Engineering formulas for clutch and brake sizing

These core formulas are used for the preliminary selection of electromagnetic clutches, brakes and powder brakes. They give the required torque from motor power and speed, the acceleration torque from inertia, and the energy a brake must absorb per stop.

Worked example: a motor with P = 5.5 kW at n = 1450 rpm delivers T = 9550 × 5.5 / 1450 ≈ 36.2 Nm. With a safety factor of 1.5 for shock load, a clutch or brake with at least about 55 Nm dynamic torque should be considered.

Engineering Formula Reference

Core formulas used during preliminary clutch and brake selection.

Torque from powerT [Nm] = 9550 × P [kW] / n [rpm]
Power from torqueP [kW] = T [Nm] × n [rpm] / 9550
Angular speedω [rad/s] = 2π × n [rpm] / 60
Acceleration torqueT = J × α
Brake energyE = 1/2 × J × ω²
Selection noteApply a safety factor for shock load, heat, duty cycle and wear.

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