Ways to Transmit Power Flashcards
belt drives
a belt mounted on a pulley to transmit power
VCR, sewing machines, clothes dryers and bikes
adjustment is critical because slippage occurs when belts are too loose and friction increases when belts are too tight
Which has more MA?
a small pulley with a belt turning a larger pulley
or
a large pulley with a belt turning a smaller pulley
a small pulley with a belt turning a larger pulley
smaller pulley is easier to turn & will rotate at a higher rpm
when the input pulley is larger than the output pulley, there will be an increase in the speed of the output pulley but it will be harder to turn the input pulley
RPM
revolution per minute
How do you find the ratio between two pulleys?
counting the number of input pulley turns needed to turn the output pulley one turn
Equation for the MA of belt drives
comparing the ratio of diameter of the pulleys
MA Ratio = output pulley diamete / input pulley diamete
Compound belt drives
used to increase or decrease the rpm when a greater MA is needed
two or more sets of pulleys are used to assemble a belt drive train
Compound belt drives formulas
MA Ratio = output D / input D x output D / input D
Chain drives
chain mounted pm a sprocket to transmit power
can transmit more power because of the strength of the chain
chain adjustment, weight, noise and chain wear are disadvantages
gear system
a wheel with teeth spaced around the circumference of the rim
performs the same function as a belt or chain drive but can transmit more power and never slips
Why do gears last longer than belts?
each gear wheel transmits power to the next gear directly through the meshed teeth
Spur gear
most common type of gear
Idler gears
the gear that is placed between the input and output gears
their purpose is to change the direction the output gear turns, but does not affect the ratio between the input and output gear
How can the MA of an gear system increase?
by using a smaller input gear and meshing it with a larger output gear
MA Ratio = output gear teeth / input gear teeth
Gearing up
when the bigger gear turns the smaller gear
Gearing down
when the smaller gear turns the bigger gear
When are gear trains used?
when MA or rpm has to be greater than one set of gears can handle
MA Ratio = (output gear teeth / input gear teeth)(output gear teeth/input gear teeth)
Worm gear
designed to mesh with spur gears and allows a 90 degree change in the direction of the motion
can only be used as input gears
crown gear
change the direction of motion
does not have as much MA as the worm gear because of its size
to change direction, a crown gear can be combined with a small spur gear
bevel gear
formed by cutting a 45 degree angle into one side of the gear teeth
can also be used to change direction of motion
when two 45 degree bevel gears are meshed, rotational energy is transferred by 90 degrees
no speed reduction – same amount of teeth
rack and pinion gears
used when straight line linear motion is needed
rack
a block of material with teeth mounted on it
How does a rack and pinion gear cause linear movement?
when the pinion gear rotates and moves the rack
one revolution of the a pinion gear will move the rack the circumference of the pinion
the large the gear, the more the rack will move
automobile steering systems uses the rack and pinion
Why do cars use rack and pinions?
Rack and pinions are simple mechanisms where a pair of gears come together to steer a vehicle by circular and lateral motions. As the pinion, which interlocks with the rack, makes circular movements, the rack is moved side-to side.
Steering Mechanism Processes
As a steering wheel is turned, it spins the pinion, resulting in a series of other movements. Because the pinion moves in a circular fashion, and is attached to the rack, centrifugal force slides the rack back and forth. Tie rods are connected to each end of the rack, which activate the steering arms. Steering arms are connected to each wheel, and cause them to turn.
Differential gears
used so that each wheel of a motor vehicle can travel a different distance when making a turn
can automatically transfer energy to two different shafts
the shaft with the least amount of friction will turn
Cams
used when repeating linear motion is needed
trains & conveyor belts
periodic motion
movement for a certain amount of time in the same direction
oscillatory motion
axle movement first in one direction and then in another
achieved by connecting a bar to two gears
