Getting Started Tutorials - MechDesigner > Tutorial 2A: Four-bar Kinematic-Chains > Step 2.7: Reconfigure to a 6-bar Whitworth Quick Return

Assemble a Whitworth Quick Return

You are about to design a Whitworth Quick-Return Mechanism.

Why not start a new mechanism on a new Plane?

See also this link: http://youtu.be/MrvAKlePm3k?t=11s

A Whitworth Quick Return Mechanism has:

•One Motion-Part

•Two dyads

Whitworth : Motion-Part (Crank), Dyad 1, and Dyad 2

Motion-Part

GST-2-701

Motion-Part

1.Edit the Base-Part

2.Add two perpendicular Lines.

3.Exit the Part-Editor

The vertical line anticipates that the output of the Whitworth mechanism is a sliding-Part.

GST-2-702

4.Add a Part

5.Add a Pin-Joint between the start-Point of the Part and the start-Point of the Line in the Base-Part.

6.Add a Motion-Dimension FB to control the angle of the Crank

Dyad 1

GST-T2-7-A

Dyad 1

1.Add two Parts: add one long Part and one short Part

2.Add three Joints: a R-P-R dyad - two Pin-Joints, one Slide-Joint

• Pin-Joint (R-x-x) join the start-Point of the long Part to a Point in the Base-Part (frame)

• Pin-Joint (x-x-R) join the start-Point of the short Part to the end-Point of the Crank

• Slide-Joint (x-P-x) join the CAD-Line in the long Part to the CAD-Line in the short Part.

Dyad 1 R-P-R - is now complete.

In this configuration of the Whitworth mechanisms, the input Crank rotates with a uniform constant velocity, and the output oscillates.

Can you see what will happen if the length of the Crank is greater than the distance between the two Pin-Joints?

See Change Closure of a dyad if the dyad is not in a closure you want. Use the Change-Dyad-Closure tool until the dyad is in the closure you want.

Dyad 2

GST-T2-7-B

Dyad 2

1.Add two Parts: add Part and one short Part

2.Add three Joints: a R-R-P dyad - two Pin-Joints, one Slide-Joint

• Pin-Joint (R-x-x) join the start-Point of Part to the end-Point of the long Part

• Slide-Joint (x-x-P) join the CAD-Line of the Part to the vertical Line in the Base-Part

• Pin-Joint (x-R-x) join the end-Point of Part to the start-Point of Part

Dyad 2 R-R-P - is now complete.

Note:

If when you cycle the model (ALT+C), the Parts break somewhere in the machine-cycle, you will need to move the Lines in the Base-Part, or edit the length of Parts.

See Change Closure of a dyad if the dyad is not in a closure you want. Use the Change-Dyad-Closure tool until the dyad is in the closure you want.

Other Configurations with the R-P-R dyad - Dyad 1 only.

GST-2-703

The Crank is longer than the distance between the two Pin-Joints that join Parts to the Base-Part.

In this case, each time the Crank rotates 360º the long Part will also rotate 360º. However, the angular-velocity of long Part varies (modulates).

How much the angular-velocity of the long Part varies, is a function of how much longer the Crank is than the distance between the two Pin-Joints. When the Crank is only a little longer than the distance between the Pin-Joints, the angular velocity of the long Part varies significantly.

GST-2-704

The Slide-Joint is offset from:

•End of the Crank by the length of the Line

•Fixed Pin-Joint by the length of the Line

When the configuration of the Slide-Joint is offset from the Pin-joints, the R-P-R dyad also has four Dyad-Closures - experiment.