{"id":620,"date":"2026-05-29T02:24:22","date_gmt":"2026-05-29T02:24:22","guid":{"rendered":"https:\/\/planetary-gearboxes.com\/?p=620"},"modified":"2026-05-29T06:12:06","modified_gmt":"2026-05-29T06:12:06","slug":"precision-planetary-gearbox-selection-guide-servo-motor","status":"publish","type":"post","link":"https:\/\/planetary-gearboxes.com\/sr\/precision-planetary-gearbox-selection-guide-servo-motor\/","title":{"rendered":"How to Select a Precision Planetary Gearbox for Servo Motor Applications"},"content":{"rendered":"
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Selection Guide \u00b7 5-Step Framework<\/div>\n

How to Select a Precision Planetary Gearbox
\nfor Servo Motor Applications<\/h1>\n

Choosing the wrong planetary gearbox costs more than the price difference \u2014 it costs positioning accuracy, motor life, and machine uptime. This five-step guide covers every parameter engineers need to match a precision planetary gearbox to a servo motor axis<\/strong>, from output torque calculation to backlash grade, inertia matching, and frame size verification.<\/p>\n

Explore the EP Precision Series \u2192
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Why the Gearbox \u2014 Not the Servo Motor \u2014 Controls Axis Accuracy<\/h2>\n
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A servo motor without a gearbox runs at 1,000\u20135,000 rpm with low output torque \u2014 far from what most industrial axes require. A planetary gearbox converts that high-speed, low-torque input into the low-speed, high-torque output the load needs, while simultaneously resolving the inertia mismatch between the compact motor rotor and the often much heavier load it must accelerate.<\/p>\n

When engineers select a precision planetary gearbox for a servo motor<\/strong> correctly, the result is a closed-loop axis with repeatable positioning, efficient energy conversion, and a service life measured in years. When they select incorrectly, three failure modes dominate:<\/p>\n

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Premature backlash growth<\/strong>
\nGearbox overshooting peak load \u2192 tooth flank wear \u2192 positioning drift within months<\/span><\/div>\n<\/div>\n
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2<\/span><\/p>\n

Servo motor thermal overload<\/strong>
\nInertia mismatch forces the motor to deliver 3\u20135\u00d7 rated current on each acceleration cycle<\/span><\/div>\n<\/div>\n
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3<\/span><\/p>\n

Axis tuning instability<\/strong>
\nHigh inertia ratio produces oscillation that no PID adjustment can fully correct<\/span><\/div>\n<\/div>\n<\/div>\n

The five-step planetary gearbox selection framework below walks through each parameter in the correct sequence \u2014 starting with torque, then ratio, then backlash grade, then inertia, and finally physical interface. Skipping steps or reversing the order is the single most common source of servo axis specification errors in Korean machine design.<\/p>\n<\/div>\n

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5-STEP SELECTION FRAMEWORK<\/p>\n

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01<\/span> Calculate output torque (T2N)<\/div>\n
02<\/span> Determine gear ratio (i)<\/div>\n
03<\/span> Select backlash grade (P0\/P1\/P2)<\/div>\n
04<\/span> Verify inertia matching (J_ratio)<\/div>\n
05<\/span> Confirm frame, flange & temp<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/section>\n

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Step 1 \u2014 Calculate the Required Output Torque<\/h2>\n
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Output torque is the first parameter to establish because it determines both the gearbox frame size and the torque rating. Two torque values matter for every axis: the continuous rated torque<\/strong> (T2N) that the gearbox handles throughout a production cycle, and the peak torque<\/strong> (T2B) occurring during acceleration and deceleration. Peak loads can reach two to three times the continuous value, and a gearbox sized only for continuous duty will suffer accelerated gear tooth wear under repeated peak loads.<\/p>\n

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OUTPUT TORQUE FORMULA<\/p>\n

T_\u0438\u0437\u043b\u0430\u0437 = T_\u043c\u043e\u0442\u043e\u0440 \u00d7 i \u00d7 \u03b7<\/div>\n
T_motor = motor rated torque (N\u00b7m)
\ni = gear ratio
\n\u03b7 = efficiency (\u22650.97 single-stage, \u22650.94 two-stage)
\nApply safety factor: 1.5\u00d7 continuous \u00b7 2.0\u00d7 shock loads<\/span><\/div>\n<\/div>\n

Worked example:<\/strong> A Korean packaging machine cross-seal jaw requires 85 N\u00b7m continuous at the jaw shaft. The servo motor delivers 8.5 N\u00b7m at rated speed. Required ratio: 85 \/ (8.5 \u00d7 0.97) \u2248 10:1. Applying a 2.5\u00d7 peak factor for jaw impact \u2192 gearbox must handle 212 N\u00b7m peak. The selected gearbox must have T2B \u2265 212 N\u00b7m at i=10.<\/p>\n<\/div>\n

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Output Torque Reference by Application Type<\/p>\n

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\u041f\u0440\u0438\u043c\u0435\u043d\u0430<\/th>\nContinuous
\n\u041e\u0431\u0440\u0442\u043d\u0438 \u043c\u043e\u043c\u0435\u043d\u0442<\/th>\n		Peak
\nFactor<\/th>\n		Min Rated
\nGearbox T2N<\/th>\n<\/tr>\n<\/thead>\n
Cobot joint (10 kg arm)<\/td>\n20\u201380 N\u00b7m<\/td>\n2.0\u00d7<\/td>\n40\u2013160 N\u00b7m<\/td>\n<\/tr>\n
CNC rotary table (general)<\/td>\n100\u2013800 N\u00b7m<\/td>\n1.5\u00d7<\/td>\n150\u20131,200 N\u00b7m<\/td>\n<\/tr>\n
Packaging cross-seal jaw<\/td>\n30\u2013150 N\u00b7m<\/td>\n2.5\u00d7<\/td>\n75\u2013375 N\u00b7m<\/td>\n<\/tr>\n
Conveyor head drive<\/td>\n50\u2013500 N\u00b7m<\/td>\n1,3\u00d7<\/td>\n65\u2013650 N\u00b7m<\/td>\n<\/tr>\n
Solar tracker azimuth axis<\/td>\n500\u20133,000 N\u00b7m<\/td>\n1.2\u00d7<\/td>\n600\u20133,600 N\u00b7m<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

Safety factors shown are starting points \u2014 always confirm with your full duty cycle analysis.<\/p>\n<\/div>\n<\/div>\n<\/section>\n

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Step 2 \u2014 Determine the Gear Ratio<\/h2>\n

The gear ratio links the motor’s speed to the required output speed. The calculation is straightforward: i = Motor rated speed (rpm) \u00f7 Required output speed (rpm)<\/strong>. A servo motor running at 3,000 rpm driving an output shaft that must rotate at 150 rpm requires a ratio of 20:1. What most engineers underestimate is how the choice of ratio stage count \u2014 single versus two-stage \u2014 affects both efficiency and the inertia seen by the motor.<\/p>\n

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i = 3\u201310<\/div>\n
Single-Stage<\/div>\n