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Specify a linear combination of the linear and angular velocities of two bodies as a function of time
Library
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.
Let vB, vF be the two body velocity vectors and B,
F be the two body angular velocity vectors. Let cB, cF, dB, dF be constant vectors. The subscripts `B' and `F' refer to base and follower bodies. The Velocity Driver block specifies this linear combination:
as a function of time f(t). You specify the vectors cB, cF, dB, dF. You also connect the Velocity 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 Velocity Driver, this block acts as a time-independent constraint that freezes the constraint linear combination at its initial value 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.
You can also connect a Driver block to a Constraint & Driver Sensor, which measures the reaction forces/torques between the driven bodies.
Dialog Box and Parameters
The dialog box has two active areas, Connection parameters and Parameters.
Connection Parameters
0
.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.
Velocity Driver base and follower Body Connector Ports
Parameters
deg/s
(degrees/second).m/s
(meters/second).[1 0 0]
.WORLD
or BASE
) whose coordinate axes the vectors dB and cB are oriented with respect to. The defaults are WORLD
.[1 0 0]
.WORLD
or FOLLOWER
) whose coordinate axes the vectors dF and cF are oriented with respect to. The defaults are WORLD
.See Also
Angle Driver, Constraint & Driver Sensor, Driver Actuator, Parallel Constraint
See Modeling Constraints and Drivers for more on restricting DoFs with Drivers.
See Checking Schematic Topology and How SimMechanics Works for more on using drivers in closed loops.
See Creating Constraints and Drivers.
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