Getting Started Tutorials - MechDesigner > Tutorial 2A: Four-bar Kinematic-Chains > Step 2.6: Reconfigure to a 4-bar Scotch-Yoke

Scotch-Yoke: the RPP Dyad

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

What is a Scotch-Yoke?

Below, there are two typical images of a Scotch-Yoke as they are often found in many kinematics books.

Scotch-Yoke Mechanism - False!

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?

Where is the second Part in the Dyad?

In the image above, the second Part of the Dyad does not seem to exist.

Scotch-Yoke - Kinematic-chain

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.

Video:

Tutorial 2; Step 2.6

Edit model to design a simple Scotch-Yoke mechanism

Step by Step

Change the Kinematic-chain from a Slider-Crank to a Scotch-Yoke

The Scotch-Yoke looks like the images above.
	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.
	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 - so it becomes Horizontal 5.Part-Editor: Click the Point on the Y-axis and the Point at the start-Point of Line (see image) 6.Exit the Part-Editor
	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 the Line in the Base-Part, and Line along the Part. 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.
	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 graphic-area. It shows in the Selection-Window. In the Selection-Window: 2.Right-click the Pin-Joint 3.Click Delete in the menu.
	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.
	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.
	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 along the center of the Sliding-Part
	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.