A 'Whitworth' kinematic-chain – or a Quick-Return kinematic-chain

A 'Whitworth Quick Return' changes rotary movement to a back-and-forth movement. The Part moves faster in one direction than the other.

This kinematic-chain has:

1.A Motion-Part – a Crank
2.Two Dyads – an RPR and an RRP Dyad

The video shows the 'Whitworth Quick-Return' kinematic-chain.

The 'Input': A Crank – the Motion-Part

The 'Output': It slides quickly in one direction and slowly in the other direction. This is the 'Quick-Return' Part.


STEP 1: Add the 'Input' Part – a Crank

The Crank1s-red is the 'input' Part to the mechanism. See Tutorial 1, or:

1.Add a Part to a new Mechanism-Editor
2.Add a Line to the Base-Part
3.Join the Part to the Base-Part with Pin-Joint
4.Add a Motion-Dimension FB to give the Angle of the Part relative to the Line
5.Add a Linear FB and connect it to the Motion-Dimension FB

Step 1.5 is complete.


STEP 2: Add Dyad 1

Add the first Dyad

Remember: A Dyad ALWAYS has two Parts and three Joints.


Dyad 1: Part 2 and Joint 3

1.Add a vertical line to the Base-Part, directly down from the centre of the Crank 1s-red
2.Add a new Part 2s
3.Join it with a Pin-Joint 3sto a Point at the end of the Line1s-red in the Base-Part


Dyad 1: Part 1 and Joint 1

Add a Part, and join it to the end of the Crank.

There is a Pin at the end of the Crank. This suggests we add a part and join it to the end of the Crank with a Pin-Joint

1.Add a new Part 1s-red
2.Join it with a Pin-Joint to the Point at the end of the Crank 2s


Dyad 1: Joint 2

Use Add Slide-Joint and select the Lines along the centre of the two Added-Parts with the Blue Part-Outlines.

1.Click Add Slide-Joint

Select a Line in each Part.

2.Click the Line in Part 1 - see above
3.Click the Line in Part 2 - see above

MechDesigner adds the Slide-Joint1s-red to complete the new RPR Dyad.

The Parts become Green to indicate the kinematic-chain is now kinematically-defined.

This is the basic Whitworth Quick Return kinematic-chain. The output Part moves quickly in one direction and returns more slowly.

The length of the Crank and the distance between the Pin-Joints in the Base-Part give the 'Return Ratio'.

Return Ratio =

Crank Angle Rotation[Degrees] to move the Rocking Part in one direction

Crank Angle Rotation [degrees] to move the Rocking Part in the other direction

Experiment with the length of the Crank.


Add one more Dyad.

Remember: a Dyad ALWAYS has two Parts2s and three Joints1s-red.

1.Dyad 2: Part 2, Joint 3: Add a Part and Slide-Joint. This is the 'output' Part.
2.Dyad 2: Part 1, Joint 1: Add a Part with a Pin-Joint to the end of the Quick-Return Part of Dyad 1
3.Dyad 2: Joint 3: Connect the sliding-part to the other Part with a Pin-Joint.
4.If necessary, click the graphic-area to complete the command.


This is the kinematics-chain for a 'Whitworth Quick-Return'.

It has a:

Rocker (this is the Crank)
R-P-R Dyad: Pin-Joint, Slide-Joint, Pin-Joint
R-R-P Dyad: Pin-Joint, Pin-Joint, Slide-Joint

Tutorial and Reference Help Files for MechDesigner and MotionDesigner 13.2 + © Machine, Mechanism, Motion and Cam Design Software by PSMotion Ltd