2.4 CONTROLLED / POSITIONER VERIFICATION TEST
Turn power on. Wait for self-check to complete. Hit mode button once to reach display / function
mode. Since positioner is vertical, the display should read:
SLOW
ELEVATION
20.0 DEGREES
(APPROXIMATELY)
AZIMUTH
0.0 DEGREES
STOW (WITHIN 1°)
POLARIZATION
0.0 DEGREES
STOW (WITHIN 1°)
Press speed button to change speed to FAST
Caution!
HAVE SOMEONE OUTSIDE AND ELEVATED SO THEY CAN OBSERVE ANTENNA
MOVEMENT DURING TEST!
Push El UP button. Antenna elevation reading should increase. Move until elevation reading is 18.8
degrees for the 1.8M.
Push Az CW and reading should increase. Run to CW Limit (120°).
Observe antenna movement for potential interference.
Push Az CCW and reading should increase. Run to CCW Limit (-120°).
The Az CCW and CW limits can be increased depending on waveguide and control wire clearance at
truck interface. Refer to Section 3.6 of this manual and Section 4.1.3 of controller manual.
Push Az CW and reading should increase. Run to approximately -15°.
Push Pol CW and reading should increase. Run to CW Limit (55°).
Push Pol CCW and reading should decrease. Run to CCW Limit (-55°).
Push STOW, then BACKSPACE. Antenna should begin moving to 0° Polarization in slow speed. It
should stop at approximately 0° (+ / - 5°). STOW indication should occur in polarization.
Antenna should begin moving in fast speed in azimuth and slow down when approaching 0°. STOW
indication should occur in azimuth. If not, see Section 3.6.
Antenna should begin moving down in fast speed.
PRESS STOP WHEN ELEVATION DOWN LIMIT IS REACHED!
Verify that both azimuth and polarization CW and CCW are disabled.
2.5 ELEVATION STOW SWITCH VERIFICATION
NOTE:
This step is provided in the event that the stow height must be adjusted. The stow switch is
set at the factory.
If the antenna is mounted facing the front of the vehicle, remove passenger side cover on the
elevation axis to gain access to elevation limit switches.
Press SPEED button to change to slow speed.
Press El Down button and watch system stow.
The motor drives the input worm via a quill / female hole and square key. The worm shaft is extended
with a hex shape for the hand crank. The dual elevation drive shafts are driven with a square key. Zero
backlash hubs are used to eliminate any backlash between keyed shafts. They are factory tightened
and should never be tightened again. Over-tightening can bind gearbox bearings. The elevation
capstan is secured to the dual output shafts with four cap screws. These screws are the “safety link”
and will shear under excessive loading conditions to protect the elevation drive system if the reflector
is not stowed and hits an obstacle while the vehicle is in motion.
The low backlash is achieved with a variable pitch worm. The width of the worm tooth slowly increases
along the worm. Since only one small portion of the worm tooth is meshing with the worm gear moving
the worm axially allows one to vary which section / width of the worm tooth is being used to drive the
worm gear. Therefore the backlash can always be minimized to 1 – 3 arc minutes. (Figure 3.2)
The gear box contains synthetic oil filled half way to the level plugs. Due to the design capacity of the
gear box, low rpm and comparative limited cycles experienced by an SNG system, no wear or
maintenance is expected.
4.2 ELEVATION MOTOR
The elevation drive motor is a flat armature, servo quality, 18V DC motor with integral 75:1 spur gear
train. The motor armature rotates at up to 7000 rpm causing a high frequency noise that will vary
depending on the loading condition of the motor. (Figure 4.1)
The maximum output speed is 80 rpm. The output shaft is a standard keyed shaft. The output torque
capacity of the motor is rated for the operational wind load.
Since the low backlash worm gear drive isolates the backlash from the motor, any backlash between
the square key or motor gear train will never be seen by the reflector boresight. Any backlash at any of
these points is of no consequence to the system performance. No maintenance or wear of the
elevation motor is expected.
4.3 ELEVATION CABLE DRIVE
The elevation drive produces a near zero backlash, high stiffness, low wear, no lubrication, maximum
reliability drive system. The system consists of sixteen 3/32, 9 x 17 stainless steel aircraft control
cables reverse wrapped three times around the capstan with a solid connection on one end and high
force, belleville springs on the other end occurring at the elevation cable termination block. It requires
only eight of the cables to provide enough capacity to withstand the required 80-mph wind load. The
additional cables are used to provide increased stiffness and drive redundancy.
If a cable becomes
damaged during use merely cut off cable and continue to use the positioner. The cable may b
replaced as time permits at a typical mainten
ance facility.
The cables are sized to last the life of the positioner. No replacement from wear is expected. The
spring package at one end will automatically compensate for any elongation of the cable.
At installation the belleville springs are collapsed until no “air” is seen between the springs. You should
check this condition yearly to account for the slow settling of the cable strands. Use a 3/16 open
wrench or pliers to hold stud and 7/16 box end wrench to tighten nut.
Care should be taken to not
over tighten the assembly, the belleville springs should be almost fully collapsed to provid
the necessary tension on the cables.
(Figure 4.2)
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