Motor Driving Hollow Cylinder Rotating Torque Equation and Calculator

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These equations will determine the torque requirements for a electric motor operating with a hollow shaft driven by the motor.

To determine a fan or blowers horsepower when driving a hollow cylinder/shaft use the following equation. 

Hollow Cylinder
Hollow Cylinder


  Torque Formula      and     WK formula   

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T =   Required Torque, lb-ft
WK2 =   Mass Moment of Inertia of load to be accelerated  lb-ft2
(See Mass moment of inertia calculations)
Change of speed, rpm
t =  Time to accelerate the load, seconds
W = Weight of object, lb
R1 = Outside Radius of cylinder, ft
R2 = Inside Radius of cylinder, ft