﻿ Getting Started Tutorials - MechDesigner > Tutorial 16: Motion-Path FB and Blend-Curves > Step 16.1: About the Blend-Curve & Motion-Path FB

# Step 16.1: About the Blend-Curve & Motion-Path FB

### Compare a Motion-Part to a Motion-Point

A Motion-Part and a Motion-Point are very similar elements:

Motion-Part: a Part, whose motion is constrained by a joint, whose position is identified by its Motion Dimension, and whose motion is defined by the input to the Motion-Dimension FB.

Motion-Point: a Point, whose motion is constrained by a sketch, whose position is identified by its Motion-Point Dimension, and whose motion is defined by the input to the Motion-Path FB.

#### The Motion-Path FB and Motion-Dimension FB - compared

 Motion-Path FB & Motion-Point  Add Motion-Path FB: 1.Adds a Motion-Point to a sketch-element/sketch-path AND specifies its position relative to the start-Point of the sketch-element/sketch-path. 2.Adds a Motion-Path FB to the graphic-area3.Adds a dimension to the Motion-Point to indicate how far the Motion-Point is from the start-Point of the sketch-element in 1.Note: To see the Motion-Point Dimension you must: 1.Edit the Motion-Path FB In the Motion-Path dialog-box > Point List and Data Display  separator: 2.Click the Displacement / Phase radio-button Displacement: the linear distance along the sketch-path. Phase: the distance along the sketch-path normalized between 0 and 360. 360 is the complete length of the sketch-path. Motion-Dimension FB & Motion-Part Add Motion-Dimension FB does three things. It: 1.Specifies the position of a sketch-element (Line or Point) in a Motion-Part relative to a different sketch-element (Line or Point) in another Part 2.Adds a Motion-Dimension FB to the graphic-area.3.Adds a Motion Dimension to indicate the dimension between the sketch-elements in the two Parts.Motion-Part: a Part constrained by a joint. Its position from a sketch-element in a different Part, is the total of values given by: •Motion-values at the input-connector of the Motion-Dimension FB.•Base-Value as entered in the Motion-Dimension dialog-box.

#### Why use a Blend-Curve About the Blend-Curve A Blend-Curve is a sketch-element. Use the Blend-Curve dialog-box to specify, at its start-Point and its end-Point , these parameters: oAngleoCurvature oRate-of-Change of CurvatureoVelocity-Scaling a normalisation parameter that controls the overall length and shape of the Blend-Curve. Question: Why do we need a Blend-Curve? Answer: To eliminate a curvature-discontinuity. Question: What is a curvature-discontinuity? Answer: Even with tangency, at the instant a Motion-Point moves between sketch-elements that have different radii, (e.g. from an Arc to a Line (and vice versa), or from an Arc to a different Arc with a different radii) it experiences a curvature-discontinuity. Question: What is wrong with a curvature-discontinuity? Answer: If you join a machine element to the moving Motion-Point, the curvature-discontinuity between different sketch-elements will give rise to vibrations of the machine-element. To reduce mechanical vibrations, you must eliminate the curvature-discontinuity. The purpose of the Blend-Curve element is to eliminate curvature-discontinuities as the Motion-Point moves along the sketch-path and between sketch-elements.