<< Click to Display Table of Contents >> Navigation: Getting Started Tutorials - MechDesigner > Tutorial 2A: Four-bar Kinematic-Chains > Step 2.6: Reconfigure to a 4-bar Scotch-Yoke |
In this step, you will change the kinematic-chain to a Scotch-Yoke.
You will add a Slide-Joint that is not along the default CAD-Line that is from the start-Point to the end-Point of all added Parts.
In this step, we dd a new Line to the Part, and then use it for the Slide-Joint.
See http://youtu.be/MrvAKlePm3k?t=33s
To assemble simple, four-bar kinematic-chains, We need: •One Motion-Part : A Motion-Dimension FB identifies the Part that is the Motion-Part. A Motion-Part is a Rocker or a Slider. •One Dyad : All Dyads ALWAYS has: oTwo Parts oThree Joints |
Below, there are two typical images of a Scotch-Yoke as they are often found in many kinematics books. |
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The Motion-Part is a: •Crank – colored Black. A Dyad uses: •Three Joints: a horizontal Slide-Joint, a vertical Slide-Joint, a Pin-Joint in the Slot •Two Parts: one horizontal sliding-part – colored Red – and the other Part is... where? |
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Where is the second Part in the Dyad? In the image above, the second Part of the Dyad does not seem to exist. |
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The image to the left shows the other Part in the Dyad. It is a: •Vertical sliding-part – it is 'sliding-block' - colored Green. The kinematic-chains in the images to the left are kinematically identical, but they are slightly different physical designs of a scotch yoke. One top image shows a pin that is in a slot. The bottom image shows a pin that is in a sliding-block, and the sliding-block is in a slot. Kinematically they are the same, and you must model them in MechDesigner in the same way. |
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Tutorial 2; Step 2.6 Edit model to design a simple Scotch-Yoke mechanism |
The Scotch-Yoke looks like the images above. |
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STEP 1: Delete the Motion-Dimension FB 1.Mechanism-Editor: Click the Motion-Dimension FB 2.Mechanism-Editor: Press the Delete key on your keyboard. The Part-Outlines in the kinematic-chain are Blue again. Blue Part-Outlines indicate the Parts are NOT kinematically-defined.
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STEP 2: Edit the Base-Part 1.Double-click the Green rectangular Part-Outline to edit the Base-Part 2.Part-Editor: Delete the dimensions that constrain the Line we used for the Slide-Joint. 3.Part-Editor: Click Constraints toolbar > Add Horizontal 4.Part-Editor: Click the Line 5.Part-Editor: Click the Point on the Y-axis 6.Exit the Part-Editor |
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We need a Crank as the input to the Scotch-Yoke. STEP 3: Add a Motion-Dimension FB to the Pin-Joint 1.Mechanism-Editor: Click Kinematic-FB > Add Motion-Dimension FB | Click the Pin-Joint 2.Mechanism-Editor: Connect the Linear-Motion FB to the Motion-Dimension FB In the Kinematics-Tree, there is a Rocker and R-R-P Dyad. However, we need an R-P-P Dyad. This is one Pin-Joint and two Slide-Joints. |
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We will replace the middle R joint ( Pin-Joint), with a P (Slide-Joint). STEP 4: Delete the Pin-Joint between the horizontal Sliding-Part and the long Part To do this: 1.Click the Pin-Joint In the Selection-Window: 2.Right-click the Pin-Joint 3.Click Delete in the menu. |
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I have moved the Blue Parts apart slightly to show they not joined. Blue Parts are not kinematically-defined. We need to add a Vertical Line in the Sliding-Part. Refer to the schematic of the Scotch-Yoke at the top of this topic. STEP 5: Add a vertical line to the Sliding-Part. |
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The vertical line is in the Sliding-Part. It is not important where you add the vertical Line 1.Edit the Sliding-Part 2.Part-Editor: Geometry toolbar > Add Line, | Drag to add a Line •If you drag upwards to add the Line, a Part that you join to it with a Slide-Joint will point upwards. •If you drag downwards to add the Line, a Part that you join to it with a Slide-Joint will point downwards. 3.Part-Editor: Constraints toolbar > Add Vertical Line | Click the Line 4.Part-Editor: Geometry toolbar > Add Dimensions | Add dimension as needed so that the Line becomes Fully Defined. |
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5.Exit the Part-Editor. | Double-click the Line STEP 6: Add the Slide-Joint between the two Parts to complete the Dyad. 1.Click Kinematic-elements toolbar > Add Slide-Joint 2.Click the CAD-Line in the Part 3.Click the vertical Line |
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The two Lines snap together to add the Slide-Joint STEP 7: Cycle the Kinematic-chain Use the shortcut: Alt+C The crank rotates continuously. The output slides back-and-forth with Simple Harmonic Motion. |
The Rocker has three elements: a.Pin-Joint b.Part c.Mot-Dim Rocker – a Motion-Dimension FB for a Rocker The RP-P Dyad has five elements, as do ALL Dyads. d.Pin-Joint1 e.Part3 f.Slide-Joint2 g.Part2 h.Slide-Joint |