<< Click to Display Table of Contents >> Navigation: Getting Started Tutorials - MechDesigner > Tutorial 2B: Six-bar Kinematic-Chains > 6-bar Kinematic-chains - R-R-R+R-R-R |
The four-bar is a Crank plus an R-R-R Dyad. In this tutorial we will add a new R-R-R Dyad to the four-bar we built in Tutorial 2A - or a new one if you want.
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.
To build the classic six-bar kinematic-chains. They have Pin-Joints only. Why Pin-Joints only?
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: a Crank and R-R-R dyad - all Pin-Joints - see Step 2A 2.Add a new R-R-R Dyad. It has two Parts and three Pin-Joints |
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We have a four-bar similar to this model - see image to the left. The four-bar has a Rocker (1) which is the Motion-Part, and an R-R-R Dyad. The Motion-Part(1) has a motion relative to 4 - the Base-Part. The R-R-R 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 the R-R-R Dyad. |
Watt 1 The standard four-bar mechanism plus one R-R-R Dyad: The Four-Bar Mechanism: Parts '1','2','3','4'. The new R-R-R Dyad: Parts '5' & '6'. •Part 5: •Part 6: •Join the Part 5 and Part 6 together. |
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STEP 1: Add Points P1 and P2: Edit Parts 2 and 3 to add sketch-elements. You can add a Point, or two Lines, 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. |
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STEP 2: Add the R-R-R Dyad Add two Parts: 5 & 6 and three Pin-Joints Pin-Joint P1 with Part5 to , the Pin-Joint P2 with Part6, then add one Pin-Joint to join Part 5& Part6. |
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6-Bar Mechanism Watt 1 |
Example Watt 1 Mechanism: Cabinet Hinge Mechanism |
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. |
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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. |
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Add the R-R-R 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 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. |
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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. |
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Add the R-R-R Dyad Add two Parts: 5 & 6. Join one Part to P1, the other to P2, then join the two Parts, 5&6, together. |
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Stephenson 1 Mechanism: Car Hood. |
What does a Stephenson 2 look like? |
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It is not possible to make this a 'kinematically-defined chain'. You can connect the Parts, but they will not become Green! |
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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 Very similar to the Watt 1. The Watt 1 has a Dyad across the(Output)Rocker and the Coupler. The Stephenson 3 has a Dyad across the (Input)Crank and the Coupler The 'standard' four-bar mechanism with four Parts - 1,2,3,4.. + the R-R-R Dyad, the two Parts 5 & 6. Part 5: Part 6: 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 R-R-R Dyad Add two Parts: 5 & 6. Join Part 5 at Pin-Joint, P1, Joint Part 6 at Pin-Joint, P2, Parts 5 & Part 6, to each other, with Pin-Joint. |
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