Table 5. Wheel rotations to failure, plastic shields over bearings, no MoS2 on gears or bearings -- --  unit # Date Wheel cycles --  CP046 03 Mar 2003 524 Failed, bearing 1,3,4 - bad, bearing 2 - good  CPO14 03 Mar 2003 520+ No failure, bearing 1 - bad, 2 - fair, 3, 4 - good  CP020 04 Mar 2003 820+ No failure, bearing 1,3 - bad, , bearing 2,4 - good  CPO16 13 Mar 2003 404 Failed, bearing 1, 4 - bad, bearing 2 ,3 - fair  Ball bearings with MoS2 lubricant were received and put into solenoids with the plastic shields next to the  inboard ball bearings and were cycle tested with very favorable results (Table 6). A fix or a solution to our  early wheel cycle failure was found. The solenoid used in the first test of CP028 showed an unrelated  assembly issue, resulting in a frictional rub between the inboard rotor and the stator. After being rebuilt  with an additional 13-micron shim added under the inboard rotor but with the original bearings, the second  cycle test of CP028 performed very well.  Table 6. Wheel rotations to failure, plastic shields over bearings with MoS2, no Mo~ on gears  Unit#m U ate wh eel cycles  CP046 21 Mar2003 101 4+ No failure, bearing 1, 2, 3, 4 - good  CP048 25 Mar 2003 1 ooo+ No failure, bearing 1,2 -fair, bearing 3,4 - good  CP028 25 Mar 2003 52 Failed, bearings - good, inboard rotor rub  CP028 26 Mar 2003 1 ooo+ No failure, bearing 1, 3, 4 - good, bearing 2 - fair  As previously discussed, the dynamic axial load was 71 N versus the manufacturer’s rated load of 116 N.  Since our load condition is a small reversing stroke rather than continuous rotation, the duty is more  severe than the rated condition. The dry film lubrication used in the bearings of the units of Table 6  appears beneficial when compared to the dry bearings of Table 5 and confirms the bearing manufacturer’s  recommendation that lubrication becomes more important as the bearings are more severely loaded.  The drive arm bearings are very close to the gear teeth but did not show any wear when compared to the  solenoid bearings. Many of the gear particles stayed on the gear teeth as shown in Figures 3 and 5, but  some of the particles will migrate to other parts as shown in Figures 7 and 8. The electric coils in the  solenoids produce a magnetic flux field when the coils are energized. The flux field is in the shape of a  toroid that makes a complete loop about the coil from the inside coil diameter to the outside coil diameter.  Most of the flux passes through the rotor and stator due to the high permeability of electrical iron, but  some flux passes through the air between the races of the bearings. Loose magnetic particles will align on  these flux lines and then move along the flux lines to high magnetomotive force. Some of the particles are  pulled into the bearings where they become scabs as the balls roll aginst the races.  The large axial loads on the solenoid rotors are present only when the coils are energized. The wear  particles are pulled into the bearings and rolled flat when the coils are energized; the rotors are returned to  their home positions by helical extension springs. Hence, the slower and erratic motion of the rotor was  observed during the energized stroke only and not during the return stroke. Likewise, a manual rotation  and a zero-volt solenoid torque test would not show the large friction that is present when the coil is  energized. The inboard rotor motion was erratic and caused the operational failure since the inboard rotor  bearings are very close to the gear teeth and the resulting wear particles. When the plastic shields are in  place as shown in Tables 5 and 6, the inboard bearings (3 and 4) are not consistently worse than the  outboard bearings (1 and 2).  33