KEVOS® MAKEOS · Power Transmission
RMS Torque for a Motor Duty Cycle
What is the RMS torque of this duty cycle, and can the motor carry it continuously?
Root-mean-square (thermal) torque and peak torque over a repeating duty cycle of up to five segments, compared with a motor’s continuous and peak torque ratings.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Segment 1 | ||
| Torque | N·m | Torque in segment 1 (accelerating, for example). |
| Duration | s | Duration of segment 1. |
| Segment 2 | ||
| Torque | N·m | Torque in segment 2 (constant speed). |
| Duration | s | Duration of segment 2. |
| Segment 3 | ||
| Torque | N·m | Torque in segment 3 (decelerating, negative if braking). |
| Duration | s | Duration of segment 3. |
| Segment 4 | ||
| Torque | N·m | Torque in segment 4 (dwell, 0 if standing). |
| Duration | s | Duration of segment 4. |
| Segment 5 | ||
| Torque | N·m | Torque in segment 5 (0 if not used). |
| Duration | s | Duration of segment 5. |
| Motor | ||
| Continuous rated torque | N·m | Motor continuous (rated) torque at the operating speed. |
| Peak torque rating | N·m | Motor or drive peak torque. |
Method and formulas
- T_rms = √(Σ Tᵢ² tᵢ ÷ Σ tᵢ), including dwell time at zero torque.
- Peak = largest |Tᵢ|.
- Motor acceptable when T_rms ≤ continuous rating and peak ≤ peak rating.
- Example: the default cycle has T_rms = 5.2058 N·m and a peak of 12 N·m.
Limitations
- Torque only; speed and the motor’s thermal time constant also matter for long cycles.
- Dwell segments help cooling only if the motor is actually at zero torque.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a servo or VFD motor for an indexing or reciprocating cycle
- Check that a motor will not overheat
- Compare motion profiles
Who it is for
- Automation engineers
- Electrical engineers
What you get
- RMS torque
- Peak torque
- Utilisation of continuous and peak ratings
Interpreting the result
- Keep a margin (often 20%) below the continuous rating for ambient temperature and ageing.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2569–2580, 180–186. Topic reference; no source tables or recommended settings are reproduced.
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