But spur gears have some disadvantages. The axes of spur gears all have to be parallel to each other within the gear train, so there’s no way to transmit power to another rotational plane.

Gears transmit motion and force in machines, with types like spur, bevel, worm and wormwheel, rack and pinion, meshed gears, and threaded bars, selected based on speed, direction, force, space ...