Planetary Gearbox for AGV and AMR
Mobile Robot Drive Wheel Selection

A planetary gearbox AGV drive application differs from industrial robot joints in five critical ways that Korean engineers often overlook when first specifying mobile robot drives. Engineers coming from their experience with industrial robot joint gearboxes — and arrive at the wrong specifications. The surface similarity (both are compact, precision, servo-driven gearboxes) conceals five fundamental specification differences that produce incorrect selections if robot joint criteria are applied directly to AGV drives.

The most important insight in this comparison: backlash grade is not the primary specification for AGV drive wheel gearboxes. An AGV drive wheel gearbox with P0 ≤1 arcmin backlash will still derail the AGV if the two drive wheels have different gear ratios — even a 0.01% ratio difference accumulates visible trajectory drift over a 10-metre travel segment. Ratio matching accuracy between the two drive gearboxes matters far more than individual backlash grade for AGV trajectory control.

The drive wheel gearbox output torque for an AGV combines three components: rolling resistance torque, incline torque, and acceleration torque. Unlike industrial robot joints where arm weight and cutting forces dominate, AGV drive torque is primarily determined by the total vehicle weight (AGV chassis + payload) and the floor surface condition.

Note that the acceleration torque (17.5 N·m) dominates over rolling resistance (5.15 N·m) in this example — because e-commerce AMRs accelerate aggressively (0.5 m/s²) to maintain throughput. For automotive assembly AGVs that accelerate gently (0.1 m/s²) but carry heavier payloads, the rolling resistance and incline terms dominate. Always calculate all three components; never estimate from a single term.

AGV Type → Drive Torque and Series Selection

For any planetary gearbox AGV with differential drive architecture — the most common Korean AGV navigation configuration — the dominant navigation consideration is: two independently driven wheels on either side of the vehicle centreline, with speed difference between the two wheels producing turning. Straight-line travel requires both wheels to rotate at exactly the same speed. Any permanent speed difference between the two drive wheels — caused by a gear ratio mismatch between the two gearboxes — produces a systematic trajectory curve that the navigation system must continuously correct.

The quantitative relationship between gearbox ratio mismatch and trajectory drift is derived geometrically. If the left wheel travels at speed v_L and the right wheel at v_R, the AGV traces an arc of radius R = W × v_mean / (v_L – v_R), where W is the wheel track width. Over a distance D of straight-line travel, the lateral deviation Δy from the commanded straight path is:

This calculation shows why Korea Ever-Power recommends ordering AGV drive gearbox pairs from the same production batch. Units from the same production batch have consistent gear grinding that produces ratio variation of ±0.005% or less — orders of magnitude better than the worst-case catalogue tolerance of ±0.1–0.5%. When the two drive gearboxes come from different batches, the batch-to-batch ratio variation can reach 0.05–0.1%, producing drift of 50–100 mm per 10 metres — enough to cause repeated navigation corrections and eventual lane departure at longer travel distances.

Unlike traditional industrial robots operating behind safety fences, Korean AGVs and AMRs share workspace with human operators — this is the defining architectural difference that makes noise a safety issue rather than a comfort preference. When an AGV approaches a human operator from behind, the ambient warning is its operating sound. A quiet AGV gives the operator more time to notice and step aside; a noisy AGV’s approach signal is masked by surrounding machinery noise.

Korean occupational safety regulations require collaborative mobile robots to emit an audible warning when approaching humans — but the regulations also set workplace noise limits at 85 dB(A). The effective warning sound from an AGV drive system must be detectable above ambient but must not itself contribute to the cumulative workplace noise exposure that approaches the regulatory limit. This creates a design band: the AGV drive gearbox noise should be low enough to not contribute to ambient noise accumulation, while the AGV’s separate audible warning system provides the detectable approach signal.

For Korean hospital AMRs, pharmaceutical cleanroom AGVs, and electronics assembly AMRs, drive noise directly affects operator environment quality in sustained work settings. The EP-KF/KH hypoid gear series produces measurably lower operating noise than standard planetary at equivalent torque — the curved spiral contact geometry distributes tooth engagement load over a larger face area, reducing the peak mesh impact and the resulting acoustic radiation. Measured at 1 m, EP-KF at equivalent torque and speed is typically 6–8 dB(A) lower than a standard EP-AB planetary unit.

Industrial robot joints and CNC machine tool gearboxes can be accessed for annual inspection during planned maintenance shutdowns. AGVs and AMRs in Korean operations typically run 24 hours a day, 365 days a year, with the only scheduled stops being battery charging cycles (for battery-powered AGVs) or wire-guided charging pauses. These charging pauses (typically 15–30 minutes every 4–8 hours) are the only available maintenance windows — and they are not long enough, nor are they appropriately equipped for gearbox maintenance.

This operational reality transforms sealed-grease gearbox construction from a convenience feature to a functional requirement. A gearbox that requires periodic re-lubrication, oil level checks, or seal inspection is simply incompatible with 24/7 AGV operation unless the entire fleet is scheduled for maintenance shutdowns — which defeats the economic case for AGV automation.

All Korea Ever-Power EP planetary series use permanently sealed grease that does not require periodic replacement — the factory fill is designed to last the full gearbox service life (20,000 operating hours) under normal conditions. At 8,760 operating hours per year for a 24/7 AGV, this provides approximately 2.3 years of maintenance-free operation per gearbox. At 6,000 hours per year (accounting for charging and downtime), the gearbox life extends to 3.3 years before replacement is warranted.

Omnidirectional AGVs and Mecanum wheel AMRs use a dedicated steering axis that rotates the entire drive module (motor + gearbox + wheel) around a vertical axis, allowing the AGV to navigate in any direction without turning the vehicle body. This steering turntable drive has different requirements from the drive wheel gearbox: very low output speed (full rotation in 2–5 seconds, or 0.2–0.5 rpm), high torque to overcome the friction of the loaded drive wheel against the floor, and a compact axial depth to minimise the turntable height within the AGV chassis.

The right-angle planetary gearbox is the standard solution for omnidirectional AGV steering: the motor mounts horizontally inside the AGV chassis, and the right-angle output shaft drives the turntable vertically. This eliminates the vertical motor height that would be required by an inline gearbox — a critical dimension reduction in flat AGVs designed to slide under shelving units.

The EP-ABR right-angle series at i=80–100 covers the typical steering turntable requirement: 0.3–0.8 rpm output from a 3,000 rpm servo motor at the ratio. P1 backlash is adequate for steering — the angular positioning of the drive module direction requires ±2–5 arcmin repeatability to achieve the target heading, well within P1 capability. The right-angle output positions the motor outside the turntable footprint, maintaining the minimum AGV body height.

Korean semiconductor wafer fab AGVs operating in ISO Class 4–6 cleanrooms impose the most stringent gearbox environmental specifications in Korean industry. The cleanroom AGV gearbox must be designed and documented to demonstrate three properties beyond normal industrial specifications: low particle generation, low outgassing, and non-magnetic construction where required for MRAM or magnetic storage layer fab environments.

Particle generation: A standard planetary gearbox uses greases containing compounds that can migrate as aerosol particles when the gearbox temperature cycles. Cleanroom gearboxes use PFPE (perfluoropolyether) or equivalent cleanroom-certified lubricants with ultra-low particle generation rates, combined with sealed housings that prevent any lubricant migration to the external surfaces. Korea Ever-Power can specify cleanroom-compatible lubricant in lieu of standard EP grease for semiconductor fab AGV orders — request “semiconductor cleanroom grease” at order time.

Outgassing: Standard plastics used in gearbox seals and coatings can outgas volatile organic compounds (VOCs) in cleanroom environments, contaminating the controlled atmosphere. Cleanroom-specified EP gearboxes use low-outgassing seal materials (FFKM fluoroelastomer) and coating systems with measured outgassing rates within fab facility specifications.

Non-magnetic materials: Advanced MRAM (Magnetic Random Access Memory) and spin-torque device fabrication lines require a magnetic-field-free environment in the wafer transport zone. Standard steel gear components are ferromagnetic — in sensitive fab zones, non-magnetic stainless steel variants or aluminium housing configurations may be required. Discuss this requirement explicitly with Korea Ever-Power for any semiconductor fab AGV order where magnetic contamination is a process concern.

Q
Our AGV follows magnetic tape guidance but drifts progressively to one side over long straight runs. The navigation system corrects continuously but this reduces speed. What is the likely gearbox cause?

Progressive one-side drift during straight-line travel with continuous servo correction is the classic signature of a gear ratio mismatch between the two drive wheel gearboxes. The drift direction (always to the same side) confirms it is systematic, not random — ruling out floor irregularity or wheel wear as the primary cause. Measure the actual output speed of both drive gearboxes at the same input command: even a 0.05% speed difference produces 5 mm drift per 10 metres. As calculated in Module 3, this compounds to 50 mm drift over 100 metres — enough to trigger frequent tape-following corrections that cap the AGV’s achievable speed. The solution is to replace both drive gearboxes with a matched pair from the same Korea Ever-Power production batch, specified with ≤0.01% ratio variation certificate.

Q
Do AGV drive gearboxes need P0 backlash like industrial robot joints?

No — for straight-line driving and gradual curve navigation, backlash grade is not the primary AGV accuracy specification. The AGV navigation system uses odometry from wheel encoders and independent position sensors (magnetic tape, LIDAR reflectors, or QR codes) to correct absolute position at every guidance reference point — backlash in the drive gearbox is a short-duration reversal error that the navigation loop corrects within the next sensor update. P1 or even P2 backlash is adequate for most AGV drive wheel applications. P0 becomes relevant only for very high-precision AGV applications such as semiconductor FOUP loading/unloading where the AGV must position its docking port to within ±0.5 mm of a fixed station — in that case, the final approach positioning accuracy requires P0 on the drive axis used for fine positioning.

Q
Can we use the same EP-AB gearbox model for both the AGV drive wheel and the steering turntable axis?

For the inline (EP-AB) variant, the same frame size body can be used for both axes if torque requirements match — but different ratios are required. The drive wheel axis typically uses i=10–25 to achieve 1–3 m/s wheel speed from a 3,000 rpm motor at 0.1–0.15 m wheel radius. The steering axis typically uses i=80–100 to achieve 0.3–0.5 rpm turntable speed from the same motor. Both ratios are available in the EP-AB series. For the steering axis, if chassis height is constrained, the EP-ABR right-angle variant at the same frame size is preferable — horizontal motor placement reduces total assembly height as described in Module 6. Specify the motor adapter plate size and flange dimension consistently across both axes from the same Korea Ever-Power frame scale to enable motor standardisation across the AGV drivetrain.

Q
For AGV fleets operating in Korean agricultural post-harvest processing facilities, what gearbox specification applies?

Korean post-harvest facilities (grain drying, vegetable sorting, fruit packing) often deploy AGVs for bin transport and sorting line supply. These facilities typically maintain temperatures of 5–25°C in the processing area — within the EP-KF/KH 0°C limit for indoor operation. However, the AGV may also traverse outdoor yard sections between storage buildings and processing lines, where Korean winter temperatures reach −5 to −10°C. For multi-zone AGVs that cross outdoor segments, the EP-AB series (−10°C) is the correct specification for the drive wheel gearboxes. For multi-output power distribution from a central drive system within the facility to multiple processing head drives, agricultural bevel gearboxes distribute the EP planetary output to individual sorting or conveyor heads — a common Korean post-harvest facility architecture.