Slide Gate Operator Force, Grade, and Duty Cycle

The force calculation is straightforward and usually not the problem: a 2,400 lb gate on good rollers at a 0.1 coefficient needs 240 lb to move, and operators are generally sized with margin. Put it on a 5% grade and the weight component along the slope adds 120 lb -- a third of the total demand from a driveway that barely looks sloped. THEN THE DUTY. That same gate, 24 ft long at 1 ft/s, takes 24 seconds each way and 48 per cycle. At 150 cycles a day over a 10 hour window it runs for 2.0 hours: a 20% duty cycle. An operator rated for intermittent duty in a residential application will not survive it, and it gets replaced with the same model, twice, before anyone does the arithmetic. Worse, the average understates the problem, because the cycles are not evenly spread -- a shift change puts twenty of them in ten minutes. The application needs a continuous-duty operator, and buying one at the start is cheaper than buying three of the wrong one. The force term has a second trap: a gate that binds -- a settled post, a damaged roller, debris in the track -- raises the demand without warning, which is why an operator drawing more current than it used to is reporting a gate problem rather than a motor problem. ENTRAPMENT PROTECTION IS NOT PART OF THIS ARITHMETIC AND IS NOT NEGOTIABLE. A gate operator is a machine that can kill a child. The required sensing devices, the classification of the installation, and the inherent force limits are safety requirements independent of anything computed here, and a correctly sized operator does not satisfy them. A force and duty estimate. It does not select an operator -- manufacturer duty classifications, thermal ratings, and how cycles are distributed through the day matter more than an average percentage -- and it does not size the gate structure, the rollers, the track, or the posts, or evaluate wind load on the gate leaf, which for a solid or heavily clad gate can dominate everything else. Automatic gates have killed children. UL 325, ASTM F2200, the operator manufacturer's instructions, and the AHJ govern.

rolling force = gate weight x rolling coefficient; grade force = gate weight x sin(arctan(grade / 100)); travel time = length / speed; duty cycle = cycles per day x 2 x travel time / the operating window.

The rolling force relation and the duty cycle as run time over the operating window, by name, with UL 325 named as governing entrapment protection and ASTM F2200 the gate construction. Neither is satisfied by a correctly sized operator.

Force and time arithmetic on the user's own gate and traffic figures; no operator rating table is reproduced.

Estimate. AHJ and licensed professional govern.

Field names used by the API: gate_weight_lb, rolling_coefficient, grade_pct, gate_length_ft, operator_speed_fps, cycles_per_day, operating_hours, operator_rated_force_lb, intermittent_duty_limit_pct, rolling_force_lb, grade_force_lb, total_force_lb, travel_time_s, cycle_time_s, run_time_hr, duty_cycle_pct

• Duty kills operators, not force an intermittent-rated unit on a commercial cycle count overheats and failsoperator manufacturer data
• Grade is a large fraction of the demand a slope that barely looks like one can add a third to the forcestatics
• Entrapment protection is separate and mandatory a correctly sized operator does not satisfy itUL 325