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

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

Dyad : also known as Assur Group :	A dyad is an assembly of two Parts and three joints. There is one joint that joins the two Parts together. The two other joints join the Parts to two other Parts that are kinematically-defined. The two Parts and three joints in a dyad are kinematically-defined.
Assur Groups :	Another name for a dyad
Dyad Closures :	The different ways you can assemble the two Parts of a dyad
Configuration of the Dyad's Assembly is a different way to express Dyad Closure.
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
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 (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.

<<< To the left, compare the bottom image with the top image.

STEP 4: Do again, if needed

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 not easy to see which Dyad whose closure you need to change.

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

2.Kinematics-Tree: Click each Dyad

If you click a dyad in the Kinematics-Tree, the five elements in the dyad (2 Parts + 3 Joints) are red in the graphics-area.

Assembly-Configurations of the RRP Dyad

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

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

There are 4 possible assembly configurations (Dyad Closures).

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, it does NOT move.

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

To imagine the four assembly-configurations, do not add the Pin-Joint (R2) between Part and Part.

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

Therefore, Pin-Joint R2 can ONLY be around 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 the Pin-Joint (R2) is offset from the Slide-Joint and not on the Slide-Joint.

Therefore, Pin-Joint R2 can, also, ONLY be along 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 ONLY be at 4 places.

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