GEARS

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GEARS
Gears and shafts are basically wheel and axles,
but gears have cogs, or teeth on their
circumference.
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GEARS
Gears turn either clockwise or counter-clockwise.
When gears touch, we call it meshing. As gears
mesh, they turn in opposite directions.
3
GEARS
In multiple gear sets, all odd numbered gears
turn the same direction, and the even numbered
gears turn in the opposite direction.
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GEARS
To make two gears turn in the same direction, (A
C) another gear (B) needs to be between the
two. This gear, without a load, is called the
idler. It can be any size, or there can be
multiple idler gears.
C
A
B
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GEARS

• Gears are generally used for one of four
  different reasons
• To reverse the direction of a rotational force.
• To increase or decrease the speed of rotation.
• To move rotational motion to a different axis.
• To keep the rotation of two axis synchronized.

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GEARS
Another option exist with a rack and pinion gear
set. Rack and pinions convert rotary motion to
linear motion.
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GEARS
Bevel gears can change the direction of the
rotational axis.
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GEARS
Worm gears are like screws. They prevent
slippage, and reduce rotational speed and
increase torque.
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GEARS
Planetary gears utilize a system that consists
of one or more outer gears, or planet gears,
revolving about a central, or sun gear.
Typically, planet gears are mounted on a movable
arm or carrier which itself may rotate relative
to the sun gear.
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GEARS
A common example of this type of gearing system
is the manual pencil sharpener. In this instance,
the planet gear is stationary and the sun gear
moves.
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GEARS
Another way to make two gears turn the same
direction is to use a chain. The gears are shaped
a little different, and are called sprockets.
Advantages include greater distance between
gears, a greater tolerance for alignment, and
less damage to the system should a chain break.
12
GEARS
Conservation of energy requires that the amount
of power delivered by the output gear or shaft
will never exceed the power applied to the input
gear, regardless of the gear ratio.
13
GEARS
Actual output will never reach theoretical
outputs due to friction, errors, entropy, or any
number of other external forces or situations
involved.
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GEARS
Gear of Teeth on Driven Gear Ratio
of Teeth on Driving Gear example 35 7
60 12 The 60 teeth gear
will spin 7 times, while the 35 teeth gear will
spin 12 times.
60
35
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GEARS
Compound Gears are gears consisting of two gears
turning on the same axle. The have the same rate
of rotation.
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GEARS
Gear ratios for each individual gear pair are
multiplied together to compute the overall
compound gear ratio.
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GEARS
Example Gear ratio between A and B is 1236 or
13. The gear ratio between C and D is 1260 or
15 Overall gear ratio is 1/3 x 1/5 115. A
will spin once for D to spin 15 times.
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GEARS
Torque is rotational force. Torque is often
talked about in using it to drive in screws,
fasten nuts onto bolts and other such activities.
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GEARS
Torque Force x Lever Arm (distance between
force and the objects center of mass) In our
case, the radius of the wheel. Formula t f x L
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GEARS
Torque is measured in the relationship between
the measurements used in determining force and
length, i.e. torque is measured in foot-pounds if
the force is lbs. and the distance feet or
Newton meters if Newton and meter are used
inch-ounces if these two force and distance
measurements are used.
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GEARS
The relationship between torque, gear ratio,
speed, etc. increases or decreases on a linear
scale. This could be either a direct relationship
(as gear ration increases from 13 to 15 speed
increases) or an indirect or inverse
relationship, (torque decreases as speed
increases.) As a consequence, more torque less
speed and vise-versa.
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GEARS
When gears mesh, both gears exert the same amount
of force in opposite directions at any given
point.
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GEARS
If a driving gear of 60 teeth is meshed with a
driven gear of 36 teeth, then the force where the
two gears meet is equal to f36 f60. Torque
ratio is therefore equal to the gear ratio.
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GEARS
Safety must be a consideration when working with
gears. Extreme pressure can cause gears to
shatter or strip out teeth. Pinching hazards
exist as well.