{"id":1619,"date":"2026-04-16T07:08:03","date_gmt":"2026-04-16T07:08:03","guid":{"rendered":"https:\/\/planetarygeardrive.top\/?p=1619"},"modified":"2026-04-16T07:08:03","modified_gmt":"2026-04-16T07:08:03","slug":"how-to-size-planetary-gearbox-guide","status":"publish","type":"post","link":"https:\/\/planetarygeardrive.top\/it\/application\/how-to-size-planetary-gearbox-guide\/","title":{"rendered":"How to size a planetary gearbox? Torque, speed, inertia, and service factor step by step"},"content":{"rendered":"
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Planetary Gearbox Basics<\/p>\n

Core Keyword: planetary gearbox sizing \u00a0\u00b7\u00a0 Category: planetary-gearbox-basics<\/p>\n<\/div>\n

How to Size a Planetary Gearbox: Torque, Speed, Inertia, and Service Factor Step-by-Step<\/h2>\n

Planetary gearbox sizing<\/strong> is a systematic process that begins with the load requirements and works backward through the drivetrain to identify the gearbox specifications \u2014 gear ratio, rated output torque, radial load capacity, and input speed limit \u2014 that ensure reliable long-term operation. Under-sizing a gearbox causes premature failure (bearing fatigue, tooth fracture, or housing cracks within the first 500\u20131,000 hours); over-sizing wastes money and adds unnecessary mass and inertia to the driven axis, reducing system bandwidth and acceleration capability. This guide walks through the complete sizing procedure with formulas and worked examples applicable to servo, stepper, and induction motor drives.<\/p>\n

Step 1: Define Load Torque at the Output Shaft<\/h2>\n

Start by calculating the torque required at the gearbox output shaft under the worst operating conditions. For a linear axis driven by a ball screw:<\/p>\n

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T_load = (F \u00d7 p) \/ (2\u03c0 \u00d7 \u03b7_screw)<\/p>\n

Where: F = axial force (N), p = ball screw lead (m), \u03b7_screw = ball screw efficiency (typically 0.85\u20130.95)<\/p>\n<\/div>\n

For a rotary load (conveyor drum, turntable, roller): T_load = J_load \u00d7 \u03b1 + T_friction, where \u03b1 is angular acceleration (rad\/s\u00b2) and T_friction includes all friction losses at the output (bearing drag, seal drag, gear mesh losses if any).<\/p>\n

For gravity-loaded vertical axes, include the static holding torque required to prevent the axis from back-driving when the motor is powered off: T_static = (m \u00d7 g \u00d7 p) \/ (2\u03c0 \u00d7 \u03b7_screw). This value must be less than the gearbox output shaft static torque rating, and the motor brake (if used) must be sized to hold this torque.<\/p>\n

Step 2: Apply the Service Factor<\/h2>\n

The required output torque calculated from load analysis should be multiplied by a service factor (SF)<\/strong> to account for shock loads, startup transients, vibration, ambient temperature, and safety margin. Service factors for planetary gearboxes typically range:<\/p>\n