Kinematics: Closure

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Kinematics: Closure

Kinematic Closure of Dyads

It is possible to assemble Parts in a Dyad so that the Parts are in different positions.

The different positions are called 'Dyad-Closures', or simply 'Closures'.

When you first add a Dyad, MechDesigner can only guess which closure you want in your design.

Therefore, we have a tool - Change Dyad Closure - to move the Dyad to the closure you want.

Use 'Change Dyad Closure' more than one time when the Dyad has more than two closures, and finally to return to the original closure.

After you have set the Dyad to the correct closure, it will not change again when you open the model.

Objective of this Step.

Use the Change Dyad Closure tool

How to identify

oValid, or Solved, Dyad-Closures

oInvalid, or Not-Solved, Dyad-Closures.


I have prepared four important videos. They help us understand Closures, and when they become valid or invalid.

The videos show:

Valid and Invalid Closures

of these two dyads:

R-R-R Dyad and R-R-P Dyad.

As you look at these videos, identify the Motion-Part. The Motion-Part ALWAYS moves with the motion-values at the input-connector of the Motion-Dimension FB. , or Motion-Path FB, Pulley-Rocker, Geared-Rocker, ...


Video 1: CRANK + R-R-R Dyad - 2 VALID Closures

Tutorial 2; Step 2.4

R-R-R-Dyad & 2 VALID Closures.

The joints do not break.

Video 2: CRANK + R-R-R Dyad - 2 INVALID Closures (Broken Closures)

Tutorial 2; Step 2.4

R-R-R-Dyad & 2 INVALID Closures.

The joints do break.

Video 3: CRANK + R-R-P Dyad - 4 VALID Closures

Tutorial 2; Step 2.4

R-R-P Dyad & 4 VALID Closures.

The joints do not break.


tog_minusSolved Closures - RRR Dyad

tog_minus        Closure that are Solved and Not-Solved - 'Offset' RRP DYAD

tog_minusTo change the Closure of a Dyad

tog_minusMore than two Closures: Four Closures of the Offset RRP Dyad