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4.2.
Reciprocating rotary-linear transformation
The pedal mechanism of a bicycle transforms the reciprocating movements of our legs
into continuous
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rotary motion. In a similar way, the pistons of a car engine produce
a reciprocating linear motion that turns the wheels. Some mechanisms work in the
opposite way, transforming rotary motion into reciprocating linear motion.
Crank and rod mechanism
crankshaft
cranks
rods
wheel
frame
crank
Pedal
ball
bearings
BB
cartridge
lock
ring
chain
wheel
Analyse
27.
In your exercise book,
copy the illustration of
the leg and the bicycle
pedal above. Label
the crank and the rod.
What motion does the
person’s knee make?
What motion does the
pedal make?
28.
Think of more examples
of machines that use
cranks and rods. Identify
the location of these
parts for each machine.
This rod transmits motion
to the next wheel
rod
steam engine
Reciprocating motion
crank
wheel
piston
A crankshaft mechanism can synchronise the movements of various parts, such
as the multiple pistons of a car engine. In the case of a bicycle, our legs act like
connecting rods that turn the crank mechanism of the pedals.
Applications
:
we use crankshafts for combustion motors that use pistons. We
also use them for sewing machines.
In the picture, you can see the parts of a crank and rod mechanism. The piston
moves a rod forward and backward. This rod turns the first wheel. The second
wheel turns because it is connected to the first wheel by another rod.
Applications
:
this mechanism was important for the first steam engines. Today
we find cranks and rods in internal combustion engines, as well as windscreen
wiper
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mechanisms.
Crankshaft mechanism
We can connect
multiple rods
to one shaft. The rods are connected to cranks,
and the cranks are connected to the crankshaft.
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continuous
: without stopping
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windscreen wiper
:
a device on the
front of a car for keeping the window
free of rain
ADVANCE
EDITION
