MOMENT OF INERTIA 
MEASUREMENT INSTRUMENTS

Space Electronics is the world leader in moment of inertia measurement. We manufacture more than 25 different moment of inertia instruments. Our largest instrument can measure objects weighing up to 22,000 pounds (10,000 kg). Our smallest instrument measures tiny mechanisms weighing less than 1 gram. Since 1960, Space Electronics has sold more moment of inertia instruments than the combined sales of all other companies in the world. We are the originator of the torsion flexure measurement concept used in most small moment of inertia instruments (U.S. patent 3,693,413). Some of our moment of inertia instruments also measure center of gravity location and product of inertia (spin balance).

TYPES OF INSTRUMENTS We make six types of moment of inertia instruments covering a range of prices and accuracies:

KSR Series Instruments (Mass Properties) - These dual purpose instruments measure both moment of inertia and center of gravity. A dedicated microcomputer included with these systems computes both MOI and CG data, provides hard copy printout, and prompts the operator through each procedure, making the operation easy and foolproof. These instruments use a spherical air bearing to support a rotary table, and act as a pivot axis for measuring unbalance moments due to the displacement of the test part CG relative to the central axis of the bearing. A hollow tube is attached to the bearing; the lower end of this tube is restrained by a second air bearing. This lower restraint serves to stabilize the test surface of the bearing and provides a means for measuring unbalance moments.

GB Series Instruments (Moment of Inertia of Heavy Test Parts) - GB instruments will measure test parts as heavy as 22,000 lbs. and are often used for critical tests on space or re-entry vehicles. These instruments use an air bearing to support the test part and a torsion rod to provide a rotational spring. The lower end of the rod is attached to a vertical flexure to prevent changes in torsion stiffness as a function of air bearing gap.

XR Series Instruments (Moment of Inertia of objects weighing up to 250 lbs.) - XR instruments have been designed for general use where a reliable well built instrument with high accuracy (0.25%) is required. These instruments employ a patented technique which we call the torsion flexure. It consists of a silicon-manganese alloy torsion rod supported at both ends and placed in tension; the rod is twisted at its center. A slotted tube surrounding the rod couples the rod center to the output shaft of the instrument. The ends of this oscillating tube are restrained by bearings to limit the motion of the oscillating assembly to pure rotation. Since the weight of the test part is supported by the torsion rod, negligible damping occurs in the restraint system. This design results in an inverted torsion pendulum which is less expensive than a gas thrust bearing pendulum and has a lower tare inertia. The hollow tapered output shaft of the instrument accepts a range of precision collets and test fixtures.

XKR Series Instruments (Moment of Inertia of extremely small test parts)

MP Series instruments (Weight, Center of Gravity and Moment of Inertia) - MP instruments measure weight, center of gravity and moment of inertia. They have a lower accuracy than our KSR series and are not suited for the measurement of tall test objects. They are rugged instruments that are recommended as portable mass properties systems.

POI Series Instruments (Spin balance machines that also measure moment of inertia) - These slow speed aerospace balancing machines use an air bearing spindle. Product of inertia (spin balance), CG, and MOI can be measured on a single instrument.