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Apply Velocity to Wheels VI

LabVIEW 2013 Robotics Module Help

Edition Date: June 2013

Part Number: 372983D-01

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Owning Palette: Steering VIs

Requires: Robotics Module

Calculates the state of each wheel necessary to satisfy the steering frame velocity or arc velocity at the center of the steering frame. You must manually select the polymorphic instance to use.

Examples

Use the pull-down menu to select an instance of this VI.

Apply Steering Frame Velocity to Wheels

wheel indexes specifies the indexes of the wheels on which to operate, where 0 corresponds to the first wheel you added to the steering frame, 1 corresponds to the second wheel, and so on.
apply data to motors determines whether this VI applies the calculated wheel states this VI calculates for each wheel to any corresponding motors. The default is FALSE.

If you used the Motor Communication VIs to connect wheels on the steering frame with motors, you must specify TRUE to update the communication sessions with the new motor velocity and angle setpoints this VI calculates.
steering frame in is a reference to the steering frame on which to operate. Use the Create Steering Frame VI to generate this LabVIEW class object.
steering frame velocity specifies the velocity of the steering frame in the form of [x_dot, y_dot, theta_dot] where x_dot is the velocity in the lateral, or right, direction, y_dot is the velocity in the forward direction, and theta_dot is the angular velocity in the counterclockwise direction.
error in describes error conditions that occur before this node runs. This input provides standard error in functionality.
constraint error tolerance is the maximum allowable difference between the value this VI calculates for the steering angle of a wheel and possible values for the steering angle given kinematic constraints of the steering frame. If the difference is greater than constraint error tolerance, LabVIEW returns a warning with the name of the last wheel whose steering angle is out of range. The default is 1E-12.
steering frame out is a reference to the steering frame. You can wire this output to other Steering VIs.
coerced steering frame velocity contains a coerced value of the steering frame velocity if any kinematic constraints of the steering frame cause the velocity to change from the input value. Otherwise, coerced steering frame velocity is the same as steering frame velocity.
calculated wheel states is an array of clusters that define the state of each wheel on the steering frame.
wheel name contains the identifier for the wheel.
forward angular velocity contains the rate of rotation, specified in radians per second, of the wheel in the forward direction.
caster angular velocity contains the rate of rotation of a caster wheel around the wheel pivot that attaches to the steering frame. If the wheel is not a caster wheel, LabVIEW returns 0.
caster wheel angle (rad) contains the orientation of a caster wheel with respect to the wheel pivot that attaches to the steering frame. If the wheel is not a caster wheel, LabVIEW returns 0.
steering angle (rad) contains the orientation of the wheel with respect to the wheel frame. If the wheel is not a steering wheel, LabVIEW returns 0.
error out contains error information. This output provides standard error out functionality.

Apply Arc Velocity to Wheels

wheel indexes specifies the indexes of the wheels on which to operate, where 0 corresponds to the first wheel you added to the steering frame, 1 corresponds to the second wheel, and so on.
apply data to motors determines whether this VI applies the calculated wheel states this VI calculates for each wheel to any corresponding motors. The default is FALSE.

If you used the Motor Communication VIs to connect wheels on the steering frame with motors, you must specify TRUE to update the communication sessions with the new motor velocity and angle setpoints this VI calculates.
steering frame in is a reference to the steering frame on which to operate. Use the Create Steering Frame VI to generate this LabVIEW class object.
arc velocity is a cluster whose elements define the arc velocity of the steering frame.
turning radius specifies the turning radius of the circular arc. A value greater than 0 indicates counterclockwise rotation, and a value less than 0 indicates clockwise rotation.
tangential velocity specifies the velocity of the vehicle in the direction tangential to the circular arc, or perpendicular to a line between the center of the circle and the vehicle.
angle from tangent (rad) specifies the angle of the steering frame, measured counterclockwise from the vector tangent to the circular arc.
error in describes error conditions that occur before this node runs. This input provides standard error in functionality.
constraint error tolerance is the maximum allowable difference between the value this VI calculates for the steering angle of a wheel and possible values for the steering angle given kinematic constraints of the steering frame. If the difference is greater than constraint error tolerance, LabVIEW returns a warning with the name of the last wheel whose steering angle is out of range. The default is 1E-12.
steering frame out is a reference to the steering frame. You can wire this output to other Steering VIs.
coerced arc velocity contains coerced values of the arc velocity of the steering frame if any kinematic constraints of the steering frame cause the velocity to change from the input value. Otherwise, coerced arc velocity is the same as arc velocity.
turning radius contains the calculated turning radius of the circular arc. A value greater than 0 indicates counterclockwise rotation, and a value less than 0 indicates clockwise rotation.
tangential velocity contains the velocity of the vehicle in the direction tangential to the circular arc, or perpendicular to a line between the center of the circle and the vehicle.
angle from tangent (rad) contains the angle of the steering frame, measured counterclockwise from the vector tangent to the circular arc.
calculated wheel states is an array of clusters that define the state of each wheel on the steering frame.
wheel name contains the identifier for the wheel.
forward angular velocity contains the rate of rotation, specified in radians per second, of the wheel in the forward direction.
caster angular velocity contains the rate of rotation of a caster wheel around the wheel pivot that attaches to the steering frame. If the wheel is not a caster wheel, LabVIEW returns 0.
caster wheel angle (rad) contains the orientation of a caster wheel with respect to the wheel pivot that attaches to the steering frame. If the wheel is not a caster wheel, LabVIEW returns 0.
steering angle (rad) contains the orientation of the wheel with respect to the wheel frame. If the wheel is not a steering wheel, LabVIEW returns 0.
error out contains error information. This output provides standard error out functionality.

Examples

Refer to the following VIs for examples of using the Apply Velocity to Wheels VI:

  • labview\examples\robotics\Steering\Differential Steering\Differential Steering.lvproj
  • labview\examples\robotics\Steering\Ackermann Steering\Ackermann Steering.lvproj

 

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