# Documentation

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# Revolute

Primitive joint with one rotational degree of freedom

## Library

First Generation/Joints

## Description

The Revolute block represents a single rotational degrees of freedom (DoF) about a specified axis between two bodies. The rotational sense is defined by the right-hand rule. A revolute joint is one of Simscape™ Multibody™ primitive joints, along with prismatic and spherical.

Revolute Motion of Follower (blue) Relative to Base (red)

### 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 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) port.

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

#### Assembly Restrictions on Assembled Joints

This Joint block is assembled and places restrictions on the connected Body CSs.

• If the Joint has no prismatic primitives, the origins of the connected Body CSs on either side of the Joint must be spatially collocated points, to within assembly tolerances.

• If the Joint has one or more prismatic primitives, the origins of the connected Body CSs must lie in the span of the prismatic axes:

Number of Prismatic PrimitivesSpan of Primitive Axes
OneAlong the primitive axis
TwoIn the plane of the primitive axes
ThreeAnywhere in three-dimensional space

## 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 follower rotating in the right-hand rule about the rotation axis.

Current base

When you connect the base (B) connector port on the 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 Base and Follower Body Connector Ports.

Current follower

When you connect the follower (F) connector port on the 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 Base and Follower Body Connector Ports.

Number of sensor/actuator ports

Using this spinner menu, you can set the number of extra connector ports needed for connecting Joint Actuator and Joint Sensor blocks to this Joint. The default is `0`.

The motion of a Revolute is specified in angular units.

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 axis of the DoF that the Revolute represents.

Name

This column automatically displays the name of each primitive joint contained in the Joint block. For Revolute, there is only one primitive joint, a revolute, labeled `R1`.

Primitive

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

Axis of rotation [x y z]

Enter here as a three-component vector the directional axis about which this rotational DoF can move. The default vector is ```[0 0 1]```. The axis is a directed vector whose overall sign matters.

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 axis of rotation is oriented with respect to. This CS also determines the absolute meaning of torque and motion about the joint axis. The default is `World`.

The Advanced tab is optional. You use it to control the way Simscape Multibody 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 Modeling Degrees of Freedom for more on representing DoFs with Joints.

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