﻿ Getting Started Tutorials - MechDesigner > Tutorial 10: Model Mechanical Devices > Step 10.1: The Scotch-Yoke Kinematic-Chain

# Step 10.1: The Scotch-Yoke Kinematic-Chain

## The Scotch-Yoke Kinematic-Chain

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

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

 Note: When the crank has constant angular velocity, the motion of output Slider is Simple Harmonic Motion However, there are two Motion-Laws in MotionDesigner that can modulate* the rotation of the Crank in a useful way. The Y-Inverse-Sinusoid and the Crank-Constant-Velocity modulate the Crank rotation so that the Slider moves with a Constant Linear Velocity. * Modulate is to change the speed of the Crank as it rotates.

The video shows a Scotch-Yoke.

STEP 1: Add the Input – a Crank

1.Edit the Base-Part :

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

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

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

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)

3.Close the Part-Editor

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

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

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

a.Click the vertical Line

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