Kinematics of an RPR Dyad

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Kinematics of an RPR Dyad

RPR 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, add the Dyad to a Rocker

In Case 2, add the Dyad to a Slider

There are two Pin-Joints and one Slide-Joint in the RPR 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 be able to reach the Joints. To correct the problem, you may need to change the Dyad closure until the assembly operates as you expect it to.

See Kinematic Closure

tog_minus        '3D Sample Video of Case2: Slider connected to an RPR Dyad'.

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



Step 1: Two New Parts

Add two Parts.



Step 2: Two 'Outer' Joints

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

Pin-Joint with a new Part and the Motion PartRed-14-1b

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

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

RPR Dyad with Rocker

RPR Dyad with Slider

Step 3: One 'Inner' Joint

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

The Kinematic-Chain becomes Kinematically Defined

Note: The Parts seem to 'flip' into a different 'assembly' closure. In fact, the orientation of the Parts are a function of the direction of the Lines in each Part.




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