Planetary Gear Sets – Helical/Spur, M3-M12, Custom Made

Planetary gear sets are gear systems in which at least one gear rotates on a shaft that also revolves around another fixed central shaft. Each planet gear rotates on its own support shaft fixed to the planet carrier — this rotation around its own shaft is called "rotation," and the simultaneous movement of the planet carrier around the central axis is called "revolution" — just as the planets in the solar system rotate on their own axes while revolving around the sun. This dual motion is what gives planetary gears their unique kinematic characteristics: the ability to produce high transmission ratios in a compact, coaxial assembly and to realise motion synthesis and decomposition that simple fixed-axis gear trains cannot achieve.

Korea Ever-Power manufactures planetary gear sets in spur and helical tooth profiles, modules M3–M12, in all standard and custom materials. Planetary gear sets have been widely used as reducers, speed-increasers, and differential devices in aircraft, vehicles, and industrial machinery — primarily because of their high load capacity, large transmission ratio, and coaxial input/output configuration. Payment: 30% down payment, 70% balance. Custom gears manufactured with excellent delivery options. Reverse engineering from damaged gears available.

Sun Gear — The Input Driver

The sun gear is the smallest gear in the planetary set and is positioned at the exact geometric centre. Just as the sun is at the centre of the solar system, the sun wheel is named for its central position. In the standard reduction configuration, the sun gear is the high-speed input — connected to the motor shaft. Its tooth count (Z_sun) determines the set's transmission ratio in combination with the ring gear tooth count (Z_ring): i = 1 + Z_ring/Z_sun. The sun gear meshes with all planet gears simultaneously, distributing its input torque equally among them.

Planet Gears and Carrier — The Load Splitter

The planet gears are supported on pins fixed to the planet carrier — allowing them to rotate freely around their own axes while the carrier constrains their revolution around the sun gear. Under the circumstances of the carrier, the planet gears revolve around the central axis just like the Earth's revolution around the sun. When the planet carrier is fixed (no revolution), the planetary set operates as a simple fixed-axis transmission — a state similar to a parallel shaft transmission called fixed-shaft transmission. When the carrier rotates, the full planetary motion is active and the speed reduction ratio applies.

Ring Gear — The Reaction Member

The ring gear is an internal gear that always meshes with the planet gears from the outside. In the standard reduction configuration, the ring gear is fixed to the housing and acts as the reaction member — absorbing the planet gear reaction torque and transmitting it to the housing structure. The internal-external gear mesh (ring-planet) produces the same rotation direction for both. The ring gear's tooth count must satisfy the assembly condition: Z_ring = Z_sun + 2 × Z_planet, ensuring all planet gears fit in the space between the sun and ring without interference and are equally spaced around the circumference.

Helical Tooth Profile Option

Standard planetary gear sets use helical gears to improve operational stability. Helical sun and planet gears mesh progressively rather than instantaneously, reducing the transmission error (TE) at the gear mesh frequency and lowering operating noise by 3–6 dB(A) compared with equivalent spur gears. The penalty is an axial thrust force at each gear mesh — typically absorbed by thrust bearings on the carrier pins, or cancelled by using herringbone (double-helical) tooth profiles. Korea Ever-Power produces both spur and helical planetary gear sets per the customer's application requirement.

Helical Gears for Lower Transmission Error

Using helical tooth profiles (both sun and planet gears) reduces transmission error at the gear mesh frequency — the primary noise source in planetary gear sets. The progressive helical engagement produces a smoother torque transfer and lower peak tooth load per unit time, reducing the vibration excitation at the mesh frequency and its harmonics.

Planet Load Equalisation

Unequal load distribution among the planet gears is the most significant cause of premature planetary gear set failure. Korea Ever-Power controls the planet pin hole position accuracy on the planet carrier to ±0.01 mm and the planet gear tooth-to-tooth spacing to within the DIN accuracy class specification — ensuring that load is distributed within ±5% across all planet gears in the set.

Tooth Profile Modification

Tip relief (tooth tip modification) on the sun and planet gears reduces the impact load at the start and end of tooth contact — where the highest transmission error and noise excitation occur in an unmodified spur or helical gear pair. Korea Ever-Power applies tip relief on planetary gear sets specified for higher accuracy grades (DIN 6–7) where low transmission error and low noise are primary requirements.

Lubrication Engineering

Studying elastic hydrodynamic lubrication (EHL) theory and applying synthetic gear oils with extreme pressure (EP) additives improves the bearing capacity of the tooth surface and transmission efficiency of planetary gear sets. Korea Ever-Power provides lubrication recommendations for each planetary gear set based on the speed, torque, and temperature specification — a critical but often overlooked factor in achieving the specified gear set service life.

Automotive Automatic Transmissions

Two or three planetary gear sets combined in automatic transmissions to produce 6–10 forward ratios and reverse. Each ratio is selected by applying different clutches and brakes. Planetary gear sets also play an important role in engine torque transmission — converting the engine's narrow speed-torque range into the broad speed-torque range needed for road driving.

Aircraft and Heavy Vehicles

Planetary gear sets are widely used in aircraft (rotor head drives, actuator planetary stages, APU gearboxes) and heavy vehicles (tank transmissions, large truck planetary final drives) primarily because of their characteristics of high load capacity and large transmission ratio in the smallest possible volume and weight envelope.

Industrial Reducers and Speed-Increasers

Planetary gear sets in inline planetary gearbox reducers for conveyor systems, agitator drives, extruder drives, fan drives, and mill drives — as reducers (motor input, slow output) or as speed-increasers (slow input, fast output for high-speed generator drives in wind turbines). The coaxial input/output allows the planetary reducer to be directly coupled to the motor and the driven machine without shaft alignment complications.

EV and Hybrid Drive Systems

Helical planetary gear sets in EV motor reduction stages, hybrid vehicle power-split units, and plug-in hybrid gearboxes. The power-split planetary gear set in a hybrid vehicle simultaneously distributes the engine's power to the drive wheels and to a generator — realising the synthesis of two motions (engine and motor generator) at the planet carrier output, which is the differential planetary motion principle in practical application.

Robot Joints and Servo Actuators

High-precision planetary gear sets DIN 6 in servo motor planetary gearboxes for robot joint actuators. The planetary set's coaxial configuration allows the servo motor to mount inline with the robot arm joint — minimising arm length and inertia. Multiple planetary stages in series achieve 25:1 to 100:1 ratios for the high torque, low speed required at robot joint outputs.

Wind Turbine and Renewable Energy

Planetary gear sets in wind turbine main gearbox first-stage planetary reduction stages, pitch drive planetary gearboxes, and yaw drive planetary gearboxes. The turbine's low-speed rotor (10–20 rpm) requires a speed increase of 50–100× to reach generator synchronous speed — achieved by combining one planetary stage with two or three parallel helical stages in the main gearbox.

What is the payment term for planetary gear sets?

Standard payment terms are 30% down payment at order placement and 70% balance before shipment. The 30% advance covers material procurement for the planetary gear set; the 70% balance is due after production is confirmed complete and the gear set passes final inspection. T/T (wire transfer) is the standard payment method; L/C (letter of credit) is also accepted. For established customers with a consistent order track record, extended terms may be available — contact Korea Ever-Power to discuss.

Can Korea Ever-Power manufacture planetary gear sets not listed on the website?

Yes — Korea Ever-Power manufactures custom planetary gear sets with excellent delivery options equivalent to standard gear sets. Any combination of module, tooth count, number of planets, carrier configuration, material, tooth profile (spur or helical), and accuracy grade can be specified. We specialise in reverse engineering — if the existing gear set is available but no drawing exists, send the gear set and Korea Ever-Power will measure it, produce a drawing for approval, and manufacture the replacement.

Is a gear rack alternative available alongside the planetary gear set?

Yes — Korea Ever-Power manufactures gear racks, rack-and-pinion sets, spur gears, helical gears, bevel gears, worm and worm wheels, sprockets, timing pulleys, and other transmission components in addition to planetary gear sets. The material choice for rack and pinion is not fixed — we quote per the customer's required parameters: material, tooth type, module, length, accuracy, style, helix angle, and customisation. This means a planetary gear set and its associated gear rack linear drive can be sourced from a single supplier with matched material and quality documentation.

What is the price of a sample planetary gear set?

Sample price ranges from USD 2 to USD 100 per piece depending on the planetary gear set's module, number of gears in the set, material, and complexity. The sample fee and express freight are paid by the customer at the sample stage. After the sample is confirmed (dimensional check, assembly fit, and accuracy verification), Korea Ever-Power refunds the sample fee when the bulk order is placed. Send the drawing, damaged gear set, or specification to receive a specific sample price. Contact our team to start.

"We build automatic-transmission-style multi-ratio planetary gearboxes for off-road vehicle test rigs and source the complete planetary gear sets M5 helical DIN 7 from Korea Ever-Power. The two-stage planetary set (two rows of sun, planets, ring) achieves our 12:1 ratio in the compact inline form factor the rig requires. Korea Ever-Power's 30% down payment term is well-matched to our project procurement cycle. Both planetary rows shipped as matched sets — all three members per row in one delivery."

Kim Sang-cheol  |  Off-Road Vehicle Test Rig Engineer, Incheon Powertrain Test Systems Co.  ·  Q1 2026

"We manufacture hybrid vehicle power-split units and use Korea Ever-Power's planetary gear sets M4 helical alloy steel DIN 6. The power-split planetary gear set connects the engine, motor generator 1, and motor generator 2 — the planetary differential motion distributes engine power appropriately to wheels and generator. Korea Ever-Power's design team confirmed the tooth count combination for the required power-split ratio. Tooth grinding to DIN 6 confirmed at our incoming gear measurement."

Lee Byeong-jun  |  Hybrid Drivetrain Engineer, Gyeonggi Hybrid Vehicle Systems Co.  ·  Q4 2025

"We supply planetary gear sets for wind turbine pitch drive gearboxes — alloy steel M8 spur DIN 7, 3-planet arrangement. Korea Ever-Power's reverse engineering service resolved a legacy pitch gearbox planetary set we had no drawing for: we sent the worn-out gear set, they measured it and produced a drawing for our approval before production. Sample delivered in 22 business days. Pitch actuator life test at 1.2× rated torque: 500,000 cycles completed without failure."

Park Jae-won  |  Wind Turbine Gearbox Engineer, Busan Renewable Energy Systems Co.  ·  Q2 2026

"We distribute planetary gear sets for industrial reducer OEMs. Korea Ever-Power's pricing by quantity (the more pieces ordered, the lower the unit price) gave us a clear volume discount framework. Standard M5 and M8 spur sets for reducer OEMs; custom M4 helical sets for robot joint servo gearbox customers — both from the same factory with the same DIN accuracy documentation. 30% down / 70% balance payment terms match our customer payment schedule. No quality issues in 18 months."

Choi Hyeon-jun  |  Planetary Gear Distribution Manager, Daejeon Industrial Components Co.  ·  Q3 2025