Escalator Step Chain Tension, Drive Power, and Brake Load

The two force components behave differently with the angle. The gravity component grows with the sine and dominates on a standard 30 degree escalator; friction grows with the cosine and matters more on a shallow moving walk. A 12,000 lb moving load at 30 degrees on 0.03 roller friction is 6,000 lb of gravity against 312 lb of friction -- gravity is 95% of the 6,312 lb chain tension, 3,156 lb per chain on two, and 19.1 hp at 100 fpm. The escalator is essentially a hoist and friction is a rounding error. Put the same load on a 6 degree moving walk and it is 1,254 lb of gravity against 358 lb of friction: now the two are comparable, and the drive is a much smaller machine for the same capacity. THE GOVERNING CASE IS NOT THE ONE PEOPLE PICTURE. A fully loaded escalator running UP is the highest power draw, but a fully loaded escalator running DOWN is what sizes the BRAKE, because the load is driving the machine and the brake has to stop it within a defined distance without throwing passengers. Note the sign: running down, friction acts with the brake rather than against it, so the brake takes the difference -- about 5,688 lb here rather than the full 6,000. That is a stopping-distance requirement rather than a holding one, and it is why escalator brakes are tested with load. Chain condition ties back to ordinary roller chain practice: a step chain elongates with wear like any other, and elongation changes how it engages the sprockets and the step alignment at the comb plates, which is where a worn chain shows itself before it fails. A statics and power calculation. It does not size a drive, chain, or brake: chain selection includes fatigue and articulation life at the sprocket, the drive includes starting and inertial loads, and the brake must meet a stopping-distance requirement under defined load conditions. It does not address the step band, step rollers, tracks, comb plates, handrail drive, or the safety devices an escalator carries -- step upthrust, missing step, handrail speed, comb impact, and skirt obstruction among them -- and it does not set the design passenger load, which is a code value per step rather than an observed one. ASME A17.1 and A17.2, the equipment manufacturer, the elevator authority having jurisdiction, and a licensed mechanic govern.

gravity component = load x sin(incline); friction component = load x cos(incline) x coefficient; tension = the sum; power = tension x chain speed / 33,000; running down loaded, the brake takes the gravity component LESS the friction component.

The incline force resolution as standard escalator practice, by name, with ASME A17.1 named as governing the brake, its stopping distance, and the escalator safety devices. Statics and power only; the drive, chain and brake are sized to the code and the manufacturer's data.

Trigonometric force resolution on the user's own load and geometry; no code value or manufacturer table is reproduced.

Estimate. AHJ and licensed professional govern.

Field names used by the API: total_load_lb, incline_deg, friction_coefficient, chain_speed_fpm, chain_count, alternative_incline_deg, gravity_lb, friction_lb, tension_lb, per_chain_lb, power_hp, descending_brake_lb, alt_gravity_lb

• Gravity dominates at 30 degrees and friction dominates on a shallow moving walk, which is why their drives differ so muchescalator practice
• The descending loaded case sizes the brake the load drives the machine and the brake must stop it within a defined distanceASME A17.1
• Friction helps the brake going down so the brake takes the gravity component less the friction component, not the whole of itstatics