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Mechanisms, 5.3. Connecting mechanisms, 1º Mechanism, 2.2. Fixed pulley, 2…
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1º Mechanism
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Mechamsms are devices that transmit and convert forces and motion from a dnvmg force or input element to an output element. They allow us to carry out certam tasks more easily and more effioently
transporting people from A to B
telling the time
entertaining children in the park
liftmg and carrying objects
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2.2. Fixed pulley
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A fixed pulley is a wheel that has a groove around lt into which a rope, cham or belt fits It rotates around an axle that is fixed to an immobile surface
A fixed pulley is balanced when the effort F is equal to the resistance of the load, R: F = R
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2.3. Movable pulley
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A moveable pulley ts a set of two pulleys one ts fixed while the other can move tn a linear direction.
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2.4. Compound pulley
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This ts a system of fixed and moveable pulleys, often called block and tackle
On rhe left you can see two different types of block and tackle pulleys (n = the number of movable pulleys).
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3.1. Friction drives
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Fnctton dnves 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 ratio between the rotation veloaty of the wheels or pulleys depends on the relative size of the wheels.
N1 · D1 = N2 · D2 =} D1/D2 = N2/N1
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3.2. Pulleys with belt
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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.
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3.6. Gear train
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This is a system of more than two gears, connected together as shown in the diagram The rotary motion of the first wheel ( I) doves the second wheel (2), and so on
The gear ratio between the drive wheel (I) and the dnven wheel (4) depends on the number ol geared teeth m the system:
N4/N1 = Z1 · Z3/ Z2 · Z4
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3.4. Worm gear
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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 many teeth as there are grooves in the screw, usually a small number I, 2 or 3
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Types of levers
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There are three types of levers: class l, class 2 and class 3. These classilications are based on the relative position of the lever, the effort applied and the resistance.
Rack and pinion syste
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The ratio between the number of rotations of the pinion and the veloaty of the movement of the rack is expressed by this equation:
L = P· Z·N
Crank-link-slider
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This is composed of a crank and a rod called a connecting rod or link. This rod has articulated Ioints at each end — one is connected to the crank and the other to the slider. The slider produces a reciprocating motion.
Cam
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This is basically a rotating objectthat pushes a follower as it moves A cern transforms rotary motion into reciprocating motion in the follower or bar
Eccentric cam
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This consists of a wheel with an off centre rotation axle that doesn't coincide with the centre of its circumference
