BLDC Motor for Automatic Doors: Sliding Door, Swing Gate & Revolving Door Motor Selection Guide

Automatic doors are one of the most demanding applications for brushless DC motors. The motor must start and stop thousands of times per day, operate near-silently in public spaces, and meet strict safety standards that limit closing force to prevent injuries. This guide covers motor sizing, gear ratio selection, voltage choice, and compliance requirements for three major automatic door categories: sliding doors, swing gates, and revolving doors.

Why BLDC Motors Dominate the Automatic Door Market

Before 2010, most automatic doors used brushed DC motors or AC induction motors with mechanical brakes. The shift to BLDC technology was driven by three factors that matter enormously in door applications:

Noise. Commercial automatic doors operate in hotel lobbies, hospital corridors, and retail entrances where ambient noise levels are 35 to 50 dB. A brushed motor with commutator sparking produces 55 to 65 dB at 1 meter. A well-designed BLDC gear motor with helical gears operates below 42 dB, which is practically inaudible in a typical indoor environment.

Maintenance. A busy commercial entrance may cycle 500 to 1,000 times per day, which translates to 180,000 to 365,000 cycles per year. Brushed motors require brush replacement every 3,000 to 5,000 operating hours. A BLDC motor with sealed bearings runs for 20,000+ hours without service, effectively lasting the entire lifetime of the door system (typically 10 to 15 years).

Speed control precision. Safety standards like EN 16005 and ANSI/BHMA A156.10 require doors to decelerate smoothly before reaching the closed position, and to reverse immediately if an obstacle is detected. BLDC motors with hall sensor feedback enable the controller to implement S-curve acceleration profiles with position accuracy within 2 mm, something that is extremely difficult to achieve with AC motors and mechanical brakes.

Motor Sizing for Automatic Sliding Doors

Sliding doors are the most common automatic door type. The motor drives a toothed belt or rack-and-pinion mechanism to move one or two door leaves along a horizontal track.

Step 1: Calculate the Required Driving Force

The total force the motor must produce at the belt or rack includes three components:

Friction force: F_f = m × g × μ, where m is the total mass of the moving door leaf (including glass, frame, and hardware), g is 9.81 m/s², and μ is the friction coefficient of the guide rail system. For modern linear guide bearings, μ ranges from 0.02 to 0.05. For older roller-based systems, μ can reach 0.08 to 0.12.

Acceleration force: F_a = m × a, where a is the desired acceleration. Typical opening acceleration for a commercial sliding door is 0.5 to 1.0 m/s², reaching a maximum speed of 400 to 600 mm/s.

Wind load (if applicable): For entrance doors exposed to wind, add a force component based on the door surface area and expected wind pressure. A 2 m × 2.5 m glass door in a 50 km/h crosswind can experience 200 to 400 N of lateral force, though only a fraction translates to track-direction resistance.

Example: A standard commercial sliding door with a 120 kg leaf, linear guide (μ = 0.03), target speed 500 mm/s, and acceleration 0.8 m/s²:

F_total = (120 × 9.81 × 0.03) + (120 × 0.8) = 35.3 + 96 = 131.3 N

With a 30 mm radius drive pulley, the required torque at the pulley shaft is: T = 131.3 × 0.03 = 3.94 N·m

Step 2: Select Motor Power and Gear Ratio

The mechanical power requirement is P = F × v = 131.3 × 0.5 = 65.7 W. Accounting for gear efficiency (85% for worm gear, 92% for planetary gear), the motor output power should be 75 to 100 W minimum. In practice, 100 W to 150 W motors are specified to provide a comfortable safety margin for cold starts, aging friction, and occasional wind gusts.

The gear ratio for a belt-driven system: i = (n_motor × 2π × r_pulley) / (v_door × 60), where n_motor is rated RPM. With a 3,000 RPM motor and 30 mm pulley at 500 mm/s door speed: i = (3000 × 6.283 × 0.03) / (0.5 × 60) = 565.5 / 30 = 18.8:1.

A worm gear reducer at 20:1 is a common choice because it provides self-locking, preventing the door from being pushed open when the system is in locked mode. For doors requiring manual push-open capability during power failure, a planetary gear reducer at the same ratio (with an electromagnetic brake) is preferred.

Motor Selection for Swing Gate Operators

Swing gates present different challenges. The motor drives the gate leaf through a rotational arc (typically 90 to 110 degrees), and the torque requirement changes with the gate position due to wind loading and gravity on sloped installations.

For a residential swing gate (single leaf, 2.5 m wide, 50 kg), the hinge torque at maximum wind load is typically 15 to 25 N·m. A BLDC gear motor rated 80 to 120 W with a 60:1 to 80:1 reduction is standard. The motor runs at low speed (30 to 60 RPM at the output shaft) for 10 to 15 seconds per cycle.

For commercial or industrial swing gates (3 to 5 m wide, 150 to 400 kg per leaf), motors in the 200 W to 500 W range with heavy-duty planetary or worm reducers are required. The IP rating must be at least IP44 (outdoor installation), and IP65 is recommended for coastal or dusty environments.

Voltage selection: 24 V DC is standard for residential and light commercial gates, allowing direct integration with solar panels and battery backup. 48 V systems are used for heavy industrial gates where higher continuous current draw would require impractically thick wiring at 24 V.

Revolving Door Motor Requirements

Revolving doors have the highest torque requirements among automatic door types. A four-wing revolving door with a 2.4 m diameter enclosure and glass wings weighing 200 to 300 kg total requires continuous torque of 20 to 50 N·m at the central drive shaft.

The rotation speed is very slow (1.5 to 3.0 RPM at the door), so the gear reduction is extreme, typically 100:1 to 200:1. A 200 W to 400 W BLDC motor with a two-stage planetary reducer or a worm-planetary combination is typical. The speed controller must handle frequent direction changes (night-lock mode to daytime rotation) and maintain smooth, constant-speed rotation despite varying passenger loads pushing against or with the door wings.

Safety is paramount in revolving doors. The motor controller monitors current continuously and must reduce speed or stop within 200 ms if current spikes indicate a person or object is trapped. The driver circuit implements torque limiting at 150 N maximum contact force per EN 16005, measured at the leading edge of the door wing.

Noise Optimization for Indoor Installations

Noise is often the deciding factor in automatic door motor selection. The total noise comes from three sources:

Motor electromagnetic noise (15 to 25 dB): minimized by using sinusoidal commutation (FOC) instead of trapezoidal (six-step) commutation. FOC reduces torque ripple from 15-20% to below 5%, which directly reduces vibration-induced acoustic noise.

Gear noise (25 to 45 dB): the dominant noise source. Helical gears produce 8 to 12 dB less noise than spur gears at the same speed. For premium installations, helical worm gears with ground tooth profiles achieve the lowest noise. Worm gear motors with polymer worm wheels (e.g., POM or PA66+GF) run 5 to 8 dB quieter than all-metal gearboxes.

Mechanical transmission noise (20 to 35 dB): belt tension, guide rail condition, and mounting vibration isolation all affect system-level noise. Rubber vibration isolators between the motor housing and the door header reduce structure-borne noise transmission by 10 to 15 dB.

Safety Compliance and Motor Controller Requirements

Automatic door motor systems must meet these key regulatory requirements:

Force limitation: EN 16005 limits closing force to 150 N static and 65 N dynamic (measured after the initial 50 mm of travel for sliding doors or 5 degrees for swing doors). The motor controller achieves this through real-time current monitoring: since torque is proportional to current in a BLDC motor, the controller sets a current limit that corresponds to the maximum allowable force.

Anti-entrapment: The controller must detect obstacles and reverse direction within 0.3 seconds. Hall sensor position feedback enables the controller to detect stalled or slowed motion and trigger reversal before force limits are exceeded.

Emergency egress: For fire exits, the door must fail to the open position. This requires a spring-return mechanism or a battery backup system that drives the door fully open when power fails. The 24 V BLDC motor system integrates naturally with sealed lead-acid or LiFePO4 backup batteries.

Low voltage safety: IEC 60335-2-103 covers motor-operated gates, doors, and windows. The 24 V DC BLDC system operates within the Safety Extra Low Voltage (SELV) classification, simplifying electrical safety certification.

BLDC Motor Specifications for Common Door Types

Frequently Asked Questions