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 has:

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

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

Planetary Gear Design Arrangements

GST-T14-B2-A

The typical arrangement of the gears is shown to the left.

There is a:

•Sun-Gear (S), with External Teeth

•Annulus-Gear (A), with Internal Teeth, with the same center as the Sun Gear. The Annulus is also called the Ring.

•Planet-Gear(P), usually more than one gears that engage with the Sun and Ring Gear

•Carrier (C), which “carries” the Planet gears.

The Gear-Ratio of a Planetary gear-box is a function of which gear or carrier is fixed to the frame. See YouTube video here: http://youtu.be/hXTzO1UXnLs

Note:

There is also a possibilities in which all three gears and the carrier (A, S, P, and C) rotate. They are called Differential Gears (to be updated for MD16)

Planetary Gears
Schematic of Variation 3

Planetary Gears

There are six design variations with one stationary gear.

The three common variations 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 three other Variations are:

•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 a Line to the Base-Part

1.Edit 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 CAD-Line in Part to the start-Point of Line in the Base-Part 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