# Documentation

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# Angle Driver

Driver specifying a time-dependent angle between two body axis vectors

## Library

First Generation/Constraints & Drivers

## Description

The Angle Driver block drives axis vectors defined on two Bodies. You specify fixed base and fixed follower body axis vectors aB, aF in the Body CS on either side of the Driver on each body, then drive the angle between the body axis vectors as a function of time.

The Angle Driver block specifies the angle θ defined by

as a function of time: θ = θ(t=0) + f(t). You connect the Angle Driver to a Driver Actuator block.

The Simulink® input signal into the Driver Actuator specifies the time-dependent driving function f(t) and its first two derivatives, as well as their units. If you do not actuate Angle Driver, this block acts as a time-independent constraint that freezes the angle between the two body axes at its initial value θ(t=0) during the simulation.

Drivers restrict relative degrees of freedom (DoFs) between a pair of bodies as specified functions of time. Locally in a machine, they replace a Joint as the expression of the DoFs. Globally, Driver blocks must occur topologically in closed loops. Like Bodies connected to a Joint, the two Bodies connected to a Drivers are ordered as base and follower, fixing the direction of relative motion.

 Caution:   If the two axes come close to aligning, that is, if θ approaches zero, the constraint between the two axes becomes singular, and the simulation slows down. See How Simscape Multibody Software Works and Handling Motion Singularities.

You can also connect a Constraint & Driver Sensor to any Driver measure the reaction forces/torques between the driven bodies.

## 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-handed sense about the rotation axis.

Current base

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

Current follower

When you connect the follower (F) connector port on the Angle Driver 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, Angle Driver 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 Driver Actuator and Constraint & Driver Sensor blocks to this Driver. The default is `0`.

To activate the Driver, connect a Driver Actuator.

Angle Driver Base and Follower Body Connector Ports

## Parameters

Fixed axis [x y z]

For the Base and Follower bodies, respectively, enter the body axis vectors. The defaults are `[1 0 0]`.

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 Base and Follower body axis vectors are oriented with respect to. This CS also determines the absolute meaning of reaction forces/torques at this Driver. The defaults are `World`.

See Constraining and Driving Degrees of Freedom for more on restricting DoFs with Drivers.

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