Driven roller conveyors: torque selection
How to select a driven roller conveyor's torque for the load: drive types, calculation, speed control and accumulation zones.
When horizontal transport, precise speed or lifting of a unit load is needed, a gravity scheme no longer works — a driven roller conveyor is required. Here the main question is not “which motor” but “which torque” to deliver to each roller. The article covers drive types and how to correctly calculate the torque for your load.
How a driven roller conveyor differs from a gravity one
A gravity roller conveyor rolls a load down an incline, a driven one moves it at a controlled speed horizontally or even upward. The rollers rotate not freely but receive torque from a motor. This delivers what a gravity scheme cannot: stable tempo, reverse, stop on command, accumulation zones with pressure control between loads. We covered the limits of the gravity scheme in the article gravity roller conveyors.
Roller drive types
The way torque is transmitted to the rollers determines the conveyor’s cost and flexibility:
- Chain drive — each roller is linked by a chain to the next. Reliable, holds high torque, suitable for heavy loads.
- Belt (poly-V) — quieter, cheaper, for medium loads.
- Round-belt drive — for light roller conveyors and accumulation zones with slip capability.
- Motor rollers (24 V) — a separate motor inside the roller, ideal for zonal accumulation and energy efficiency.
Torque calculation
The torque must overcome three components: the load’s rolling resistance, the inertia of acceleration and, where present, the lifting component. The basic logic is that the torque on the rollers multiplied by their radius must exceed the total tractive force with a 20–25% margin. Insufficient torque causes slipping and jamming under load, excessive torque means surplus cost and energy overspend.
The starting torque is calculated separately. A conveyor loaded along its whole length overcomes, at start-up, the inertia of all the loads at once — this load is noticeably higher than the running one. If the motor is selected only for the steady-state mode, it overheats already on the first start under a full mat. That is why we check the starting torque separately and provide a drive with a sufficient overload factor or with a VFD that gradually ramps up the speed.
| Load per 1 m | Drive type | Approximate torque | Speed |
|---|---|---|---|
| up to 20 kg | Round belt | 1–3 N·m | 0.1–0.4 m/s |
| 20–50 kg | Poly-V belt | 3–8 N·m | 0.1–0.5 m/s |
| 50–120 kg | Chain | 8–20 N·m | 0.1–0.5 m/s |
| over 120 kg | Reinforced chain | 20–40 N·m | 0.05–0.3 m/s |
Engineer’s tip. For accumulation zones do not take one powerful motor for the whole route. Split the conveyor into zones with motor rollers and photo sensors — loads stop without pressing on each other, and the motors of idle zones switch off, saving energy.
Speed control
If the line tempo changes or the roller conveyor joins sections of different throughput, we fit a variable frequency drive. It allows smooth speed change, provides a soft start without inrush currents and makes it possible to synchronise the conveyor with the adjacent one. For zonal schemes with motor rollers, control is built into the zone controller — each section has its own logic.
Accumulation without pressure
The most valuable property of a driven roller conveyor is the ability to accumulate loads without one crate pressing on another. In a simple scheme, stopped loads press on each other with their whole mass — and this means container deformation, jamming and drive overload. A zonal roller conveyor solves the problem: the route is split into sections, each with its own motor roller and photo sensor. When the sensor sees an occupied zone exit, it stops that zone’s drive, and the load stands without contact with the next one. When the zone ahead frees up, the system starts the drive and the load moves on.
Typical faults and maintenance
A driven roller conveyor fails predictably, and three causes cover most cases. The first is wear of the transmission chain or belt: an elongated chain skips the sprocket teeth, a slack belt slips under load. A tension check once a month and replacement to a schedule remove the problem. The second is the roller bearings: a single seized roller in a driven line brakes the whole route, because the motor is forced to pull a stationary roller as well. The third is the electronics of zonal schemes: a dirty or misaligned photo sensor gives a false trigger, and the zone stands idle for no reason or, conversely, does not stop.
We keep the maintenance schedule simple: a walk-round and a check for unusual noise every shift, a transmission tension check once a month, a revision of the drive-shaft bearings and cleaning of the sensor optics once a quarter. For wet food zones we separately control the tightness of the motor rollers: ingress of cleaning solution disables the motor within a few weeks.
How to choose a conveyor for the line
The sequence we go through with the customer: first the load — weight, dimensions, bottom type; then geometry — length, width, inclines; then the mode — constant transport or accumulation; finally the environment — humidity, contact with product, washing regime. From these data we choose the drive type, calculate the torque and motor power. A ready driven roller conveyor is matched by speed and height with the rest of the line.
Conclusion
A driven roller conveyor is controlled transport of a unit load where gravity is not enough. The key to reliable operation is a correct torque calculation with a 20–25% margin and a drive-type choice matched to the load weight. Need a roller conveyor for your line? Get in touch — we will calculate the torque and select the drive.
