The slewing drive is a

gearbox Propulsion transmission is the mode of transmitting and controlling propulsion power of a machine. The term ''transmission'' properly refers to the whole drivetrain, including clutch, gearbox, prop shaft (for rear-wheel drive vehicles), differe ...

that can safely hold radial and axial loads without

brake A brake is a mechanical device that inhibits motion by absorbing energy from a moving system. It is used for slowing or stopping a moving vehicle, wheel, axle, or to prevent its motion, most often accomplished by means of friction. Background ...

s, as well as transmit a

torque In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...

for rotating. The rotation can be in a single axis, or in multiple axes together. Slewing drives are made by manufacturing gearing, bearings, seals, housing,

motor An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power gen ...

and other auxiliary components and assembling them into a finished gearbox.

History

The slewing drive is a modernized take on the

worm drive A worm drive is a gear arrangement in which a worm (which is a gear in the form of a screw) meshes with a worm wheel (which is similar in appearance to a spur gear). The two elements are also called the worm screw and worm gear. The terminolo ...

mechanism, which dates back many centuries and was widely used during the

Renaissance Era The Renaissance ( , ) , from , with the same meanings. is a period in European history marking the transition from the Middle Ages to modernity and covering the 15th and 16th centuries, characterized by an effort to revive and surpass ideas ...

Pappus of Alexandria Pappus of Alexandria (; grc-gre, Πάππος ὁ Ἀλεξανδρεύς; AD) was one of the last great Greek mathematicians of antiquity known for his ''Synagoge'' (Συναγωγή) or ''Collection'' (), and for Pappus's hexagon theorem i ...

(3rd century AD), a Greek mathematician, is credited with an early version of the endless screw, which would later evolve into the worm drive. This mechanism was also used by

Leonardo da Vinci Leonardo di ser Piero da Vinci (15 April 14522 May 1519) was an Italian polymath of the High Renaissance who was active as a painter, Drawing, draughtsman, engineer, scientist, theorist, sculptor, and architect. While his fame initially res ...

as a component in many of his designs for machines. It can also be found in the notebooks of

Francesco di Giorgio Francesco di Giorgio Martini (1439–1501) was an Italian architect, engineer, painter, sculptor, and writer. As a painter, he belonged to the Sienese School. He was considered a visionary architectural theorist—in Nikolaus Pevsner's terms ...

Siena Siena ( , ; lat, Sena Iulia) is a city in Tuscany, Italy. It is the capital of the province of Siena. The city is historically linked to commercial and banking activities, having been a major banking center until the 13th and 14th centuri ...

. Many slewing drive concepts found prominence with the emergence of larger scale construction and engineering in the height of the Greek and Roman Empires.

Technology

Slewing drives function with standard worm technology, in which the worm on the horizontal shaft acts as the driver for the gear. The rotation of the horizontal screw turns a gear about an axis perpendicular to the screw axis. This combination reduces the speed of the driven member and also multiplies its torque; increasing it proportionally as the speed decreases.Kinematics MFG The speed ratio of shafts depends upon the relation of the number of threads on the worm to the number of teeth in the worm wheel or gear.Virginia Downward & William M. Clark, 1930 As technology has improved, more slewing drives are using hourglass worm technology, in which the worm is shaped to engage more teeth in the gear. This increased tooth engagement results in greater strength, efficiency and durability.

Performance characteristics

Because of their multiple uses, slewing drives come in a variety of model sizes, performance ranges and mounting characteristics. The drives are well suited for applications that require both load holding and rotational torque from the same gear box. They can also be made with dual axes of rotation, (turning axes at the same time) or with dual drives on the same axis, (two worm threads driving the same ring gear in one axis).Machinery's Handbook Ortberg, Jones, Horton.

Materials

The specifications for drives and gears varies depending on the material the gear is composed of. However, a majority of the drives and gears commonly used are composed of steel and phosphor bronze. According to an extensive series of tests by the Hamilton Gear & Machine Co., chill-cast nickel-phosphor bronze ranked first in resistance to wear and deformation. Number two on the list was SAE No. 65 bronze. For bronze gears a good casting should have the following minimum physical characteristics:

Applications

There are many applications in which the slewing drive can be utilized, primarily because it is perfect for applications that require both load-holding power and rotational torque strength. Typical slewing drive applications include but are not limited to:

References