QUICKLINKS
• 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)
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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.
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| Figure 1 - Torsion Pendulum |
Figure 2 - Amplitude decays but time period
remains constant |
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| 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: |
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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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