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MIL-DTL-81963 Servocomponents, Precision Instrument, Rotating, Common Requirements And Tests, General Specification ForThis specification covers common requirements and tests for analog, digital and analog/digital precision instrument rotating servocomponents \(synchros, electrical resolvers, electrical, linear resolvers, transolvers, shaft angle encoders, servomotors, tachometer-generators, servomotor-tachometer generators, stepping motors, and gear heads\). This specification will be used with the applicable general specification, which covers a particular class of servocomponents \(for example, synchros\), together with the documents and the specification sheet that cite MIL-DTL-81963 as a direct reference detailing the specific requirement for the individual servocomponent.

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. . .
MIL-DTL-81963C
81963 as a direct reference shall be applied axially to the shaft, first in one direction and then in the
opposite direction. The difference between the two dial gauge readings shall be taken as the shaft end
play. The shaft end play shall not exceed the allowable shaft end play specified in accordance with 3.6.2.
4.9.3 Shaft runout. The servocomponent housing shall be rigidly mounted. A dial gauge shall be
applied to the shaft within 0.125 inch of the bearing face and the shaft rotated. The difference between
the extreme indicator readings shall be the shaft runout and shall meet the requirements of 3.6.3.
4.9.4 Rotor moment of inertia (see 3.6.4). The rotor moment of inertia shall be measured by one of the
following methods and shall not exceed the value specified in the applicable documents and the
specification sheet that cite MIL-DTL-81963 as a direct reference.
4.9.4.1 Moment of inertia by torsional oscillations. The rotor of the servocomponent shall be fixed to an
adaptor of the lowest possible inertia (which shall be measured or calculated) and the adaptor and rotor
shall be suspended from a steel wire at least 10 feet long, so that the axis of the rotor coincides with that
of the suspension wire. The suspended mass shall be protected from air currents and extraneous
vibrations which may cause it to sway. The adaptor-rotor assembly shall be twisted so that oscillation
occurs about the axis of suspension. The period ta, of the oscillation shall be determined. With the same
procedure and adaptor being used, the period, tb, of a body of known inertia shall then be determined.
The moment of inertia of the rotor may then be determined from the expression:
2
Ja = [ (Jb + Jad) x (ta) ­ Jad ]
2
(tb)
where:
2
Ja = moment of inertia of rotor in gram-centimeters
2
Jb = moment of inertia of known body in gram-centimeters
2
Jad = calculated moment of inertia of adaptor in gram-centimeters
ta = period of oscillation of rotor plus adaptor, in seconds
tb = period of oscillation of body of known inertia plus adaptor, in seconds
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