Inline vs right-angle planetary gearbox: Which one do you need for your servo drive?

Inline vs Right-Angle Planetary Gearbox: Key Differences and Selection Guide

When specifying a planetary gearbox for a new machine or retrofitting an existing drive system, one of the earliest and most consequential decisions is the output geometry: inline (coaxial) or right-angle. Both configurations use a planetary gear stage as the primary reduction element, but they differ fundamentally in how the output shaft is oriented relative to the input. Choosing the wrong type adds mechanical complexity, cost, and potential failure points. This guide clarifies the differences, performance trade-offs, and application scenarios for each.

What Is an Inline Planetary Gearbox?

An inline planetary gearbox — also called a coaxial planetary gearbox — is one in which the output shaft emerges from the same axis as the input shaft. The input (typically from a motor) enters one end; the reduced-speed, higher-torque output exits the opposite end on the same centerline. This is the most common configuration in servo-driven automation, robotics, and precision positioning equipment.

The coaxial arrangement is a natural result of the planetary gear architecture: sun gear, planet gears, and ring gear all share a common rotational axis, so the input and output shafts align without any additional gearing stage. This contributes to the configuration’s high mechanical efficiency — typically 97–98% per stage — because no bevel or worm gear stage is added to redirect motion.

Explore our range of inline planetary gearboxes, available in single and multi-stage configurations for servo, stepper, and direct motor mounting.

What Is a Right-Angle Planetary Gearbox?

A right-angle planetary gearbox incorporates an additional bevel gear stage (or in some designs, a spiral bevel or hypoid stage) that redirects the output shaft 90° relative to the input. The planetary stage provides the primary speed reduction; the bevel stage redirects the torque to the perpendicular output axis. Some designs place the bevel stage at the input; others place it at the output — each approach has implications for efficiency, backlash, and torsional stiffness.

Right-angle configurations are mechanically more complex and slightly less efficient than equivalent inline units (typically 90–95% total vs 94–98% for inline), but they solve a specific geometric problem that inline gearboxes cannot: changing the drive direction within a compact housing without external shafting, couplings, or redirecting mechanisms.

Performance Comparison: Inline vs Right-Angle

When to Choose an Inline Planetary Gearbox

An inline planetary gearbox is the correct choice in the following scenarios:

• Motor-coupled servo drives: When mounting directly to a servo or stepper motor flange, an inline unit provides the most compact, stiff, and efficient coupling. Most motor manufacturers publish adapter kits for inline planetary gearboxes.
• Ball screw and linear axis drives: CNC machine feed axes typically use inline planetary gearboxes between the servo motor and ball screw to provide the required speed reduction and torque multiplication while maintaining coaxial alignment.
• Rotary table and indexing drives: Precision rotary positioning applications benefit from the superior backlash and torsional stiffness of inline configurations.
• High-cycle, high-efficiency applications: When duty cycle is high and energy efficiency directly impacts operating cost, the 2–5% efficiency advantage of inline over right-angle matters across thousands of operating hours.

When to Choose a Right-Angle Planetary Gearbox

Right-angle configurations are the appropriate choice when machine geometry imposes a 90° direction change that cannot be resolved by shaft redirecting hardware:

• Cross-shaft conveyors: When a motor must drive a shaft running perpendicular to the motor axis — common in horizontal conveyor drives fed from a vertical motor shaft.
• Gantry and portal machines: Multi-axis portal systems often require perpendicular drive arrangements to minimize the machine envelope while keeping the motor within the carriage profile.
• Mixing and agitator drives: Overhead or side-mounted motor arrangements in processing equipment frequently require right-angle power transmission to a vertically or horizontally positioned agitator shaft.
• Agricultural and mobile equipment: Many farm machinery and vehicle-mounted implements use right-angle planetary drives to transfer PTO (power take-off) power to operating implements at 90°.

Motor Compatibility and Mounting Standards

Both inline and right-angle planetary gearboxes are available with standardized motor input flanges. The most common international standards are:

• IEC (International Electrotechnical Commission): IEC B5 and B14 flange standards are widely used in European and Asian servo motors and are supported by most planetary gearbox manufacturers.
• NEMA (National Electrical Manufacturers Association): NEMA 23, 34, and 42 frame sizes are common in North American servo and stepper motor applications.
• Custom or direct-mount flanges: For high-production OEM applications, custom input flanges eliminate the need for adapter plates, reducing both component count and potential misalignment.

Our EP-306 Inline Planetary Gearbox is available with multiple IEC and NEMA motor input options, providing the flexibility to mate with standard servo and stepper motors without custom machining.

Output Shaft vs Output Flange: What’s the Difference?

Regardless of inline or right-angle configuration, planetary gearboxes are available with either a round output shaft or an output flange (also called a flange output or hollow shaft output). A round shaft is the standard connection for coupling to a driven shaft via a coupling or keyway. An output flange is a rigid mounting surface with bolt holes that bolts directly to a driven component — common in rotary table drives, tire press applications, and any case where a rigid, zero-backlash mechanical connection is needed without a coupling.

Hollow shaft configurations — where the driven shaft inserts directly into the gearbox output — are particularly space-efficient in conveyor and mixer applications.