Mechanism | Change Dyad Closure

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Mechanism | Change Dyad Closure

Change Dyad Closure / Change Configuration of Dyad's Assembly.


Dyad :

Assur Group :

A Dyad is combination of two Parts and three joints.

One joint joins the two Parts together.

The other two joints join the two Parts to different kinematically-defined Parts.

A Dyad is the smallest kinematic chain which when added to, or subtracted from, a mechanism results in a mechanism that has the same mobility (degrees-of-freedom) as the original mechanism.

Assur Groups :

Another name for a Dyad

Dyad Closure :

It is one arrangement, or assembly, of the two(2) parts in the Dyad.

Configuration of Dyad's Assembly = another way of expressing 'Dyad Closure'.

Types of Dyad :

Planar Dyads: RRR, RRP, RPR, RPP, PRP

Spatial Dyads: SSR, SSP

R :

Revolute Joint = Pin-Joint

P :

Prismatic Joint = Slide-Joint

S :

Spherical Joint = Ball-Joint

See more: Dyads

Change Dyad Closure

RRR Dyad - Closure 1

RRR Dyad
Closure 1

RRR Dyad - Closure 2

RRR Dyad
Closure 2

STEP 1: Do Change Dyad Closure

Change Dyad Closure icon

1.Mechanism-Editor: Add menu > Mechanism menu  > Change Dyad Closure

- or -

1.Mechanism-Editor: Kinematic elements toolbar > Change-Dyad Closure

STEP 2: Select a Part

2.Click a Part-Outline of one of the two(2) Parts with the assembly-configuration you want to change.

STEP 3: Complete the Command

3.Click OK-tiny-11-15 in the Command-Manager .

The configuration of the assembly should now have changed.

Compare the bottom image with the top image.

STEP 4: Do again, if needed

4.Do 1 to 3 again and again to find the configuration of the assembly you want to apply to your design.


If there are many Dyads in the model, you can use the Kinematics-Tree to help you identify each Dyad.

In the Kinematics-Tree

1.Click and explore each Kinematic-Chain in the Kinematics-Tree

2.Click each Dyad

The Parts and Joints of each Dyad become red in the graphic-area

tog_plusAssembly-Configurations of the RRP Dyad

The joints in the R-R-P Dyad are: Revolute - Revolute - Prismatic

In MechDesigner, the joint names are: Pin-Joint - Pin-Joint - Slide-Joint.

The image below shows an Offset-Slider-Crank mechanism.

Assembly Configurations of an Offset-Crank-Slider

Assembly Configurations of an Offset-Crank-Slider

Refer to the image above.

PartRed-14-1b is the Crank. We do not need to rotate the crank.

The two Parts in the R-R-P dyad are Parts Red-14-2Red-14-3. To imagine the four assembly-configurations, we will imagine we have yet to add the middle Pin-Joint.

PartRed-14-2 can ONLY rotate about Pin-Joint R1 (R-x-x) at the end of the Crank

This means the Pin-Joint (x-R-x) can ONLY be on the red circle at the end of PartRed-14-2.

PartRed-14-3 can ONLY move the along the Slide-JointRed-14-5 (x-x-P) along the fixed LineRed-14-4.

Important: The Point in PartRed-14-3 we will use for the middle Pin-Joint (x-R-x) is offset from the Slide-Joint and not on the Slide-Joint.

This means the middle Pin-Joint (x-R-x) in PartRed-14-3 can ONLY be above LineRed-14-4 by the offset distance to the Point or below LineRed-14-4 be the same distance.

This means the Pin-Joint (x-R-x) can ONLY be on the red lines

There are 4 places the red circle intersects the red lines.

Thus, the Pin-Joint R2 can ONLY be at 4 places.

Therefore, the Offset Slider-Crank has 4 possible assembly configurations.