Getting Started Tutorials - MechDesigner > Tutorial 17: Belts and Pulleys > Step 17.2: Option 1 - Fixed Pulley Centers

Control the Length of the Belt with a Dimension.

Real Belts have an integer number-of-teeth. Also, manufacturers of Belts have preferred lengths.

We use the Motion-Path dialog to enter the Target Path Length.

We use the Target Belt Length to select and control a dimension in the Part-Editor. You must select a dimension that can control the length of the Belt. We call the dimension the control-dimension.

Usually, we edit the length of the Belt to a length that is exactly divisible by the Belt Tooth-Pitch - for an integer number of teeth on the Belt.

In the design to the left, we will make the dimension to the Arc at the top the sketch-path the Control-Dimension.

In the image, the dimension is RED (102.2).

The length of the Control-Dimension changes as we edit the Target Path Length.

The Control-Dimension can only be a dimension that is Point to Point (DimPtoP#) or Length of a Line (DimL#).

STEP 1: Edit the Motion Path FB.

1.Double-click the Motion-Path FB to open its dialog (or see How to open a dialog)

2.Motion-Path dialog > Length Control tab > Control-Length of Path > Belt Tooth Pitch =10 (mm)

You will see that Actual Path Length divided by the Belt Tooth-Pitch is not an integer.

3.Click the Start Length-Control button

We open Part-Editor for you to edit the Part in which the sketch-path controls the path of the Belt.

4.Click the dimension you want to use to change the length Belt - see above

We close the Part-Editor for you..

The dimension value is in the Control-Dimension Length box.

The default Target Path Length = Actual Path Length

The Control-Dimension Min and Control-Dimension Max are Soft-Limits to the Controlling-Dimension.

You can edit the Controlling Dimension Maximum and Minimum if required.

5.Edit the Target Path Length SLOWLY with the Spin-Box tool to increase or decrease the Actual Belt Length.

Troubleshooting.

If the Actual Path Length does not change:

6.Increase the Control-Dimension Min until it is near to the actual Control-Dimension in the sketch.

7.Then edit Target Path Length again.