Mechanism Design and Mechanism Dynamics > Mechanism Design > Creating Mechanism Models > Modeling Entities > Servo Motors > User Defined Expression Definition > About the Variables Dialog Box
About the Variables Dialog Box
Access this dialog box from the Expression Definition dialog box, or when creating a user-defined measure in the Measure Definition dialog box. Use this dialog box to select a variable to use in your expression. You can select time (t) or a predefined measure. The list includes only valid measures. These requirements apply to measures you select for expression variables:
You can include one or more measures as part of your expression definition for force motors, forces, torques, or user-defined measures.
You can include one or more parameters as part of your expression. You can use any parameter, including those based on measures you derive from Mechanism Design or Mechanism Dynamics analyses or from analysis feature measures such as distance. The software uses the value of the parameter at analysis start time as the basis for the expression.
The measure name must contain only alphanumeric characters or underscores (_) and the first character must be alphabetic. The alphanumeric characters can be in any language, including Asian-language characters. Measure names cannot include blank spaces.
When defining an expression for force motors, forces or torques, you may select a position, velocity, or system measure, or a user-defined measure that contains only position, velocity, or system measures.
If you are working at the top assembly level, only measures created for the top-level assembly are listed. If you are working with a subassembly or component, only measures created for the current subassembly or component are listed.
Only valid measures appear in the list on the Variables dialog box.
Select a variable by double-clicking or by highlighting the variable and clicking Close to return to the Expression Definition or Measure Definition dialog box. When you close the Variables dialog box, the selected variable appears as part of your expression definition.