Peak and RMS Torque: Separate Acceleration Demand from Sustained Motor Duty

Preserve torque and duration by segment

Kollmorgen's RMS-torque explanation keeps each motion segment's torque and duration in the calculation. Peak demand and the duty-based RMS quantity are separate checks. Primary reference: Kollmorgen RMS torque.

Build the complete defined cycle, including relevant acceleration, movement, deceleration and dwell states. An omitted loaded dwell can change the modeled duty. The calculation's applicability still needs the actual motor, speed and thermal basis; the summary is not a universal motor-capacity approval.

A hypothetical two-segment duty

Assume a fictional cycle requires 4 N·m for 1 second and 1 N·m for 3 seconds. The simple time-weighted model gives √[(4²×1 +1²×3)/4], about 2.18 N·m, while the peak is 4 N·m. An arithmetic torque average would be 1.75 N·m and is not the same RMS result.

Make columns for segment, torque, duration, squared-torque contribution and model assumptions. The values are teaching inputs, not an HM motion record or a rated current. They specify no acceptable peak duration, motor size or thermal margin.

Keep both requirements in the offer review

Ask how the proposed motor and drive satisfy the actual peak and sustained conditions across the relevant speeds. A favorable RMS number does not remove the need to represent the transient demand, and a peak rating alone does not establish the complete cyclic duty.

When dwell time or motion profile changes, preserve the changed cycle in the sizing record. The guide helps a buyer interpret the two quantities without copying a manufacturer's motion example, promising a temperature rise or converting one simple RMS calculation into a complete motor-and-drive selection.

Customer Questions

Primary References

These references support the technical principles discussed in this guide. The worked examples and review questions are educational.

• Primary reference: Kollmorgen RMS torque