonzero.

Dialog Box and Parameters

The dialog has two active areas, Connection parameters and Parameters.

Connection Parameters

The base (B)-follower (F) Body sequence determines the sense of positive motion. Positive rotation is the base or follower rotating in the right-handed sense about its respective rotation axis.

Current base

When you connect the base (B) connector port on the Revolute-Revolute block to a Body CS Port on a Body, this parameter is automatically reset to the name of this Body CS. See the following figure, Revolute-Revolute Base and Follower Body Connector Ports.

Current follower

When you connect the follower (F) connector port on the Revolute-Revolute block to a Body CS Port on a Body, this parameter is automatically reset to the name of this Body CS. See the following figure, Revolute-Revolute Base and Follower Body Connector Ports.

Revolute-Revolute Base and Follower Body Connector Ports

Parameters

Switch between the Axes and Advanced tabs.

Axes Tab

The entries on the Axes tab are required. They specify the direction of the rotation axes of these DoFs that the Revolute-Revolute represents.

Name

This column automatically displays the name of each primitive joint contained in the Joint block. For Revolute-Revolute, there are two revolute primitives, labeled R1 and R2, connecting to base and follower, respectively.

Primitive

This column automatically displays the type of each primitive joint contained in the Joint block. For Revolute-Revolute, there is only one primitive type, labeled Revolute.

Axis of Action [x y z]

Enter here as a three-component vector the directional axis about which these rotational DoFs can move. The default vectors are [0 0 1] and [0 1 0]. The axes are directed vectors whose overall signs matter.

Reference CS

Using the pull-down menu, choose the coordinate system (World, the base Body CS, or the follower Body CS) whose coordinate axes the vector axes of rotation are oriented with respect to. These CSs also determine the absolute meaning of torque and motion about the primitive axes. The defaults are World.

 Restricted Parameters

Advanced Tab

The Advanced tab is optional. You use it to control the way SimMechanics™ simulation interprets the topology of your schematic diagram.

Mark as the preferred cut joint

In a closed loop, the simulation internally and automatically cuts one and only one joint.

If you want this particular joint to be weighted preferentially for cutting during the simulation, select the check box. The default is not selected.

See Also

Revolute

See Modeling Degrees of Freedom for more on representing DoFs with Massless Connectors.

See Checking Model Topology and How SimMechanics Software Works for more on closed loops and cutting.

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