Option 2: Orbiting Centre Gear-Pairs

It is possible to orbit a gear around the outside of a gear and also a gear around the inside of a gear.

Preparation for Option 2

Elements to select to add an Epicyclic Gear

STEP 1: Edit a kinematically-defined Part 3s
STEP 2: Add a Line 1s-red
STEP 3: Close the Part-Editor
STEP 4: Add two Parts 3s2s
STEP 5: Join Part3s to Line1s-red with a Pin-Joint5s
STEP 6: Join the Part2s to the other end of Part3s with a Pin-Joint6s

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 Line3s and the Line in the Part 1.

Note:  The CAD-Line3s along the centre of a Part has a dimension.

Use Add Gear-Pair


Click Machine-elements toolbar > Add Gear-Pair


Add Gear-Pair opens in the Command-Manager.

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

1.The 'Green Line' on Gear Part 1 1s-red
2.The 'Blue Line' on Gear Part 2 2s
3.The 'Green Line' that Joins the Gear centres 3s
4.The Dimension of the Cad-Line that joins the Gear centres 7s

In the Command-Manager we use the terms:

'Green Line' is usually the CAD-Line in a kinematically-defined Part.
'Blue Line' is usually the CAD-Line in the Part that is not kinematically-defined.

The 'Green Line' and the 'Blue Line' might be a CAD-Line - and dark green in the graphic-area.

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

In the default, the two Gears have:

an external tooth form.
the same number-of-teeth
module that will minimize a change of length to the Line-of-centres.

The module and the number-of-teeth on each Gear give the length of the Line-of-centres3s.


Edit the Number-of-Teeth and Module

Gear 1 = 60 1s-red
Gear 2 = 20 2s
Module = 2

Gear Diameter = Module * number-of-teeth

Length of Line-of-centres = Module * ((Number-of-Teeth Gear 1 + Number-of-Teeth Gear 2) / 2).

= 2 * ((60 + 20)/2) = 80mm


Make the Orbiting Gear rotate around the inside of a Ring Gear

When the Gears have a different number-of-teeth, it is possible to make one of the gears internal.

Gear 2 moves inside Gear 1.

Length of the Line-of-centres is now:

= 2 * ((60 - 20)/2) = 40mm

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