﻿ MechDesigner Reference & User Interface > 2.2 Mechanism-Editor: > Machine elements > Add Pulley

#### Terminology and definitions:

 Pulley : A rotating wheel with teeth on its outside diameter that engages with a Belt. The angular motion of the Pulley and the linear motion of a Belt are related by the radius of the Pulley. The radius of the Pulley is defined by the number-of-teeth around its diameter, and the Tooth-Pitch. There are two types of Pulley. Type 1: Driving Pulley : The pre-defined angular motion of the Pulley specifies the linear motion of the Belt. Type 2: Driven Pulley : The pre-defined linear motion of the Belt specifies the angular motion of the Pulley. Belt: It is a Timing-Belt (we do not show the Teeth on the Belt). The Belt does not slip relative to the Teeth on the Pulley. The motion of a Motion-Point on a sketch-loop represents the motion of the Belt; the shape of the sketch-loop represents the path of the Belt. The sketch-loop should have an Arc sketch-element for each Pulley. The Pulleys must rotate about the center-Point of each Arc.

#### Kinematic State before you do Add Pulley.

 Type 1: Driving-Pulley: A rotating-Part is kinematically-defined. Type 2: Driven-Pulley: A rotating-Part is not kinematically-defined.

#### Kinematic State after you do Add Pulley.

 Type 1: The rotating-Part is kinematically-defined. It is a Driving-Pulley. The motion of the Pulley, its number-of-teeth, and the tooth-pitch now specify the motion of the Motion-Point along the sketch-loop (the Belt). Type 2: The rotating-Part is kinematically-defined. It is a Driven-Pulley. The motion of the Motion-Point along the sketch-loop (the Belt), the Tooth-Pitch and the Number-of-Teeth on the Pulley, now specify the motion of the Pulley.

### Kinematics-Tree of Pulley

A Driving-Pulley is not in the Kinematics-Tree.

A Driven-Pulley is a Pulley-Rocker in the Kinematics-Tree.

A Driving-Pulley is NOT in the Kinematics-Tree.
A Driven-Pulley is a Pulley-Rocker.

Pulley that you add to a free Part:

 Before you do Add Pulley, to a rotating-Part that is not kinematically-defined, the rotating-Part has one degree-of-freedom. After you do Add Pulley, the rotating-Part becomes a Pulley-Rocker and kinematically-defined. A Path-Joint is a child to the Pulley-Rocker.

### Prepare the Sketch-Path for the Belt.

Preparation 1: Add a sketch-path to represent the path of the Belt.

The sketch-path should include only Lines and Arcs. Usually, add Tangent-Constraints between each Line and Arc. Do not add equal constraint to the Arcs.

The sketch-path is usually a closed sketch-loop. It is usually helpful to fully define the sketch-path.

 1.Mechanism-Editor: Edit the Base-Part (usually) or an Added-Part 2.Part-Editor: Add a sketch-path to represent the path of the Belt 3.Part-Editor: Add Tangent Constraints between each Line and Arc. 4.Part-Editor: Add a dimension to the radius of each Arc.

Note: If a rotating-Part (and Pulley) is a Rocker:

 5.Part-Editor: Add a Line from the center-Point of the Arc that will be the rotating-axis of the Rocker.

Then, you will be able to add a Motion-Dimension FB to the rotating-Part in the Mechanism-Editor.

### Add the Motion-Path FB to the Sketch-Path

Preparation 2: MOTION-PATH FB

Add ONE Motion-Path FB to the sketch-path.

 1.Click Kinematic FB toolbar > Add Motion-Path FB. 2.Click a sketch-element in the sketch-path

The Motion-Path FB is in the graphic-area and the Motion-Point is at the start-Point of the sketch-element you select.

### Prepare the Rotating-Parts that become the Pulleys.

Preparation 3A: TYPE 1: DRIVING-PULLEY

You can add a ZERO or a maximum of ONE Driving-Pulley to each Belt. The rotating-Part is kinematically-defined before we do Add Pulley.

 3.Add a Rocker with its Pin-Joint at the center-Point of the Arc with a Line (see Preparation 1: 5, above) OR 3.Add Parts to the model, in which there is a rotating-Part with a Pin-Joint at the center of the Arc in the sketch-path of the Belt and it is kinematically-defined.

Preparation 3b: TYPE 2: DRIVEN-PULLEY

The motion of the Belt and the Pitch-Circle Diameter specify the motion of Driven-Pulleys.

The rotating-Part is not kinematically-defined before we do Add Pulley.

 4.Add rotating-Parts to be Driven-Pulleys, with a Pin-Joints at the centre-Point of each Arc with a Driven-Pulley.

There are four elements to select in the Command-Manager

STEP 2: Click the four elements

 1.Click a Pin-Joint at the center of a rotating-Part*. 2.Click the Motion-Path FB. The Part-Editor opens 3.Click the dimension that defines the radius of the Arc. The Part-Editor closes 4.Click the rotating-Part* that has a Pin-Joint (see 1) at the center-Point of the Arc (see 3)

* If the rotating-Part is :

kinematically-defined - the motion of the Pulley will move the Belt (Driving-Pulley).

not kinematically-defined - the motion of the Belt will move the Pulley (Driven-Pulley).

STEP 3: Complete the Command

 5.Command-Manager: Click in the Command-Manager.

Result:

The image shows two Pulleys. You must do Add Pulley two times.

 New Pulley schematic shows in the graphic-area. •Use the Motion-Path dialog-box to edit the Tooth-Pitch and length of the Belt. The Pulley has an integer number-of-teeth. •Use the Pulley dialog-box to edit the number-of-teeth on each Pulley.