How to Choose a Slew Drive for Aerial Platforms

What is a slew drive for aerial platform use? It is a sealed unit that combines a slewing bearing, a gear drive (worm or spur), and a housing. One part carries the load and turns the boom or deck.

The choice comes down to a tension. A compact drive saves weight and cost, but an undersized one fails under tip-over loads. A bigger drive adds mass the machine has to carry. Our rule: size the drive from two numbers first, the worst-case overturning moment and the wind-case holding torque. Then check radial load, axial load, sealing, and gearing type. If you do not yet have those two numbers, you cannot select a drive with confidence, and the first task is a load calculation at the worst boom pose.

Which Inputs Decide the Drive Before You Compare Catalogs

Most spec sheets list static load ratings. An aerial platform does not live at static conditions. The boom moves, the basket sways, and wind pushes on a large surface.

Gather these inputs before you talk to any supplier:

• Overturning moment at rated load: payload, basket, boom, and jib at the pose that gives the longest lever arm.
• Wind or side-load case: the torque the drive must hold without creeping when the machine is parked at height.
• Radial load: horizontal forces from braking, travel on slopes, and wind.
• Axial load: total weight carried straight down through the bearing.
• Slew speed and duty: how many starts and stops per shift, and any inching control.
• Environment: outdoor, washdown, coastal, or dusty sites.

Our design team at Luoyang Slewring Bearing Co., Ltd. can start a technical proposal from these inputs. We return it within 24 hours. A basic slew drive range exists for standard sizes, and anything outside it goes to a custom route.

Comparison of Overturning Moment, Holding Torque, Radial Load, and Axial Load Across Articulated, Telescopic, and Scissor-Lift Platforms

The three platform types load the slewing drive in different ways. The table below ranks them in relative terms only. Actual values depend on your boom geometry, rated load, and safety factors, so run the calculation before you pick a size.

Requirement	Articulated boom	Telescopic boom	Scissor lift (rotating-deck variants only)
Overturning moment	Medium to high. Varies a lot with pose; the jib and up-and-over reach add to it.	Highest. Peaks at full extension and low boom angle.	Low. The load stays near the vertical centerline.
Holding torque	Medium to high. Wind on the basket and boom inertia drive the need.	High. Long lever arm makes wind loads more severe.	Low. Little exposed side area at the rotation point.
Radial load	Medium. Dynamic loads from frequent boom moves.	Medium to high. Side wind on a long boom and braking forces.	Low.
Axial load	Medium to high. Turntable, boom, basket, and payload.	High. Heavier boom sections and counterweight.	Moderate. Most deck load goes through the scissor stack, not the slew bearing.
Main sizing driver	Worst-pose moment plus start-stop duty	Full-extension moment plus wind hold	Axial load and compact height

Most scissor lifts do not slew at all. A drive only appears in special designs, such as a rotating work deck. If your machine is one of them, axial load and low profile usually matter more than moment capacity.

How to read the table as decision rules

• Choose a high-moment design basis (larger bearing, heavier gear set) when the machine is a telescopic boom or a long-reach articulated unit. Moment is the number that sets bearing size.
• Prioritize holding torque and self-locking behavior when the boom parks at height in open sites. Wind creep is a safety item, not a comfort issue.
• Prioritize smooth start-stop control and backlash on articulated booms. Basket sway makes operators notice every jerk.
• Do not oversize on moment alone for a scissor-based rotating deck. A smaller, flatter unit usually fits better and saves weight.

These rules fail when your duty is unusual. A boom used mostly at low angles may have a lower peak moment than its length suggests. Always calculate, never guess from the platform label.

Worm, Double Worm, or Spur Gear: Matching the Gearing to the Duty

Gearing sets holding behavior, efficiency, and control feel. Each type has a clear place, and each has limits.

Drive type	Choose it when	Watch out for
Worm Gear Slew Drive	You need compact size and self-locking to hold the boom against wind. Fits most standard manlift and lift-truck work.	Lower efficiency, so more heat and motor power at high duty. Self-locking is not a substitute for a brake in a vibrating system.
Double Worm Slew Drive	Torque demand is high or you want to reduce backlash. Two worms share the load and improve positioning.	Larger housing and higher cost. Overkill for a light basket and short reach.
Spur Gear Slew Drive	Efficiency and speed matter more than holding. Works with a separate brake or gearmotor with holding function.	No self-locking, so you must add a holding brake. Needs more careful control design.

Real projects show how this plays out in other heavy machines. A Houston, Texas machinery maker ordered 150 units of WED17-104-25HR double worm drives for heavy-duty wheel steering. A British Columbia forestry equipment maker ordered 30 units of WED14-86-25BHR.5 for grapple machines, with tracking precision of 0.13° or better. Neither is an aerial platform, but both show double worm drives handling high torque with tight positioning. We have no aerial platform case in our supplied record, so treat these as application parallels, not proof for your boom.

For a South Korean port equipment maker, we supplied 20 units of WEA9-62-25HR single worm drives for crane systems. That order called for 0.15° tracking precision, IP65 sealing, and self-locking. It shows the single worm route working where compact holding is the goal.

Sealing, Corrosion Rating, and Material Choices for Outdoor Booms

Aerial platforms work in rain, dust, road salt, and sometimes washdown. Drive life depends on the seal and the coating as much as on gear strength.

Our slew drives offer protection up to IP66 and anti-corrosion ratings up to C4H. Pick the level by site. Use IP65 for general outdoor use. Step up to IP66 and C4H when units see jet washing, coastal air, or chemical plants. Do not pay for the top rating if the machine only runs in dry, indoor facilities.

Material is chosen by working condition: ductile cast iron, alloy steel, stainless steel, or forged alloy steel. Forged alloy steel suits high-load turntables. Stainless fits corrosive sites, but check strength limits against your moment.

Bearing type also matters. A three-row roller slewing bearing is the usual choice when moment loads are very high, while smaller booms can use lighter raceway designs. The slew drive range covers these options inside one housing.

A Step-by-Step Way to Specify the Drive

1. Find the worst pose. Check full reach, jib raised, and basket at rated load. Record the moment.
2. Add the wind case. Use your design standard to get the side load on the basket and boom. Convert it to holding torque at the slew axis.
3. Apply your safety factor. Use the factor required by your market and design code. Do not use a catalog factor in place of your own.
4. Check radial and axial loads. Confirm both sit inside the rating curve at the same time as the moment, not on their own.
5. Pick gearing. Use the table above. Decide if self-locking is enough or if you will add a brake.
6. Set sealing and coating. Match IP and corrosion class to your sites.
7. Request a prototype. Test on the real machine before committing to volume.

Here is a worked case in outline. A designer has a telescopic boom for outdoor construction. Moment at full extension sets the bearing size, so step 1 decides the frame. Wind hold at height then points to a worm drive with self-locking and a brake as backup. The result is a high-moment bearing with a worm gearset, IP66 sealing for site washdown, and a check on backlash. Specific numbers come from the designer's own calculation, which we then verify in the proposal.

Common Mistakes When Selecting a Drive for an Aerial Work Platform

• Sizing by static rating only. The slew drive sees dynamic and wind loads. Static ratings alone leave no margin for them.
• Relying on self-locking as the only holding method. Vibration and wear can back-drive a worm gear. Add a brake where the safety case demands it.
• Ignoring pose-dependent moment. A boom's worst case is not always at full extension. Check several poses.
• Copying a scissor-lift spec to a boom. The load paths differ completely, as the table shows.
• Skipping mounting stiffness. A strong drive on a flexible frame wears fast and loses accuracy.
• Buying the top corrosion class by default. It costs more and may not improve life at an indoor site.

Selection Rule and What to Confirm Before You Order

Choose a standard worm drive when your moment sits within a catalog size, you need compact self-locking, and the duty is moderate. See our Manlift Slew Drive and Aerial Work Vehicle Slew Drive pages for the closest product families.

Choose a double worm or custom design when torque, backlash, or mounting envelope falls outside standard sizes. A customized slew drive starts at 5 sets, while standard products start at 1 set. We do 3-day rapid prototyping and a 9-day standard production cycle, so you can test a sample before scaling.

Choose a spur gear drive only when you have a separate holding brake and want the efficiency gain.

Before you lock the choice, confirm these items:

• Moment, wind torque, radial and axial loads at the same worst pose.
• Required safety factor and the design standard it comes from.
• Backlash and positioning accuracy target.
• IP and corrosion class by site.
• Brake plan and motor interface.

Quality records matter too. Our factory is ISO 9001:2015 certified, and we run CMM three-coordinate inspection on bearings, with details on our slew drive quality control page. Confirmed manufacturing defects get free replacement under our 2-year extended quality warranty. For a slew drive for aerial platform projects, send your load case and drawings, and our engineers will answer technical questions within 48 hours.