Formulas 

The following formulas cover the basic calculations used in brake application engineering. 

REQUIRED	GIVEN	FORMULA
Full load motor torque	Horsepower (P), hp Shaft speed (N), rpm 5252 = Constant
Average dynamic braking torque	Total inertia reflected to brake   Shaft speed at brake (N), rpm Desired stopping time (t), seconds 308 = Constant
Static torque (T), lb-ft	Force (F), lb Pulley or drum radius, (R), ft
Overhauling dynamic torque reflected to brake shaft	Weight of overhauling load (W), lb Linear velocity of descending load (V), ft/min Shaft speed at brake (N), rpm 0.158 = Constant
Static torque of brake	Dynamic braking torque required  0.8 = Constant (derating factor)
Inertia of rotating load reflected to brake shaft	Inertia of rotating load  Shaft speed at load  Shaft speed at brake
Equivalent inertia of linear moving load reflected to brake shaft	Weight of linear moving load (W), lb Linear velocity of load (V), ft/min Shaft speed at brake  2 = Constant
Kinetic energy of rotating load,	Inertia of rotating load reflected to brake shaft   Shaft speed at brake  5875 = Constant
Kinetic energy of linear moving load	Weight of load (W), lb Linear velocity of load (v), ft/sec g = Gravitational acceleration constant
Change in potential energy (PE), ft-lb	Weight of overhauling load (W), lb Distance load travels (s), ft	PE = Ws
Total energy absorbed by brake	Total linear kinetic energy  Total rotary kinetic energy  Potential energy converted to kinetic energy (PE), ft-lb
Thermal capacity required for rotational or linear moving loads (TC), hp-sec/min	Total system inertia reflected to brake shaft  Shaft speed at brake  Number of stops per minute (n), not less than one
Thermal capacity required for overhauling loads (TC), hp-sec/min	Total energy brake absorbs  Number of stops per minute (n), not less than one 550 = Constant
Linear velocity, ft/min	N = rpm Diameter (D), ft