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Configure Steering Frame Express 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

Generates a wheeled steering frame that you design in an interactive dialog box. You can choose from pre-defined steering frame designs or create a custom frame design.

Tip  You can click and drag a wheel in the preview section of the dialog box to change the position of the wheel. If the steering frame is user-defined, you also can press the <Shift> key and then click and drag a wheel to change its angle relative to the steering frame.

You also can programmatically generate a steering frame.

Example

Dialog Box Options
Block Diagram Inputs
Block Diagram Outputs

Dialog Box Options

ParameterDescription
Steering TypeSets the overall design of the steering frame you want to create. The design you choose determines which properties of the steering frame you can edit in this dialog box. Select from the following designs:
  • User Defined—Frame is fully customizable, allowing you to set all properties of wheels, such as the number of wheels and their types and positions.
  • Differential—Frame consists of two fixed wheels. The center of a differential steering frame is at the midpoint of the wheel separation.
  • Ackermann—Frame consists of two steering front wheels and two fixed rear wheels. The center of the steering frame is at the midpoint of the width between the rear wheels.
  • Mecanum—Frame consists of four Mecanum wheels. The center of the steering frame is at the midpoint of the rectangle formed by the four wheels.
Angle UnitsSpecifies whether to express the angles of wheels relative to the steering frame in degrees or radians.
WheelsLists wheels that are currently part of the steering frame design. If you select a Steering Type that is not User Defined, you cannot edit this list because pre-defined frames require specific configurations of wheels.

Use the buttons below the Wheels list to add, remove, and copy wheels.
Wheel TypeSpecifies the design for the wheel selected in the Wheels list. Select from the following options:
  • Fixed—Fixed wheels travel forward and backward and cannot change steering angle.
  • Steering—LabVIEW assumes that the steering angle of steering wheels can change instantaneously to satisfy nonslip and pure-rolling constraints.
  • Caster—The steering angle of a caster wheel is the location of the wheel about the pivot attached to the steering frame. Caster wheels have a forward offset from the center point but no lateral offset.
  • Mecanum—Mecanum wheels consist of a series of rollers around the circumference, oriented 45 degrees from the wheel axis.
  • Omni—Omni wheels consist of a series of rollers around the circumference, oriented perpendicular to the wheel axis.


Availability: When Steering Type is User Defined.
Wheel NameSpecifies the identifier assigned to the wheel. You can pass this name to VIs on the Advanced steering palette to programmatically act on a specific wheel.

Availability: When Steering Type is User Defined.
X PositionSpecifies the x-coordinate of the wheel with respect to the center of the steering frame. Negative values represent positions to the left of the center, and positive values represent positions to the right of the center.

Availability: When Steering Type is User Defined.
Y PositionSpecifies the y-coordinates of the wheels with respect to the center of the steering frame. Negative values represent positions to the rear of the center, and positive values represent positions to the front of the center.

Availability: When Steering Type is User Defined.
Frame AngleSpecifies the angle of the wheel frame, measured counterclockwise from the direction of forward travel of the steering frame as viewed from above. A frame angle of 0 is parallel to the direction of forward travel of the steering frame. Express this value in radians or degrees according to the option you select in the Angle Units pull-down menu.

Availability: When Steering Type is User Defined.
Wheel RadiusSpecifies the radius of the wheel. You can use any unit of measurement to specify distance values. However, always use consistent units when you specify these values.
Gear RatioSpecifies the ratio of motor velocity to wheel velocity in the forward direction.
Forward Rotation DirectionSpecifies the direction in which the wheel turns when the wheel rotates forward, given an end-on view of the wheel axle. Choose from clockwise or counterclockwise.

Availability: When Steering Type is User Defined.
Max Steering AngleSpecifies the largest possible counterclockwise angle formed between the wheel axle and the frame of reference of the steering frame.

Availability: When Steering Type is User Defined and Wheel Type is Steering.
Min Steering AngleSpecifies the largest possible clockwise angle formed between the wheel axle and the frame of reference of the steering frame.

Availability: When Steering Type is User Defined and Wheel Type is Steering.
Steering Gear RatioSpecifies the ratio of motor angle to wheel angle in the direction of steering.

Availability: When Steering Type is User Defined and Wheel Type is Steering.
Motor Angle OffsetSpecifies the difference of the motor angle and the product of the steering gear ratio and the steering angle.

Availability: When Steering Type is User Defined and Wheel Type is Steering.
Steering RangeDefines possible steering angles of the wheel. You can use either this control or the Max Steering Angle and Min Steering Angle options to set this range. This VI measures steering angles counterclockwise from the wheel frame angle as viewed from above, so angles to the left of the frame angle are positive values and angles to the right are negative values.

Availability: When Steering Type is User Defined and Wheel Type is Steering.
Forward OffsetSpecifies the distance between the center of the wheel and the center point attached to the steering frame.

Availability: When Steering Type is User Defined and Wheel Type is Caster.
Caster Gear RatioSpecifies the ratio of motor velocity to wheel velocity in the caster steering angle. This VI uses caster gear ratio only if you use the caster motor communication input to connect the wheel to a motor and then communicate wheel data to the motor.

Availability: When Steering Type is User Defined and Wheel Type is Caster.
Roller OrientationSpecifies the direction in which the Mecanum wheel rollers angle. Left means the rollers meet the ground surface angle 45 degrees from the wheel shaft in the counterclockwise direction. Right means the rollers meet the ground surface angle 45 degrees from the wheel shaft in the clockwise direction.

Availability: When Steering Type is User Defined and Wheel Type is Mecanum.
Wheel SeparationSpecifies the distance between the two fixed wheels.

Availability: When Steering Type is Differential.
Wheel Separation WidthSpecifies the distance between the wheels on the left and right sides of the steering frame.

Availability: When Steering Type is Ackermann or Mecanum.
Wheel Separation LengthSpecifies the distance between the front and rear wheels of the steering frame.

Availability: When Steering Type is Ackermann or Mecanum.

Block Diagram Inputs

ParameterDescription
error inDescribes error conditions that occur before this node runs.

Block Diagram Outputs

ParameterDescription
steering frame outReturns a reference to the steering frame you designed in the interactive dialog box. You can wire this output to other Steering VIs.
error outContains error information. This output provides standard error out functionality.

Example

Refer to the Configurable Steering.lvproj in the labview\examples\robotics\Steering\Configurable Steering directory for an example of using the Configure Steering Frame VI.


 

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