Revolute-Rotational Interface

Connection interface between revolute primitive and Simscape mechanical rotational elements


First Generation/Interface Elements



This content is specific to Simscape™ Multibody™ First Generation software. First-generation features are slated to be deprecated and should be avoided.

This block connects a Simscape Multibody revolute joint primitive with mechanical rotational elements from the Simscape Foundation library. Dynamically, such a connection is equivalent to connecting the mechanical rotational elements between the two bodies that are connected to the revolute primitive. The validity of the connection is guaranteed only if the Simscape Multibody and Simscape mechanical modeling rules are both respected.

Simscape software supports a domain representing one-dimensional rotational motion. In a Simscape mechanical rotational circuit, torque flows through a connection line, while angular velocity is defined across nodes connected by connection lines. The Revolute-Rotational Interface block rigidly couples a Simscape Multibody revolute primitive to a Simscape mechanical rotational degree of freedom. By itself, this interface adds or removes no degrees of freedom (DoFs) to or from the combined machine-circuit. Revolute-Rotational Interface preserves torque through and angular motion across the block, conserving mechanical power.

  • The mechanical connector port acts, on the Simscape Multibody side, like a torque-actuated Joint Actuator, feeding torque from the circuit through the connected Joint to its connected Bodies, while maintaining the angular velocity across the block. The torque exerted by the Simscape mechanical rotational elements is applied between the two Simscape Multibody bodies about the Joint revolute primitive axis.

  • The physical conserving ports act, on the Simscape side, like a motion actuator, feeding a prescribed motion from the machine into the circuit, while preserving the flow of torque through the block. The motion of the Simscape Multibody bodies about the Joint revolute primitive axis is applied as relative motion between the Simscape mechanical rotational ports of the block.

  • The directionality of motion (base-to-follower, or B-to-F) is preserved across the interface, from the directionality of the connected Joint to the directionality of torque and angular motion in the Simscape circuit.

You interface the machine and the mechanical circuit through the block ports.

  • Connect the Simscape Multibody port P to a Sensor/Actuator port on a Joint. In the Interface block dialog, you then choose which revolute primitive in that Joint should be connected to the Simscape circuit through this interface.

  • Connect the Simscape mechanical rotational ports (B and F) along the circuit connection line, which in turn connects to Simscape mechanical rotational elements.

Joint Block Required for Complete Interface

The complete interface between a Simscape Multibody machine and a Simscape mechanical circuit includes both an Interface block and its connected Joint block containing the joint primitive chosen to couple to the one-dimensional circuit.

Avoiding Inertias in the Interfaced Simscape Circuit


Simulating with inertia elements in a Simscape circuit interfaced to a Simscape Multibody machine leads to unphysical results.

To avoid such unphysical situations, model all inertias in your machine using Simscape Multibody Body blocks, and do not include inertia elements in the Simscape circuit interfaced to a Simscape Multibody machine.

The dynamics of a Simscape inertia element is simulated only:

  • About one dimension (the chosen revolute primitive axis)

  • With torques on the inertia element explicitly modeled by blocks and connections in the circuit

If a Simscape mechanical circuit is interfaced to a Simscape Multibody machine and includes inertia elements:

  • The acceleration of the circuit's frame within the larger machine and thus noninertial pseudoforces are neglected in the dynamics of the circuit's inertia elements.

  • The interfaced Joint, from the point of view of the machine, effectively carries any inertias modeled in the interfaced circuit. Simscape Multibody Joints are assumed massless.

Dialog Box and Parameters

The dialog has one active area, Primitive. The block parameters are not displayed unless you connect it to a specific Joint block.


When connected to a Joint block, the dialog lists all the revolute primitives present in the Joint.

Connected to primitive

From the pull-down menu, select the revolute primitive in the Joint that you want to connect to the mechanical rotational elements.


These demos illustrate how to interface between a three-dimensional machine and a one-dimensional mechanical rotational circuit.

See Also

For more about using Interface Element blocks, see Combining One- and Three-Dimensional Mechanical Elements.

For more about dynamics, see Mechanical Dynamics.

Consult the Simscape documentation for more about one-dimensional domains.

Body, Joint Actuator, Prismatic-Translational Interface, Revolute

Introduced in R2007b

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