Planetary gearbox
WITTENSTEIN alpha alpha SP+ planetary gearbox
alpha Advanced Line low-backlash coaxial planetary servo gearbox with shaft output, in standard and high-speed versions.
Key specifications
| Peak torque (max) | 5,700 Nm |
|---|---|
| Speed (max) | 9,000 rpm |
| Ratio | 3–100:1 |
| 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 · Source 2
Notes on this data
Max torque T2a 48-5700 Nm stored as torque_Nm_peak_max. Backlash <=3 arcmin standard, <=1 reduced. HIGH SPEED (MC) version: 68-3600 Nm, 7000 rpm, <=4/<=2 arcmin. Product grid lists backlash range <=1-4 arcmin. 7 sizes.
Specify Motion is not affiliated with WITTENSTEIN SE. WITTENSTEIN alpha and alpha SP+ 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.
High-rigidity Wanshsin inline planetary with three backlash classes down to super-precision, for machine tools, automation and AGVs.
| Published maximum | alpha SP+ | WSH |
|---|---|---|
| Rated torque | — | 2,400 Nm |
| Peak torque | 5,700 Nm | 7,200 Nm meets or exceeds |
| Ratio (max) | 100:1 | 100:1 meets or exceeds |
| Backlash (lower is better) | 3 arcmin | 1.5 arcmin meets or exceeds |
Wanshsin inline planetary designed for high radial loads, offered in three precision classes.
| Published maximum | alpha SP+ | WTH |
|---|---|---|
| Rated torque | — | 2,050 Nm |
| Peak torque | 5,700 Nm | 6,150 Nm meets or exceeds |
| Ratio (max) | 100:1 | 100:1 meets or exceeds |
| Backlash (lower is better) | 3 arcmin | 1.5 arcmin meets or exceeds |
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 SP+ | P-II / P-IIR |
|---|---|---|
| Rated torque | — | 459 Nm |
| Peak torque | 5,700 Nm | — |
| Ratio (max) | 100:1 | 1,000:1 meets or exceeds |
| Backlash (lower is better) | 3 arcmin | — |
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 SP+
Send these with your enquiry and an engineer can confirm the right alpha SP+ 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 SP+: frequently asked questions
What is the WITTENSTEIN alpha alpha SP+?
alpha Advanced Line low-backlash coaxial planetary servo gearbox with shaft output, in standard and high-speed versions. Published series figures include peak torque 5,700 Nm, speed 9,000 rpm, ratio 3:1, ratio 100:1. It is made by WITTENSTEIN SE; Specify Motion can help source it or propose an equivalent.
Who makes the WITTENSTEIN alpha alpha SP+?
The WITTENSTEIN alpha alpha SP+ 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 SP+?
The published series maximum peak torque is 5,700 Nm. Individual models and sizes in the alpha SP+ 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 SP+?
Yes. On published figures, Wanshsin WSH and Wanshsin WTH 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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