Harmonic actuator
Harmonic Drive RSF servo actuators (17A/20A/25A/32A)
A compact solid-shaft servo actuator that pairs a strain wave gear with an AC servo motor and incremental encoder, for precise rotary motion without a hollow shaft.
Key specifications
| Rated torque (max) | 98 Nm |
|---|---|
| Peak torque (max) | 330 Nm |
| Supply | 200 VAC (via RTL-230-18 / REL-230-18 / HA-800-3B-200 drives) |
| Ratio | 50–100:1 |
| Backlash (max) | 0 arcmin |
| Sizes | 17, 20, 25, 32 |
Summarised in our own words from Harmonic Drive SE / Harmonic Drive LLC's published data; series maxima, individual models vary. Last checked 2026-10-29. Source 1
Notes on this data
Maxima are for RSF-32A-100: rated 98 Nm and maximum momentary 330 Nm. The page lists only rated speed (60 rpm at 50:1, 30 rpm at 100:1), so speed_rpm_max is null. 'Zero backlash' is stated; one-way accuracy is 90–120 arcsec, although the key-features text claims <1 arcmin. RSF Mini (sizes 3–14) and RSF Supermini are separate series.
Specify Motion is not affiliated with Harmonic Drive SE / Harmonic Drive LLC. Harmonic Drive and RSF servo actuators (17A/20A/25A/32A) are used only to identify the product. Comparisons use published figures; always confirm against the current datasheet.
Typical applications
Alternatives that meet or exceed these figures
Engineers often come to us with a Harmonic Drive part number and leave with an alternative that is easier to source, quicker to deliver or a better fit for the machine. These 3 series from our supply network are the closest match on published figures.
Hollow-shaft harmonic servo actuator: strain-wave gearing, motor, encoder and brake in one unit, run from a separate servo drive. Six frame sizes, from 48 VDC to 220 VAC.
| Published maximum | RSF servo actuators (17A/20A/25A/32A) | MAH |
|---|---|---|
| Peak torque | 330 Nm | 800 Nm meets or exceeds |
| Rated torque | 98 Nm | 557 Nm meets or exceeds |
| Speed | — | 125 rpm |
Large-bore version of the harmonic actuator with a frameless 16-pole motor, giving a much bigger through-hole for cabling. Two sizes.
| Published maximum | RSF servo actuators (17A/20A/25A/32A) | MAT |
|---|---|---|
| Peak torque | 330 Nm | 800 Nm meets or exceeds |
| Rated torque | 98 Nm | 557 Nm meets or exceeds |
| Speed | — | 102 rpm |
Harmonic actuator with an integrated German-made Synapticon Circulo servo drive on EtherCAT, with STO and optional FSoE functional safety.
| Published maximum | RSF servo actuators (17A/20A/25A/32A) | MGM |
|---|---|---|
| Peak torque | 330 Nm | 459 Nm meets or exceeds |
| Rated torque | 98 Nm | 267 Nm meets or exceeds |
| Speed | — | 108 rpm |
Figures are the highest published for each series and are not always measured the same way. A higher figure is not automatically a better choice: mounting, duty cycle, feedback, connectors and approvals matter too. An engineer will check the fit against your application before recommending anything.
Other harmonic actuator series
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