MechDesigner Reference & User Interface > 2.2 Mechanism-Editor > Mechanisms > Kinematic elements

Change Dyad Closure / Change Configuration Assembly of a Dyad

Dyad :	A dyad is an assembly of two Parts and three joints. Each Joint can be a Slide-Joint, a Pin-Joint, or a Ball-Joint. - One joint joins the two Parts together - The other two joints join the two Parts to two other Parts that are kinematically-defined. When you add the last joint, two Parts in the dyad will be kinematically-defined.
Assur Groups :	A different name for a dyad.
Dyad Closures :	The different ways you can assemble the two Parts of a dyad. Often, we will use the term Closure for Dyad-Closure.
“Configuration of the Dyad's Assembly” is a different way to express “Dyad Closure”. It might be easier to translate
Types of Dyad :	Planar Dyads: R-R-R ; R-R-P ; R-P-R* ; R-P-P ; P-R-P Spatial Dyads: S-S-R ; S-S-P
R :	Revolute Joint = Pin-Joint
P :	Prismatic Joint = Slide-Joint
S :	Spherical Joint = Ball-Joint
*	This dyad does not correctly change its closure if the Pin-Joints(R) are offset from the Slide-Joint and along the y-axis of each Part in the dyad.
See more: Dyads

RRR Dyad
Closure 1

Command-Manager: Change Dyad Closure

RRR Dyad
Closure 2

STEP 1: Start the Change Dyad Closure command

1.Mechanism menu > Change Dyad Closure

1.Kinematic elements toolbar > Change-Dyad Closure

The Command-Manager indicates you must select a Part in the Dyad.

STEP 2: Select one Part in the Dyad

2.Click the Part-Outline of a Part in the Dyad whose assembly-configuration (or Dyad-Closure) you want to change.

STEP 3: Complete the Command

3.Click in the Command-Manager

The configuration of the assembly (Dyad Closure) should now be different.

<<< compare the bottom image with the top image.

Note

STEP 4: Do again, to find the Dyad-Closure you want.

4.If necessary, do 1 to 3 again, and again, to find the configuration of the assembly you want to apply to your design.

Top-Tip:

When there are many dyads in the model, it is sometime difficult to see which dyad whose closure you need or want to change.

1.Kinematics-Tree: Click to expand each Kinematic-Chain in the Kinematics-Tree

2.Kinematics-Tree: Click each dyad

The color of the five elements in the dyad (2 Parts + 3 Joints) change to the Selected Color (usually red) in the graphics-area.

Assembly-Configurations of the R-R-P Dyad

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

In MechDesigner, the joints are: Pin-Joint – Pin-Joint – Slide-Joint.

There are 4 possible assembly configurations (Dyad Closures) for this dyad.

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

4 x Assembly Configurations of an Offset-Crank-Slider

Part is the Crank - to illustrate the 4 dyad closures. The Crank is not in the Dyad.

Dyad: The Parts in the R-R-P dyad are Parts and .

To imagine the four assembly-configurations, we imagine we have not yet added the Pin-Joint (R2) between Part and Part.

Part : can rotate around the Pin-Joint, R1, at the end of the Crank.

Therefore, Pin-Joint R2 can ONLY be on the red circle at the end of Part.

Part : can only slide along the Slide-Joint, P1, along Line.

Important: The Point in Part for Pin-Joint (R2) is offset from the Slide-Joint and not on the Slide-Joint.

Therefore, Pin-Joint R2 can ONLY be on one of the red lines that are offset from the Slide-Joint.

The red circle intersects the red lines at 4 places.

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

Therefore, the Offset Slider-Crank and the R-R-P dyad has 4 possible assembly configurations (Dyad Closures).