I use the table to stage my motor, but after digging around found this and it may be the way you want to go
Magnitude as a User-Defined Function
User Defined generates the magnitude of a servo motor, force motor, or force/torque with a function you create using sets of expressions and domain constraints.
For servo motors, you must define magnitude as a function of analysis time.
For force motors and forces/torques, you can define magnitude as a function of time, or as a function of multiple variables that may include time and one or more existing measures. For example, to define a force that decreases directly as the inverse of the separation between two points, first create a distance separation measure named septn1. Then define the force magnitude with the expression 1/septn1.
When you select User Defined as an option for the magnitude definition of a servo motor, force motor, or force/torque, the corresponding dialog box expands displaying the following buttons and fields:
Click to add a new row to the table. The table has a two-column format:
Expression—When you add a new row, this column contains a default expression, representing either time or, if applicable, a measure. You can edit the default expression directly in the table cell.
Domain—When you add a new row, this column contains no values for the expression domain. You can specify the domain values directly in the cell. For example, to enter a range of time between 1 and 10, enter 1 < t < 10.
Be aware that you must define each domain segment in the expression using only the primary variable.
Click if you need to delete selected rows from the expression table.
Click to edit the selected expression or domain. The Expression Definition dialog box appears. Use the dialog box to enter a new algebraic expression and domain. After you enter the new values, Mechanism Design places them in the expression table on the Servo Motor Definition, Force Motor Definition, or Force/Torque Definition dialog box.
Primary Variable—Use the drop-down list to select time or a predefined measure. The selected variable appears in the formula in the Expression column here and in the Expression Definition dialog box. This field is available only on the Force Motor Definition and Force/Torque Definition dialog boxes.
For Mechanism Design to provide a two-dimensional plot of your expression, you must select one variable as a primary variable. Mechanism Design uses the primary variable for the X axis when it graphs your expression, and requires you to supply constant values for the other variables—the secondary variables—in the expression. In addition, you must use the primary variable to specify all domain segments in the expression.
Unit Conversion Factor—This uneditable field becomes visible only when you initially defined the user-defined function in a unit system different from the current one. The field lists the variables included in the expression and the magnitude of the expression and displays the multiplication factors that Mechanism Design uses to convert the numerical values to the current unit system.
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