In this Tutorial

Add an RRR Dyad to an existing four-bar.

The 'existing four-bar' is a Crank with an RRR Dyad.

The names of the five 'Classic' six-bar kinematic-chains are Watt 1 & 2, and Stephenson 1, 2 & 3.  You do not need to be concerned with their names.

Objective of the Tutorial

To make the 'classic' six-bar kinematic-chains. They have Pin-Joints only.

Why are they 'classic' and important?

In the past, Pin-Joints were much easier to manufacture, reproduce and less costly than Slide-Joints - they still are! Hence, there is a motivation to design useful kinematic-chains with only pin-joints.

In the 21st Century, you can purchase accurate slide-ways from reputable manufacturers (for example, from SKF, THK) with incredible accuracy. It might seem, therefore, you can put slide-ways in your designs whenever you want a tool or end-effector to move along a straight-line. However, even now, there are advantages with pin-joints. If you can find a mechanism that has only pin-joints, the mechanism might perform better, if correctly engineered, be cheaper, easy to seal, faster, and have more convenient locations of machine components.

The six-bar kinematic-chains with Pin-Joints are usually called:

Watt 1
Watt 2
Stephenson 1
Stephenson 2 - this is not easy to model in MechDesigner.
Stephenson 3

The six-bar kinematic-chains are very simple to do[with the exception of the Stephenson 2].

1.Start with a four-bar mechanism - see Step 2.1
2.Add an RRR Dyad. It has two Parts and three Pin-Joints

Standard-4-bar

We use this 'four-bar' before we add the final RRR dyad - see image to the left.

The four-bar has a Rocker [Part 1] which is the Motion-Part, and an RRR Dyad.

The Motion-Part[1] has a motion relative to 4 - the Base-Part.

The RRR Dyad consists of Parts 2 and 3, and Pin-Joints, R1, R2, R3.


Remember, a Pin-Joint is equivalent to a Revolute Joint, hence the letter 'R' for Revolute in a Dyad, and not the letter 'P'.

The Classic Six-Bar Mechanisms

Watt 1

What does a Watt 1 look like?

Watt1

This is a standard Watt 1

The 'standard' four-bar mechanism plus another Dyad: A motion-Part (Rocker)+Dyad+Dyad

The Four-Bar Mechanism: Parts '1','2','3','4'.

The new RRR Dyad: Parts '5' & '6'.

Part 5:
Join to the Coupler [Part 2], at P1.
Part 6:
Join to the output 'Rocker' [Part 3], at P2.
Join the Part 5 and Part 6 together.

Standard-Watt1Prep

To add Points P1 and P2: Edit Parts 2 and 3 to add sketch-elements.

You can add a Point, or two Lines sketch-elements to give a Point.

For example, add two Lines to the Coupler and two Lines to the Rocker, to construct a triangle in each Part.

Each triangle gives the Points: P1 and P2.

Standard-Watt1Final

Add the RRR Dyad

Add two Parts: 5 & 6.

Join one Part to P1, the other to P2, then join the two Parts, 5&6, together.


6-Bar Mechanism Watt 1

Example Watt 1 Linkage: Cabinet Hinge Mechanism

Watt 2

What does a Watt 2 look like?

Watt2

This is a standard Watt 2

The 'standard' four-bar kinematic-chain is Parts - 1,2,3,4.

The extra Dyad, Parts 5 & 6, is joined to the Rocker, Part 3, and the Ground, Part 4.

Standard-Watt2Prep

Edit Parts to add Points P1 and P2.

You can add a Point, or a sketch-element with a Point.

For example: add two lines to the Frame and two Lines to the Rocker to give a triangle in each Part.

The apex of each triangle give the Points: P1 and P2.

Standard-Watt2Final

Add the RRR Dyad

Add two Parts: 5 & 6.

Join one Part to P1, the other to P2, then join the two Parts, 5&6, together.


Stephenson 1

What does a Stephenson I look like?

Stephenson1

This is a standard representation of a Stephenson 1

The 'standard' four-bar kinematic-chain -  Parts 1,2,3,4.

The extra Dyad, Parts 5 & 6, is joined to the Crank, Part 1, and the Rocker, Part 3.

Standard-Stephensson1Prep

Edit Parts to add Points P1 and P2.

Add two lines to the Rocker and two Lines to the Crank to give a triangle in each Part.

Each triangle gives the Point: P1 and P2.

Standard-Stephenson1final

Add the RRR Dyad

Add two Parts: 5 & 6.

Join one Part to P1, the other to P2, then join the two Parts, 5&6, together.

Example Stephenson 1 Linkage: Car Hood.

Stephenson 2

What does a Stephenson 2 look like?

Stephenson2

It is not possible to make this a 'kinematically-defined chain'.

You can connect the Parts, but they will not become Green!

Stephenson2-1

Only the Motion-Part is Green.

The Stephenson 2 cannot be created in MechDesigner. Can you see why?

The Parts and Joints move correctly, but not as quickly as when the Parts have Green Part-Outlines.

Stephenson 3

What does a Stephenson 3 look like?

Stephenson3

The 'standard' four-bar mechanism with four Parts - 1,2,3,4..

+ the RRR Dyad, the two Parts 5 & 6.

Part 5:
To the Frame, Part 1, at P1.
Part 6:
To the output Coupler, Part 3, at P2.

Stephenson-3a

What to do:

Edit Parts 2 and 4 to add Points P1 and P2.

Add two lines to the Coupler and two Lines to the Frame to give a triangle in each Part.

Each triangle gives the Point: P1 and P2.

Add the RRR Dyad

Add two Parts: 5 & 6.

Join one Part to P1, the other to P2, then join the two Parts, 5&6, together.

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