Getting Started Tutorials - MechDesigner > Tutorial 14: Gear-Pairs / Rack-Pinions > B: Orbiting Gear Centers > Gear-Trains: Planetary and Compound-Planetary

B: ORBITING GEARS

Planetary Gear-Trains

A Planetary Gear Train.

•One or more gears (Planets) are held in a Carrier.

•The Planet gears rotate about their own axes and also rotate about the central axis of the Sun and Annulus Gears.

Note: The Rule: you cannot use the same Line as the Line-of-Centers for more than one Gear-Pair.

Planetary Gear Design Arrangements

GST-T14-B2-A

The typical arrangement is shown to the left. It consists of a:

•Sun (S) Gear with External Teeth

•Annulus (A) Gear with Internal Teeth, with the same center as the Sun Gear

•Planet (P) Gears that engage with the Sun and Ring Gear

•Carrier (C) in which the Planet Pinions are supported.

Note: The Annulus is also called the Ring.

The Gear Ratios are a function of the gear - A, S or C - you lock. See YouTube video here: http://youtu.be/hXTzO1UXnLs

There are also possibilities where all three members (A, S or C) rotate. They are called Differential Gears (to be updated for MD16)

Planetary Gears
Schematic of Variation 3

Simple Planetary Gear-Trains

There are six drive variations when there is one stationary gear .

The three Variations that we describe for you are

•Variation 1: The Carrier (C) is the Input; the Sun (S) is Stationary; the Output is (A).
Gear Ratio = (ω(1 +1/ω) input turns : 1 output turn)

•Variation 2: The Sun (S), is the Input; the Carrier is Stationary (C); the Output is (A).
Gear Ratio = (-ω input turns : 1 output turn)

•Variation 3: The Sun (S), is the Input; the Annulus (A) is Stationary; the Output is (C).
Gear Ratio = (1+ω input turns : 1 output turn)

Other Variations

•Variation 4: The Carrier (C), is the Input; the Annulus (A) is Stationary; the Output is (S).
Gear Ratio = (1/(1+ω) input turns : 1 output turn)

•Variation 5: The Annulus (A), is the Input; the Carrier (C) is Stationary; the Output is (S).
Gear Ratio = (-1/ω input turns : 1 output turn)

•Variation 6: The Annulus (A); is the Input: the Sun is Stationary (S); the Output is (C).
Gear Ratio = ((1+ω)/ω input turns : 1 output turn)

ω = Number of Sun-Teeth / Number of Annulus-Teeth

VARIATION 1: Driving Carrier (C) ; Driven Annulus (A) ; Stationary Sun (S)

This is a video of Variation 1

Prepare Gear-Pair 1

GST-14-B-201

STEP 1: Add Line to the Base-Part

1.Edit a kinematically-defined Part (usually the Base-Part) with the Part-Editor.

2.Add a Line ; Add Constraints and Dimensions, as needed.

3.Close the Part-Editor

Dimension to Line for Gear-Centers

STEP 2: Add a rotating-Part that is kinematically-defined

1.Add a Part

2.Join the start-Point of Line in Part to the start-Point of Line with a Pin-Joint

3.Kinematic FB toolbar > Add Motion-Dimension FB

Click Pin-Joint

Click Line

4.Click in the Command-Manager

5.Add a Linear-Motion FB and connect a wire to the Motion-Dimension FB

Model is prepared for Epicyclic Gears

rotating-Part(6) that is NOT kinematically-defined

STEP 3: Add a Line to the rotating-Part

1.Edit the rotating-Part that is kinematically-defined.

2.Geometry toolbar > Add Line

It is important that you merge the start-Point of the Line with the end-Point of the CAD-Line.

To merge the start-Point with the end-Point at :

3.Drag from the end-Point of CAD-Line to add the new Line

Note 1: Make the length of Line approximately equal to the length of the CAD-Line.

Note 2: Drag towards the start-Point of the CAD-Line

4.Geometry toolbar > Add Dimension

5.Click to add a dimension to the new Line. The actual dimension is not important.

Exit the Part-Editor

STEP 4: Add a Part to the end of the rotating-Part

1.Kinematic elements toolbar > Add Part

2.Drag from the end-Point of the CAD-Line in the rotating-Part to add the new Part

The new Part has a Pin-Joint that joins it with Part

Add Gear-Pair 1

Epicyclick Gear-Pair ; Z1=60 ; Z2=20

See Add a Gear-Pair with an Orbiting center

1.Number-of-Teeth, Z1 = 60

2.Number-of-Teeth, Z2 =20

3.External Mesh

The Length of the Line-of-Centers should be 40mm

Length of Line-of-Centers with External Mesh

Prepare Gear-Pair 2

Planetary-Prepare

STEP 1: Add a Part to the end of the Line

1.Kinematic elements toolbar > Add Part

2.Drag from the end-Point of the Line to add the new Part

The new Part has a Pin-Joint that joins it with Part

Add Gear-Pair 2

Gear-Pair 1 and 2

STEP 1: Add Gear-Pair 2

1.Machine elements toolbar > Add Gear-Pair

Click CAD-Line along the center of Part

Click Line in Part

Click Dimension of Line

Click in the Command-Manager

Gear-Pair 1 [1,2] and Gear-Parr 2 [3,4]

STEP 2: Edit Gear-Pair 2

1.Number-of-Teeth, Z1 = 20

2.Number-of-Teeth, Z2 =100

3.Internal Mesh

The length of the Line-of-Centers should be 40mm

The Length of Line-of-Centers with Internal Mesh

GST-14-B-209

STEP 3: Make the Line-of-Center of Gear-Pair 2 collinear with Line-of-Center of Gear-Pair 1

1.Edit Part

Note: the length of the CAD-Line is equal to the length of the Line.

2.Constraints toolbar > Add Horizontal to Line

3.Exit the Part-Editor

GST-14-B-210

RESULT

Planetary Gears of Variation 1