Parallel-Shaft vs Right-Angle Gear Motor: Which Fits Your Machine

Choosing between a parallel-shaft drive and a right angle gear motor looks like a preference. It is actually a constraint. The shaft direction decides whether the drive can be mounted at all, and the gear type behind that 90-degree turn decides what it costs you in efficiency, torque and holding behaviour. Get the direction right and the rest follows; get it wrong and the machine needs a second reduction stage to compensate.

This comparison is written from published data for the two families in this range: the inline 4RK, 5RK and 6RK units, and the right-angle 4GN, 5GU and 6GU units that share the same motors with a bevel gearbox in front. It covers where the two really differ, where they do not, and the assumption that trips up most first-time buyers.

The only structural difference: shaft direction

An inline, or parallel-shaft, gear motor keeps the motor shaft and the output shaft parallel. Power goes straight through a train of spur or helical gears, so the whole assembly is long and narrow. A right-angle gear motor turns the power through 90 degrees, so the motor body can sit beside the driven shaft instead of behind it.

That single change has three consequences that matter to a machine designer. The assembly length along the driven shaft drops dramatically, which is usually the reason the right-angle version exists. The motor can be tucked under, beside or behind a frame instead of projecting from it. And the housing becomes deeper in the direction perpendicular to the output shaft, so the drive is compact in one axis and larger in another.

The efficiency row is where most online comparisons go wrong. They quote 60–85% for right-angle drives, because they are describing a worm gearbox. A worm drive is a right-angle gearbox, but not every right-angle gearbox is a worm. Our right-angle units use a bevel pair, which keeps efficiency in the low 90s — close enough to inline that efficiency alone is a poor reason to reject a right-angle layout.

Does a right angle cost you torque? Usually not

This is the second assumption worth testing with real numbers. Because the 4GN, 5GU and 6GU units use the same motors as their inline counterparts, the allowable load tables can be compared directly at the shaft.

At 25W the two tables are identical line for line — the right-angle gearbox carries exactly the same load as the inline one on the same 80 mm frame. At 120W the right-angle unit actually carries more at high ratios, because its 100 mm frame housing is deeper and takes a wider gear set than the 90 mm inline gearbox, which tops out at 19.6 N·m. So the widespread belief that “right angle means less torque” is not supported by the data in this range. It costs length in a different axis, some efficiency, and money — not load capacity.

The assumption that causes real damage: self-locking

Right-angle units are widely assumed to hold their load when power is removed, because worm gearboxes have that property. A bevel gear train does not. It is a rolling contact between two cone-shaped gears with no sliding wedge to lock the mesh, so a right-angle bevel gear motor will back-drive under an unbalanced load exactly as an inline unit will.

On a horizontal conveyor this never matters. On a vertical lift, a hoist, an inclined gate or a barrier arm it matters completely: the load will run down when the motor stops unless something else holds it. The correct solutions are a mechanical brake motor, a service brake on the drive shaft, or a counterbalance that leaves the load in equilibrium. Not a bigger right-angle gearbox, and not a higher ratio — ratio changes speed, not the ability to hold.

If holding is a requirement, say so at the specification stage, because a brake is a factory option rather than a field addition on most of these frames.

When the machine forces a right angle

Three situations genuinely require a 90-degree output, and they are all mechanical rather than electrical.

• The driven shaft is perpendicular to the available motor space. A roller conveyor driven from the side, a door or gate operator with the motor inside a narrow head frame, or a machine where the drive must sit within the base footprint.
• Assembly length is the binding constraint. If the drive cannot project along the shaft axis — because the machine is up against a wall, a column or another module — no inline unit will fit regardless of power.
• The motor must stay inside an enclosure. A right-angle arrangement lets the motor body sit parallel to the panel instead of protruding through it.

Swing and sliding door operators are the classic example: the motor sits inside the head frame and the output drives a vertical spindle through a 90-degree gearbox. The swing door gear motor guide covers that geometry, including the holding requirement that a bevel drive does not provide.

When inline is the better answer

If the driven shaft is parallel to the mounting surface and there is room along it, the inline unit wins on three counts. It is cheaper at equal power because the gear train has fewer parts. It is more efficient, which matters on a drive that runs eight hours a day. And its housing is narrow, which suits conveyor frames and roller drives where the gear motor sits inside the frame profile.

Inline is also the simpler choice for high-ratio applications within the small frames. A 90 mm inline 5RK unit reaches 500:1 on the standard gearbox; the right-angle families in this range are typically specified to lower maximum ratios. Where an application needs very slow output, check the published ratio range for the exact model rather than assuming both families match.

Matching the right-angle family to your power

The right-angle range is organised by motor frame, which makes the selection straightforward once the power class is fixed.

• 4GN, 25–30W, 80 mm frame. Rated torque 154–220 mN·m at 1250–1550 r/min, allowable load up to 7.84 N·m. Suits door operators, dampers, small diverters and light indexing. See the 4GN right-angle 25W gear motor.
• 5GU, 40–140W, 90 mm frame. Rated torque from 246 mN·m upward, allowable load to roughly 9.8 N·m on the 40W row and 19.6 N·m on the 60W row. Suits side-drive conveyors, packaging stations and gate drives. See the 5GU right-angle gear motor.
• 6GU, 120–300W, 100 mm frame. Rated torque 740–1840 mN·m, allowable load up to 43 N·m at the top of the range. Suits heavier side drives, mixers with vertical shafts, and gates that must move a real leaf weight. See the 6GU right-angle gear motor.

If the inline arrangement is possible, the equivalent power exists on the small AC gear reducer motor range, where the same motors are offered with spur and helical gearboxes. Frame dimensions for both families are compared in the gear motor size chart.

Deciding in five steps

1. Draw the driven shaft. Its direction and position determine the configuration. Everything else is secondary.
2. Measure the three clearances — along the shaft axis, perpendicular to it, and vertically. Whichever is tightest eliminates one of the two families.
3. Fix output speed and read the ratio from that. Then read the allowable load at that ratio from the correct table for the family you are considering; do not carry a figure across from the other family.
4. Check holding. If the load can move when power is off, specify a brake. A bevel right-angle unit will back-drive exactly as an inline one does.
5. Check efficiency cost. If the drive runs continuously and energy matters, put a number on the 3–5 point efficiency difference before accepting the right-angle layout for space reasons alone.

The ratio arithmetic is the same for both families and is set out in how to calculate gear ratio, with the wider family taxonomy in types of gear motors.

Five mistakes in configuration selection

1. Assuming right angle means self-locking. True for worm gearboxes, false for bevel units. This is the mistake that drops loads.
2. Assuming right angle means less torque. At 25W the allowable load tables are identical; at 120W the right-angle 100 mm frame carries more.
3. Using a right angle to solve a clearance problem by adding a chain drive instead. A second reduction adds cost, backlash and a maintenance point to avoid ordering the correct configuration.
4. Comparing model numbers across families. A 4RK and a 4GN are not the same drive rotated; the gearboxes are different and the load tables must be read separately.
5. Choosing on power alone. Two 120W drives at different ratios differ by more than 4× in output torque.

What to send for a configuration quotation

Send the direction of the driven shaft and the three available clearances, the mounting face and bolt pattern, required output speed in r/min, load torque or mass and radius, duty cycle including reversing, and whether the load must be held with power off. With those, the configuration question answers itself before the ratio is even discussed.

The 4GN 25W right-angle unit is the smallest frame in the range and the quickest way to confirm dimensions against a tight layout.

FAQ

Does a right-angle gear motor lose torque compared with an inline one?

Not in this range. At 25W the 4GN and 4RK allowable load tables are identical line for line. At 120W the right-angle 6GU on a 100 mm frame carries up to 31 N·m at 50:1 against a 19.6 N·m ceiling on the 90 mm inline gearbox.

Is a right-angle gear motor self-locking?

Not if it uses a bevel gear pair, which is what the 4GN, 5GU and 6GU units use. Bevel drives back-drive under an unbalanced load. If the load must hold with power off, specify a brake motor.

Which is more efficient, right angle or inline?

Inline is slightly more efficient, typically 95% or more per stage against roughly 90–94% for a bevel right-angle stage. The large 60–85% figures often quoted for right-angle drives refer to worm gearboxes, not bevel ones.

Can I mount an inline gear motor vertically instead of buying a right-angle unit?

Only if the driven shaft is vertical. If the driven shaft is horizontal and you simply need the motor out of the way, an inline unit cannot deliver a horizontal output from a vertical motor axis — that geometry requires a right-angle gearbox.

Why is a right-angle gear motor more expensive?

The bevel gear set needs a second precision mesh, a deeper housing and more machining than a parallel gear train, so cost is higher at equal power. The premium buys layout flexibility, not extra output torque.

Do both families use the same motors?

Yes. The 4GN uses the same 4RK 80 mm motors as the inline 25W units, the 5GU uses the 5RK 90 mm motors, and the 6GU uses the 6RK 100 mm motors. Only the gearbox and output arrangement change.

Bottom line

Choose the configuration from the direction of the driven shaft and the tightest of your three clearances, then read the allowable load from the correct table for that family. Expect to pay a little more and lose a few points of efficiency for a right angle, but not to lose torque. And never assume a 90-degree gearbox holds its load — bevel units back-drive, so anything that must stay put with the power off needs a brake.