Inertia / Load




		Manufacturers Representatives


	Moment Of Inertia


	*Disc or Shaft*


	J (g·m²)


	=


	*Cylinder*


	J (g·m²)


	=


	(R²₁ + R²₂)


	M = Mass in grams R = Radius in meters


	REFLECTED LOADS WHEN USING GEARS OR PULLEYS


	Torque required of motor


	=


	gear or pulley ratio GR


	=


	Inertia reflected to motor


	=

EQUIVALENT INERTIAL LOAD

J eqv. (g·m²)

=

MR²

For a pulley and weight or a rack and pinion
M = Mass of load in grams
R = Radius of pulley in meters

TOTAL LOAD
Note: Be sure to include all load components.

J_T

=

Rotor Inertia + all J Loads

T_F

=

Frictional and Forces

Note: In the pulley example earlier, the total load would be:

J_T

=

J rotor + J pulley + J eqv.

T_F

=

T frictional + Load Weight × Radius

Total T

=

J_T αa + T_F

Load weight

=

mass × 9.8 mN




	©Copyright 2006, C. Kaufman & Assoc., Inc.. All rights reserved. Updated: December 2006