Summary of this Step

A Dyad is a kinematic term for the connection of

Two Parts
Three Joints

The Dyad is know by its sequence of three Joints.

For example: an RRR Dyad is a Revolute-Revolute-Revolute Dyad. Revolute is the kinematic term for a Pin-Joint.

Note 1: Dyads ALWAYS have two Parts and three Joints.

Note 2: The dyad name is a Derived Name for the three Joint types. This step is practice. Also, it introduces the concept of Inverse Kinematics. This concept will become clear after we add the 2D-Cam.

tog_minus        Video of this Step


Tutorial 6A-3

tog_minus        Edit the BasePart

Why Edit the Base-Part?

In this tutorial, we will add a

Pin-Joint between the Base-Part and a Part that becomes the 'parent' to the rotating 2D-Cam
Pin-Joint between the Base-Part and one Part in the Dyad

There must be al least two Point sketch-element in the Base-Par; one for each joint.

We must edit the Base-Part to add the Point sketch-elements, or a sketch-element that has at least one Point. It is best practice to add a Line. There are a number of advantages. In time, these advantages become clearer.


STEP 1: Double-click on the Part-Outline of the Base-Part to open the Part-Editor.
STEP 2: Add two new Lines1s-red2s , approximately as shown to the left.
STEP 3: Dimension the Lines.

Step 3 is complete

[Note: I have used Show/Hide Dimensions to hide the dimensions in the image]

As noted, we will use the Points that are at the left end of these Lines for the:

Pin-Joint that will connect a Part to the Base-Part – see below
Pin-Joint that will connect the cam-shaft to the Base-Part – see Step 6A.5

tog_minus        Add two Parts and three Pin-Joints – an RRR Dyad


Add two Parts

STEP 1: Click Add Part in the Kinematic-elements toolbar.
- or -
Mechanism > Add Part
STEP 2: Drag in the graphic-area to add a Part1s-red
STEP 3: Do Steps 1 and 2 again to add the other Part2s

The new Parts have a blue Part-Outline.

They are not kinematically-defined parts.


Add three Pin-Joints

STEP 4: Click Add Pin-Joint in Kinematic-elements toolbar
- or -
Mechanism menu > Add Pin-Joint
STEP 5: Add 3 Joints to join the Parts:
Joint 11s-red: Click one end a new Part and a Point in the Base-Part
Joint 22s: Click one end of the other new Part and then a Point in the Slider
Joint 33s: Select a Point at each end of the two new parts to join them together

Run menu > Cycle and you will see the new Dyad move as the Slider moves.

The kinematic-chain may 'brake' if the Parts in the Dyad cannot reach the Slider!

If necessary:

edit the Length of the Parts, or
change the Position of the Pin-Joint with the Base-Part, or
reduce the distance of the motion in MotionDesigner.

Tutorial and Reference Help Files for MechDesigner and MotionDesigner 13.2 + © Machine, Mechanism, Motion and Cam Design Software by PSMotion Ltd