Servo Motor Sizing – Avoid These 5 Common Mistakes

Getting the Basics Right
Selecting the wrong servo motor size is a costly error that leads to poor acceleration, overheating, or inadequate torque. Many engineers overlook the RMS torque calculation, focusing only on peak torque. For a typical pick-and-place application with Yaskawa servos, the continuous torque must cover both acceleration and deceleration phases. Also, don’t forget inertia matching—the load-to-motor inertia ratio should stay below 10:1 for stable control.

Speed and Encoder Resolution
Another pitfall is choosing a motor based solely on rated speed without considering the actual operating speed range. Panasonic servos excel in low-speed, high-precision tasks, while Mitsubishi HG series handles high-speed spindle applications better. Additionally, encoder resolution (17-bit vs. 23-bit) directly affects positioning accuracy. For robotic arms, opt for absolute encoders to avoid homing delays after power loss.

Real-World Sizing Strategy
Always use manufacturer sizing software—like Siemens SIZER or Schneider EcoStruxure Machine Advisor—to simulate your load cycle. Include friction, windage, and safety margins (typically 20%). Test the selected motor under maximum load before full deployment. When in doubt, choose one frame size larger; the slight cost premium is far less than a motor replacement during peak production.

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