2. • Epicyclic means one gear revolving upon and around another.
• The design involves planet and sun gears as one orbits the other like a planet around the sun.
• The gear at the centre is called the Sun gear and the gears whose axes move are called
Planet gears.
In a star arrangement
The carrier is fixed.
In a planetary arrangement
The ring gear is fixed
3. Planetary gear sets is that they can produce different gear ratios depending
on which gear you use as the input, which gear you use as the output, and
which one you hold still.
ARM SUN PLANET RING
0 X
−TS
TP
X
TS
TR
X
Y X+Y
Y - −TS
TP
X Y - TS
TR
X
GEAR RATIOS
TS = Number of teeth on gear A, and TB = Number of teeth on gear B.
4. APPLICATION
• Wide range of applications from marine gearboxes to electric screwdrivers.
• These are used in the back gear of lathes, hoists, pulley blocks, wristwatches etc…
• Theyare famous for automatic transmissions in automobiles.
• Theyare used in bicycles for controlling the power of pedaling automatically or manually.
• Theyare also used for power trains between internal combustion engines and electric
motors.
• Epicyclic gearboxes will be lighter and more compact than countershaft gear boxes.
In most cases, they will be more efficient.
• Moreexpensive and complex than conventional transmission gears.
