• Center of Gravity
• Moment of Inertia
• Product of Inertia
• Instrument Selection
• Glossary
• UAVs
• Golf

MOI questions
• Why Measure MOI?
• Principle of operation of an MOI instrument
• Torsion pendulum theory
• Finding MOI through CG without knowing the CG location

MOI of golf club heads
• Comply with the USGA ruling on MOI
• Use an XR10 to measure MOI
• Optimize club head design

MOI instruments
• All MOI instruments
• GB Series (MOI of large parts)
• XR Series (MOI of mid size parts)
• XKR Series (MOI of small parts)
• KSR Series (MOI and CG)
• MP Series (MOI, CG and weight)
• POI Series (POI, MOI and CG)

TORSION PENDULUM THEORY


Consider the torsion pendulum of Figure 1 consisting of a disk of mass moment of inertia I lb-in-sec2, restrained in rotation by a wire of torsional stiffness K in-lb/radian. If the disk is turned an initial angle and sharply released, it will oscillate with damped harmonic motion as shown in Figure 2.

Figure 1 - Torsion Pendulum Figure 2 - Amplitude decays but time period remains constant
The period of oscillation will remain constant while the amplitude of oscillation will decay gradually until the pendulum eventually comes to rest. For very small viscous damping, the torsion pendulum oscillates at its natural frequency and the moment of inertia can be determined by the simple relationship:

where C is a calibration constant which can be determined experimentally. For significant damping, the period of oscillation is greater than the undamped natural period by an amount determined by the damping ratio. This results in a measured moment of inertia which is slightly greater than true value.

Calibration - A calibration weight of known moment of inertia (Ic) is supplied with all of our instrument. The operator first measures the period of oscillation with this weight mounted on the instrument (Tc). The weight is removed and the tare period (To) is measured. The calibration constant (C) may now be calculated as follows

Our moment of inertia instruments are linear. Only a single calibration weight is required to establish the value of the calibration constant for the instrument. Therefore, the calibration constant need not be changed when measuring different size or weight parts.



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Space Electronics LLC - 81 Fuller Way - Berlin, CT 06037 (USA) - Phone: +1 860 829 0001 - Fax: +1 860 829 0005 - Email: sales@space-electronics.com
Our Mass Properties Measurement Products: 
Center of Gravity Measurement Instruments  
Moment of Inertia Measurement Instruments  
Product of Inertia Measurement Instruments  
Combined Mass Properties Measurement Instruments