﻿ Getting Started Tutorials - MechDesigner > Tutorial 15: Patterns - Indexing-Chain example > Step 15.4: Add a Chain-Link and Drive Pulleys

A Chain-Link rotates as it moves around each Pulley. Currently, we do not have a Part that rotates.

We can add a rotating-Part that makes a kinematic-link between the two Slider Sets.

The Chain-Link is represented by one of the two Parts in an R-P-R Dyad.

As always, a Dyad has two Parts and three Joints.

Add a new Part - add a Pin-Joint (R--). Join it to a Point on Y-Slider of Slider-Set 1

Add a new Part - add a Pin-Joint (--R). Join a Point on Y-Slider of Slider-Set 2

Add a Slide-Joint (-P-) - between the CAD-Lines in each of the two new Parts

The two Parts and three Joints make the R-P-R Dyad.

### The Pulleys

We add a rotating-Part at each end of the Chain to represent the Pulleys

They must rotate (12÷5) times each time the Chain cycles one time.

Remember, Dyads always have two Parts and three Joints.

This dyad is: R(Pin-Joint) - P(Slide-Joint) - R(Pin-Joint)

Top-Tip: Temporarily hide the Motion-Dimension FBs.

STEP 1: Add two Parts and R Joints

 1.Add a Part (Part 1) 2.Rename the Part as Tool-Part. 3.Add a Pin-Joint between the Part and the start-Point of Y-Slider1 4.Add a Part (Part 2) 5.Add a Pin-Joint between the Part and the start-Point of Y-Slider2

The two Pin-Joints are the Revolute joints in the RPR dyad.

STEP 1: Add a Slide-Joint to join the Part 1 and Part 2

The Slide-Joint completes the RPR Dyad.

The Part-Outlines of the Part 1 and Part 2 become Green.

When you cycle the machine, you will see the RPR Dyad move with the Slider-Sets.

STEP 2: Add a Measurement FB between the Pin-Joints

 1.Kinematic FB toolbar > Add Measurement FB 2.Click the Point at the Pin-Joint at R-P-R 3.Click the Point at the Pin-Joint at R-P-R 4.Click the graphic-area to place

As you cycle the model you will see the length variation between the Pin-Joints is from 100mm to 93.55mm.