A drop tower or big drop is a type of amusement ride incorporating a central structure or tower. Drop towers vary in height, passenger capacity, lift type, and brake type. Many are custom-made, although there are some mass-produced designs. The most widely sold drop towers have been manufactured by Intamin and S&S Sansei, however Larson International and Funtime have their own drop tower models available as well. Riders experience free-fall initially, followed by rapid heavy deceleration.
With most drop towers, a gondola carrying riders is lifted to the top of a large vertical structure, then released to free-fall down the tower. Brakes slow the gondola as it approaches the bottom of the ride. Some designs expand on this concept with features such as rotating gondolas, or several bounces before coming to rest.
Most drop towers require child riders to exceed a minimum height; limits vary widely depending upon the nature of the tower, with a 9-metre (30 ft) tower for smaller children from 95 centimetres (37 in) tall, and a 35-metre (115 ft) tower having a 130-centimetre (51 in) restriction.Most drop towers use a magnetic braking system to slow the carriage quickly and smoothly once it reaches the bottom of the tower. This system is fail-safe because magnets do not need to be powered by electricity or other sources; they work intrinsically by the laws of magnetism.
The compressed air system used to power drop towers manufactured by S&S Sansei doubles as a braking mechanism, so magnets are not needed.