Automation & Control
Servo Motor & Drive Sizing
Calculate required servo motor torque and power for a positioning application, including acceleration, friction and gravity components.
Units:
The RMS torque (for thermal sizing) is usually 60–70% of the peak torque. Size the motor so continuous RMS torque ≤ 80% of rated motor torque, and peak torque ≤ 300% of rated (typical servo peak factor). Also check that the drive can supply the peak current.
T_accel = J_total × α | T_total = T_accel + T_friction + T_gravity | T_rms = √(ΣT²×t / t_cycle)
Input
Load inertia J_load iMoment of inertia of the load referred to the motor shaft in kg·m². For linear loads: J = m × (pitch/2π)².
kg·m²
Motor rotor inertia J_motor iRotor inertia from motor datasheet in kg·m². Good match: J_load / J_motor < 5–10.
kg·m²
Acceleration time t_a iTime to accelerate from 0 to target speed in seconds.
s
Target speed n iRequired shaft speed at the motor in rpm.
rpm
Friction torque T_f iConstant friction and load torque during motion in N·m.
N·m
Total cycle time iTotal repetition cycle time including dwell in seconds.
s
Result
Total inertia J_total [kg·m²]
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Inertia ratio J_load/J_motor
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Acceleration torque T_a [N·m]
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Peak torque T_peak [N·m]
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RMS torque T_rms [N·m]
—
Required power P [kW]
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Inertia match rating
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