AC Gear Motor Configurations: Parallel-Shaft vs Right-Angle (4RK / 5GU / 6RK)

Ask ten suppliers for a “gear reducer” and you will get ten different products, because the word covers everything from a 15 W integrated gear motor on a lab instrument to a 250 kW helical-bevel industrial gear unit bolted to a mine conveyor. This guide stays inside one category: compact integrated AC gear motors in the 15 W to 3.7 kW class, where the motor and reduction gearbox share a single housing and mount as one unit.

Within that class there are only two configurations that matter for selection — parallel-shaft (inline) and right-angle — plus a handful of variations in frame size, ratio and supply. Getting the configuration right first saves more design rework than any torque calculation.

What a compact gear motor is, precisely

An integrated gear motor has four functional groups in one assembly:

• Stator and rotor — the AC induction motor, single-phase or three-phase.
• First-stage pinion — machined on the motor shaft, driving the reduction train.
• Reduction gears — one to three stages, depending on ratio.
• Output shaft and housing — solid shaft, in a die-cast or machined gearbox housing, with foot or flange mounting.

Because everything is in one housing, the unit has no coupling to align, no separate reducer to foot-mount, and one part number to stock. That is the entire commercial argument for integrated gear motors over a motor plus separate gearbox, and it is why they dominate packaging, conveying, dispensing and light automation equipment.

It also means the gearbox and motor share a thermal environment. That constraint drives much of what follows.

Configuration 1: Parallel-shaft (inline)

The motor shaft and output shaft are parallel, and the gear train is a stack of spur or helical stages. On our range this is the 4RK (25–30 W, 80 mm frame), 5RK (40–90 W) and 6RK (120–300 W) families.

Where inline wins

• Higher efficiency. A parallel-shaft stage typically runs at 95–98% per stage, against 85–92% for a right-angle bevel pair. Over three stages that difference is real heat, not just a number.
• Quieter at speed. Helical parallel stages engage gradually and are noticeably quieter than bevel gears at the same input speed.
• Longer life at the same rating, because less energy is lost in the mesh.
• Simpler shaft support, which means better overhung load capability for the same housing size.

Where inline loses

• It is long. A three-stage inline unit projects straight out from the machine, which is often impossible inside a compact enclosure.
• Output direction is fixed along the motor axis. If the machine needs the shaft to exit at 90°, inline cannot do it.

Configuration 2: Right-angle

The output shaft exits at 90° to the motor axis through a bevel or hypoid final stage. On our range this is the 4GN (25 W), 5GU (40–140 W) and 6GU (120–300 W) families.

Where right-angle wins

• Layout freedom. The motor can lie along the machine frame while the shaft drives across it — the standard solution for conveyors where the drive has to sit beside the belt rather than in front of it.
• Shorter overall length for the same ratio, which matters inside door headers, dispenser cabinets and under-bench equipment.
• Two shaft orientations are usually available (shaft left or shaft right relative to the motor), so the unit can be flipped to suit the installation.

Where right-angle loses

• Lower efficiency. Bevel and hypoid stages lose more energy than spur or helical stages, and that loss becomes heat in a shared housing.
• Higher noise at high input speed. Bevel mesh is more sensitive to speed than helical mesh.
• Not self-locking. A bevel or hypoid final stage will back-drive. If the axis must hold position on power loss, you need a brake or a mechanical stop — not a deeper ratio.

One clarification worth stating plainly: a right-angle gear motor is not the same thing as a worm gear motor. Worm drives achieve high ratios in a compact right-angle form and can be self-locking, but they run at 40–85% efficiency and are a distinct product. Right-angle bevel units are more efficient and are not self-locking. Confusing the two is the most common cause of a “the door creeps when the power goes off” complaint.

Side-by-side

Frame size: the second decision

Configuration sets the geometry; frame size sets the power. In our range the frames step cleanly:

Two things change at the 400 W boundary: the supply becomes three-phase 220V/380V as standard, and mounting becomes a genuine vertical-or-horizontal decision rather than a bracket detail. Above 3.7 kW you have left this product class entirely and are in industrial gear unit territory.

Ratio: the third decision, and the one with a ceiling

Ratio is chosen from output speed, not from a wish for more torque. On the 25 W 4RK, the catalogue runs from 3:1 (500 r/min) to 300:1 (5 r/min), and the allowable load plateaus:

Past roughly 100:1 the gearbox becomes the limit and additional ratio buys only lower speed. Anyone who needs more torque than the plateau at a given frame must change frame, not ratio.

Supply and duty: the two specs buyers forget

• Supply. Small frames run single-phase 110V/220V or three-phase 220V. Medium frames run three-phase 220V/380V. If the site is single-phase only, that caps you at the small frames — check this before the mechanical design is frozen.
• Duty. Our small AC series is rated reversible 30 min for reversing duty and continuous for one-direction running. These are thermal ratings, not torque ratings. A station that reverses continuously is not the same application as one that runs one way.

Selection order that avoids rework

1. Configuration — can the shaft exit along the motor axis, or must it turn 90°?
2. Output speed — from machine speed and transmission ratio.
3. Required torque — from load, with a 1.3–2.0 service factor.
4. Ratio — from speed, then read allowable load at that ratio.
5. Frame size — the first frame whose plateau exceeds the required torque.
6. Supply and duty — phase availability, continuous vs reversible, ambient temperature.
7. Mounting — foot, flange, shaft side, overhung load check.

FAQ

Is a parallel-shaft or right-angle gear motor better?

Parallel-shaft is more efficient, quieter and better for overhung loads. Right-angle is shorter and gives layout freedom. Choose right-angle only when the machine geometry actually needs a 90° turn — otherwise take the efficiency.

What is the difference between 4RK, 5RK and 6RK?

They are parallel-shaft series in ascending frame size and power: 4RK covers 25–30 W on an 80 mm frame, 5RK covers 40–90 W, and 6RK covers 120–300 W. The 4GN / 5GU / 6GU equivalents are the right-angle versions of the same power tiers.

Can I get a gear motor above 3.7 kW?

Not from our range. Above 3.7 kW the market moves to separate motor-and-reducer assemblies with oil lubrication and AGMA or ISO service classification — a different product category.

Does a right-angle gear motor self-lock?

No. Bevel and hypoid right-angle stages back-drive freely. Only worm gearboxes achieve self-locking, and even then only at low lead angles.

Gear Reducer Types by Power Range

Type selection usually follows the load. For light machinery up to 300W, the small AC gear reducer motors range covers 4RK, 5RK and 6RK frames; above that, the medium gear reducer motors series runs from 400W to 3700W with output shafts up to 50mm. Where the gearbox has to turn the drive through 90 degrees, the right angle gear reducer motors use a bevel configuration instead of a parallel shaft.

The small gear motor selection page compares frame sizes and ratios side by side, and the 6GU right angle gear reducer motor is a practical example of the 90-degree arrangement in the 120W–300W band.

If you want the type confirmed against a specific duty, send the details through our contact form.

Identifying Gear Reducer Type From a Nameplate

When you are replacing an existing drive rather than specifying a new one, the nameplate and type code tell you the type before you measure anything. A 4GN, 5GU or 6GU prefix indicates a right-angle (bevel) unit in our range; 4RK, 5RK or 6RK indicates a parallel-shaft unit. The number before the letters is the frame size, which scales with power.

That matters because the two types are not interchangeable in a machine: a right-angle unit changes where the output shaft exits, so the mounting face and available depth have to be checked as well. Our right angle gear reducer motors page lists the 90-degree options, and the small AC gear reducer motors page groups the parallel-shaft frames.

Gear Reducer Type by Application

Conveyors and packaging lines usually take a parallel-shaft unit where there is room along the frame, or a right-angle unit where the drive has to sit under the belt. Turntables, mixers and gate operators more often need the 90-degree exit. Above 300W, the medium gear reducer motors series uses the same logic at 400W-3700W.

Send a photo of the nameplate and the machine layout through the contact form if you want the type confirmed.