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.

PREPARATION (TYPICAL)

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)

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.

ADD PULLEY

STEP 1: Click Add Pulley

1.Mechanism-Editor: Add menu > Mechanism menu > Add Pulley

- or -

1.Mechanism-Editor: Machine-elements toolbar > Add 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.

2 x Add Pulley:
- 1 x Driving-Pulley (Purple)
- 1 x Driven-Pulley (Magenta)

1 x Add Pulley to add 1 x Pulley.

Add Pulley

Add Pulley

Add Pulley

Terminology and definitions:

Kinematic State before you do Add Pulley.

Kinematic State after you do Add Pulley.

Kinematics-Tree of Pulley

PREPARATION (TYPICAL)

Prepare the Sketch-Path for the Belt.

Add the Motion-Path FB to the Sketch-Path

Prepare the Rotating-Parts that become the Pulleys.

ADD PULLEY

Video: Add Pulley: