ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
ix  Development of Variable Reluctance Resolver for Position Feedback  Gregory Leibovich, Ducommun LaBarge Technologies, Carson, CA; et al   FeF 3 Catalytic Influence on PFPE Lubricants Lifetime under Loaded Conditions  Lionel Gaillard, European Space Agency, Noordwijk, The Netherlands; et al   Trade Studies for a High Torque Density Planetary Gearbox  Jeffrey Mobley, Sierra Nevada Corporation, Durham, NC   Single Motion Actuated Shape Memory Alloy Coupling  Alberto Perez, Naval Postgraduate School, Monterey, CA; et al    Development and Testing of a High Compact Stepper Motor Mechanism  Jörg Schmidt, Phytron Elektronik GmbH, Grabenzell, Germany; et al   Cryogenic Temperature Testing of NEA Fuse Wire Mechanism  Edwin Vega, NEA Electronics, Inc., Moorpark, CA; et al 

6:00 -10:00  RECEPTION  - California Ballroom, Hilton Pasadena  Invited component suppliers display current products and provide tutorials. Local high school  FIRST Robotics Team demonstrations, and a light buffet meal.  

THURSDAY, 17 MAY 2012   7:00  Thursday Presenters' Breakfast - San Marino Room, Hilton Pasadena   8:00  SESSION IV – ROCKETS TO ROBOTS    Brett Kennedy, Session Chair  Jet Propulsion Laboratory, Pasadena, CA   Developmental Testing of Electric Thrust Vector Control Systems for Manned Launch Vehicle  Applications Lisa Bates, NASA Marshall Space Flight Center, Huntsville, AL; David Young, Raytheon – Jacobs ESTS Group / NASA MSFC, Huntsville, AL   Development of High Temperature High Current Contact Technology in Slipring Assemblies for  the BepiColombo MPO & MTM Spacecrafts Fabrice Rottmeier, RUAG Space Switzerland, Nyon, Switzerland, et al   Lessons Learned to Avoid Coax Cable Failure in Moving Mechanical Mechanisms  Sheah Pirnack, Lockheed Martin Space Systems, Denver, CO   DLR’s Dynamic Actuator Modules for Robotic Space Applications  Armin Wedler, German Aerospace Center (DLR), Wessling, Germany; et al 

10:00  BREAK    10:15  SESSION V – MARS SCIENCE LABORATORY  Ruben Nalbandian, Session Chair Moog, Inc., Chatsworth, CA   Mars Science Laboratory Rover Integrated Pump Assembly Bellows Jamming Failure  Michael Johnson, Jet Propulsion Laboratory, Pasadena, CA, et al   Development of the Descent Brake Mechanism for the Mars Science Laboratory  David Dowen, Sierra Nevada Corp., Louisville, CO; et al   Mars Science Laboratory Differential Restraint:  The Devil is in the Details  Elizabeth Jordan, Jet Propulsion Laboratory, Pasadena, CA   Mars Science Laboratory’s Dust Removal Tool  Kiel Davis, Honeybee Robotics Spacecraft Mechanisms Corp., New York, NY; et al 

12:15  LUNCH   Lunch for AMS Attendees in the California Ballroom, Hilton Pasadena
x 1:15  SESSION VI – MORE MSL, INSTRUMENTS & SEPARATION   Doug Packard, Session Chair  NEA Electronics, Inc / Rocketstar Robotics, Inc, Moorpark, CA   A Zoom Lens for the MSL Mast Cameras: Mechanical Design and Development  Daniel DiBiase, MDA Information Systems, Inc. – Space Division, Pasadena, CA, et al   Wet Chemistry Automated Sample Processing System (WASP)  Juancarlos Soto, Ball Aerospace & Technologies Corp., Boulder, CO; et al   Refinement of a Low-Shock Separation System  Chuck Lazansky, Sierra Nevada Corporation, Louisville, CO   Ares I Linear Mate Umbilical Plate and Collet  William Manley, NASA Kennedy Space Center, FL; et al 

3:15  BREAK  

3:30  SESSION VII – INSTRUMENTS   Charlie Hodges, Session Chair  Sierra Nevada Corporation, Durham, NC   GMI Spin Mechanism Assembly Design, Development, and Test Results  Scott Woolaway, Ball Aerospace & Technologies Corp., Boulder, CO; et al   Lessons Learned from the TIRS Instrument Mechanisms Development  Jason Budinoff, NASA Goddard Space Flight Center, Greenbelt, MD; et al   Resolution for Fretting Wear Contamination on Cryogenic Mechanism  Charles Clark, Lockheed Martin Space Systems, Palo Alto, CA 

6:30-10:00  BANQUET  – Pasadena Conference Center   6:30 – 8:30  Social Hour, Dinner and Live Jazz Band   8:30 – 10:00 Entertainment and Show   FRIDAY, 18 MAY 2012 

7:00  Friday Presenters’ Breakfast - San Marino Room, Hilton Pasadena   8:00  SESSION VIII – TRIBOLOGY/BEARINGS    Terri Taylor, Session Chair Honeywell International, Glendale, AZ   Design and Manufacturing Considerations for Shockproof and Corrosion-Immune Superelastic  Nickel-Titanium Bearings for a Space Station Application  Christopher DellaCorte, NASA Glenn Research Center, Cleveland, OH; et al   Wear of Steel Ti6Al4V in Vacuum  Timothy Krantz, NASA Glenn Research Center, Cleveland, OH; et al   Angular Runout Test Setup for High-Precision Ball Bearings  Scott Miller, Lockheed Martin Space Systems, Palo Alto, CA; et al   9:30  BREAK
xi 9:45  SESSION IX – SMALL SESSION ON SMALL SATELLITES  Scotty Allen, Session Chair  ATK Space Systems, Goleta, CA   LightSail-1 Solar Sail Design and Qualification   Chris Biddy, Stellar Exploration, San Luis Obispo, CA; et al   A Novel Release Mechanism Employing the Principle of Differential Coefficients of Thermal  Expansion Clint Apland, Johns Hopkins University / Applied Physics Laboratory, Laurel, MD; et al   A Nichrome Burn Wire Release Mechanism for CubeSats  Adam Thurn, Naval Research Laboratory, Washington, D.C.; et al   Antenna Deployment Mechanism for the Cubesat Xatcobeo. Lessons, Evolution and Final Design  Jose Antonio Vilán Vilán, Universidad de Vigo, Vigo, Spain; et al 

11:45  SPECIAL PRESENTATION   Development of the Mars Science Laboratory Rover “Curiosity”, from Concept to Launch   12:15  TECHNICAL SESSIONS CONCLUSION   Edward Boesiger, Operations Chairman, Lockheed Martin Space Systems, Sunnyvale, CA  • Herzl Award Presentation • Closing Remarks 

12:30  LUNCH   Lunch for AMS Attendees in the California Ballroom, Hilton Pasadena   1:30 – 4:30 JPL TOUR     1:30  Buses depart hotel for JPL     2:00-4:00 Facility tour at JPL    4:30  Buses return to hotel
xii SYMPOSIUM ORGANIZING COMMITTEE 

Donald R. Sevilla, Host Chairman, JPL   Louise Jandura, Co-Host Chair, JPL 

Stuart H. Loewenthal, General Chairman, Lockheed Martin  Edward A. Boesiger, Operations Chairman, Lockheed Martin 

Steven W. Bauman, NASA GRC  William Caldwell, NASA Ames  Jared Dervan, NASA MSFC  Carlton F. Foster, NASA MSFC (retired)  Claef F. Hakun, NASA GSFC  Christopher P. Hansen, NASA JSC  Wayne Jermstad, NASA JSC  Alan C. Littlefield, NASA KSC   Ronald E. Mancini, NASA Ames (retired)  Fred G. Martwick, NASA ARC  Donald H. McQueen, Jr., NASA MSFC  Gérard Migliorero, ESA/ESTeC  Robert P. Mueller, NASA KSC  Fred B. Oswald, NASA GRC  Minh Phan, NASA GSFC   Joseph P. Schepis, NASA GSFC  Mark F. Turner, NASA ARC  Robin Tutterow, NASA LaRC  James E. Wells, NASA LaRC
1 Development of Brushed and Br ushless DC Motors for use  in the ExoMars Drilling and Sampling Mechanism 

Robin Phillips*, Massimo Palladino** and Camille Courtois+  

Abstract 

This paper presents a summary of work performed to qualify two COTS (Commercial Off The Shelf)  motor types (one Ø13 mm brushed and one Ø22 mm brushless) for operation in a Martian atmosphere for the ExoMars Drilling and Sampling Mechanism. We present all the major steps in this process, which included an analysis of features that needed changing from the standard industrial motor design, a development program that was undertaken to select an appropriate design, and a qualification campaign that was then applied to the modified motors.   Introduction   Maxon motor is well known for having built all the drive and steering motors for JPL’s Mars Pathfinder (Sojourner) and MER (Spirit & Opportunity) rovers where the soundness of the basic design has been demonstrated over the 7+ years that Opportunity has now spent roving on the Martian surface.  Maxon was also selected by ESA to develop motors for its ExoMars rover mission. However, the significant differences in requirements for the Drilling and Sampling mechanism did not allow the selection of the same type of motors as MER used. Specifically, the specified lifetime and power output for the main drill drive motor required the use of a brushless motor since the expected lifetime of a brushed motor was not sufficient for this application. Additionally, space restrictions inside the drill required the use of a smaller brushed motor (Ø13 mm) than had been used in either of the previous JPL missions.   As with the JPL RE25 development, the aim was to adapt industrial standard motors (i.e., a so called “Commercial Off The Shelf” or COTS design) rather than to develop a custom solution in order to lower development costs. The process followed in the development program included three main steps:   1. A detailed analysis of the standard industrial motor design to identify features that were unlikely to  work correctly when exposed to the environmental conditions and duty cycles requirements of the ExoMars mission.  2. Research into possible solutions to the identified design problems and then an appropriate  redesign of the motors.  3. Manufacture and qualification testing to simulate all relevant aspects of the ExoMars mission on  the new design.   Mars Rover Electric Motors Background 

Successful operation of electric motors on the Martian surface was initiated by the Viking project which put two landers on Mars in 1976. The Viking landers used numerous motors in the twin cameras (e.g., for rotating the camera housing and moving the scanning mirror) as well as for the sampling boom and communications antenna pointing. That electric motors have a history of causing technical difficulties for                                                    * maxon motor ag, Sachseln, Switzerland   ** ESA, ESTEC, Noordwijk, The Netherlands  + RUAG Space, Nyon, Switzerland 

Proceedings of the 41st Aerospace Mechanisms Symposium, Jet Propulsion Laboratory, May 16-18, 2012
3 motor which due to the required lifetime and power requirements need to be a Ø40-mm brushless motor  and the drill translation unit which due to power requirements was best achieved with a Ø22-mm brushless motor.  In order to avoid the motor problems that plagued the MSL development, a program was started to design and qualify both of these two new motor types. This program also had the express goal of making sure that the technology needed for making such motors was available outside of the USA so as to be free of ITAR restrictions. The first stage of this program was to analyze the existing commercial motor designs for features that were unlikely to be compatible with the ExoMars environmental and operating specifications.   

Figure 1: The ExoMars drill box breadboard (left) and drill mandrel EM (right)   Specifications Summary   Although much of the specification for the motors is similar to that for a terrestrial application, there are a few key areas that a significantly outside of the normal application regime that a COTS motor would be expected to be designed for, these are summarized in Table 2. 

Table 2: Summary of ExoMars specification that is significantly different to an industrial standard  application  Non-operating temperature range -120 °C to 125 °C  Operating temperature range -55 °C to 30 °C  Operating atmospheric conditions 1 bar, Earth standard  5-10 mbar CO 2 (Martian atmosphere)  Vibration environment Sine 100 Hz, 33 g  Random 20-2000 Hz, 17.2 g rms  Shock loading 100 Hz: 25 g , 300 Hz: 400 g  2 kHz – 10 kHz: 1500 g 

Several features of both motors that were incompatible with these specifications had common solutions,  such as modifying the bearing grease to Braycote 601EF for the low temperature pressure environment and changing the wiring to a type compatible with standard ESA wiring specifications. Various materials in the standard motor designs were modified, such as the aluminium housing and front flange of the EC22 which were changed to titanium, in order to avoid problems with differential expansion (aluminium bearing seat to stainless steel bearing race for example) or to reduce the mass. Other features, however, were specific to each motor type and are described in more detail in the next two sections.
4 Key Problems for Brushed Motors 

Derating factor   The RE13 standard motor has a specification sheet defining the maximum mechanical output power (i.e., torque and speed) allowed. The extremes of the continuous operating regime are determined by the maximum allowed winding temperatures (125 °C in the case of the RE13). Normally the winding will cool via a mixture of conduction (via the shaft), convection (via the air surrounding the winding) and radiation. A reduction of atmospheric pressure will cause a corresponding reduction in the convection component of this cooling and hence in the available performance from the motor.  In order to quantify the size of this effect, a simple test was conducted with an RE13 motor in a vacuum chamber. The resultant measured thermal resistances (Table 3) could then the programmed into maxon’s standard motor simulation software and new maximum continuous torque calculated. As can be seen from Table 3, the presence of even a small atmosphere causes a dramatic improvement in thermal conductivity.    Table 3: Measured winding to housing ther mal resistance and corresponding maximum  continuous torques for RE13  Atmospheric pressure  (all with Earth standard composition) Thermal Resistance  (Winding->Housing) [K/W] Maximum continuous  torque [mN-m]  1 bar 7 2.39  7±1 mbar 9 1.85  <1x10-3 mbar 50 0.811   Vibration and Shock Considerations for Brushed Motors  For the RE13 motor, there was concern that during shock and vibrations (mainly from launch and landing) there is no contact between the motor winding and the housing. This is particularly of concern since the RE13 motor winding is a cantilever (Figure 2) and the gap between the winding and housing can in the worst case tolerances be only 170 µm, as shown in (Figure 3). 

Figure 2: RE13 rotor showing bell shaped  winding attached to shaft   Figure 3: Detail of gap between RE13 winding  and housing   Based on a resonance search performed on the rotor by itself (see Figure 4), the winding fundamental frequency and the associated amplification factor were found to be 529 Hz and 3.5 respectively. Considering the random vibration requirement, by using the Miles equation for displacements, the winding displacement is given by:  Winding  Housing  Magnet
5 3 332) ( fresQfres PSDdispRMS     where fres is the motor winding fundamental frequency, Q is the amplification factor at resonance,  PSD( fres) is the specified power spectral density of acceleration at frequency f and dispRMS is the RMS  displacement. The motor winding RMS displacement during random vibration was found to be 25 µm with  a 3 sigma peak of 75 µm. Therefore, any contact between the motor winding and the housing is excluded, even at 3 sigma (since the gap is no less than 170 µm). A random vibration test was performed on the fully assembled RE13 as part of the qualification testing and no signs of contact between winding and housing were seen after the test.  A shock analysis was performed to assess the behavior of the RE13 motor winding, considering the  required shock response spectrum. A half-sine shock of 1500 g amplitude and 0.5 ms was applied. Figure 5 shows that the shock generated (in red) envelopes the required shock response spectrum (in dotted blue). 

Figure 4: Test setup for the random vibration  test conducted on the RE13 winding   Figure 5: Shock response spectrum applied on  the motors  The displacement of the motor winding during shock, evaluated by analysis, is about 1 mm. This shows that the contact is likely. However, the shock will only create a contact between the motor winding and the housing during a very short period of time. This is considered acceptable (the time is short enough to avoid any damage). The shock test performed on the assembled RE13 motor showed that indeed no effects from such contact were observable.  Brush material  Although brushed motors have the advantage of not needing complex commutation electronics, they determine the lifetime of the motors and cause the life to be much lower than for an equivalent brushless motor. Unfortunately the most common brush materials for high current applications used in industrial motors (copper or silver graphite mixtures) require the presence of water vapor and oxygen to build up a hardened patina on the wear surface of the brush. If the water vapor is not present, then extremely rapid wear can occur.   The situation with no water vapor applies on Mars and was noticed during qualification testing for the Viking lander camera scan mirror motors in the mid 1970’s (Mutch 1978, p. 17). Twenty years later for the Sojourner rover the problem was circumvented by the use of precious metal brushes without lubrication in otherwise nearly standard RE-16 motors. This is a simple solution for situations where required torques are low and only limited lifetimes are required. Testing for Sojourner showed that under load and start-stop conditions motor failure occurred after about 30-40 million revolutions (Braun 1998) which was more than sufficient for the planned mission.
7 Table 5: Brush material types tested. Motor  group number is used elsewhere in this report to refer to a particular brush material type. Group 7 with a very high silver content was an attempt to produce a brush that was optimized for vacuum operation.  Motor  Group Brush Material  1 50% Cu 45% C 5% MoS 2  2 50% Cu 40% C 10% MoS 2  3 50% Cu 35% C 15% MoS 2  4 50% Ag 45% C 5% MoS 2  5 50% Ag 40% C 10% MoS 2  6 50% Ag 35% C 15% MoS 2  7 85% Ag 3% C 12% MoS 2  8 50% Cu 50% C     Figure 6: Motor holder setup. The eddy current  brake magnets are visible on the inside. 

Table 6: The test sequence followed. The motor revolutions column shows the approximate  number of revolutions the motors  made during each test phase (based on actual number of hours  run and the approximate speed settings).  Period Gas Pressure  No. of motor revolutions   3 days 78% N 2, 21% O 2 + other traces ~1000mbar 30 million  2 weeks CO 2 5-10mbar 165 million  1 week none <10-6mbar 60 million 

 Figure 7: Current draw for all motors in 8 mbar  CO 2 test.   Figure 8: Motor currents during the 2nd week in  8 mbar CO 2 atmosphere. The gaps in the data  are caused by the logging PC crashing - the motors continued to run in these gaps.
8   In order to simulate a near worst-case thermal situation, the motors were mounted in a plastic Polyoxymethylene (POM) holder (see Figure 6) so there would be minimal thermal conductivity. Eddy-current brake disks were used to provide the required load. Each motor was individually monitored and its current draw logged.   At the end of each test phase, 2 of the 3 motors with a particular brush type were opened up and pictures of the brushes and collectors taken under a microscope. The 3 rd motors of each brush type were not  opened so as to retain the worn material inside the motors. The motors that were opened had all loose brush material vacuumed out before re-assembly. Other than vacuuming, no attempt to clean them was made; in particular the collector slots were not cleaned (other than vacuuming).  The initial 2.5-day run under normal Earth atmospheric conditions produced the main result that the group 7 motors all failed within the first 14 hours. Inspection of these brushes showed that the cause of failure was the complete wear of the brushes. Thus these brushes are shown to be unsuitable. The following one week of operation in an 8 mbar CO 2 atmosphere was performed with the motors operating with loads  of between 1.65 mN-m and 2.05 mN-m and speeds of between 8500 rpm and 9200 rpm. The differences were caused by a mixture of motor manufacturing tolerances (all motors shared the same power supply) and variations in how the eddy current brakes responded variably to running in a vacuum after being set under atmospheric conditions (brake adjustment after being placed in the vacuum chamber was not possible).    The first week of operation in an 8 mbar CO 2 atmosphere also produced a number of failed motors. The  first motor (equipped with maxon standard brushes) failed after 1.5 days followed a few days later by additional motors. By day 6, all group 8 motors (standard brushes), all group 1 motors, all group 2 motors, and 2 of 3 group 4 motors had failed. These were the groups with lower MoS 2 content. Additionally, all  group 3 (Cu 15% MoS 2 brushes) showed increase current draw. We therefore decided to interrupt the test  and open all failed motors to inspect the brushes.  It immediately became clear upon inspecting the brushes that the motors were failing due to the complete wear of the brushes. As the brushes come to the end of their life, the section in contact with the collectors becomes wider causing several collectors to be in contact with the brush at the same time. This leads to winding segments being short circuited and hence a higher current draw. 

One problem that had not been anticipated was that as the motors start to fail they dramatically heat up. In the case of motor 8.2, which had a temperature sensor on it, the housing reached over 180°C (implying Figure 9: Motor current from the best  performing brush types where no deterioration is seen after two weeks near continuous operation.   Figure 10: Motor currents during operation in  vacuum. Brush type 5 all failed within 25  minutes of starting the test!
9 a winding temperature of >200°C!). This caused the POM support structure to melt and hence their brake  disks to contact the brake magnets. Thus no significance can be attributed to the presence or variation of spikes and other features in the current curves once the motors start to fail.  The major results of this first week of testing are that copper-based brushes do not work as well as silver-based brushes for high load situations like this, and that in both material types more MoS 2 results in  slower wear rates.   Brush Type 2 (Motor 2.2)  Brush Type 4 (Motor 4.3) Brush Type 6 (Motor 6.2)

After 1 week CO 2 After 1 week CO 2 After 2 weeks CO 2  Figure 11: Pictures of the RE13 brushes after 1 week operation in Earth atmospheric conditions  (top row) and 1 week operation (2 weeks for type 6) in an 8 mbar CO 2 atmosphere (bottom row).  Since the results from the first week of tests were now understood, we decided to run the second half of the CO 2 test at a lower voltage to test a different working point. The eddy current brakes were set to a  value corresponding to a load of 0.65-0.8 mN-m at 8000 rpm. Since the ExoMars specification of  2.3 mN-m includes all possible margins, actual operation would be expected at a lower power setting so it is also important to test at these lower current settings.  The results from the second week of CO 2 testing clearly re-enforce the results of the first week. The  silver-based brushes work considerably better than the copper-based brushes and the higher the quantity of MoS 2, the longer the brush lasts. No significant wear is present in group 6 brushes, even after 2 weeks  of operation (see Figure 9). It seems likely that some significance can be attributed to the result that both motors 3.3 and 5.3 (i.e. those which were not opened and hence retained the worn brush dust) started to fail before those motors which were opened and cleaned, however the effect is not large.  The results from the vacuum testing were consistent with what was been reported by (D. E. Noon 1999) in that failure is extremely rapid and is caused by brush wear residue accumulating between the collector bars and causing partial shorts. Type 5 motors were already starting to wear out at the end of the CO 2  testing as they were showing increased current draw. Despite this, we were surprised at how fast they failed; after less than half an hour of running in vacuum all three group 5 motors had failed.