Assemble a Whitworth Quick Return

You are going to design a 'Whitworth Quick-Return Mechanism'.

Why not start a new mechanism on a new Plane?

See also this link:

A new definition of a Kinematic-Chain:

A kinematic-chain may have:

One, or more, Motion-Parts
One, or more, Dyads

Notice 'or more' in the new definition of a kinematic-chain. This is because it is easy to add Dyads and to add more than one Motion-Part to a kinematic-chain.

A Whitworth Kinematic-Chain:

One Motion-Part
Two dyads

Remember, ALL Dyads have:

Two Parts
Three Joints

Whitworth : Dyads 1 and Dyad 2

Notes about Dyad 1


First, we should look at the Motion-Part and the first Dyad.

A Motion-Part – a Crank6s
A Dyad

The Dyad is assembled with:

Two Parts: one long1s-red and one short2s
Three Joints: a RPR Dyad
otwo Pin-Joint and the Base-Part3s (frame) and the end of the Crank4s
oone Slide-Joint5s to join the long and the short Parts together

Which order do we add the Joints to add a new Dyad?

After you have added the two Parts as 'Free Blue Parts', it is frequently easiest to:

First, add the 'outer' two Joints. They join the two new Parts to two other Parts in the kinematic-chain.
Then, join the two new Parts in the Dyad together – this makes the 'middle' Joint in the Dyad.

Now you do it....Add the first and last joints of the Dyad:

Pin-Joint3s between the long part and the Base-Part: R – –
Pin-Joint4s at the end of the Crank: R – R

Join the Parts together.

Slide-Joint5s to join the two Parts together: RPR

Now - remember about 'Closures'? See Change Closure of a Dyad if the Dyad is in a Closure you do not expect. Keep using the same Change-Closure tool until the Dyad is in the closure you need.

Notes on Dyad 2


The image shows the second Dyad (I have rotated the image by 90º!). When you have a kinematically derived-chain, it is simple to add more Dyads to it, to make a more complex kinematic-chain.

In the image, the second Dyad shows:

two more Parts: 7s and8s.
the Parts are joined to two other Parts
oPart1s-red - which is the Long Part of the first Dyad
oThe Base-Part
the Parts are also joined together.

Now you do it....Add the first and last joints of the Dyad:

Pin-Joint9s between the long part and one of the new Parts: R – –
Slide-Joint10s along the Base-Part: R –  P
Pin-Joint11s joining the two Parts together: R–R–P

Your challenge is to complete this mechanism. and put each Dyad in the correct 'Closure'.

Why not start a new mechanism on a new Plane?

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