Introduction: This guide explains what a parallel shaft helical geared motor is, how its parallel input and output shafts are arranged, and how that layout fits around the driven shaft.
A geared motor is an electric motor combined with a gear reducer and supplied as one unit, so the output turns far slower and with far more torque than the motor shaft itself. What separates one type from another is not the motor or the ratio, but where the output shaft sits relative to the input. In a parallel shaft helical geared motor, those two shafts run on parallel axes, offset by a fixed center distance. That single geometric fact decides how the drive bolts onto a conveyor, a hoist drum, or a mixer, and it is the detail worth understanding before anything else.
The input shaft is the motor shaft. The output shaft is the one that turns the machine. In this category both run parallel, separated by a center distance, so the machine builder gets an output axis that sits below, beside, or above the motor axis instead of directly behind it. Power moves from the input through one or more pairs of helical gears mounted on those parallel axes, and each reduction stage adds to the offset between the two shafts. The result is a drive with a defined center height and a known pocket of space it occupies, which is exactly the information a designer needs when laying out a frame. That offset is what most people actually notice on a machine. On a belt conveyor, the output shaft drives the head pulley and the drive has to stay inside the frame width, so a parallel layout lets the motor body sit above or beside the pulley shaft rather than trailing behind it. On a hoisting drum the same logic applies in reverse, with the motor sitting alongside the drum shaft instead of projecting past it. The published FC range shows how widely that geometry scales: FC37 through FC157, standard torque from 180 Nm to 18,000 Nm, ratios from 4 to 205, and a standard selection table covering 0.12 kW to 160 kW. Higher figures such as 50,000 Nm and 200 kW belong to extended or custom heavy-duty configurations rather than the standard FC157 frame.
Helical gearing and parallel axes depend on each other. The tooth form determines how smoothly the load transfers from one shaft to the next, while the axis spacing determines where the housing has to grow to hold the gear pairs. Read the two together and the shape of a gearbox stops looking arbitrary.
A helical tooth is not cut straight across the gear face; it runs at an angle, so contact begins at one end of the tooth and travels across the face as the pair rotates. Instead of one tooth taking the full load at the instant of engagement, the load builds gradually and is shared across several teeth at once. That gradual transfer is the mechanical reason helical mesh runs smoother and quieter than a straight spur mesh at the same speed. Backlash, the small gap between the non-working flanks, has to exist so the teeth do not bind, and it needs to stay in a controlled range, as KHK's gear reference describes. Ground tooth flanks plus correct shaft alignment hold the contact pattern centred on the face, and quiet running comes from those two conditions working together.
Every reduction stage adds another pair of gears, and every pair adds to the center distance between input and output axes. Fewer stages give a shorter, tighter housing; more stages push the motor further from the driven shaft but reach much lower output speeds within the same frame family, which is how ratios up to 205 fit into one series. The same offset also decides how the unit is fixed to the machine: horizontal foot mounting, vertical mounting, a small flange, or a torque arm. A hollow-shaft unit slides straight onto the driven shaft and uses a torque arm to stop the housing rotating, which removes the coupling and shortens the shaft train.
Coaxial, or in-line, drives place the input and output on the same axis. The motor sits directly behind the driven shaft, so the drive train is narrow but long — convenient when there is free space at the back of the machine, awkward when there is not. Right-angle drives turn the output 90 degrees from the input, usually through a bevel or worm stage, so the motor can stand at a right angle to the driven shaft. That solves a footprint problem in tight axial space, but it introduces a different gear type with its own thrust behaviour and efficiency profile. A parallel shaft unit sits between those two: the output turns in the same direction as the input, just offset. There is no right-angle stage and no long in-line stack. On a conveyor, a right-angle unit puts the motor perpendicular to the frame and adds width, while a coaxial unit puts it behind the pulley and adds length; the parallel unit puts it alongside, which is often the only arrangement that stays inside the machine outline. The trade-off is that the offset has to be absorbed somewhere, and the housing grows to hold the gear pairs that create it. Getting that offset and the mating shaft fit right matters, because misalignment loads bearings and seals long before the gears themselves complain, a principle EASA's technical material covers in detail.
Understanding the category comes down to one idea: the input and output shafts are parallel and offset, and everything else — housing shape, mounting style, where the motor sits on the machine — follows from that offset. Helical teeth make the mesh gradual and quiet, parallel axes keep the drive compact in the direction that matters, and the choice between parallel, coaxial, and right-angle comes down to which direction has room. Anyone checking whether a specific frame fits should compare published shaft and mounting dimensions against the real space around the driven shaft; the FC series page lists those dimensions for each frame size.
A: It means the motor shaft and the output shaft run on parallel axes that are offset by a center distance. Power passes through one or more helical gear pairs between them, so the output turns in the same direction as the input but sits below, beside, or above it. That offset is what lets the drive sit alongside a conveyor pulley or hoist drum instead of behind it.
A: A right-angle gearbox turns the output 90 degrees to the input, usually through a bevel or worm stage, so the motor stands perpendicular to the driven shaft. A parallel shaft unit keeps the same direction and only offsets the axis. The right-angle version saves axial length but adds a different gear type; the parallel version keeps a simple helical train in a longer housing.
A: Yes. The FC range lists solid output shafts from 25k6 to 120m6 mm and hollow shafts with key from 30 mm to 120 mm H7. Solid shafts connect through a coupling, pulley, or flange, while a hollow shaft slides directly onto the driven shaft and is usually held with a torque arm. Which one suits depends on whether the driven shaft already exists in the machine.
Gear Backlash | KHK Gear Manufacturer
