What Is a Slewing Drive?

The term "slewing drive" most often refers to a mechanism that consists of a radial gear, an axial shaft called a worm, and a connected driving component. More advanced slew drives might include specific worm designs, protective enclosures and other auxiliary components. Slewing drives are capable of transferring forces and torque as well as sustaining those forces over time. There are many applications for slewing drives, a few different materials to choose from, and a long history.

The most basic slewing drive has a radial gear driven by the worm. The teeth of the gear meet with the grooves in the worm and, as the worm turns, the gear also turns. Common features for different slewing drives can include an hourglass-shaped worm, which is often considered more efficient because multiple teeth on the gear can be engaged at once. Other features can include a protective enclosure meant to keep the mechanisms clean. The motor or driving component, like the spinning of a wind turbine, also might change the specific design of a slewing drive.

In general, the purpose of these machines is to change axial movement to radial movement. Depending on the number of threads on the worm and the number of teeth on the gear, the speed and power of the axial force will be converted to a specific radial force. Depending on the application, a slewing drive might be useful for amplifying the torque that rotates a mechanism.

Slew drives have many applications. For instance, wind energy systems often use a slewing drive to convert the axial movement created by the turbine to an amplified radial movement that can be converted into energy. Solar tracking systems also might include slew drives to maintain the best location for solar panels as the sun moves across the sky. Further applications of a slewing drive can include hydraulic systems and mechanical lifts.

Materials used to create slewing drives are somewhat consistent. Most often, steel with phosphor bronze provides high strength and consistent protection from corrosion. Materials also might include varieties of bronze such as nickel-phosphor bronze added to steel, depending on the application.

These devices have a long history, perhaps starting in ancient Greece with a device called the endless screw. Slewing drives were common in the Renaissance, as well. Though modern slew drives perform more complex tasks and are made out of more advanced materials, the ultimate goal of a slewing drive hasn’t changed much over time.