Markers

Use the Markers tool to create coordinate systems and reference frames.

A marker entity is an orthonormal, right-handed coordinate system and reference frame in MotionView. A marker must belong to a body. The body can be any type: rigid, flexible, or point mass. The default marker that belongs to the ground body (Newtonian reference frame) at the global origin is called global frame.

The topological information required to define a marker is shown in the figure below:



Figure 1.
In MotionView you can create the following types of markers:
  • Non-Floating (single or pair)
  • Floating (single or pair)

A fixed marker belonging to a body is fixed with regard to the body’s reference frame. To attach a marker on a body, a location and orientation need to be specified.

Even though a floating marker belongs to a body, it is not fixed within the body reference frame. Floating markers are generally used in entities such as a vector, force, or a bushing.

Marker is a primary entity in a multibody system. All entities that comprise of a multibody system are represented in the solver using markers. For example, a CG marker represents a body at the specified marker location and the mass is assumed be located at the origin of the CG marker. A revolute joint is represented by imposing constraints along five directions between two markers (referred as I & J markers), each on the two bodies between which the joint is defined. A similar concept exists for other entities, such as forces. Some entities, such as vectors, forces, or bushings require their J marker to be coincident with the I marker. Hence the J marker needs to move with respect to its body reference frame, thereby such markers are defined as floating markers.

While defining entities such as bodies, joints, and forces in MotionView, markers are implicitly created. However, there are occasions where markers need to be explicitly created. For example, to define an output at a certain location where there are no other entities, or to define a reference frame for a force.

Create Markers

A marker is a coordinate system attached to a body that is used as a reference for other entities such as joints, forces, motions, and output requests.

  1. From the Browser, select the system to which the marker entity is to be added.
  2. From the Geometry ribbon, click the Markers tool.
    A guide bar for entity creation appears.
  3. Optional: Select the Pair check box to create a pair entity.
    A marker entity, like most of the entities that are created in MotionView, can be a single entity or a pair entity. Pair entities help to create models that are symmetric about the Z-X plane of the model. Their properties can also be symmetric about the Z-X plane (in other words, the Y property is mirrored). Asymmetry or symmetry of the markers can be decided or specified when editing the created marker.
  4. Select a body reference.
    • Select a body in the modeling window.
    • On the guide bar, click the Advanced Selector and make your selection in the Model Tree.
  5. Select an origin reference.
    • Select a point in the modeling window.
    • On the guide bar, click the Advanced Selector and make your selection in the Model Tree.
  6. Optional: Click to reset the entity selections and select new entities.
  7. Once the reference selections are made, create the marker using one of the following methods:
    • Click on the guide bar to create and orient the entity.
    • Click the button that appears at the mouse location in the modeling window.
    • Click to create the entity and exit the guide bar selections for this marker.
    Once the marker has been added to the model, the corresponding marker will automatically be displayed in the browser area.
    Note: By default, variables names of entities in MotionView follow a certain convention. For example, all markers entities have a variable name starting with 'm'. This is the recommended convention to follow when building models in since it has many advantages in model editing and model manipulation.
Tip: A new marker can be created from the Project Browser by right-clicking on the Model label (or any system/analysis of your choice) and selecting Add > Reference Entity > Marker or by right-clicking Markers and selecting Add Marker.

Edit Markers

In addition to specifying an associated body and an origin, you must specify the axes' rules to define a marker.

  1. If the Marker panel is not currently displayed, select the desired marker by clicking on it in the Project Browser or in the modeling window.
    The Marker panel is automatically displayed.
  2. Review your selections for the parent body and point of origin.
  3. If needed, modify any of the defined reference entities.
    • Click a collector to activate it then make your selection in the modeling window.
    • Double-click a collector and make your selection in the Model Tree
    Note: If the selected marker is a pair entity, first distinguish between the Left and Right tabs in the panel, and then edit the properties. When defining a pair marker, use pair entities for Body, Point, etc.
  4. Use the orientation options to orient the coordinate system.