Thermal-loaded gear selection hinges on three numbers: continuous torque, peak shock torque, and service-factor duty cycle. The Siti NRG planetary line, published on DirectIndustry, is rated to a maximum 25,000 Nm torque and 200 kW (271.92 hp) input across ratios up to 3657:1, with cast-iron housing and oversized bearings sized for heavy-duty continuous operation [S1].
RV reducers, by contrast, are cycloidal-pin designs optimised for high shock tolerance and torsional stiffness rather than raw continuous-torque class. Dongguan Fu Bao Electromechanical, a Chinese supplier active on GoldSupplier, lists its main product lines as RV reducer, planetary reducer, and harmonic reducer, with the WF series high-precision cycloidal RV gearbox priced at US$ 35-60 per set on a 1-set MOQ [S3]. RV series 2-stage units dominate articulated-robot joints, while planetary units dominate long-run conveyor and mixer drives where thermal soak is constant.
Continuous-Torque Class and Heat Rejection
The NRG planetary platform spans 6 frame sizes with 4 input and 4 output configurations and accepts up to 200 kW input at 25,000 Nm peak, per the OEM datasheet on DirectIndustry [S1]. Cast-iron housings and "largely proportioned bearings" are explicitly named for heavy-duty applications, which translates in practice to better steady-state thermal mass than aluminium-housed precision planetary stages.
For a thermal-loaded conveyor, mixer, or extruder where motor slip dissipates as gearbox case heat, the larger planetary housings spread the thermal gradient more evenly. For precision servo axes where the load is intermittent and back-drivability matters, planetary stages with backlash under 5 arc-min are the norm and were the dominant "servo planetary reducer" SKU class in a 2026-07-14 chinamecha.com product-directory snapshot [S2]. RV reducers in that same directory category are listed separately under cycloidal-pinion robot-joint configurations rather than continuous-torque process drives.
Shock Tolerance, Stiffness, and Torsional Backlash
RV reducers achieve torsional stiffness an order of magnitude higher than standard planetary stages because the cycloidal disc is loaded by 2-3 simultaneous pin engagements. The Fu Bao WF-series RV gearbox, priced at US$ 35-60/set, is positioned in the high-precision cycloidal class used for robot articulation and indexing tables [S3]. For thermal load profiles with high inrush shock (start-stop cycling, indexing under load), that multi-tooth contact area is the deciding factor.
Planetary reducers compensate with single-stage reductions and higher ratios (NRG goes to 3657:1 across 4 reduction stages [S1]), but at the cost of higher backlash and lower torsional rigidity per stage. The chinamecha product taxonomy lists at least 18 distinct servo-planetary variants — helical-gear-on-hard-tooth-surface, disc-output, flange-output, right-angle, and miniature — all of which trade off stiffness against inertia and clearance class [S2]. Selecting between RV and planetary therefore means deciding whether the binding gate is peak shock stiffness (RV) or steady-state thermal class (planetary).
Duty-Cycle and Service-Factor Mapping for Thermal Loads
Thermal load is not a single number: it is the integral of torque × speed × time, minus whatever the housing can shed. For 24/7 mixer or kiln drives, planetary gearheads with cast-iron housings and external fan-cooled options (Siti lists the NRG with up to 4 reduction stages for high-ratio continuous duty [S1]) are the engineering default. The thermal ceiling on a standard oil-sealed planetary gearbox in industrial service is set by the seal elastomer and lubricant, not the gears themselves.
For cyclic, high-shock thermal profiles — palletiser joints in a hot forging cell, for example, or pick-and-place above a heat-treat furnace — the RV reducer's low-backlash cycloidal contact survives repeated start-stop thermal cycling better than a precision planetary stage. The Fu Bao company profile, dated 2008, lists welding, semiconductor, and military applications among RV deployment fields alongside machine tools, all of which share the high-shock / intermittent-thermal signature [S3]. Picking by service factor S = P_actual / P_rated is therefore more reliable than picking by peak Nm alone.
Selection Criteria Matrix: Decision Gates
Gate 1: continuous torque ≥ rated — planetary holds the wider catalogue, with the NRG at 25,000 Nm / 200 kW as a documented upper bound [S1]. Gate 2: torsional stiffness for positioning — RV cycloidal wins at low backlash. Gate 3: thermal mass and heat rejection — cast-iron planetary housings shed more kW continuously. Gate 4: ratio range — planetary goes to 3657:1 in 4 stages [S1], RV is typically limited to 30:1-150:1 per stage and stacks to 2 stages for high ratios.
Gate 5: cost per Nm — Chinese suppliers (Fu Bao, multiple chinamecha-listed factories) price RV gearboxes from US$ 35-60/set and planetary stages typically higher depending on backlash class [S3][S2]. The right-angle servo planetary variants in the chinamecha 2026-07-14 catalogue, including "robot arm joint special servo planetary reducer", close the gap for cost-sensitive articulated axes [S2]. For thermal-load process drives, however, the cast-iron industrial planetary is the lower-risk default because the housing itself is a heat sink.
Standards, Sourcing, and Who This Is NOT For
No IEC or ISO gear-rating standard is named in the cited supplier material, so rated-torque claims should be cross-checked against AGMA 2001 or ISO 6336 in your own procurement spec. The Fu Bao RFQ flow on GoldSupplier and the chinamecha category page are B2B sourcing channels — useful for cost benchmarking, not for engineering sign-off [S3][S2]. For a thermal-loaded process drive above 75 kW, verify gearbox oil-spec, seal temperature class, and thermal probe port with the OEM before order release; this is not addressed in the cited sources.
Planetary stages are also the wrong tool for ultra-precision rotary indexing below 1 arc-min backlash, where harmonic drives (also listed by Fu Bao as a main product line [S3]) outperform both RV and planetary on positioning repeatability. For process engineers weighing harmonic vs RV vs planetary against thermal load, the deciding axes are back-drivability, continuous torque class, and housing thermal mass — three numbers any gearbox supplier should publish before you sign the PO. Related engineering reading on spec-first selection for adjacent motion components is mapped in the Brake Resistor vs VFD-Duty Motor spec-first selection decision guide.
Trackable next node: confirm thermal probe port and oil-seal temperature class on the gearbox data sheet before order release, and cross-check the AGMA service-factor against your true 24-h torque profile. For servomotor-side selection, the Vision Controller selection criteria: 5 binding gates for 2026 spec maps and the Harmonic Filter selection criteria: spec-first map for 2026 cover upstream and downstream hardware gates worth aligning to whichever reducer you choose.
Component reference pages worth checking: planetary reducer, rv reducer, and electronic load.