Mechanism Design and Mechanism Dynamics > Mechanism Design > Creating Mechanism Models > Measures, Graphs, and Evaluation Methods > Measures > Position, Velocity, and Acceleratioin > About Position, Velocity, and Acceleration Measures
About Position, Velocity, and Acceleration Measures
You can create measures to evaluate position, velocity, or acceleration for points or motion axes in your assembly.
To define position, velocity, or acceleration measures on the Measure Definition dialog box, you must specify a motion axis or a point on your model, a component of the direction vector, and an evaluation method.
If you select a point, you must also select a coordinate system as a frame of reference for the direction of the position, velocity, or acceleration vector. You can select the WCS, an LCS, or a UCS. A shaded, magenta arrow appears on the selected point indicating the direction of the X, Y, or Z axis that is actually used in the calculation. No arrow appears if the component is Magnitude. Consider carefully whether this direction is actually the one for which you want the measurement.
If you select a motion axis, the value of the measure is the position, velocity, or acceleration in the direction allowed by the motion axis' DOF. When you select the motion axis, a shaded, magenta arrow appears. The arrow points in the direction of the DOF for translational motion axes. For rotational motion axes, a double-headed arrow is displayed parallel to the motion axis, indicating the rotational direction.
You can create position measures, for example, if you want to determine the maximum and minimum position of a piston stroke. If you define a piston with force motors, you can use a velocity or acceleration measure to follow the changes in velocity or acceleration during a dynamics analysis. For example, if you are sizing a motor, use these measures to verify that the motion axis has enough speed and acceleration. If you graph the velocity and acceleration and it indicates that the motion axis is moving too slowly, you may not have enough force applied to the mechanism.