Which type of drive provides a directional change of the rotary motion in parallel shaft power transmission?

A gear drive is specifically designed to provide a directional change of rotary motion through the use of gears. In a gear system, two or more gears intermesh to transmit power and rotate at different speeds or in opposite directions, making it an effective method for changing the direction of rotary motion in parallel shaft power transmission.

Belt drives, while commonly used for power transmission, generally transmit motion while keeping the rotational direction of the input and output shafts the same, unless they are configured in a particular way with crossed belts, which is less common. Chain drives operate on similar principles to belt drives, as they transmit rotary motion without changing the direction unless specifically designed to do so. Universal drives are designed for transmitting motion between shafts that are not in line with each other, allowing for greater flexibility but not specifically for parallel shafts.

Therefore, gear drives are ideal for applications requiring a change in the direction of motion, making them the most suitable choice for this scenario.