Define gravity and other external forces and torques

External forces and torques act on assembly components, but are not part of a joint in the mechanism. Gravity is a special case of an external force that acts upon the entire mechanism.

Use an entity to define gravity

  1. On the Dynamic Simulation browser, under the External Loads folder, right-click Gravity .
  2. From the context menu that appears, select Define Gravity.

    The Gravity dialog box opens.

  3. If necessary, clear the check mark from the Suppress box.

    Gravity is suppressed by default.

  4. Click Entity.

    The Direction and Value parameter fields become available.

  5. Click the selection arrow .
  6. In the graphics window, select the entity where you want to define gravity.

    The entity must belong to the Grounded group.

    A yellow arrow appears on the selected entity.

  7. If you must change the direction of the gravity arrow, click Reverse direction .
  8. If necessary, enter the value you want to set for gravity in the Value box.

    By default, this value is set to 386.220 in/s 2 or 9810,0 mm/s 2 .

  9. Click OK.

Show Me how to define gravity

Use vector components to define gravity

  1. On the Dynamic Simulation browser, under the External Loads folder, right-click Gravity .
  2. From the context menu that appears, select Define Gravity.

    The Gravity dialog box opens.

  3. If necessary, clear the check mark from the Suppress box.

    Gravity is suppressed by default.

  4. Click Vector Components.

    The g[X], g[Y], and g[Z] fields become available.

  5. In g[X], enter the value of the X axis vector component of gravity in the assembly’s coordinate system.
  6. In g[Y], enter the value of the Y axis vector component of gravity in the assembly coordinate system.
  7. In g[Z], enter the value of the Z axis vector component of gravity in the assembly coordinate system.
  8. Click OK.

Use two locations to define an external force or torque

  1. On the ribbon, click Dynamic Simulation tab Load panel Force .
  2. Alternatively, click Dynamic Simulation tab Load panel Torque if you want to add a torque.

    The Torque dialog box opens.

  3. Click Location and then select the force or torque application point on a component in the graphics window.
  4. Click the second Location and then select a second point in the graphics window.

    The two selected points define the direction of the force or torque vector , with the base at the first point selected and the tip of the arrow at the second point selected.

  5. If necessary, click Reverse direction to flip the direction of the force or torque vector.
  6. In the Magnitude text box, define the value of the force or torque magnitude.

    You have the option of entering a constant value or a value that varies during simulation .

    • Click at the right of the box to open a menu.
    • From the data type menu, select either Constant value or Input grapher.
    • If you select Constant value, enter the value in the Magnitude text box.
    • If you select Input grapher , click the icon that appears in the Magnitude text box and use the Input Grapher to define a value that varies during the simulation.
  7. Click Fixed Load Direction to fix the direction of the force or torque in the absolute coordinate system of the assembly.
  8. Alternatively, click Associative Load Direction to associate the direction of the force or toque with the component containing the force or torque.
  9. For the force or torque vector to appear in the graphics window, click Display to make the force or torque vector visible.
    • If necessary, change the scale of the force or torque vector so that all of the vector is visible.

      This value defaults to 0.01.

    • If you want to change the color of the force or torque vector, click the color box to open the Microsoft Color dialog box and select a color for the force or torque vectors
  10. Click OK.

Use vector components to define an external force or torque

  1. On the ribbon, click Dynamic Simulation tab Load panel Force .
  2. Alternatively, click Dynamic Simulation tab Load panel Torque if you want to add a torque.

    The Torque dialog box opens.

  3. Click Location and select the force or torque application point on a component in the graphics window.
  4. To use vector components to define the force or torque, click More .
  5. Click Use Vector Components.

    The Fx or Tx, Fy or Ty, and Fz or Tz component fields become active. The vector components are expressed in the displayed coordinate system.

  6. In each Force or Torque Vector Component text box, define the value of the force or torque component magnitude.

    You have the option of entering a constant value or a value that varies during simulation.

    • Click at the right of the box to open a menu.
    • From the data type menu, select either Constant value or Input grapher .
    • If you select Constant value, enter the value in the vector component magnitude text box.
    • If you select Input grapher, click the icon that appears in the vector component magnitude text box and use the Input Grapher to define a value that varies during the simulation.
  7. For the force or torque vector to appear in the graphics window, click Display to make the force or torque vector visible.
    • If necessary, change the scale of the force or torque vector so that all of the vector is visible.

      This value defaults to 0.01.

    • If you want to change the color of the force or torque vector, click the color box to open the Microsoft Color dialog box and select a color for the force or torque vectors
  8. Click OK.

Show Me how to add force and torque

Parent topic: Physical environment