Which type of gears are used to reverse the direction of gear rotation?

Idler gears are specifically designed to reverse the direction of rotation in gear systems. When an idler gear is placed between two gears, it acts as a mediator that allows power to be transmitted while changing the rotational direction. By introducing an idler gear between the drive gear and the driven gear, the direction of rotation of the output gear can be reversed without altering the speed ratio.

In contrast, while bevel gears and planetary gears serve specific functional roles in angle transmission and multi-speed applications respectively, they do not inherently reverse rotation in the same manner as idler gears. Spur gears typically maintain the direction of rotation and are primarily used for parallel shafts, making them unsuitable for reversing purposes without additional components.