Two of the most common ASRS solutions – Vertical Lift Modules (VLMs) and Vertical Carousels – can look similar on the surface. But how they perform (and where they shine) are significantly different depending on what you store, how you work, and where you’re headed. This guide will help you understand how they differ and choose the right solution with confidence.
Not sure which direction to go? You’ll find the key comparisons and often-overlooked factors below, but first, a quick primer to level-set.
Want to skip ahead? Jump to: 7 Things to Know
Before we dive into the decision points, let’s define the two systems we’re talking about:
What is a Vertical Lift Module (VLM)?
A Vertical Lift Module (VLM) is a dynamic storage system that works like an elevator, using two columns of trays and a central extractor to retrieve and deliver inventory to an ergonomic access point. As items are stored, the system automatically measures their height and adjusts tray placement to maximize space. It’s ideal for high-density storage in compact footprints and excels at organizing inventory that varies in size, weight, or frequency of access. VLMs also integrate easily with warehouse management software to boost accuracy, efficiency, and throughput.
What is a Vertical Carousel?
A vertical carousel uses a motorized series of carriers that rotate vertically along a track, similar to a Ferris wheel, to deliver items to a fixed access point. This system excels with consistent inventory profiles and high-frequency picking tasks. Pan Carousels are a common model, especially effective for storing uniform items like packaged parts, garments, tires, or print cylinders. Carousels are mechanically simpler, which often makes them easier to maintain and quicker to install.
The 7 Decision Points Everyone Thinks About
Most people start their decision-making here, and for good reason. These are the performance factors that tend to show up on spec sheets and in product demos. But specs don’t tell the whole story. The best choice depends on how these factors show up in your warehouse.
1. Inventory Profile
If your inventory includes a wide range of item sizes, weights, and pick frequencies, a VLM gives you the flexibility to adapt. It automatically adjusts tray heights for optimal space usage and can easily accommodate irregular or bulky items. That’s why the service department at Mark Motors Porsche uses a VLM to manage its diverse parts inventory efficiently, keeping everything accessible and organized without taking up more space.
On the other hand, if you’re storing a high volume of consistent, similarly sized SKUs – like packaged parts or uniform tools – a vertical carousel offers fast, simple access and excels at repetition. They’re especially well-suited for specific, high-volume use cases. The Vidir pan carousel can store up to 32,000 lbs of inventory.
2. Storage Density & Footprint
Compared to traditional industrial shelving, both systems maximize vertical capacity while improving accuracy and accessibility.
Both vertical storage systems dramatically reduce the amount of floor space needed to store inventory. But VLMs take space optimization a step further – automatically adjusting tray placement to maximize every vertical inch. That’s how they can shrink your storage footprint by up to 85%. Storage capacity is only limited by your ceiling height; a Vidir VLM is capable of storing up to 132,000 lbs of inventory in a single unit.
Vertical carousels also offer significant space savings – up to 75% – and can be a better fit in facilities where ceiling height is limited or the layout favors a more compact install. They’re often faster to install and require less structural prep, making them ideal for retrofit projects.
3. Picking Speed & Throughput
If speed is your top priority and your inventory is consistent, a vertical carousel can be hard to beat. It brings items to the operator quickly and in a predictable loop, which minimizes downtime between picks.
That said, VLMs hold their own in fast-paced environments. With batch picking capabilities, pick-to-light systems, and the ability to handle a wider variety of items in a single sequence, they offer speed through flexibility. Especially when order profiles are complex, a VLM may save more time overall.
4. Ergonomics & Worker Safety
Both vertical storage systems eliminate the need to bend, climb, or stretch, bringing goods directly to an ergonomic pick window. This reduces strain, speeds up fulfillment, and improves safety – critical benefits in light of recent data from the U.S. Government Accountability Office, which found that overexertion and “bodily reaction” are the most common hazards facing warehouse workers in traditional warehouses with industrial shelving.
Where VLMs go further is in handling heavy or awkward items. They can be paired with hoists, tray extractors, and weight verification systems to make lifting safer and more precise; ideal for operations moving large or valuable components.
5. Software Integration
If you’re thinking long-term about automation or digital transformation, VLMs tend to offer significantly more potential here. They connect with WMS, ERP, and inventory systems to support real-time tracking, automated picking workflows, barcode scanning, and even robotics, making them a strong fit for operations planning long-term automation.
Carousels typically offer lighter integration, often enough for small to mid-size operations. They’re great for batching and basic inventory tracking, but may hit their limits if your tech stack is more advanced.
6. Maintenance & Reliability
Because they have fewer moving parts, vertical carousels are mechanically simpler and easier to service in-house. They’re known for reliability and relatively low maintenance demands.
VLMs are more complex, but the Vidir VLM is engineered for long-term performance. Unlike many systems that rely on belts, it uses durable chain drives and precision servo motors to reduce wear and improve performance. These components contribute to smoother operation, higher reliability, and easier maintenance over time, especially in demanding environments where uptime matters.
7. Cost & ROI
Vertical carousels are typically more affordable up front, with quicker installs and faster ROI in the right applications. If your inventory is consistent and your needs are straightforward, a carousel can be a smart, cost-effective move.
VLMs cost more initially, but they deliver value over time. Their scalability, space efficiency, and flexibility often pay for themselves quickly, especially in dynamic environments where adaptability matters.
Your ASRS investment doesn’t stop at the price tag. Learn more about Total Cost of Ownership.
At A Glance: VLM vs. Vertical Carousel
The 7 Factors You Probably Haven’t Considered (But Should)
It’s one thing to compare the obvious features. It’s another to know what might cost you down the road. These seven considerations are about protecting your investment, avoiding buyer’s remorse, and making sure your system delivers the experience you’re counting on.
1. Will It Pass Inspection?
Unfortunately, it’s not unheard of for a VLM to be removed after installation – not because the client wants to, but because it fails to meet local code or spec requirements. Vidir VLMs are overbuilt to comply with local safety and operational codes, right out of the gate. That includes impact resistance (yes, even if you clip it with a forklift).
Most vertical carousels don’t need to reach the same height or weight-bearing standards, but make sure they still meet your local regulations.
2. Is Your Building Even Ready?
VLMs are taller, heavier systems that may require floor reinforcement, ceiling clearance, or structural review – especially in older buildings or facilities with mezzanines. That said, they can make excellent use of vertical space if your infrastructure allows for it.
Vertical carousels are generally shorter and lighter, which may simplify installation, but they also provide less vertical storage per square foot. The better fit depends on your space constraints and capacity goals.
3. How Disruptive Is the Install?
Installing any ASRS comes with planning. VLMs may involve more staging, floor prep, or temporary work zone closures, particularly in retrofits.
Carousels are often simpler to install, but keep in mind that both systems benefit from proper site prep and coordination. The difference isn’t always drastic; it depends on the specifics of your space and team.
4. What Happens When It Breaks?
The Vidir VLM is designed with long-life components – servo motors, chain drives, and robust construction – to reduce downtime and maintenance. Still, complex systems may occasionally require remote service technician support.
Vertical carousels, being mechanically simpler, can often be maintained by in-house staff. Your decision may hinge on how much hands-on servicing you can realistically support. Before you make a final decision, ask your short-list about standard maintenance and the typical repair schedule you should expect.
5. How Will My Team Adapt?
The best ASRS system is the one your team will actually use – and use well. VLMs typically come with more features and configuration options, which can require more training at the outset but make workloads lighter once up and running.
Carousels are often more intuitive, especially for teams used to manual systems. The right choice comes down to your team’s experience, training capacity, and how much complexity your operation needs (or wants to manage).
6. Do You Need to Lock It Down?
If you’re handling high-value, sensitive, or regulated items, access control matters. VLMs can be equipped with login permissions, audit trails, and secure software integrations. While carousels typically offer more limited access control options, Vidir does offer specialized solutions, like the Medical Supplies Carousel, designed specifically for regulated environments where cleanliness, traceability, and accountability are critical. If traceability and compliance are non-negotiable, it’s worth weighing your options carefully.
7. Are You Future-Proofing?
VLMs are often more modular and scalable. You can upgrade software, add integrations, or connect them to robotics later. Carousels are more fixed in what they can do, which is fine if your operation is stable, but limiting if you’re growing or modernizing. Choose the system that can evolve with you.
▶️ Related: How ASRS supports lean teams
At A Glance: VLM vs. Vertical Carousel
Still Not Sure?
Choosing between a VLM and a Vertical Carousel isn’t always black and white. If you’re still weighing the options – or just want to make sure you’re making the right call – our team is here to help. We’ll walk you through your inventory profile, space constraints, operational needs, and growth plans to find the best-fit solution.
Let’s find the right system for your space, your team, and your future.
