IIJIID~(i1lJ
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INSTRUCTION MANUAL
HTM.25
Gear Trains Apparatus
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GearTrains
INTRODUCTION
Therearetwo mainpurposesfor usinga train of gears. The most importantis to establisha speed
ratio betweentwo rotating shafts:the other is to transferrotation from one axisto anotherwith or
without a changein the directionof rotation (that is clockwiseor anticlockwise). If spur gearsare
usedthe axesmay be parallelor coincident. The use of bevelgearsenablesthe axesto be at an
angleto eachother.
In the following experimentsthe speedratio is the subj~ctbeing studied. Neverthelesssome
accountwill be taken of the direction of rotation as this can be changedindependentlyof the
speedratio. Only simple spur gearswill be used, although an introduction to the principlesof
epicyclicgear trains is includedin an elementaryform. Hencethere are severalaspectsof the
applicationof gearsandgeartrainsto be learnedby doing this experiment.
LIST OF PARTS
The standardset of itemssupplied(HTM.2S) consistsof:
- Geartrainsapparatusclw four spurgearsandaxle pins
- Box of washersandnuts
APPARATUS
A pivoted slotted arm mountedon a horizontal basecarriestwo movableshort axles on which
four interchangeable
spur gearscan be arranged. One pair of the gearscan be pinnedtogetherin
order to assemblea compoundgeartrain. The slottedarm canbe locked in positionfor geartrain
HTM25. Page I.
Issue I. .January,1994.
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work, or it can be rotated about its pivot to simulatethe planet ring of an epicyclicsystem The
spurgearshave40,60,80 and 100teethwith 32 diametralpitch anda 200pressureangle.
EXPERIMENT
Thereare two separateexperimentsto be performedon this apparatus,one on gear trains and the
otheran introductionto epicyclicgears.
OBJECTNo.1
The object is to study the speedratios and directionsof rotation of simpleand compoundgear
trains
PROCEDURE
Part
Simple gear trains.
MeciumPWI
Any two Gear Wheels
"
Spacer,
ShortPm
v
Wi1gnut
Assemblea two wheelgeartrain with the 80 tooth wheelasthe driver on the fixed pivot as shown
in diagram A. Mark the teeth of both gearsat the point where they mesh. Turn the driver
throughone revolution clockwiseand note how many revolutions(and partsof a revolution) the
drivenwheelexecutes.
As an alternativekeepturning the driver throughenoughcompleterevolutionsfor the two marks
to corne together again. and note the correspondingnumber of completeturns of the driven
wheel
Recordthe directionin which the drivenfollower wheelrotates.
Repeatthe aboveprocedureusingthe other two gearwheelsin turn
Medium Pin
""
"
Medium Pin
Spacer
A
/
Any three gears
Shcxtp.,
/
/
1/
/
Washer
""J-
Wingnut
Diagram 8
Next assemblea threewheelgeartrain as in diagramB with the 80 tooth driver and the 100 tooth
wheelat the endsof the train. Note the initial positionsof markson the driver and final wheel of
the train, andthen determinethe turns ratio by one of the abovemethods. Also note the direction
of roation of the final wheel when the driver turns clockwise. Repeatthis work using the other
gearwheelasthe idler betweenthe driver andfollower.
Part 2. Compound gear trains.
Keepingthe 80 and 100 tooth wheelsas driver and final wheel respectively,arrangea compound
geartrain as shownin diagramC. Note the positionsof the markson thesetwo wheelsand then
proceedto determinethe turns ratio and correspondingdirectionsof rotation. Repeatthis with
the intermediatepinnedpair the otherway up.
RESULTS
Comparethe experimentalresultswith the theoreticalpredictions
Nr; No : To
TF
where N= speed(revolutions/unittime)
r = teethon gearwheel
D standsfor driver
F standsfor follower
For the threewheeltrain the fQrmulabecomes
NF%
NI
.
T",
,
and N1=
~~
TF
NF=ND.
T1
To
TF
The compoundgear train is resolvedin a similar manner. Let the first driver and follower be
designatedA and B, and the secondsetC andD Then
IIT,\f25. Page 3.
\"UeI. May, 1994.
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ButN.
Nr. hence
ND:
T(..:
NA1A
-r;;-e-r::
OBSERVATIONS
What are the differencesbetweena simpletwo and three wheel gear train? Predict what would
happenif a four wheeltrain usingtwo idlerswas set up,
What advantageis therein usinga compoundgeartrain?
OBJECT No.2
The purposeof this experimentis to study the first principles of an epicyclic gear systemwith
particularreferenceto the speedratio anddirectionof rotation
PROCEDURE
[n its simplestor typical fonn an epicyclicsystemcomprisesa central(sun) wheel aroundwhich a
planet wheel or, for better balance,wheels circulate while an outer ring gear with the teeth
pointinginward mesheswith the planetwheelsas in the figure shownbelow.
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v,
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Outer ring
Planet
Wheel
Planet wheel
frame
,
Sun wheel
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Experimental simulation
k--
of outerring
To simplify the designfor the purposeof the experimentthe planet wheel frame is a single arm
that revolves on the same axis as the sun wheel (but independently)while the outer ring is
represented
by a normalspurgear(with manylessteeth).
~
Part 1. Planet Wheel.
Washer
L
... Short pin
-~~-
-
Wingnut
Diagram D
Set up the 80 tooth wheel as the sun wheel with the 40 tooth wheel in meshas a planet wheel
The ann carryingthe planetwheelshouldbe in its "locked" position. SeediagramD.
As the velocity ratio of an epicyclic gear train is not easily observedwhen one considersthe
simultaneous
movementof gearwheelsand arm, it is usuallybetter to studythe relativemovement
of the gear wheelswith the arm stationary,then the revolution of the gear trains without any
relativemotion of the wheelsand, finally, the combinationof thesetwo operations. This system
of establishingthe relative motion of the wheels and arm is illustrated in the following
arrangements
wherethe sun wheelis designatedA and the planetB. Use table I for recordingthe
revolutionsanddirectionof rotation taking clockwiseas +ve.
Table 1
Relative motions of 80 tooth sun & 40 tooth planet "'heels
Mark the sun and planet wheels at their meshingpoint. With the arm fixed turn the sun one
revolution anticlockwiseand observethe number of revolutions of the planet wheel and their
direction. Next clampthe sunwheelto the arm and rotate the arm one turn clockwise. Watchthe
markson the sun and planetwheelsto determinetheir rotation with respectto the axesof each
wheel(it may help to follow the mark on the planet wheel with one'sfinger). Finally rotate the
arm while holding the sun wheel stationaryand count the number of revolutions of the planet
wheelandnote their direction
Repeatthe whole procedureusingthe 100tooth wheelasthe sun wheel
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Part 2. Simple epicyclic gear.
Diagram E
Add an 80 tooth "outer" ring wheel C to the 100 sun and 40 tooth planet wheelsas shown in
diagramE. The experimentis to detenninethe speedanddirectionof rotation of wheelC whenA
turns one revolution clockwise while the planet arm makes one anticlockwise turn. Follow
througha similarprocedureto the above,startingwith the arm stationaryin table2.
Table 2
Relative motions of 100tooth sun, 40 tooth planet & 80 tooth outer
The final action is to simultaneouslyrotate the sun wheel once clockwise while turning the ann
once anticlockwise,and to count the numberof revolutionsof the outer wheel. Also note the
directionin which C turns.
Part 3. Compound epicyclic gear.
Diagram F
H1M.
lOUPI
Assemblea gear train using the 100 tooth wheel as the sun meshingwith the 40 tooth gear of a
pinned40/60 pair in the planetposition. Thenusethe 80 tooth wheelmeshingwith the 60 gear to
providethe "outer ring", as in diagramF. Repeatthe experimentdescribedin Part 2.
Finallydeterminethe speedand directionof the sunwheel whenthe arm makesone anticlockwise
turn while the 'outer ring' is stationary(relativeto the baseof the apparatus- NOT the arm). A
tablelike 2 abovecanbe used.
RESULTS
Produceformulae for the spacesin the tables and comparethe experimentalresults with the
theoretical.
OBSERVATIONS
In the caseof a real epicyclicgear systemthe outer ring must inevitablyhavea large numberof
teeth. Estimatehow manyteeth it would havebeen for the simpleepicyclicgear of Part 2, and
hencedeterminethe speedratio.
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