﻿ Getting Started Tutorials - MechDesigner > Tutorial 14: Gear-Pairs / Rack-Pinions > B: Orbiting Gear Centres > Add a Gear-Pair with an Orbiting Centre

# Add a Gear-Pair with an Orbiting center

B: Orbiting Center Gear-Pairs

Arrangement 1: Orbit a gear around the outside of a fixed-gear - External Mesh.

Arrangement 2: Orbit gear around the inside of a fixed-gear - Internal Mesh.

#### Preparation for Orbiting Gear-Pair

 1.Edit a kinematically-defined Part 2.Add a Line 3.Close the Part-Editor 4.Add two Parts 5.Join Part to Line with a Pin-Joint 6.Join the Part to the other end of Part with a Pin-Joint In this configuration, you MUST use the Points that are at the end of the CAD-Lines in the Parts. STEP 7: Add a Motion-Dimension FB between the Line and the CAD-Line Note: The CAD-Line along the center of a Part has a dimension.

Click Machine-elements toolbar > Add Gear-Pair

Add Gear-Pair opens in the Command-Manager.

Select these four(4) elements. Refer to the images above to identify the Elements.

1.Click the Green Line

2.Click the Blue Line

3.Click the Green Line between the Gear centers

The Part-Editor opens automatically.

4.Click the Dimension of the Cad-Line that joins the Gear centers

Click in the Command Manager to Add the Gear-Pair.

In the Command-Manager we use the terms:

 Green Line for -usually - the CAD-Line in a kinematically-defined Part. Blue Line for - usually - the CAD-Line in a free Part

After you add the Gear-Pair - the free Part becomes a kinematically-defined Part.

#### Video - Add Orbiting Gear-Pair

 Tutorial 14: Add Gear-Pair - Orbiting

#### Edit Number-of-Teeth, Module and Mesh

 Default Gear-Pair: Orbiting Gear rotates around the outside of a Sun Gear The default Gear-Pair has: •an External Mesh form, equal number-of-teeth •a module that minimizes a change to the length of the Line that is the Line-of-centers. Length of the Line-of-Centers = Module × ( (Number-of-Teeth Gear 1 + Number-of-Teeth Gear 2) ÷ 2). Edit the Number-of-Teeth and Module: •Gear 1 = 60 •Gear 2 = 20 •Module = 2 Length of Line-of-Centers = Module × ((Number-of-Teeth Gear 1 + Number-of-Teeth Gear 2) / 2) = 2 × ((60 + 20)÷2) = 80mm Edit the Mesh - Orbiting Gear rotates inside the Stationary Gear. •Internal Mesh When the Gears have a different number-of-teeth, it is possible to move the smaller gear to the inside of the larger gear. Length of the Line-of-Centers with an Internal Mesh is: = 2 × ((60 – 20)÷2) = 40mm