Planetary Gear
Aim:
- To create a planetary gear Parts and assemble all the parts with carrier and perform a motion analysis.
- To plot Angular velocity by fixing the different part of the assembly.
THEORY ABOUT PLANETARY GEAR:
An epicyclic gear train (also known as planetary gear) consists of two gears mounted so that the center of one gear revolves around the center of the other. A carrier connects the centers of the two gears and rotates to carry one gear, called the planet gear or planet pinion, around the other, called the sun gear or sun wheel. The planet and sun gears mesh so that their pitch circles roll without slip. A point on the pitch circle of the planet gear traces an epicycloid curve. In this simplified case, the sun gear is fixed and the planetary gear(s) roll around the sun gear.
An planetary 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 planetary 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.
Planetary gears get their name from their earliest application, which was the modelling of the movements of the planets in the heavens. Believing the planets, as everything in the heavens, to be perfect, they could only travel in perfect circles, but their motions as viewed from Earth could not be reconciled with circular motion.
Given data:
Module = 2.5
Number of teeth in ring gear = 46
Number of teeth in sun gear = 14
Input speed of the gear = 200 rpm
Number of planetary gears = 4
Formula used
=> M=D/Z
Where,
M = Module
D = Pitch circle diameter
Z = Number of teeth
Pitch circle diameter of ring = 2.5*46=115mm
Pitch circle diameter of sun gear = 2.5*14=35mm
Pitch circle diameter of Planetary gear = `(115-35)/2`=40mm
Number of teeth in planetary gears =`40/2.5`=16 teeths
| sl no. | type of gears | pitch circle diameter(MM) | No. of teeths |
| 1 | Ring gear | 115 | 46 |
| 2 | Sun gear | 35 | 14 |
| 3 | planet gear | 40 | 16 |
Creating the 3D model :
For creating gear
Design library --> Toolbox --> ANSI metric --> Power transmission --> gears for sun and planet gears choose Spur gear, for Ring gear choose Internal Spur Gear.
The created models are as shown.
Pressure angle = 20 degree
Face Width = 20 mm
Ring gear (Internal spur gear)
Sun gear (spur gear)(14 teeths)
Planet gear (spur gear)(16 teeths)
Carrier model
Final assembly Model
Motion analysis
In the motion study, make contacts between the followings.
- Carrier and the Planet gears
- Sun gear and the Planet gears
- Ring gear and the Planet gears
The material for each contact is Steel (Dry).
here are Three cases
| Sl.No | Input | Output | Fixed |
| 1 | Sun Gear | Carrier | Ring Gear |
| 2 | Ring Gear | Carrier | Sun Gear |
| 3 | Sun Gear | Ring Gear | Carrier |
The input speed to the motor in each case is 200 RPM. The motion analysis is done for 5 seconds.
Case 1:
Ring gear is fixed. Motor - sun gear(input).
The plot of an angular velocity of the carrier vs time.
Case 2:
Sun gear fixed. Motor - Ring gear(input).
The plot of an angular velocity of the carrier vs time.
Case 3 :
Carrier fixed. Motor - Sun gear(input).
The plot of an angular velocity of the Ring vs time.
ANIMATION
- Ring gear is fixed. Motor - sun gear(input).
- Sun gear fixed. Motor - Ring gear(input).
- Carrier fixed. Motor - Sun gear(input).
CONCLUSION:
- In the case-1 when the input is given to the sun gear and output is obtained at the carrier and the ring gear fixed, the planet gear not only rotates about their axis but are also forced to roll on the inside of the ring gear along with the carrier as the Ring gear is fixed. The angular velocity obtained for this case is between 235-313 deg/sec.
- In the case-2 when the input is given to the ring gear and output is obtained from the carrier and the sun gear fixed. The angular velocity achieved is maximum since the internal gear is big and planet gears are small comparatively so when a large gear meshes with a small gear the velocity achieved from the small gear is high because the velocity ratio is high. The angular velocity obtained for this case is between 800-1017 deg/sec.
- In the case-3, the carrier is fixed and output is to be obtained from the ring gear with the input given to Sun gear, all the gears rotate about their axis. The planet gears rotate only about their axis and transmit motion from sun to the ring and since the ring gear is big in diameter the angular velocity achieved is less. The deviations that are visible in the graphs show that there are points where sliding is occurring between the gears. For making the graph more smoother we can use precise contact. The angular velocity obtained for this case is around 340-402 deg/sec.
REFFERENCES: