Servo Peak Torque Looks Fine? RMS Torque Can Still Overheat It
A short peak-torque check can miss a demanding duty cycle. Evaluate the complete cycle, including acceleration, holding, deceleration, and repetition.
Original simplified duty-cycle calculation; not a complete motor-sizing procedure.
What is happening?
RMS torque weights higher torque more strongly than a simple arithmetic average. It is one part of motor thermal sizing, alongside speed, cooling, drive limits, and manufacturer-specific continuous operating curves.
Check these five things
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Break the full cycle into time and torque segments.
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Include holding and dwell conditions.
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Calculate RMS using squared torque and segment duration.
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Check peak limits separately.
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Compare the duty with the manufacturer sizing method.
Worked example
For a simplified cycle with 4 N·m for one second and zero torque for three seconds, RMS torque is the square root of 16 divided by 4, or 2 N·m. The arithmetic average is only 1 N·m, showing why averaging can mislead.
Quick diagnostic reference
| Measure | Example |
|---|---|
| Peak torque | 4 N·m |
| Arithmetic average | 1 N·m |
| RMS torque | 2 N·m |
The mistake to avoid
A passing RMS calculation alone does not establish a valid servo selection. Speed-dependent capability, regeneration, ambient conditions, and mounting also matter.
How to verify the fix
Review the complete duty in the approved sizing tool and compare operating temperatures and drive diagnostics during validated production cycles.
Field-work boundary: These are educational diagnostic guides. Use the exact equipment manuals and approved site procedures. Electrical testing and machinery changes belong to qualified, authorized personnel; control hazardous energy and validate affected functions before release.
Technical reference
Oriental Motor: Technical reference and motion sizing. The examples and diagnostic tables above are original teaching material; they do not replace the product manual.