Fixed Centre Pulleys
This is a typical Multi-Pulley system. Drive one Pulley with a motion, and let MechDesigner find the angular motion of other Pulleys.
Preparation
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| STEP 1: | Edit the Base-Part |
| STEP 2: | Add a closed sketch-chain (sketch-loop) to represent the Path of the Belt |
We must define which Arc we will use to add the Drive-Pulley. The rotation of the Drive-Pulley is given kinematically-defined Part.
We will add Line, so that we can add a Rocker in the Mechanism-Editor.
| STEP 3: | Add a Line  so that start-Point is merged with centre-point of an Arc. |
The start-Point of the Line MUST be merged with the centre-Point of the Arc.
[It is easier to Add the Arc, then Hover+Drag the Line from the centre-Point of the Arc].
| STEP 4: | You MUST dimension each Arc |
The exact radius of the Arc is not important.
MechDesigner uses the dimension to add a Pulley with an integer number-of-teeth that is near to the radius. (You can edit the number-of-teeth later with the Edit Pulley dialog).
| STEP 5: | Close the Part-Editor |
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| STEP 6: | Add a Motion-Path FB |
Select the sketch-loop that represents the path of the belt.
The Motion-Point shows at the start-Point of the sketch-element you select in the sketch-loop.
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| STEP 7: | Add a Part for each Pulley. |
Add the Parts near to the centre-Point of each Arc
Mouse-button-down and drag from near to the centre-Point of each Arc.
Then:
| STEP 8: | Add a Pin-Joint between the centre-Point of each Arc and the start-Point of each Part |
There should be one rotating Part (that is, a Part with a Pin-Joint) for each Pulley you will add.
Usually, one rotating Part at the centre-Point of each Arc.
The length of each Part is not important.
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| STEP 9: | Add a Motion-Dimension FB to the Part you wish to be the Drive Pulley. |
There should be one kinematically-defined Part to show which rotating Part is the DriveR Pulley.
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Use Add Pulley
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You must use Add Pulley for each Pulley.
Click Add Pulley in the:
- or -
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The Add Pulley dialog starts in the Command-Manager.
Add a Pulley to the kinematically-defined Part and Arc first.
Click, in the graphic-area, from top to bottom.
The Part-Editor opens with sketch-chain to which you add the Motion-Path FB
| 3. | The Dimension of the Arc sketch-element |
The Part-Editor closes
| 4. | The Part joined with a Pin-Joint at the centre of the Arc. |
MechDesigner adds the Pulley.
Do Add Pulley again to the four Rotating Parts.
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Notes:
| • | Driven Pulley are Magenta |
| • | The radius of each Arc changes to give an integer Number-of-Teeth. |
| • | Edit the Number-of-Teeth with the Edit Pulley dialog. |
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Use Edit Pulley dialog box
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| 1. | Open the Pulley dialog-box |
Double-click a Pulley in the:
- or -
- or -
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In the Pulley dialog-box
| 2. | Edit the Number-of-Teeth |
Repeat 1 and 2 for each Pulley.
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| 3. | Edit the Motion-Dimension FB to 0º. |
When the DriveR-Pulley is at 0º, the other Pulleys will also be at 0º.
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Edit the Length of the Belt
Belts have an integer number-of-teeth. Also, belt manufacturers have preferred lengths of belts.
To make the Motion-Path give an integer number-of-teeth and a preferred belt length, you can use the:
| • | 'Adjust Path Length' tool in the Motion-Path FB dialog-box |
The Adjust Belt Length tool in MechDesigner moves a pulley, or another dimension, to make the length of the belt equal to a target belt length.
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Frequently, you will include a belt tensioning pulley in the layout of the belt design. The centre of the Belt Tensioning Pulley moves to remove slack and to give the belt the correct tension.
| 1. | Make sure you add a dimension to the sketch-chain that can change the length of the Belt, such as a tensioning pulley. |
In the design to the left, we will make the 'Belt Tensioner Pulley'. the pulley at the top the sketch-chain.
Therefore, I will use the vertical dimension in the sketch-chain. See the dimension - in RED.
When we apply the 'Adjust Path Length' tool, MechDesigner makes a change to this dimension.
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| 3. | Double-click the Motion-Path FB dialog box top open the dialog |
| 4. | Expand the 'Path Length using dimension' separator |
You will see the 'Actual Path Length'.
In this case, the 'Actual Path Length' is 497.26mm
| 5. | Click the 'Controlling Dimension' selection-box |
| 6. | Edit the Base-Part with the sketch-chain |
| 7. | Click the dimension you want to adjust. |
The dimension value shows in the box
The dimension element name shows above the box
| 9. | Enter the Target Path Length for the Belt |
In this case, I have entered 500mm it is a standard Belt Length for a 5mm tooth pitch belt.
It is best to make the length near to the Actual Path Length.
| 10. | Click the Adjust Path Length button |
If successful, the dimension, DimL, will change to make the Actual Path Length equal to the Target Path Length.
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