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DESIGN, MODELLING AND ANALYSIS OF A3 STAGE EPICYCLIC PLANETARY REDUCTION

GEAR UNIT OF A FLIGHT VEHICLEK Akhila1* and M Amarnath Reddy2

*Corresponding Author: K Akhila,akhila.kakera@yahoo.com

In this project, a three stage epicyclic planetary reduction gear unit is designed to meet theoutput specifications. All the components are modelled in CATIA to check the assembly and theinterference. The modelled components are used for analysis to check for their strength. Heavyvehicles consists of four control surfaces for steering and stabilization purpose. The controlsurface are to be rotated depending upon the requirement of the system. This rotation of controlsystem is achieved through actuators. Actuators can be of different types. They are pneumatic,hydraulic and electro-mechanical. In the present project, we use electro mechanical actuators.Electro-mechanical actuators basically consists of prime mover, motor and transmissionmechanism. This transmission system can be screw type or gears type. In this project, we usegear type of transmission system, which is designed depending upon the requirement. Generallymotor rotates with very high speed and low torque. But the final requirement is “low speed andhigh torque”. This is achieved by connecting a reduction gear unit which reduces the speed andincreases the torque. Planetary gear is one of the epicyclic gear, which is a gear system consistingof One or more outer gears, or planet gears, revolving about a central, or sun gear. And it can bewildly used in industry, such as printing lathe, automation assembly, and semiconductorequipment and automation system since its commercial value. Our project is aimed to build a3D model of multiple layers of planetary gear by Using Catia software.

Keywords: Epicyclic planetary reduction, CATIA software, Actuators

INTRODUCTIONNecessity of Epicyclic PlanetaryReduction Gear in FlightA speed reduction unit is a gearbox or a beltand pulley device used to reduce the

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Int. J. Mech. Eng. & Rob. Res. 2014

1 M.Tech Student, Department of Mechanical Engineering, Mallareddy College of Engineering & Technology, Jawaharlal NehruTechnological University, Hyderabad, India.

2 Associate Professor, Department of Mechanical Engineering, Mallareddy College of Engineering & Technology, Jawaharlal NehruTechnological University, Hyderabad, India.

output revolutions per minute (rpm) from thehigher input rpm of the power plant. This allowsthe use of small displacement internalcombustion automotive engines to turn aircraftpropellers within an efficient speed range.

Research Paper

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Int. J. Mech. Eng. & Rob. Res. 2014 K Akhila and M Amarnath Reddy, 2014

History and OperationThe Wright brothers recognised the need forpropeller reduction gearing in 1903, but it wasnot generally used on aircraft engines untillarger engines were designed in the1920s. Large engines with high crankshaftspeeds and power outputs demandedpropeller reduction, pilots noted the increasein performance of similar aircraft fitted withreduction gearing.

Design and Working PrincipleThe heart of the planetary gearbox is thereduction group composed by the sun pinion(1) and three or more satellites (2) mountedon pins (4) which are supported by the satellitecarrier (5). The sun pinion transmits it’s motionto the satellites. The satellites then turn insidethe ring gear (3) which is static. Asconsequence the satellite carrier rotates. Themotion of the carrier can be transmitted to anoutput shaft or to another reduction group. The

reduction obtained is determined by therelation between the number of teeth on thesun pinion (Z1) and the number of teeth on thering gear (Z2).

Like a compound gear train, planetarytrains are used when a large change in speedor power is needed across a small distance.There are four different ways that a planetarytrain can be hooked up.

A planetary gear train is a little morecomplex than other types of gear trains. In aplanetary train at least one of the gears mustrevolve around another gear in the gear train.A planetary gear train is very much like our ownsolar system, and that’s how it gets its name.In the solar system the planets revolve aroundthe sun. Gravity holds them all together. In aplanetary gear train the sun gear is at the center.A planet gear revolves around the sun gear.The system is held together by the planetcarrier. In some planetary trains, more than one

Figure 1: Planetary Gearbox

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Int. J. Mech. Eng. & Rob. Res. 2014 K Akhila and M Amarnath Reddy, 2014

planet gear rotates around the sun gear. Thesystem is then held together by an armconnecting the planet gears in combinationwith a ring gear.

A planetary gear train consists of two gearsmounted so that the center of one gear revolvesaround the center of the other. A carrierconnects the centers of the two gears androtates to carry one gear, called the planetgear, around the other, called the sun gear. Theplanet and sun gears mesh so that their pitchcircles roll without slip. A point on the pitchcircle of the planet gear traces an epicycloidcurve. In this simplified case, the sun gear isfixed and the planetary gear(s) roll around thesun gear.

LITERATURE SURVEYHistoryIn the 2nd century AD treatise Almagest,Ptolemy used rotating deferent and epicyclesthat form epicyclic gear trains to predict themotions of the planets. Accurate predictionsof the movement of the Sun, Moon and the fiveplanets, Mercury, Venus, Mars, Jupiter andSaturn, across the sky assumed that eachfollowed a trajectory traced by a point on theplanet gear of an epicyclic gear train. Thiscurve is called an epitrochoid.

Epicyclic gearing was used in theAntikythera Mechanism, circa 80 BCE, toadjust the displayed position of the moon forits elasticity, and even for the precession ofthe ellipticity. Two facing gears were rotatedaround slightly different centers, and one drovethe other not with meshed teeth but with a pininserted into a slot on the second. As the slotdrove the second gear, the radius of drivingwould change, thus invoking a speeding up and

slowing down of the driven gear in eachrevolution.

The sun and planet gear converted thevertical motion of a beam, driven by a steamengine, into circular motion using a ‘planet’, acogwheel fixed at the end of the connectingrod (connected to the beam) of the engine.With the motion of the beam, this revolvedaround, and turned, the ‘sun’, a second rotatingcog fixed to the drive shaft, thus generatingrotary motion. An interesting feature of thisarrangement, when compared to that of asimple crank, is that when both sun and planethave the same number of teeth, the drive shaftcompletes two revolutions for each doublestroke of the beam instead of one. The planetgear is fixed to the connecting rod and thusdoes not rotate around its own axis.

Epicyclic gear stages provide high loadcapacity and compactness to gear drives.There is a wide variety of differentcombinations of planetary gear arrangements.For simple, epicyclic planetary stages whenthe ring gear is stationary, the practical gearratio range varies from 3:1 to 9:1. For similarepicyclic planetary stages with compoundplanet gears, the practical gear ratio rangevaries from 8:1 to 30:1. Using differential-planetary gear arrangements it is possible toachieve gear ratios of several-hundred-to-onein one-stage-drive with common planet gears,and several thousand- to-one in one-stagedrive with compound planet gears. A specialtwo stage planetary arrangement may utilizea gear ratio of over one-hundred-thousand-to-one.

The reasons why epicyclic gearing is usedhave been covered in this magazine, so we’llexpand on the topic in just a few places. Let’s

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Figure 2: Types of Gearing

Figure 3: Formulas for Calculating Gear Ratios

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Figure 3 (Cont.)

begin by examining an important aspect of anyproject: cost. Epicyclic gearing is generallyless expensive, when tooled properly. Just asone would not consider making a 100-piecelot of gears on an N/C milling machine with aform cutter or ball end mill, one should notconsider making a 100-piece lot of epicycliccarriers on an N/C mill. To keep carriers withinreasonable manufacturing costs they shouldbe made from castings and tooled on single-purpose machines with multiple cutterssimultaneously removing material.

Magnetism, which is used in everything fromtoys and door catches to electric motors and

medical imaging systems, is the subject ofongoing research by commercialorganizations and academic institutions.Improved field strengths and design techniquesmean that smaller and lighter magnets canreplace larger composite magnets or createnew opportunities.

PROPOSED SYSTEMThe main aim of the project is to design andanalyze a three stage epicyclic planetaryreduction gear unit is designed to meet theoutput specifications with a reduction ratio64:1. All the components are modelled in

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CATIA to check the assembly and theinterference. The modelled components areused for analysis to check for their strength.

Our aim is to obtain the reduction ratio 64:1for a 3-stage epicyclic planetary reductiongear.

Materials-steel

Steps involved in the project

1. Designing

2. Modeling

3. Analysis

For modeling of the planetary gear, we haveused CATIA software which is parametric 3Dmodeling software. For analysis we have usedANSYS, which is FEA software.

SYSTEM DESIGNA 3 Stage epicyclic planetary reduction hasbeen designed in the following way as follows:

Figure 4: Assembly of First Stage

Figure 5: Assembly of Second Stage

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Int. J. Mech. Eng. & Rob. Res. 2014 K Akhila and M Amarnath Reddy, 2014

Figure 6: Assembly of Third Stage

Figure 7: Final Assembly of a 3 Stage Epicyclic Planetary Reduction Gear with an Armat Each Stage

RESULTS AND DISCUSSIONA 3 stage epicyclic planetary reduction gearwas designed with the help of CATIA software.All the three stages are designed separatelyand then assembled together with the help ofarm and shaft of required dimensions. Thereduction ratio is obtained as 64:1. The

maximum and minimum stresses along withdisplacement can be obtained afterperforming analysis on the gear unit. Theanalysis is done only for the second stagebecause it gives more accurate and averagemaximum and minimum stresses. Reductionratios at the three stages are obtained as First

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Int. J. Mech. Eng. & Rob. Res. 2014 K Akhila and M Amarnath Reddy, 2014

stage ratio-3.8:1, Second stage-3.7:1, Thirdstage-4.6:1.

ANALYSISAfter performing analysis on the second stageof epicyclic planetary reduction gear unit,

Figure 8: Final Assembly of 3 Stage Epicyclic Planetary Reduction Gear

maximum stresses and minimum stresses areobtained as follows:

Nodal solutions

Maximum stress: 2.7706 N/M

Minimum stress: –5.77 N/M

Figure 9: Meshing All the Components Together in Ansys

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Maximum displacement: 2.7708 m

CONCLUSIONIn this project, we have created a CAD model,a simulation video and a solid model of a three-layer planetary gear system using Catia. Wehave learned the solid modeling technique,assembling knowledge and the simulationprocess through the project. We think ourproject could be extended to more layers ofGear system and more planet gears per

system. And the redutction ratio can also bechangeable from 64:1 to various other ratiosas 36:1, 4:1.

BIBLIOGRAPHY1. Gunston Bill (2006), Development of

Piston Aero Engines, Patrick StephensLimited, Cambridge, England.

2. Guttery T E (1969), The ShuttleworthCollection, Wm. Carling & Co., London.