Planetary Gear

AIM: To create a 3D CAD model of the Planetary Gear System and to do motion analysis.

THEORY: Epicyclic gearing or planetary gearing is a gear system consisting of one or more outer, or planet, gears or pinions, revolving about a central sun gear or sun wheel. ^[1] Typically, the planet gears are mounted on a movable arm or carrier, which itself may rotate relative to the sun gear. Epicyclic gearing systems also incorporate the use of an outer ring gear or annulus, which meshes with the planet gears. Planetary gears are typically classified as simple or compound planetary gears. Simple planetary gears have one sun, one ring, one carrier, and one planet set.

An epicyclic gear train can be assembled so the planet gear rolls on the inside of the pitch circle of a fixed, outer gear ring, or ring gear sometimes called an annular gear. In this case, the curve traced by a point on the pitch circle of the planet is a hypocycloid.

The combination of epicycle gear trains with a planet engaging both a sun gear and a ring gear is called a planetary gear train. In this case, the ring gear is usually fixed and the sun gear is driven. ^[2]

DESIGN: The 3D CAD models are designed in SolidWorks and motion analysis is analyzed on Motion Analysis add-on in SolidWorks. The following steps were taken to design the mechanism:-

Step-1: First, an internal spur gear was obtained from Design Library as a Ring gear, with teeth equal to 46 and module equal to 2.5.

Step-2: Second, a spur gear with a hub was obtained from Design Library as a Sun gear, with teeth equal to 14 and a module equal to 2.5.

Step-3: Then PCD for Planet gear was calculated using the following figure.

The outermost circle is the PCD of Ring gear, which is calculated using the formula,

PCD_Ring = (Module)×(No. of teeth)

PCD_Ring = 2.5×46 = 115mm

The innermost circle is the PCD of Sun gear.

PCD_Sun = 2.5×14 = 35

Since PCD of Planet gear must be tangent to both the gear, hence,

PCD_Planet + PCD_Sun/2 = PCD_Ring/2

PCD_Planet = 115/2 – 35/2

PCD_Planet = 57.5 – 17.5 = 40mm

No. of teeth of Planet gear = PCD_Planet/Module = 40/2.5 = 16

Step-4: Then, another spur gear was obtained from Design Library as a Planet gear, with teeth equal to 16 and module equal to 2.5.

Step-5: Then, a carrier was designed in 2D sketch and then extruded.

Step-6: Then all models were assembled, and constraints were provided.

MOTION ANALYSIS:

Motion analysis was conducted using the Motion Analysis add-on in SolidWorks. The motion features of the SolidWorks provide us a wide range of motion study, they can be divided into three categories:

Animation: If one simply wishes to create some nice visuals for presentation or marketing without consideration of mass and gravity effects, then animation is perfect for it.

Basic Motion: For an extra layer of complexity that takes into consideration the effects of mass, springs, gravity, and physical collision detection, then a Basic Motion study is more suited for the requirements.

Motion Analysis: This is the top tier of motion study and takes into account a wider range of physical interactions such as impact effects, damping, force, momentum, etc. ^[2]

Step-1: Motion Study 1

Input: Sun gear

Fixed: Ring gear

Output: Carrier

Input rpm is 200 and output rpm is low, hence this arrangement results in low rpm.

Step-2: Motion Study 2

Input: Ring gear

Fixed: Sun gear

Output: Carrier

Input rpm is 200 and output rpm is very high, hence this arrangement gears up the system.

Step-3: Motion Study 3

Input: Sun gear

Fixed: Carrier

Output: Ring gear

This arrangement also gives the high output.

CONCLUSION:

The various arrangements can be used for different purposes.

Google drive link for the model:

https://drive.google.com/drive/folders/1OeS_1yb-5UysFPcpF8r7RlOpVbUhJ_Ex?usp=sharing

REFERENCES:

[1] Hillier, V.A.W. (2001). "Planetary gearing and unidirectional clutches". Fundamentals of Motor Vehicle Technology (4th ed.). Cheltenham, UK: Nelson Thornes. p. 244. ISBN 0-74-870531-7.

[2] Harrison, H.; Nettleton, T. (1994). Principles of Engineering Mechanics (2nd ed.). Oxford, UK: Butterworth-Heinemann. p. 58. ISBN 0-34-056831-3.