ROTARY TRANSMISSION

Rotary transmission systems put two rotating elements into contact. These mechanisms have two purposes:
· Transfering rotary force from an input location to another.
· Changing the rotary speed by using rotating elements of different sizes.

We can perform these functions with various mechanisms:
· Friction wheels.
· Pulleys with belts.
· Interlocking gears.
· Sprockets with chains.

Friction wheels and pulleys are used in toys and other devices, such as industrial rollers or conveyor belt systems. Gears are in clocks. Sprockets and chains are common in home appliances.

- Changes in speed.
If we want to increase the speed of a rotary system, we must transmit motion from a large (input) element to a smaller (output) element.

When we increase the speed we also decrease the rotary force. The rotary force will also remain constant.
· Increasing speed system: the input speed is lower than the output speed.
· Constant speed system: the input speed and the output speed are equal.
· Decreasing speed system: the input speed is higher than the output speed.

The relationship between the speeds of the two wheels is inversily proportional to their sizes.

- Belt drives and gear trains.
A belt drive is a system of pulleys connected by belts. Each belt connects a pair of pulleys, so they turn together.

To calculate the ratio of transmission between the first wheel and the last wheel of a belt drive, we must multiply the ratios of transmission of the first pair of wheels and the second pair of wheels.

- Changes in direction and rotation.
We can use various systems to change the direction of rotation or the axis of rotation in a belt drive. We use different types of gears when two axes are parallel, perpendicular or crossed.

In some gear mechanisms, several cogs or teeth interlock at the same time. These mechanisms are more precise and they transmit more rotary force.

- Worm drive.
A worm drive reduces the speed of a rotary system very effectively. A worm drive has two parts: a worm shaft and a worm gear.

When the worm shaft makes one rotation, the worm gear moves forward one tooth for every groove on the shaft.

We use worm drives for tuning the strings of a guitar, for elevator mechanisms and for speed reducing systems.