KSR DESIGN DETAILS

Figure A - CG and MOI Instrument using Spherical Gas Bearing Pivot	Figure B - CG and MOI Instrument using crossed-web flexure pivot

In Figure A the test object (and fixture) is supported by a spherical gas bearing. A restraint is provided by a hollow tube which extends from the base of the spherical bearing. The lower end of this hollow tube is attached to a second (cylindrical) gas bearing which is connected through a moment restoration transducer to the rigid instrument base structure.

A torsion rod extends downward from the upper surface of the bearing (the rotary table) to a clamping mechanism at the bottom of the rod. When this clamp is released, the spherical bearing is free to turn about the vertical axis for CG measurement and when clamped, the machine is converted to a torsion pendulum for MOI measurement.

These instruments are capable of withstanding a large overturning moment and are ideal for measuring tall payloads such as rockets. MOI tare is larger than the machine shown in figure B.

In Figure B, a flat gas bearing supports the test part and a cylindrical gas bearing defines the rotational axis. The bearing and test table assembly is mounted on crossed web flexures which create a nearly frictionless pivot axis. A moment arm extends from the gas bearing body and is connected through a linkage to the moment restoration transducer. The torsion rod is mounted similar to that in figure A. The measuring principles are the same for both configurations, but the flat bearing type has a lower MOI tare and can measure smaller objects.

Equipment provided with system Instrument, computer (IBM or equivalent), calibration beam, NIST certified calibration weights, interconnecting cables, software, and instruction manual.

Test fixture ("adapter") required The payload must be mounted on the rotary table of the instrument in a precise location. Often this requires a fixture or adapter to support the payload. The accuracy of CG measurement is only as good as the fixture accuracy. A variety of universal and custom fixtures are available from Space Electronics.

Electrical and pneumatic requirements These instruments require 115 VAC, 60 Hz, 15 Amp 1 Phase electrical power. The gas bearing requires clean dry air at a pressure of 80 to 120 PSI (550-825 Kpascal). Gas flow requirements vary according to the size of the machine and are listed on the accompanying data sheet. Generally shop air contains oil and water and is not suitable. Gas can be provided from a standard high pressure bottle, or you can order a compressor-dryer from Space Electronics.

Calibration weights provided All instruments in the series are self calibrating, with weights and distances traceable to NIST.

Optional accessories available Dial indicator stand to assist alignment of payload in fixture, hydraulic load positioner to gently lower payload, and explosion proofing (Class I or II).

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