Planetary Gear

AIM : Design and motion analysis of Planetary Gear System.

INTRODUCTION : A planetary gear set is made up of three types of gears; a sun gear, planet gears, and a ring gear. The sun gear is located at the center (yellow), and transmits torque to the planet gears (blue) which are typically mounted on a moveable carrier (green). The planet gears orbit around the sun gear and mesh with an outer ring gear (pink). Planetary gear systems can vary in complexity from very simple to intricate compound systems, depending on the application.

The planetary gearbox got its name because of how the different gears move together. In a planetary gearbox we see a sun (solar) gear, satellite (ring) gear and two or more planet gears. Normally, the sun-gear is driven and thus move the planet gears locked in the planet carrier and form the output shaft. The satellite gears have a fixed position in relation to the outside world. This looks similar to our planetary solar system and that is where the name comes from. What helped was that ancient gear constructions were used extensively in astrology for mapping and following our celestial bodies. So it was not such a big step to make.

In practice, we often speak from the perspective of the use of planetary gearboxes for industrial automation. That is why we call the sun-gear the input shaft, the planet gears and carrier the output shaft and the satellite gear (or ring gear) the housing.

USE:

Planetary gears are often used when space and weight are an issue, but a large amount of speed reduction and torque are needed. This requirement applies to a variety of industries, including tractors and construction equipment where a large amount of torque is needed to drive the wheels. Other places you will find planetary gear sets include turbine engines, automatic transmissions, and even electric screwdrivers.

Planetary gear systems are able to produce a lot of torque because the load is shared among multiple planet gears. This arrangement also creates more contact surfaces and a larger contact area between the gears than a traditional parallel axis gear system. Because of this, in the load is more evenly distributed and therefore the gears are more resistant to damage.

ADVANTAGES :

• Compact size and low weight – as much as 50% reduction with same torque output.
• High power density – several planets share the load rather than one gear, the more planets the more sharing.
• Longer gear life at similar loads.
• Gearing can be very accurate with virtually no backlash.
• High efficiency – 95% per stage is common.
• Typical ratio per stage is 9:1, 4 stages 9000:1
• Coaxial arrangement – no offset output shaft
• Modular, most planetary stages can be stacked.

DISADVANTAGES :

• Noisier Operation – some planetary gearheads are noisy.
• Gearing must be accurate to assure load sharing
• High bearing loads can lead to early wear in dead stud or sleeve bearing construction
• Generally grease lubricated (oil bath is the better).
• High ratio of length to diameter when using multiple stages (gearhead gets very long).
• High cost if low backlash and long life are required.

Following objectives are to be fulfilled through this project :

• Designing of ring gear, planetary gear, sun gear and carrier with the following dimensions :

Ring Gear

Module = 2.5 (You must use the metric system in design modeler)

Number of teeth = 46

Sun Gear

Number of teeth = 14

Input Speed of the Gear = 200 rpm.

Number of planet gears = 4

• Running a simulation on the following cases,

  Sl.No	Input	Output	Fixed
  1	Sun Gear	Carrier	Ring Gear
  2	Ring Gear	Carrier	Sun Gear
  3	Sun Gear	Ring Gear	Carrier

CALCULATIONS :

Calculate pitch circle diameter for planet gear using the relation,

`(PCD)_("planet gear")= frac((PCD)_("ring gear")-(PCD)_("sun gear"))(2)`

`PCD_("planet gear")= 40 mm`

Module for all the gears are same.

PROCEDURE :

• Create 3D drawings of the ring gear, sun gear, planet gear and carrier using the design modeler and providing the correct parameter values.

ring gear

sun gear

planet gear

carrier

The final assembly is obtained as below.

After getting the final assembly perform the following mates for proper alignment of the assembly components.

Perform the motion analysis to obtain the plots for the 3 different cases.

1. Carrier fixed- plot of angular velocity v/s time.

2. Ring gear fixed- plot of angular velocity v/s time.

3. Sun gear fixed- plot of angular velocity v/s time.

The CAD files of the parts can be accessed from the below link- https://drive.google.com/drive/folders/1siupQpu7ji4iAr-iIy3cKiyVGODlrS8y?usp=sharing