Planetary gearbox
WITTENSTEIN alpha alpha RP+ planetary gearbox
alpha Premium Line high-torque planetary gearbox with flange output aimed at rack-and-pinion and heavy axes.
Key specifications
| Peak torque (max) | 10,450 Nm |
|---|---|
| Ratio | 4–220:1 |
| Backlash (max) | 3 arcmin |
Summarised in our own words from WITTENSTEIN SE's published data; series maxima, individual models vary. Last checked 2026-10-29. Source 1
Notes on this data
Grid values: 352-10,450 Nm, backlash <=1-3 arcmin.
Specify Motion is not affiliated with WITTENSTEIN SE. WITTENSTEIN alpha and alpha RP+ 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 WITTENSTEIN alpha 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.
Apex Dynamics economy planetary family (PE, PG, PA, PS, PN, PD, PL sub-series) for high-volume automation; standard backlash, inline or right-angle.
| Published maximum | alpha RP+ | P-II / P-IIR |
|---|---|---|
| Rated torque | — | 459 Nm |
| Peak torque | 10,450 Nm | — |
| Ratio (max) | 220:1 | 1,000:1 meets or exceeds |
| Backlash (lower is better) | 3 arcmin | — |
Apex Dynamics high-precision helical planetary with a one-piece stainless planet cage and very short length; ADS adds a keyed input shaft for belt pulley or coupling drive.
| Published maximum | alpha RP+ | AD / ADR / ADS |
|---|---|---|
| Peak torque | 10,450 Nm | — |
| Ratio (max) | 220:1 | — |
| Backlash (lower is better) | 3 arcmin | 1 arcmin meets or exceeds |
High-precision round-flange planetary with high input speed capability and near-zero backlash, aimed at robotics and CNC.
| Published maximum | alpha RP+ | WAE |
|---|---|---|
| Peak torque | 10,450 Nm | — |
| Ratio (max) | 220:1 | — |
| Backlash (lower is better) | 3 arcmin | 2 arcmin meets or exceeds |
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.
What a planetary gearbox is
A planetary gearbox reduces speed and multiplies torque using a central sun gear driven by the motor, several planet gears on a carrier, and an outer ring gear. Load is shared between the planets, so the gearbox is compact, coaxial and torque-dense. A single stage typically gives ratios of about 3:1 to 10:1, and stages are combined for higher ratios. Precision servo planetaries use ground helical or spur gears, preloaded output bearings and a motor adapter flange, with backlash typically a few arcminutes or less.
When engineers choose a planetary gearbox
Choose a planetary gearbox for most servo and stepper axes that need more torque, lower reflected inertia or a better inertia match. It is efficient, typically above 95% per stage, stiff and widely available in standard frames. The trade-offs are backlash, which is low but not zero, and limited single-stage ratio. For zero backlash in a compact joint, a strain-wave gear suits better. For very high shock loads, a cycloidal reducer may be more robust.
How to specify the WITTENSTEIN alpha alpha RP+
Send these with your enquiry and an engineer can confirm the right alpha RP+ variant or an equivalent:
- Ratio and output speed (:1, rpm)
- Nominal and peak output torque (Nm)
- Emergency stop torque (Nm)
- Backlash (arcmin) and torsional stiffness (Nm/arcmin)
- Radial and axial output loads (N)
- Motor flange, shaft diameter and length (mm)
- Duty cycle, mounting orientation and lubrication
Common mistakes to avoid
- Sizing on motor torque times ratio without checking acceleration torque and service factors
- Ignoring the input speed limit at high motor speeds
- Mounting a pulley or pinion that overloads the output bearing
- Forgetting the gearbox efficiency and heat in continuous duty
WITTENSTEIN alpha alpha RP+: frequently asked questions
What is the WITTENSTEIN alpha alpha RP+?
alpha Premium Line high-torque planetary gearbox with flange output aimed at rack-and-pinion and heavy axes. Published series figures include peak torque 10,450 Nm, ratio 4:1, ratio 220:1, backlash 3 arcmin. It is made by WITTENSTEIN SE; Specify Motion can help source it or propose an equivalent.
Who makes the WITTENSTEIN alpha alpha RP+?
The WITTENSTEIN alpha alpha RP+ is made by WITTENSTEIN alpha (WITTENSTEIN SE) and is listed here for engineers comparing options. Specify Motion is not affiliated with WITTENSTEIN SE; brand names are used only to identify the product.
What is the peak torque of the WITTENSTEIN alpha alpha RP+?
The published series maximum peak torque is 10,450 Nm. Individual models and sizes in the alpha RP+ range vary, so check the exact variant against your duty cycle, mounting and environment, or ask our engineers to confirm the right size for you.
Is there an alternative to the WITTENSTEIN alpha alpha RP+?
Yes. On published figures, APEX Dynamics P-II / P-IIR and APEX Dynamics AD / ADR / ADS are the closest match from our supply network. An engineer confirms the fit against your application before recommending anything.
How do I choose a planetary gearbox ratio?
Start from the load speed and motor speed range, then check inertia matching and torque. A ratio that brings the reflected load inertia close to the motor inertia improves dynamics. Then confirm peak output torque during acceleration is within the gearbox rating and that input speed stays under the limit.
What backlash does a precision planetary gearbox have?
Precision servo planetary gearboxes typically have backlash from below one arcminute to several arcminutes, depending on grade and stages. Lower backlash costs more. For most positioning axes, a few arcminutes is fine; for robot joints or optics, strain-wave or zero-backlash designs are used.
Further reading: How to select a planetary gearbox · Harmonic vs planetary vs cycloidal · Gearboxes and harmonic drives
Other planetary gearbox series
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