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MECHANISMS (TYPES OF LEVERS (Second degree levers: The resistance is…
MECHANISMS
Definition : Mechanisms are devices that trasmit and convert forces and motion for a driving force or input element to an output element
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ROTARY MOTION MECHANISMS
These mechanisms transmit motion and effort in a circular way,from the input to the output . They include friction drives, pulley systems, gears and worm gears :
Friction drivers : Friction drives are made up of two or more wheels that are in contact.
The first wheel is called the primary drive wheel.When it moves, it turns or drives the second or output wheel, causing it to move as well
The output wheel rotates in the opposite direction of the primary wheel. If we use more than two wheels, each one rotates in the opposite direction to the one next to it 
N(1) . D(1) = N(2) . D(2) - D(1) / D(2) = N(2) / N(1)
Pulleys with belt : They consist of two pulleys or wheels that are a certain distance apart.
Their axles are parallel and they rotate simultaneously due to the effect of the belt.
The rotation of one axle is transmitted to the other through the connected pulleys.
The two pulleys, and the two axles, rotate in the same direction
Gear mechanisms and cogwheels : Cogwheels are sets of wheels that have teeth called cogs . The cogs fit into the spaces between the cogs of another wheel, so that one wheel moves the other. They transmit a rotary motion between the two connected axles, which can be parallel, perpendicular or oblique
There are two types :
CYLINDRICAL GEARS
CONICAL GEARS
The ratio between the rotation velocities of the wheels depends on the number of teeth on each wheel. It`s expressed by this equation : N(1) . Z(1) = N(2) . Z(2) = Z(1) / Z(2) = N(2) / N(1)
Worm gear : This is a screw that moves a helical cogwheel that is set perpendicular to the screw. Each time the screw rotates, the gear moves forward as a many teeth as there are grooves in the screw, usually a small number : 1,2 or 3 . This is used to reduce velocity as well as functioning as a brake system
A worm screw fulfils this equation : N(wheel) = N(screw) . Z(grooves) / Z(wheel)
Gear mechanisms with a chain : These are two cogwheels with parallel axles that are a certain distance apart; they rotate simultaneously by means of a metal chain or a toothed belt stretched over both wheels . The chain transmits the rotary motion of axle 1 to axle 2 by means of gears 1 and 2, and both rotate in the same direction . This system transmits greater forces without losing velocity. The relation between the rotation velocities of the wheels depends on the number of teeth on each gear : N(1) . Z(1) = N(2) . Z(2) = Z(1) / Z(2) = N(2) / N(1)
Gear train : Gear train is a combination of gears and used for transmitting motion and power from one shaft to another shaft. Gear trains are used to achieve large and different velocity ratio in small area or space. Gear trains are use for increasing or reducing speed of driven shaft. Its formula is : N(4) / N(1) = Z(1) . Z(3) / Z(2) . Z(4)
Pulley trains with belts : The gear ratio between the drive pulley and the driven pulley depends on the relative size of the pulleys in the system. Its expressed as a function of their diameters
N(4) / N(1) = D(1) . D(3) / D(2) . D(4)