3.2 Speed changes in motion transmition systems

The systems we have just mentioned relay motion from a driver to one or more driven components without altering the nature of motion. However, the systems can change the speed of the motion during its transmission.

• • A SPEED CHANGE occurs in a motion transmission system when the driver does not turn at the same speed as the driven component or components.

SPEED CHANGES IN WORM AND WORM GEARS SYSTEMS

Worm and worm gear systems are the systems of choice for dramatically reducing the speed of rotational motion during transmission.

For each full turn of the worm the gear moves a distance equivalent to the width of only one tooth. The greater the number of teeth, on the gear, the greater the decrease of speed.

SPEED CHANGES IN OTHER MOTION TRANSMISSION SYSTEMS

In the other motion transmission systems we have studied, speed changes ocuur when the gear diameter vary. SInce the gear teeth must be identical in both gear train and chain and sprocket systems, the gear diameter varies with the number of teeth. Speed changes in these two types of systems therefore depend on the number of teeth on the gears or sprockets

It is often useful to know the ratio of speed increases or decreases in motion transmision systems. The ratio is equivalent to the ratio between the gear diameter or between the number of teeth of each gear.

Example: Find the speed of the driven gear knowing that the driver gear has 20 teeth and that is rotating at a speed of 4 r.p.m. Also the driven gear has 5 teeth