Working Principle of Electric Retractable GrandstandCangzhou Yunxinda electric retractable grandstand is a modular motorized telescopic seating system widely used in basketball gyms, school arenas and multi-purpose sports venues. Its core working logic relies on electric drive unit, bilateral synchronous transmission mechanism, limit sensing module and automatic self-locking structure to realize stable, parallel extension and retraction of multi-layer bleachers.1. Core Power Driving UnitThe power source adopts low-speed high-torque reduction motor installed on the first base frame of the grandstand.

Input power: Standard 220V single-phase power supply, with built-in overload, overheat and short-circuit protection modules inside the control box.

Speed reduction design: Integrated worm gear reducer converts high motor rotation speed into low-speed, powerful torsion force, which avoids fast sliding and ensures slow, steady movement of the whole bleacher.

Control mode: Dual control of wired panel and wireless remote controller. Users send extension / retraction / stop signals to the main circuit board to start or cut off motor operation. An emergency stop button is reserved to cut off power immediately in case of blockage or safety risks.

2. Bilateral Synchronous Chain Transmission Mechanism (Key Core)To prevent left-right offset, jamming or tilting during stretching, Yunxinda adopts double-side closed synchronous chain linkage system.

The output shaft of the reduction motor drives the main transmission sprocket on one side; the sprocket pulls the heavy-duty transmission chain to run circularly.

A connecting transmission shaft penetrates the bottom frame to connect the left and right sprocket groups, ensuring the rotation speed and displacement of chains on both sides are completely consistent.

Each layer of bleacher frame is connected to the chain through fixed sliding blocks. When the chain circulates, it pulls each tier to move forward or backward synchronously along the wheel track.

Guide limit grooves are mounted on both sides of every frame to restrict lateral displacement, so all tiers always keep parallel without skew during movement.

3. Bottom Walking Auxiliary StructureEvery base layer is equipped with silent PU load-bearing casters with built-in bearings.

When the motor outputs traction, the casters roll smoothly on the ground to reduce friction resistance and lower motor load.

The casters are matched with positioning brake blocks. When the grandstand reaches fully extended position, the brake locks the wheels to eliminate sliding displacement during spectator use.

4. Automatic Limit Sensing & Stop Protection SystemTwo groups of photoelectric limit sensors are installed at the fully extended end and fully retracted end of the slide track.

When the bleacher moves to full extension position, the trigger block touches the extension sensor, which sends a signal to the control board to cut off motor power automatically.

When folding back to the storage state, the retraction sensor triggers power-off to stop the whole machine and avoid over-retraction extrusion damage.

Anti-jam protection principle: If seats or foreign objects block the bleacher during operation, the motor load surges instantly. The overload protector will automatically cut off power within 1 second to prevent chain breakage, frame deformation or motor burnout.

5. Eccentric Self-Locking Mechanical StructureThis mechanical lock ensures the grandstand stays stable after stretching without continuous motor load.

Driven by chain linkage, the eccentric lock hook moves synchronously with frame displacement.

When fully stretched, the hook automatically clamps the fixed base beam to lock all tiers into a whole rigid structure, resisting horizontal impact and avoiding shaking when audiences sit down.

During retraction, the chain pulls the hook open first before the bleacher folds back, no manual unlocking required.

6. Circuit Control Working Logic Flow

User presses Extend button on remote / wired panel → control board energizes reduction motor.

Motor drives bilateral synchronous chains to pull each tier forward along casters.

Tiers move synchronously until touching extension limit sensor → power supply disconnected automatically, self-locking hook locks the frame.

For retraction: Press Retract button → control board reverses motor rotation, unlock eccentric hook first.

Chains pull all tiers backward to folded position, retraction sensor cuts power, casters lock for storage.

At any time, press Emergency Stop to cut off all power and suspend all mechanical movement instantly.