Which type of gear is typically used to change the rotational direction without altering speed?

Idler gears are specifically designed for the purpose of changing the direction of rotation in a gear system without affecting the speed. When an idler gear is placed between a driving gear and a driven gear, it allows the driven gear to rotate in the opposite direction to the driving gear without modifying the gear ratio. This function is essential in various mechanical applications where the orientation of the output shaft needs to match a specific direction, while maintaining the same rotational speed as the input.

The other types of gears mentioned have different roles; driving gears initiate movement and transmit power, driven gears respond to the driving gear’s movement, and friction gears utilize friction to transmit power rather than precise tooth engagement. Only the idler gear serves the unique function of direction change.