which is much more convenient
and immediately shows us that three revolutions of a driver
gear result in a single revolution of a follower gear
So what good is this ratio? We can use it to easily calcuate how speed and torque are transformed between the two
gears. Looking at the 3:1 ratio, we can tell that the speed is
reduced by a factor of three, and since the decrease of speed
results in an inversely proportional increase of torque, we
know that torque is tripled.
Now consider an example where the driver has more
teeth than the follower: We have a 20-tooth driver gear and
a 12-tooth follower gear. The gear ratio is 12:20, which is
equal to 0.6:1. This means that we need 0.6 revolutions of
the driver gear to get a single revolution of the follower gear,
so the speed is increased, but at the same time the torque
of the follower is 0.6 of the driver’s torque, so the torque is
decreased.
Our gear ratio also reveals whether we’re gearing down
or gearing up. If the first number of the gear ratio is greater
than the second (as in 3:1), we are gearing down—this is also
called gear reduction. If the first number of the gear ratio is
smaller than the second (as in 0.6:1), we are gearing up—this
is also called gear acceleration or overdrive. If we have a 1:1
gear ratio, speed and torque remain the same.
What if we want to calculate the total gear ratio of a
mechanism with many pairs of meshed gears? In this case,
we ignore all the idler gears and calculate ratios for all pairs
of driver and follower gears. Then, in order to get the final
gear ratio of the entire mechanism, we simply multiply
these gear ratios. Consider a mechanism with two pairs of
8-tooth drivers and 24-tooth followers. The gear ratio of the
first pair is 3:1, and so is the ratio of the second pair. If we
multiply these ratios, we get the final ratio of 9:1.
which is much more convenient
and immediately shows us that three revolutions of a driver
gear result in a single revolution of a follower gear
So what good is this ratio? We can use it to easily calcuate how speed and torque are transformed between the two
gears. Looking at the 3:1 ratio, we can tell that the speed is
reduced by a factor of three, and since the decrease of speed
results in an inversely proportional increase of torque, we
know that torque is tripled.
Now consider an example where the driver has more
teeth than the follower: We have a 20-tooth driver gear and
a 12-tooth follower gear. The gear ratio is 12:20, which is
equal to 0.6:1. This means that we need 0.6 revolutions of
the driver gear to get a single revolution of the follower gear,
so the speed is increased, but at the same time the torque
of the follower is 0.6 of the driver’s torque, so the torque is
decreased.
Our gear ratio also reveals whether we’re gearing down
or gearing up. If the first number of the gear ratio is greater
than the second (as in 3:1), we are gearing down—this is also
called gear reduction. If the first number of the gear ratio is
smaller than the second (as in 0.6:1), we are gearing up—this
is also called gear acceleration or overdrive. If we have a 1:1
gear ratio, speed and torque remain the same.
What if we want to calculate the total gear ratio of a
mechanism with many pairs of meshed gears? In this case,
we ignore all the idler gears and calculate ratios for all pairs
of driver and follower gears. Then, in order to get the final
gear ratio of the entire mechanism, we simply multiply
these gear ratios. Consider a mechanism with two pairs of
8-tooth drivers and 24-tooth followers. The gear ratio of the
first pair is 3:1, and so is the ratio of the second pair. If we
multiply these ratios, we get the final ratio of 9:1.
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