Kinematics of an R-R-P Dyad

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Kinematics of an R-R-P Dyad

R-R-P 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

In the R-R-P Dyad there are : two Pin-Joints, one Slide-Joint, and two Parts.

I follow a consistent three-step procedure.

General Three-Step Procedure to add a Dyad

STEP 1: Add the two new Parts

STEP 2: Add the two 'outer' Joints: Join each new Part to two separate Kinematically Defined Parts (with Green Part-Outlines)

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

Note: This Dyad is not 'symmetrical'. The 'P' joint could be joined to the Motion-Part or the 'other' kinematically-defined Part. In the two examples below, the 'P' joint is joined to the Base-Part.


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.

See Kinematic Closure

Rocker and Base-Part

CASE 2:  
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: New Parts

Add two Parts.



Step 2: 'Outer' Joints

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

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

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: R-P

RRP Dyad with Rocker

RRP Dyad with Slider

Step 3: 'Inner' Joints

Connect the two new parts together with a Pin-JointRed-14-3

The Kinematic-Chain becomes Kinematically Defined again with an R-R-P Dyad.

Note: For clarity, I have added Lines to the Sliding-Parts to offset the Pin-Joints from Sliding-Parts.




Shows the original Rocker or Slider, plus the new R-R-P Dyad.