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Monthly Report for Space Robotic FMS PreCommercialization Development Jul 31, 2019

Summary

Structure rebuilt. Testing over narrower frequency range to begin investigation of improved approach to exciting torsion measurement degree of freedom. Simulation of torsion mode Poisson effects begun.

Specification

No change.

Design

No change.

Analysis

no change.

Software Simulation

Times series model of torsion mode excitation for segment 1& 3 excitation is just beginning, in an attempt to understand how to optimize response.

Breadboard Manufacturing

somehow, during vacation period, structure was moved, and results have shifted. The structure was disassembled for inspection. Nothing seemed to be broken. Electronics of excitation was checked, because the level of sound generated during testing is reduced. The modes most influenced seem to be 3 rotation degrees of freedom. Reposition of cables has improved effect significantly, but not completely. It has been decided to proceed with swirl investigation on basis of 'modified' structure. Several modes have dropped in frequency by 20-50 Hz, but they seem fairly consistent even with several disengagement/re engagement of struts.

Breadboard Testing

Phase shifts between rocking mode segment (1 & 3) has begun, in 5 degree increments.

Plans for August.

Continue testing with frequency range narrowed to 500-1500 Hz. Complete time simulation for torsion mode excitation.

What's so tough?

Temperature Lack of atmosphere drives temperatures to be either hot in sun or cold in shade. Robots are for moving things around, so they go into and out of shade repeatedly.

Force not directly measureable. It can be inferred from strain or deflection. Such measures are affected by thermal distorsion.

Large dynamic range linear vs rotation forces. Long robot arms and the need to capture 'free flyers' generates large rotational forces.

High Stiffness A high stiffness requirement, makes measurement of strain or deflection more difficult to isolate from thermal distorsion.

Drift Space operations tend to be slow - often taken over a period of hours.

6 dof It is important to distinguish all 6 degrees of force measurement, but the shear and moment loading cases can produce difficult to distinguish effects