In the material handling industry, mobile robots rated for 1,500 kg and above are generally classified as heavy-duty AGV/AMR. This is not a marketing label but a genuine engineering threshold: once you cross it, the chassis structure, drive units, safety systems and cost model all follow a different set of rules.

Most selection mistakes come from applying light-duty thinking to heavy-duty scenarios - specifying QR-code navigation for a 2-tonne cart route, or differential two-wheel drive to tow an 8-metre steel section. The result is either a collapse in positioning accuracy or a vehicle that simply cannot operate on site.

This article breaks heavy-duty handling into five practical solution paths and explains the capability boundary and operating conditions of each. Specifications cited are taken from the public product pages of Skybridge Robot. Actual projects are subject to on-site survey.

1. First, Clarify: Heavy Duty Has Three Dimensions, Not Just a Tonnage Figure

The most common error is to look only at the rated payload. In reality, once a load crosses the 1,500 kg line the technical requirements differ completely depending on the scenario:

These three dimensions pull the design in different directions. Vertical load is about structural strength, horizontal towing about tractive force and tyre grip, eccentric long loads about centre-of-gravity management and attitude control. The first question in heavy-duty selection is therefore not "how heavy" but "in what way is it heavy".

2. Five Heavy-Duty Approaches and Their Boundaries

Approach 1: Under-ride towing type - the workhorse for long-distance heavy transport

Typical use: carts, racks and fixture trolleys that must move across multiple processes, workshops or even floors.

The core logic of the under-ride towing AGV is not to lift the load but to pull the entire cart away, and crucially the vehicle drives underneath the cart: it enters the space below the cart chassis, engages a tow pin automatically and hauls the whole train away. A single unit can tow several carts at once - the efficiency advantage in high-volume transfer. This under-ride behaviour is what separates it from the rear-towing type: a rear-towing unit carries its coupling at the tail, does not enter the space under the cart, and instead stops ahead of the cart and pulls it from behind. That removes any requirement for ground clearance under the cart, but the train is longer by the length of the vehicle, and tail swing during turns and reversing is more pronounced. Which one to choose starts with a single question: is there enough clearance under the cart for the vehicle to drive in?

Public specifications: the R1 series covers 500–3,000 kg in unidirectional, bidirectional and omnidirectional configurations, with magnetic tape navigation and ±10 mm accuracy.

Capability boundaries (confirm before selecting):

• • There must be usable clearance under the cart for the vehicle to drive in - where clearance is insufficient, move to the rear-towing type, otherwise the vehicle cannot enter and the solution is unworkable
• • Hitching and release require cart structure to match; fixture modification is a hidden cost
• • Turning radius is relatively large (around 1,300 mm); narrow legacy aisles must be measured
• • Ramps and floor flatness noticeably affect towing stability

Typical scenarios: rack transfer in automotive stamping and body shops, cell cart delivery on lithium battery PACK lines, cross-floor material flow.

Approach 2: Rear-towing type - the answer when the cart cannot be under-ridden

Typical use: heavy towing scenarios where clearance under the cart is insufficient, the cart is too low, or the cart structure simply does not allow a vehicle to drive underneath.

The rear-towing type solves the same problem as the under-ride type - hauling the entire cart away - and differs in where the vehicle sits when it couples. The coupling sits at the tail of the vehicle, so the unit does not enter the space under the cart; it stops ahead of the cart and pulls it from behind with a tail hook, or with a towing attachment on a forklift-type chassis.

That difference has three direct consequences. First, there is no clearance requirement under the cart, so standard and modified carts both work. Second, the train is longer by the length of the vehicle, so fewer carts fit in the same aisle. Third, tail swing during turns and reversing is more pronounced, requiring larger margins at narrow aisles and right-angle turns. In addition, rear-towing units offer manual, semi-automatic and fully automatic coupling, which suits older plants that have not yet standardised their carts.

Public specifications: the R4 series covers 600–3,000 kg in the L type and forklift rear-towing type, with laser/SLAM navigation, ±15 mm accuracy and reverse travel limited to 2 m.

Capability boundaries:

• • Reverse travel is limited (2 m or less), so process layouts requiring long reverse positioning must be re-planned
• • The train length includes the vehicle itself, so fewer carts can be towed in a given aisle than with an under-ride unit
• • Navigation is laser/SLAM based, which differs from the magnetic-tape installation of the under-ride type; mixed fleets require a unified landmark plan
• • The 3,000 kg class (R4-C1) is a tall unit (2,237 mm high), so doorway and lift cabin clearance must be measured in advance

Typical scenarios: multi-cart transfer in older plants with non-standard carts, dedicated racks too low for under-riding, and 3-tonne class heavy inter-process movement.

Approach 3: Lifting type - heavy lifting with flexible docking

Typical use: heavy material that must be lifted, rotated and precisely docked between workstations.

The key capabilities are lift height plus rotational freedom. The vehicle does more than transport: on arrival it adjusts the load attitude so that material aligns with a line interface or buffer position.

Public specifications: the R2 series covers 300–2,500 kg, lift height 50–250 mm, with QR-code or SLAM navigation; some models support four-way travel.

Capability boundaries:

• • Higher lift and heavier load increase vehicle weight and turning radius together - a 2.5-tonne unit can weigh 875 kg, which matters for floor loading
• • Four-way travel including lateral movement needs wider aisle margins; narrow aisles require early planning
• • Travel speed inevitably falls at high load; cycle-time calculations cannot reuse light-duty reference values

Typical scenarios: lifting transfer of energy storage PACK modules, docking of castings and machined parts, heavy buffer area storage and retrieval.

Approach 4: Transfer type - the interface specialist for line connection

Typical use: automatic exchange of empty and full containers with roller conveyors, transfer lines and buffer racks.

The transfer type solves the docking accuracy problem. A double-deck dual-rail transfer structure allows it to pick up empties and drop full containers automatically at the line end without manual intervention. Public specifications: the R3 series covers 100–1,000 kg in single-, double- and triple-deck configurations with adjustable docking height.

Capability boundaries (the category requiring most caution):

• • The heavy-duty ceiling of the transfer type is generally lower than the under-ride towing and lifting types. The public specification for the R3 series tops out at 1,000 kg. If the requirement is full-pallet transfer above 1.5 tonnes, the transfer type is usually not the best answer and towing or lifting options should be evaluated
• • Transfer depends on standardised line-end interfaces; docking height and material dimensions must match
• • A single-layer transfer mechanism places tighter demands on floor flatness and docking position accuracy

Typical scenarios: loading and unloading on 3C and SMT lines, connection with pharmaceutical packaging lines, docking at flat-panel display workstations.

Approach 5: Forklift type - the general answer for palletised heavy loads

Typical use: heavy-duty picking and stacking of standard and three-channel pallets.

The forklift type is the closest to conventional manual forklift practice and requires the least site modification - provided pallets are standard and aisles are wide enough, it can usually be deployed directly.

Public specifications: the R5 series covers 500–1,400 kg in transfer and stacker configurations, with laser/SLAM navigation and cross-floor picking. The ceiling of this series sits below 1,500 kg, so strictly speaking it falls outside the heavy-duty band; it is included to show that forklift-type units top out below towing and lifting types.

Capability boundaries:

• • Fork structure requires uniform pallet specification; non-standard racks need custom attachments
• • Vehicle height is significant (around 2,000 mm); door openings and lift cabin clearance must be measured first
• • Stability during heavy lifting depends on floor and pallet condition; damaged pallets substantially increase risk
• • Above 1,600 kg, general forklift-type product lines have limited coverage and a dedicated heavy platform should be evaluated

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3. Five Hard Constraints in Heavy-Duty Selection

Beyond the specification table, heavy-duty projects usually fail in one of five places:

1. Floor loading capacity and flatness

A 2.5-tonne lifting vehicle weighs close to 900 kg, and with material the total can exceed 3 tonnes, so wheel pressure far exceeds light-duty equipment. Slab capacity and floor strength in older plants must be calculated up front, not discovered after delivery.

2. Aisle and doorway clear dimensions

Heavy-duty turning radii typically fall between 1,300 and 2,200 mm, much larger than light-duty vehicles. Right-angle turns, fire doors and lift entrances must be measured under full-load conditions, not estimated from empty or light-duty experience.

3. Eccentric load and overturning resistance

For steel coils, long shafts and irregular parts the centre of gravity is not at the vehicle centre, and overturning during a loaded turn is the most common safety hazard in heavy-duty projects. Such scenarios require eccentric load calculation and, where necessary, custom fixture cradles.

4. Safety system level

A collision involving heavy equipment has far more serious consequences than one involving light equipment. Laser obstacle avoidance, bumpers, emergency stop and zone speed reduction are not options in heavy-duty scenarios - they are the baseline. Confirm as well whether speed reduction logic in mixed pedestrian areas is programmable.

5. Realistic cycle-time calculation

Maximum travel speed for heavy-duty vehicles is generally lower than for light-duty (1.0–1.5 m/s is typical), and acceleration and deceleration take longer. Deriving a heavy-duty solution from light-duty cycle data easily produces a system that is affordable but cannot keep up. Cycle-time calculations must use actual full-load speeds.

4. Three Common Misconceptions

Misconception 1: Heavier is always better - leave plenty of margin

Greater capacity brings higher vehicle weight, larger turning radius, more energy consumption and higher cost. A 2.5-tonne vehicle chosen for a hypothetical future need becomes a burden in a routine 800 kg operation. A 15–20% margin over actual peak load is sufficient.

Misconception 2: The lifting type can replace the forklift type

The two carry material in completely different ways. The lifting type relies on carts or fixtures, the forklift type on forks entering under the pallet. Whether the site uses standard pallets or fixture carts directly determines the solution path; they are not interchangeable.

Misconception 3: Choose the vehicle first, then modify the site

The correct order for heavy-duty projects is survey the site first (floor, aisles, load capacity, interfaces), then define the solution, then select the model. Doing it in reverse usually leads to a vehicle that cannot get in or cannot run.

5. Putting Selection on Paper: A Self-Check List

Before approaching any supplier, fill in these ten items:

• Maximum load per move (kg), and whether cart or pallet weight is included

• Material form: full pallet, cart, long section or irregular part

• Is lifting required? To what height?

• Is docking with a production line or AS/RS required? Docking height and accuracy

• Narrowest aisle width, tightest turning dimension, doorway clear height

• Floor and slab load capacity; cross-floor movement required (lift dimensions)

• Floor material and flatness, especially ramps, joints and potholes

• Throughput requirement: trips per hour and allowed time per trip

• Degree of pedestrian mixing; required safety protection level

• Are existing carts and pallets standardised, and can they be modified

Once these ten items are clear, the solution path is largely determined, and comparing specifications becomes meaningful.

6. Skybridge Heavy-Duty Product Lines

Skybridge Robot (skbrobot.com, founded in Shenzhen in 2024) organises its range into six series, R1 to R6. Five of them reach into the 1,500 kg heavy-duty band:

• R1 under-ride towing (500–3,000 kg): couples beneath the cart; unidirectional R1-11B/R1-12/R1-13, bidirectional R1-22, omnidirectional R1-33
• R2 under-ride lifting (300–2,500 kg): lifting and workstation docking; the 2,500 kg model is the R2-38B
• R3 on-board transfer (100–1,000 kg): automatic empty-full exchange at line interfaces; does not reach the heavy-duty band
• R4 rear towing (600–3,000 kg): tail-hook hauling; L type R4-L1/R4-L2 and forklift rear-towing type R4-C1
• R5 forklift (500–1,400 kg): pallet picking and stacking, split into transfer R5-B and stacker R5-D families

Further reading:

• AGV Navigation Selection Guide: Magnetic Tape To V-SLAM - 7 Types Compared
• AGV Transforms SPS Material Delivery in Automotive Assembly Lines
• AGVs Make Energy-Storage PACK Lines Flexible: Replacing Rigid Conveyors

Frequently Asked Questions

Q1: What load rating counts as heavy-duty AGV? Is 1,500 kg heavy duty?

A: Mobile robots with a rated payload of 1,500 kg and above are generally classified as heavy-duty AGV/AMR. 1,500 kg is the starting point of the heavy-duty band; 1.5–3 tonnes is the mainstream heavy-duty range and above 3 tonnes is usually considered extra-heavy, requiring a custom platform. Below 1,500 kg equipment is normally classed as light or medium duty, where the selection logic differs substantially.

Q2: What is the biggest difference between a heavy-duty AGV and a standard AGV?

A: It is not simply a larger payload. The differences lie in chassis rigidity, drive unit power, safety system level, turning radius and vehicle weight. Heavy-duty turning radii typically range from 1,300 to 2,200 mm, 1.5 to 2 times that of light-duty vehicles, placing greater demands on site aisles.

Q3: For a 2-tonne load, should I choose under-ride towing or lifting?

A: It depends on how the material is carried. If it sits in a cart and needs long-distance multi-process transfer, choose under-ride towing. If it must be lifted to a height for line docking, choose lifting. In the public specifications the R1 under-ride towing series reaches 3,000 kg and the R2 lifting series 2,500 kg. Where the cart cannot be under-ridden, the R4 rear-towing series covers 600–3,000 kg.

Q4: Will a heavy-duty AGV damage the factory floor?

A: This must be calculated. A 2.5-tonne lifting vehicle can weigh 875 kg on its own, and with material the total exceeds 3 tonnes, producing wheel pressure well above light-duty equipment. For older buildings or upper floors, slab load capacity must be assessed during solution design - it is a precondition for heavy-duty projects.

Q5: Are heavy-duty AGVs slow? Will that limit throughput?

A: Maximum travel speed is typically 1.0–1.5 m/s, lower than light-duty vehicles. Whether throughput is affected depends on the combination of time per trip and fleet size. Cycle-time calculations must use actual full-load speeds, not empty or light-duty data.

Q6: Can different heavy-duty models be mixed in one project?

A: Yes, and it is common in large projects. Under-ride towing or rear-towing units handle high-volume cross-workshop transfer, forklift units handle warehouse storage and retrieval, and transfer units handle precision line docking, all managed by a single fleet scheduling system - provided navigation methods and scheduling protocols are compatible - note that R1 runs on magnetic tape while R4 uses laser/SLAM, so mixed fleets need a unified landmark plan.

Q7: How do I choose between rear towing and under-ride towing?

A: Measure the clearance under the cart first. If the vehicle can drive beneath the cart to couple, choose under-ride towing (R1): the train is shorter, aisle utilisation is higher and magnetic tape is cheaper to install. If it cannot - cross members under the cart, too little ground clearance, or a non-standard rack - choose rear towing (R4), which hauls from a tail hook with no clearance requirement, at the cost of extra train length and reverse travel limited to 2 m.