1. Core Structure & Advantages of Planetary Gearboxes

A planetary drive consists of sun gear, multiple planet gears, internal ring gear and planet carrier. Load is evenly shared by planet gears, bringing three core strengths vs worm/parallel shaft reducers:

• High torque density: 2–3 times higher load capacity under the same volume, ideal for lightweight robot joints.
• High efficiency: Single-stage ≥96%, two-stage ≥94%, three-stage ≥92%, low heat loss for long-time operation.
• Coaxial compact layout: Directly matched with standard servo motors to save installation space.

Speed ratio range:

• Single-stage: 3–10 (4–8 for best rigidity & efficiency)
• Two-stage: 10–100
• Three-stage: 100–200

2. Seven Mandatory Selection Parameters

2.1 Output Torque (Most Critical Index)

Two torque values must be calculated separately to avoid overload damage:

• Continuous rated torque: For stable constant-speed running, safety factor 1.2–1.5
• Peak shock torque: For startup, emergency stop & reverse rotation, safety factor 1.8–2.5; heavy impact machinery adopts 2.0–2.8

Calculation rule: Reducer rated torque ≥ Actual load torque × safety factor

Common mistake: Only calculate rated torque and ignore instantaneous impact torque.

2.2 Gear Ratio & Servo Inertia Matching • Ratio formula: i = Motor input speed ÷ Target output speed
• Max allowable input speed: ≤6000 rpm, overspeeding accelerates wear and heat
• Servo inertia standard: Reflected load inertia / motor rotor inertia ≤ 5:1, optimal range 1–3:1

Excessive inertia ratio causes system jitter and inaccurate positioning.

2.3 Backlash Precision Classification (Unit: arcmin)

Backlash decides reverse positioning accuracy; higher precision brings higher cost:

• Economy standard: 8–15 arcmin | Conveyors, general packaging machines (unidirectional drive)
• Medium precision: 3–8 arcmin | CNC equipment, automation linear modules, general manipulators
• High precision: 1–3 arcmin | Industrial robot joints, precision manipulators, laser processing equipment
• Ultra-high precision: ≤1 arcmin | Collaborative robot joints, semiconductor equipment, medical devices

Note: ≤1 arcmin ultra-low backlash is achievable through specialized gear grinding and measurement processes. Not all manufacturers can deliver this consistently — it requires dedicated precision gear machining capability and strict quality control.

2.4 Torsional Rigidity & Anti-Impact Capacity

Helical-tooth high-rigidity models adopt thickened planet carriers and roller bearings, minimizing shaft deformation under frequent forward/reverse rotation.
Mandatory for stamping, heavy handling equipment with continuous impact loads.

2.5 Input & Output Mounting Interface

• Input flange: Standard servo frame 40/60/80/90/110/130, confirm shaft diameter & keyway size
• Output form: Solid shaft (coupling connection), hollow shaft (ball screw & robot cable routing), flange output
• Layout type: In-line coaxial reducer, right-angle offset reducer for narrow installation space

2.6 Thermal Continuous Torque for 24h Continuous Operation

For non-stop production lines, only mechanical torque is not enough. Long-term full load will overheat lubricant and damage gears. Add an extra 1.2 thermal safety factor for high-temperature workshops.

2.7 IP Protection Grade

• IP65: Standard workshop, dust & cutting fluid splash resistance
• IP67: Outdoor, high humidity, corrosive working environment, matched with low-temperature lubricating grease

3. Industry Matching Recommendation

• Collaborative & Industrial Robots: 3-stage ultra-precision hollow shaft gearbox, backlash ≤3 arcmin, ratio 50–120
• CNC & Laser Cutting Machines: Two-stage medium precision helical reducer, low vibration, max input speed 6000rpm
• Packaging & Conveying Lines: Single-stage economical model, cost-effective for stable low-impact operation
• Construction & Heavy Handling Machinery: Multi-stage reinforced heavy-duty series, carburized quenched thick gears
• Semiconductor & Medical Devices: Mini ultra-precision gearbox, low oil precipitation, minimum 2 arcmin backlash

4. Top 5 Selection Mistakes to Avoid

1. Neglect peak shock torque → broken gears under frequent start-stop
2. Blindly pursue ultra-low backlash for simple transmission → unnecessary cost increase
3. Ignore servo inertia matching → equipment vibration & positioning deviation
4. Poor installation coaxiality (eccentricity > 0.05mm) → rapid bearing abrasion
5. Skip thermal torque verification for continuous duty → oil leakage & short service life

5. Standard Selection Workflow

Here is our workflow

1. Collect working data: load weight, speed, start-stop frequency, daily running hours, impact strength
2. Calculate rated & peak torque with corresponding safety factor
3. Confirm gear ratio, check speed limit & inertia matching
4. Select backlash precision class based on positioning requirement
5. Match mounting flange, output shaft & space dimension
6. Verify thermal capacity & environmental IP grade
7. Complete sample test & parameter confirmation before bulk order

We produce standard & custom planetary gear reducers with DIN5/DIN6 precision gear processing across two manufacturing bases. We support torque simulation calculation, drawing customization and one-stop technical selection service.

Share your equipment parameters, load conditions and accuracy requirements — our engineering team will send you a tailored solution.