A Scotch-Yoke is a mechanism that changes rotary motion at its input to linear motion at its output.

The input rotates with constant angular speed.

The output reciprocates with Simple Harmonic Motion.

The kinematic-chain is:

1.One Motion-Part – a Rocker / Crank

2.One Dyad – an RPP Dyad.

(Closure - Review the Change Dyad Closure tool - you may need to use it when the Dyad builds the first time!).

The video shows a Scotch-Yoke.

STEP 1: Add the Input – a Crank

1.Edit the Base-Part :

2.Part-Editor: Geometry toolbar > Add Line : Drag to add the Line , Add Horizontal Constraints, Add Dimensions, Close the Part-Editor:

3.Mechanism-Editor: Click Kinematic elements- > Add Part : drag to add the new Part.

4.Mechanism-Editor: Click Kinematic elements- > Add Pin-Joint: Click the start-Point of the new Part and the start-Point of the Line in the Base-Part.

5.Mechanism-Editor: Click Kinematic FB toolbar > Add Motion-Dimension FB: Click the Pin-Joint the Line in Base-Part; the CAD-Line in Part.

6.Click in Command-Manager

7.Mechanism-Editor: Click Kinematic FB toolbar > Add Linear-Motion FB: and click the Graphic-area. Joint the FBs with a wire. You have a Crank

STEP 2: Add R-P-P DYAD

We must add 2 Parts and 3 Joints (Top Tip: Add the 'Output' Part and Joint first).

DYAD: Part & Joint

The output of the Scotch-Yoke is a Sliding-Part

1. Mechanism-Editor: Click Kinematic elements- > Add Part : Drag to add the new Part

2.Mechanism-Editor: Click Kinematic elements- > Add Slide-Joint To add the Slide-Joint: : Click the CAD-Line in Part and the horizontal Line in the Base-Part

DYAD: Part & Joint

1.Mechanism-Editor: Click Kinematic elements- > Add Part : drag to add the new Part

2.Mechanism-Editor: Click Kinematic elements- > Add Pin-Joint: To add the Pin-Joint: :Click the start-Point of the new Part and the end-Point of the Crank

The two Parts are Blue Parts

Preparation for Vertical Slide-Joint 3

Add a vertical line to give the direction of the Slide-Joint 3

1.Start Part-Editor: Edit Horizontal Sliding Part (see above)

2.Part-Editor: Geometry Tree: Add Line, Add Vertical constraint, Add Dimensions

3.Close the Part-Editor

This image shows the Vertical Line in the Part-Editor.

Add Joint 3: the Slide-Joint

This image shows the vertical Line in the Mechanism-Editor.

1.Mechanism-Editor: Click Kinematic elements- > Add Slide-Joint:

a.Click the vertical Line

b.Click the Cad-Line in Part

MechDesigner completes the Dyad to add the Slide-Joint

The Part-Outlines are green to indicate the Parts are kinematically-defined.

Note: Part along the Slide-Joint is either upwards or downwards. This does not change the kinematics.

If you want the Part to be in the other direction: Add Line(see image above), by dragging it in the opposite direction, from top to bottom, or vice versa.

Cycle the mechanism

Do ALT+C on your keyboard

This is the kinematics of a Scotch-Yoke.

It has a:

•Rocker (as a Crank)

•R-P-P Dyad: one Pin-Joint (R - - ) and two Slide-Joints (- P-P).