224   Figure 16. Harmonic D rive Lifting Efficiency vs. Time during the Final Endurance Test  

Initial startup torque values were low with an average measured value of 6.0 mNm (0.86 in- oz), compared  to the 11.1 mNm (1.57 in- oz) for the Braycote 601EF initial measurement. Variations seen in input torque  and output speed across this test series were due to operator error in tuning of the bi -directional applied  load and speed setting. Despite some setting errors, the telltale sign of the success of the Pennzane  Endurance Test was the slight but steady increase in the HD lifting efficiency over the total 400 hour period.  Corresponding with the increase in efficiency over the two times one mechanical life, the final measured  startup torque after test completion had actually reduced from 6.0 mNm (0.86 in- oz) to 5.1 mNm  (0.72 in-oz). The test was finally over.  

Conclusions  

The long standing controversial relationship between Pennzane and Braycote was challenged by the MAIA  MDDA application. The Pennzane ability to functionally rewet hardware t hat had previously been processed  with PFPE lubricant was demonstrated by the completion of the accelerated 72 hour test. The test showed  no change in the efficiency over its duration, despite the aggressive load and speed profile. This indicated  that the Pennzane effectively lubricated the rolling and sliding surfaces of the HD and Duplex bearings, and  maintained this effectivity for 72 consecutive hours in one direction. Post -test chemical analysis showed no  indications of any impact to the lubricant itself due to the operational profile. Thermal testing also showed  the re- wettability to persist over temperature. The Pin- On-Disc test results gave confidence regarding the  chemical compatibility of the lubricants over a long life, and their ability to lubric ate effectively despite their  intermixing. These test results gave the MAIA project the confidence to proceed with the unconventional  solution of changing to Pennzane- based lubricants in the middle of the program, resulting in an MDDA  assembly that has a B raycote lubricated motor, and rewetted Pennzane output gearing, all in one package.  

The relatively uncommon process of pulling flight hardware from storage to revamp for a new flight  application provided challenges to the team. The long- term storage conditions, bagged and sealed in  hydrocarbon oil, proved to be inadequate for the 52100 HD Wave Generator bearings over the two decades  the units were shelved. To reliably use this inherited hardware, a full disassembly, down to the individual  bearing-ball level, and detailed chemical and abrasive cleaning was required in order to locate and eliminate  all of the hidden locations of the corrosion that had developed over time. For certain components to be used  from long- term storage, a similar total d isassembly and detailed inspection is recommended, even if the  assemblies appear to be acceptable by external visual inspection. Specifically, those that use materials that  are sensitive to corrosion, such as 52100 steel, and are inherently difficult to inspect due to hidden  geometry, such as bearing assemblies. Trust, instead, that corrosion is sneaky and will wait hiding in a  crevice or shadow, to ruin hardware performance when least expected.  

Finally, the black oxide surprise turned out to be another unexpected result of using hardware from long  term storage. The HD units used for the MAIA project were originally received in the 1990s, at a time when