Choosing a gear motor for an automatic door comes down to a handful of mechanical specifications: output torque at the door shaft, output speed, duty cycle, and how the drive behaves when power is removed. Get those four numbers right and the rest — voltage, mounting, noise, protection rating — falls into place. This guide explains what each specification means for sliding, swing, folding and revolving door operators, shows typical values by door type, and works through a sizing example so you can shortlist the right automatic door gear motor without guesswork.
An automatic door operator converts motor rotation into door movement through one of three common transmission layouts. Understanding which one your door uses is the first step, because it defines the output speed and torque the gear motor must deliver.
In all three layouts the motor itself is typically a small gear reduction motor: high-speed motor plus a reduction stage that multiplies torque and brings output speed down to the 10–100 r/min range a door needs. For a closer look at the drive options behind gate and door automation, our guide to gear motors for door openers walks through the same physics on an operator you can inspect part by part.
Manufacturers list dozens of values, but for automatic doors these seven specifications carry almost all the selection weight.
| Specification | What it controls | Typical range for automatic doors |
|---|---|---|
| Output torque (N·m) | Whether the motor can start and move the door under worst-case friction, wind and seal load | 0.5–8 N·m (light doors); 10–50 N·m (heavy sliding/swing) |
| Output speed (r/min) | Door opening time and closing speed | 10–60 r/min at the door shaft; doors typically travel 0.3–0.8 m/s |
| গিয়ার অনুপাত | Sets the torque/speed trade-off | 10:1–300:1 depending on motor power |
| Duty cycle / rated run time | How long the motor can run before cooling; continuous vs intermittent | Reversible 30-min rated; continuous S1 for high-traffic |
| Holding behaviour (brake or self-locking) | Whether the door stays put on power loss or manual push | Electromagnetic brake or self-locking worm stage |
| Voltage & phase | Power availability on site | Single-phase 110/220 V AC; 3-phase 220/380 V; DC 24 V |
| Noise, IP rating, life | Indoor acceptance, outdoor durability, maintenance cost | <55 dB indoors; IP44+ outdoors; 20,000+ h design life |
Two specifications deserve extra attention because they are the most common causes of field failure. Torque must be sized for the worst case — cold grease, seal drag, wind load — not the average. And duty cycle must match traffic: a motor rated for 30 minutes of reversible running in a quiet office door will overheat if the operator cycles every few seconds in a busy storefront. If you are comparing models, read how geared DC vs AC motors differ on duty and control before you commit to a voltage family.
Door geometry changes the load so much that the same motor family covers very different applications depending on ratio and power. The table below summarises realistic starting points for each door type.
| Door type | Typical panel weight | Door speed | Suggested output torque | Suggested motor power |
|---|---|---|---|---|
| Light interior sliding door | 30–80 kg | 0.4–0.8 m/s | 2–5 N·m at pulley | 25–60 W |
| Heavy sliding / automatic gate | 150–400 kg | 0.3–0.5 m/s | 10–30 N·m | 120–300 W |
| Swing door (single leaf) | 40–100 kg leaf | 90° in 3–6 s | 10–25 N·m at hinge | 60–140 W |
| Folding door | 30–60 kg per leaf | 0.5–1.0 m/s | 3–8 N·m | 40–90 W |
| Revolving door (light commercial) | 200–300 kg total | 1.5–4 r/min at door | 20–50 N·m | 140–300 W |
Treat the ranges above as sanity checks, not substitutes for calculation. A door with heavy weather seals, a slope, or wind exposure needs more torque than its weight alone suggests. Where your door sits between “light interior sliding” and “heavy sliding gate” determines whether a compact 25 W unit or a 120–300 W right-angle AC gear motor is the honest choice.
A quick first-pass calculation for a belt-driven sliding door uses five numbers and confirms whether your candidate gear motor has enough margin. Worked example for a 60 kg interior sliding door:
The same five numbers apply to swing doors — replace pulley radius with the hinge-to-push-point distance, and door travel with opening angle. If ratios and torque conversions are new to you, our guide on how to calculate the gear ratio of a gear reduction motor shows the formulas step by step.
DC motors dominate premium automatic doors because speed control is easy. But AC gear motors remain a practical, low-cost choice for many operators, and the right-angle (worm or hypoid) layout is particularly well suited to door headers, where the motor axis must sit across the door while the output shaft runs along the travel direction.
A typical small AC right-angle unit — such as the 4GN AC right-angle gear reducer motor 25 W — offers single-phase 110 V or 220 V operation, reversible 30-minute duty, output speeds from 5 to 500 r/min through gear ratios of 3:1 to 300:1, and maximum allowable load up to about 7.8 N·m at high ratios. Those numbers cover light sliding doors, small swing-door operators and low-cycle applications. For heavier panels and continuous traffic, step up to the 5GU AC right-angle gear reducer motor 40–140 W or the 6GU series 120–300 W with the same compact right-angle footprint.
Two fit notes for AC drives in automatic doors. First, if the operator must hold the door against manual push or gravity when idle, choose a self-locking worm gearbox — the worm stage locks the output shaft without a brake. Second, reversing an AC gear motor every cycle needs a reversible motor and a controller that switches direction safely; count on a control board rather than a plain on/off switch.
Before you finalise a gear motor for an automatic door, run this checklist:
The most frequent mistakes are sizing on power (watts) instead of output torque, ignoring the difference between starting and running torque, and assuming a motor rated for continuous operation is needed when an intermittent reversible rating is actually the correct, cheaper match. Door weight is usually known; friction and seal drag are where projects underestimate.
Selecting a gear motor for an automatic door is a torque-and-duty exercise, not a wattage contest. Define the worst-case torque and door speed, pick the ratio that reconciles them, decide how the door must behave on power loss, and only then compare voltage families and frame sizes. For light to medium operators, compact right-angle AC gear motors deliver a cost-effective fit with the self-locking option many door systems need.
Start your selection from the right-angle gear reducer motor range and confirm the duty cycle with the supplier before ordering — the nameplate tells you the 30-minute rating, but your traffic pattern decides whether that is enough.
Most automatic door operators use a small gear reduction motor — DC planetary or right-angle AC — with an output speed of roughly 10–60 r/min and torque matched to door weight. Sliding doors usually run through a belt or rack drive, while swing and revolving doors drive the hinge or centre shaft directly.
Light interior sliding doors typically need 2–5 N·m at the pulley; heavier sliding doors and gates need 10–30 N·m; swing and revolving doors can require 10–50 N·m at the hinge or centre shaft. Calculate friction plus seal drag and add a 30–50% safety margin.
Divide the motor rated speed by the required output speed. For a 1250 r/min motor driving a sliding door at ~100–160 r/min at the pulley, the ratio is roughly 8:1 to 12:1. Door operators with heavier panels or lower speeds use 20:1 up to 100:1.
DC gear motors make speed control and soft start-stop easier and are standard in premium operators. AC gear motors are simpler and cheaper, work directly from the mains, and a self-locking worm version holds the door without a brake — a good fit for light and mid-duty operators where mains power is available.
If the door must stay put on power loss or resist being pushed open, yes. A self-locking worm gearbox holds position mechanically with no extra parts; an electromagnetic brake is used where the drive cannot self-lock or where manual override must be easy.
For a light interior sliding door with modest speed, a 25 W right-angle AC gear motor at a suitable ratio can be adequate when the calculated torque stays under its allowable load curve. Most storefront and heavy-duty doors need 40–300 W, so confirm torque and duty with the supplier rather than assuming power alone.
