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 R-R-P 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 CrankRed-14-1b 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-Motion FB and connect it to the Motion-Dimension FB



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 Red-14-1b
2.Add a new Part Red-14-2
3.Join it with a Pin-Joint Red-14-3to a Point at the end of the vertical Line in the Base-Part


Dyad 1: Part 1 and Joint 1

Add a PartRed-14-4, and join it to the end of the CrankRed-14-1b.

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.Mechanism-Editor: Kinematic elements > Add Part Drag to add a new PartRed-14-4
2.Mechanism-Editor: Kinematic elements > Add Pin-Joint
3.Mechanism-Editor: Click the end-Point of the CrankRed-14-2
4.Mechanism-Editor: Click the start-point of new PartRed-14-4


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.Mechanism-Editor: Kinematic elements > Add Slide-Joint
2.Mechanism-Editor: Click the CAD-LineRed-14-6 along PartRed-14-4 - see above
3.Mechanism-Editor: Click the CAD-LineRed-14-7 along PartRed-14-2 - see above

A Slide-Joint completes the new R-P-R Dyad.

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

This is the basic Whitworth Quick Return kinematic-chain. The output Part moves quickly in as the Crank (input) rotates from (counter clockwise) from 240 to 330 degrees, and more slowly as the crank rotates from 330 to 240 degrees.

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 PartsRed-14-2 and three JointsRed-14-1b.

1.Edit the Base-Part Add Horizontal Line (Part Red-14-1b slides along this Line
2.Dyad 2: Part and Joint: Add PartRed-14-1b , Add Slide-JointRed-14-2. This is the Quick-Return Part.
3.Dyad 2: Part and Joint: Add a PartRed-14-3 Add a Pin-JointRed-14-4 with start-Point of PartRed-14-3 the end-Point of long Part of Dyad 1
4.Dyad 2: Joint: Join the start-Point of partRed-14-1b to the end-Point of PartRed-14-3with a Pin-Joint.
5.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

Tutorials and Reference Help Files for MechDesigner and MotionDesigner 14.2 + © Machine, Cam, Mechanism, and Motion Design Software by PSMotion Ltd