Gear Ratios: i = 3, 5, 9, 10, 25
The gear ratio is the ratio between input and output speed. With a ratio of i = 5, a motor running at 1,000 rpm delivers approximately 200 rpm at the gearbox output and around five times the input torque, minus efficiency losses.
The SG Series offers reduction ratios of 3:1, 5:1, 10:1 and 25:1, as well as 9:1 on versions designed for stepper motors. Availability depends on gearbox frame size and motor compatibility.
A higher gear ratio reduces the load inertia reflected to the motor but also limits the maximum output speed.
Rated Torque and Emergency Stop Torque
When selecting an industrial planetary gearbox, rated torque is the reference value for continuous operation.
Emergency stop torque represents the maximum permissible torque under exceptional conditions, such as mechanical shocks or emergency stops, and must not be used for continuous-duty sizing.
Also check the maximum input speed (4,000–6,000 rpm for the SG Series) and the permissible radial and axial loads on the output shaft.
Backlash: Angular Play in Precision Gearboxes
Backlash, also known as angular play, is the angle through which the gearbox output shaft can rotate without transmitting motion to the input shaft. It is measured in arcmin (arcminutes).
SG Series planetary gearboxes feature backlash values of 12, 15 or 19 arcmin, depending on frame size and reduction ratio.
Low backlash is particularly important for motion axes requiring frequent direction reversals and accurate positioning.
Overall positioning accuracy also depends on mechanical couplings, bearings and motor control performance.
Planetary Gearboxes for NEMA 23 and NEMA 34 Stepper Motors
A planetary gearbox for a stepper motor is useful when an application requires lower output speeds and higher output torque. It is also beneficial when the load inertia is too high for the motor to handle directly.
SG Series gearboxes are designed for the SANYO DENKI motors specified in each product datasheet, including widely used frame sizes such as NEMA 23 and NEMA 34.
The reduction ratio also increases output positioning resolution. However, in axes performing small back-and-forth movements, backlash is often more critical than theoretical resolution.
Planetary Gearboxes for Brushless Servo Motors
In a brushless servo system, a planetary gearbox improves the ratio between load inertia and motor inertia, helping achieve more stable servo control.
For proper gearbox selection, consider acceleration torque, torsional stiffness and backlash, and match the gearbox with the appropriate SANYO DENKI servo motor and servo drive.
Plug & Go: Motor and Gearbox from a Single Supplier
With the Plug & Go solution, the motor and gearbox are supplied by a single partner, with compatibility already verified.
This means fewer product codes to manage, less mechanical adaptation work and a lower risk of assembly errors.
Simply provide the SANYO DENKI motor code, the required reduction ratio and the output torque needed for your application.
Typical Applications of Planetary Gearboxes
Planetary gearboxes are used in positioning and indexing systems, rotary tables, packaging machine axes, material handling equipment, textile machinery and industrial equipment.
In packaging applications, the gearbox matches the motor's operating speed to the required mechanism speed.
For motion axes involving rapid direction reversals, backlash, inertia and permissible loads are particularly important selection criteria.
Planetary Gearbox Selection Checklist
- Motor model
- Motor flange and shaft dimensions
- Input speed
- Required gear ratio
- Required output torque
- Frequency of direction reversals
- Radial and axial loads
- Available installation space
- Required positioning accuracy
For a complete motion axis, also consider the stepper motor drive or servo drive and the application’s motion profile.
