# Velocity Driver

Linear and angular velocity components of base and follower body coordinate systems

## Library

Constraints & Drivers

## Description

The Velocity Driver block drives a linear combination of the projected translational and angular velocities of two Bodies. The velocities are projected by inner products on to constant vectors you specify.

The subscripts B and F refer to base and follower bodies, respectively. Let

• vB, vF be the two body velocity vectors, measured in World.

• ωB, ωF be the two body angular velocity vectors, measured in World.

• cB, cF, dB, dF be constant vectors.

The Velocity Driver block specifies the linear combination Ω:

as a function of time f(t). You specify the vectors cB, cF, dB, dF. You also connect a Driver Actuator block to the Velocity Driver.

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 Velocity Driver, this block acts as a time-independent constraint that freezes the constraint linear combination at its initial value Ω(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 loop. 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.

You can also connect a Constraint & Driver Sensor to any Driver block and 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 translation is the follower moving in the direction of the translation axis. 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 Velocity 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, Velocity Driver Base and Follower Body Connector Ports.

Current follower

When you connect the follower (F) connector port on the Velocity 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, Velocity 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.

Velocity Driver Base and Follower Body Connector Ports

## Parameters

The Parameters fields are grouped into three sets, Units, Base velocity coefficients, and Follower velocity coefficients.

### Units

The vectors cB, cF, dB, dF carry the implicit units conversion to convert all velocities to the common linear velocity units of f(t) that you set in the Driver Actuator connected to the Velocity Driver block.

Angular velocity

From the pull-down menu, choose the common units for all angular velocities. The default is `rad/s` (radians/second).

The vectors dB and dF implicitly carry the units conversion of length/angle. The driving function f(t) has the linear velocity units that you set in the Driver Actuator block that you connect to Velocity Driver. If the f(t) units differ from the units set in Linear velocity units in this dialog, the vectors dB and dF implicitly carry the additional units conversion.

Linear velocity

From the pull-down menu, choose the common units for all linear velocities. The default is `m/s` (meters/second).

The driving function f(t) has the linear velocity units that you set in the Driver Actuator block that you connect to the Velocity Driver. If the f(t) units differ from the units set here, the vectors cB and cF implicitly carry the units conversion.

### Base Velocity Coefficients

Angular velocity

Under [x y z], enter the Angular velocity coefficient vectors for the base Body. These are the components of dB. The default is `[1 0 0]`.

In the Fixed in CS pull-down menu, choose which set of coordinates axes, `World` or `Base`, define these vector coefficients. The default is `World`.

Linear Velocity

Under [x y z], enter the Linear velocity coefficient vectors for the base Body. These are the components of cB. The default is `[1 0 0]`.

In the Fixed in CS pull-down menu, choose which set of coordinates axes, `World` or `Base`, define these vector coefficients. The default is `World`.

### Follower Velocity Coefficients

Angular velocity

Under [x y z], enter the Angular velocity coefficient vector for the follower Body. These are the components of dF. The default is `[1 0 0]`.

In the Fixed in CS pull-down menu, choose which set of coordinates axes, `World` or `Follower`, define these vector coefficients. The default is `World`.

Linear Velocity

Under [x y z], enter the Linear velocity coefficient vector for the base Body. These are the components of cF. The default is `[1 0 0]`.

In the Fixed in CS pull-down menu, choose which set of coordinates axes, `World` or `Follower`, define these vector coefficients. The default is `World`.