Electric Motors for Bevel Helical Gearboxes

The electric motor for a bevel helical gearbox is selected according to the flange or shaft at the gearbox input and according to the power worked out from the output torque and output speed the machine needs. These gearboxes turn the motion through 90° and are clearly more efficient than worm right-angle gearboxes; for the same output work, a motor one size smaller is often enough. The motor usually sits on the IEC input of the gearbox with a B5 flange; a B14 flange is also seen on small frames, and a coupled B3 foot-mounted motor on large industrial units.

DRG Motor does not sell gearboxes; it supplies the three-phase electric motor to be connected to your bevel helical gearbox. This page explains the gearbox side briefly so that you choose the right motor, and keeps the focus on the motor. You will find every suitable model in our Buy Electric Motors Online shop.

What does a bevel helical gearbox change for the motor?

The input stage of the gearbox holds a spiral bevel gear pair; the motion turns through 90° there, and the speed is then reduced in helical stages. As a result the motor axis is perpendicular to the output shaft. This allows the motor to be placed beside the machine, parallel to a conveyor frame or in a narrow space. One industrial gearbox catalogue offers both parallel shaft and right-angle (bevel helical) housings of the same series in two, three and four stages.

Why is the efficiency high?

In bevel and helical gears the tooth flanks mainly roll against each other. In a worm drive there is significant sliding friction between worm and wheel, and this friction turns into heat. A gearbox maker's handbook puts bevel helical efficiency at 0.94 with three stages and 0.98 with one; the same handbook notes that sliding friction is high in a worm stage and that efficiency can even fall below 0.5 as the ratio increases.

No self-locking

Being highly efficient, a bevel helical gearbox can be back-driven by load coming from the output. On an inclined conveyor or a lifting duty the load can turn the motor backwards, so a backstop or brake is required. A backstop can be built into the IEC motor adapter itself, which one catalogue offers as a separate variant. The DRG range does not include brake motors, so raise this with us before ordering.

A smaller motor for the same job: comparison with a worm drive

Suppose a mixer output shaft requires 3 kW at about 24 rpm. With a 4-pole motor the ratio needed is about 60; the output torque is 9550 × 3 / 24.2 ≈ 1,186 Nm.

The worm value is the dynamic efficiency given in a worm gearbox catalogue for a mid-size housing at ratio 60 and 1400 rpm input; in the same catalogue the value drops below 0.6 on small housings. Another catalogue states that during the running-in period of a new worm gearbox the efficiency is a few points lower again.

The difference is not only kilowatts. The 4 kW DRG-112M-4 has a 112M frame, a 28 mm shaft and a 250 mm B5 flange; the 5.5 kW DRG-132S-4 has a 132S frame, a 38 mm shaft and a 300 mm flange. So when you convert an existing worm drive to a bevel helical gearbox, the motor's power, frame, flange and shaft may all change together; if you plan to fit the old motor to the new gearbox, check the input dimensions first.

Ways of connecting the motor to a bevel helical gearbox

IEC adapter input (B5 or B14)

On most compact bevel helical gearboxes the input is an IEC motor adapter. In one catalogue the adapter range spans IEC frames 63 up to 280; each adapter carries the motor frame number in its name, and torque passes through an elastic spider coupling. The same catalogue lists B5 flange and B14 flange output versions of the bevel helical housings under separate codes. When the IEC input on the gearbox and the motor's flange and shaft are of one and the same frame size, they normally mate; a quick dimension check before ordering is still worthwhile.

Coupled input and fluid coupling

On large industrial housings the motor stands on the same baseplate as the gearbox and is connected to the input shaft by a flexible coupling; here the motor is B3 foot-mounted. For machines that start with heavy inertia, one manufacturer recommends an adapter with a hydrodynamic fluid coupling between motor and gearbox and states that 4-pole or 2-pole motors are preferred. The same manufacturer offers ready units combining a bevel helical gearbox, fluid coupling and motor on a single swing base for belt conveyors and bucket elevators.

Click to see current electric motor prices and order nowSEE PRICES →

Mounting in tight spaces and terminal box orientation

A bevel helical gearbox is often chosen because space is short, so the motor's terminal box is the point that most often causes trouble.

Terminal box position

One manufacturer's catalogue numbers the terminal box positions 0°, 90°, 180° and 270°, looking at the motor from its fan end; it states that the 0° position is supplied unless specified otherwise, and that in the 90° (bottom) position you should check whether the motor needs support. In a bevel helical drive the motor usually runs parallel to a conveyor frame or a wall, so if the box ends up on the wrong side the cable entry is blocked. Note which way the box faces on the old motor and state it in your order.

Mounting position and vertical motor

The same catalogue distinguishes six gearbox mounting positions, M1–M6. In some positions the motor stays horizontal; in others it stands vertically above or below the gearbox. If the motor is on top with the shaft pointing down, a V1 variant is required; if it is below with the shaft pointing up, a V3 variant. The DRG catalogue covers B3, B5, B14, B34 and B35 mounting types, plus V1/V3/V5/V6/V15 vertical variants depending on frame. Take the exact position from the gearbox manufacturer's mounting position drawing; for a vertical motor, also think about rain and dust at the fan cover end.

B5 flange dimensions: summary from the DRG catalogue

B5 (large flange) dimensions for frames 63–132, the sizes most often met on bevel helical gearboxes:

B14 small-flange motors are also available. Our catalogue does not list B14 dimensions, so none are given on this page; instead, we check the B14 flange against your gearbox input when you order. For motor drawings open the technical drawings section; flange selection is detailed in the article on flange motors for gearboxes.

Ratio, speed and service factor

Bevel helical gearbox catalogue values are usually given for 4-pole motor speed. In the selection example of an industrial catalogue, the ratio for a 1450 rpm motor and 65 rpm output is calculated as 1450 / 65 ≈ 22.3 and the nearest standard ratio, 22:1, is selected. The same catalogue gives a service factor of 1.00 for uniform load with an electric motor drive running 3–10 hours a day, 1.25 for moderate shock and 1.75 for heavy shock; for more than 10 hours a day these become 1.25 / 1.50 / 2.00.

• A 6-pole motor (about 1000 rpm) at the same ratio lowers the output speed by one third and raises the torque in the same proportion; the gearbox must be checked accordingly.
• A 2-pole motor (about 3000 rpm) increases noise at the bevel stage and can go beyond the permitted gearbox input speed; use it only if the gearbox catalogue lists ratings at this speed.
• We have no 750 rpm (8-pole) motor; where that speed is needed, the ratio has to be chosen again around a 4- or 6-pole motor.

The gearbox output speed and torque calculator returns ratio and output torque; the torque–service factor relationship is covered separately in the article on motor and gearbox selection.

Checklist before ordering

• Input frame number on the gearbox nameplate (e.g. "IEC 112") and the ratio.
• Power, speed, voltage and mounting type of the old motor; a new power calculation if an existing worm drive is being replaced.
• Flange type and dimensions: P/M/N for B5, measured flange values for B14; shaft D×E and key.
• Mounting position (M1–M6) and whether the motor will stand horizontal or vertical.
• Terminal box orientation and cable entry side.
• Starting: is there a loaded start, and how many per hour? If needed, see the star-delta and other starting methods page.
• Need for a backstop or brake.

DRG motors suitable for bevel helical gearboxes

DRG Motor is a manufacturer, supplier and seller of electric motors. Our range covers three-phase motors at 1000, 1500 and 3000 rpm synchronous speed, 0.25–11 kW in aluminium frames and 0.55–355 kW in cast iron frames; 230/400 V or 400/690 V windings and B3/B5/B14/B35 mounting are specified in the order note. The 4-pole small and medium ratings most used on bevel helical gearboxes:

The current price of these motors comes live from the shop:

DRG MOTOR motors are guaranteed against material and manufacturing defects for 2 years from the date of delivery (warranty certificate). What to check on the gearbox side when replacing only the motor is described in the article on motor replacement with a sound gearbox.

Motors in this power range

• DRG-90S-4 – 1.1 kW – 1445 rpm – 90S cast iron
• DRG-100L2-4 – 3 kW – 1450 rpm – 100L cast iron
• DRG-112M-4 – 4 kW – 1450 rpm – 112M cast iron
• DRG-132S-4 – 5.5 kW – 1460 rpm – 132S cast iron
• DRG-160L-4 – 15 kW – 1465 rpm – 160L cast iron

Click to see current prices and order these motors nowSEE PRICES →

Bevel helical gearbox motor: frequently asked questions

Can the motor of a worm gearbox be fitted to a bevel helical gearbox?

It can if the input frame number and flange are the same; but because the bevel helical gearbox is more efficient, the old motor is often larger than necessary. Recalculating the power lets both motor and gearbox run at the right load.

Is a bevel helical gearbox self-locking?

No. Because its efficiency is high, load at the output can turn the gearbox backwards. Inclined or lifting duties need a backstop or brake.

Will a 6-pole motor work on a bevel helical gearbox?

Yes, but the output speed falls by about one third and output torque increases. The gearbox torque rating must be sufficient for this increase.

How many amps does a 4 kW bevel helical gearbox motor draw?

The 4-pole DRG-112M-4 draws 7.95 A at 400 V; the overload setting follows from overload relay, fuse and contactor selection.

Send us the gearbox nameplate, the mounting position and a photo of the old motor; we will finalise the order together, including terminal box orientation. Phone +90 (542) 666 11 11, email [email protected], contact page. Bevel helical gearbox motor prices are kept up to date in Buy Electric Motors Online.