Kinematics of an PRP Dyad

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Kinematics of an PRP Dyad

PRP Dyad

Dyads do not change the number of Degrees-of-Freedom of a kinematic-chain. If the kinematic-chain has Green Part-Outlines before you add the Dyad, it should have Green Part-Outlines after

To show you how to add this Dyad, we have two design cases.

In Case 1, we join the two Parts in the Dyad to the Base-Part and the Rocker

In Case 2, we join the two Parts in the Dyad to the Base-Part and the Slider

There are two Slide-Joints and one Pin-Joint in the PRP Dyad, and two Parts.

I follow a consistent three-step procedure:

General Three-Step Procedure to add a Dyad

STEP 1: Add the two Parts

STEP 2: Add the two 'outer' Joints: Join each Part to two separate Kinematically Defined Parts

STEP 3: Add the 'inner' Joint: Join the two Parts together


Note: Occasionally, a Dyad does not operate correctly. The Pin-Joints 'break' when you cycle the machine, even though you cannot see why they break.

It is possible that MechDesigner has assembled the Dyad in a Closure where the Parts cannot reach the Joints - even though to you, they should assemble. To correct the problem, you may need to change the Dyad closure until the assembly operates as you expect it to.

Rocker and Base-Part

Slider and Base-Part



'Expand' then 'Play'



'Expand' then 'Play'






Two Kinematically Defined Parts:

Case 1: Part 1:Base-Part, Part 2:Rocker

Case 2: Part 1:Base-Part, Part 2:Slider

Note:  LineRed-14-1b added to the Slider. The Slide-Joint of the Dyad cannot be parallel to the Slide-Joint for the Slider.



Step 1: New Parts

Add two Parts.



Step 2: 'Outer' Joints

Add the two 'outer' Joints (R-R Joints). In this case, a:

Slide-Joint with a new Part and the Motion PartRed-14-2

Slide-Joint with the other new Part and the Base-Part Red-14-2

The two Joints are the two 'outer' Joints of the Dyad: P-P

PRP Dyad with Rocker

PRP Dyad with Slider

Step 3: 'Inner' Joint

Add the 'inner' Joint (-R-). In this case, join the two new parts together with a Slide-JointRed-14-3

The Kinematic-Chain becomes Kinematically Defined

Note: The orientation of the Parts in a Dyad with a Slide-Joint are a function of the +X-axis direction of the Lines in each Part.




Shows the original Rocker or Slider, plus the new PRP Dyad.