<< Click to Display Table of Contents >> Navigation: Getting Started Tutorials - MechDesigner > Tutorial 17: Belts and Pulleys > Option 2: Orbiting Pulley Centre > Application of Orbiting Pulley center |
This application creates a simple and cheap indexer. However, the output has motion-discontinuities. Therefore, I would not use it for a high-speed machine unless the load inertia is very low.
STEP 1: Do Orbiting Pulley center STEP 2: Add a Trace-Point to the Motion-Point.
The the Motion-Point move along the Trace-Point. To construct a 3-Stop Indexer, the Trace-Point must trace exactly three Lobes (flower-petals) around the fixed Pulley. |
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STEP 3: Add a Gearing FB to increase the number of rotations of the Crank
<<< The Trace-Point traces more lobes. However, the Trace-Point does not finish where it starts. Edit these elements to edit these parameters: •Pulley : Number of Teeth •Motion-Path FB : Length of the Belt, Tooth-Pitch STEP 4: Edit each Pulley
Pulley dialog-box also has (Read-Only): •(Read-Only ) - Pitch-Circle Diameter ( = (Tooth Pitch × Number-of-Teeth) / π ) •(Read-Only ) - Tooth Pitch (Edit Belt-Pitch in Motion-Path dialog-box) •(Read-Only ) - Belt Length (Edit Target Path Length in Motion-Path dialog-box) |
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STEP 5: Edit the Length of the Belt.
![]() Select the CONTROLLING DIMENSION The Part-Editor closes The dimension value NOW shows in the Controlling Dimension box = -168.176mm (- do not worry that the dimension is negative). STEP 7: Edit the Target Path Length SLOWLY with the Spin-Box tool to increase or decrease the Actual Belt Length. You should see that Target Path Length = Actual Path Length If this is not the case, then edit the Minimum and/or Maximum Dimension Values One of these dimensions may be constraining the limits. You may even need to increase the Minimum or decrease the Maximum Dimension Value. MD16 - the parameters are now Control-Dimension Min / Max) I want the Actual-Path-Length = 800mm. Ignore below Fixed (Moving) Pulley Circumference = Tooth-Pitch (5mm) × Number-of-Teeth 120 (60) = 600mm (300mm) 300mm × 8 = 2400 (the moving pulley) will rotate 8× as the Crank does 4 rotations The belt will make 3 x full rotations as it rotates 4-1 times relative to the Fixed Pulley.. The number of lobes (flower petals) = (Number of Crank Rotations -1) The Motion-Point will move 2400mm÷800 = 3 belt lengths |
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This will give 3 lobes (flower petals) to the motion of the Motion-Point relative to the Base-Parts
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STEP 8: Add a Dyad - RPR (Remember - a Dyad has 2 × Parts + 3 × Joints). 1.Click Kinematic-elements toolbar > Add Part | Drag to add 2 × Parts 2.Click Kinematic-elements toolbar > Add Pin-Joint | Click the start-Point of a Part and a Point at the center of the fixed Pulley. •The Select-Elements dialog opens because there is more than one Point at the center of the fixed Pulley 3.In the list of Points in the Select-Elements dialog: CTRL+CLICK the start-Point of the Part and the Point with the Base-Part as an owner (parent) 4.Click Kinematic-elements toolbar > Add Pin-Joint | Click the start-Point of a Part and a Motion-Point on the Belt. Note: When the MMA =0, and the Motion-Dimension = 0 , the Motion-Point is at the start-Point of a sketch-element on the belt-path. To make it easier to click the Motion-Point, edit the MMA = ~5 |
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We must add one more Joint: a Slide-Joint between CAD-Lines of the two new Parts. 5.Click Kinematic-elements toolbar > Add Slide-Joint | Click the two CAD-Lines along the centers of each new Part. The Slide-Joint will make the two CAD-Lines, and Parts, become collinear. Cycle the mechanism. You can see the new output Part that has the Pin-Joint with the center of the fixed Pulley moves then dwells 3x as the Crank rotates 4x Because the Motion-Point traces three lobes, the output Part is a three stop indexer.
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