Model 1278K Mobile VSAT Antenna System
10
Operation and Maintenance Manual
SECTION 3 - AZIMUTH POSITIONING SYSTEM
3,1 AZIMUTH BEARING
The azimuth platform sits on top of a ball bearing platform with a dynamic and static moment capacity of
over four times the worst-case wind load specification. It is surrounded by double seal to protect the
bearing platform, which is permanently lubricated. This rests on the azimuth drum and the azimuth cables
wrap around the drum and capstan.
Because of the excess capacity, low rpm, and low number of cycles compared to the bearings B10 design
life, no wear is expected. No maintenance should be required over the life of the positioner.
3.2 AZIMUTH GEAR BOX
The azimuth gearbox is a low backlash worm gear box. The
worm gear drive isolates any backlash in the motor drive from
the system. In addition, since it is a 40:1 ratio it will not back
drive, eliminating any need for a brake on the drive train. (Fig.
3.1)
The motor drives the input worm via a quill/female hole and
square key. The worm shaft is extended with a hex shape
installed for the hand crank. The azimuth capstan is secured to
the output shaft with a square key knurl plus permanent
locktite to eliminate any backlash between the capstan and
gearbox.
The low backlash is achieved by selective fit of the worm and worm gear. The nominal backlash for the
gearbox is 30’ which is reduced by the AvL cable drive to less than 4’of the beam of the antenna. The
gearbox contains synthetic oil filled half way to the level plugs. Because of the design capacity of the
gearbox, low rpm and limited cycles experienced by the system, no maintenance is required.
3.3 AZIMUTH MOTOR
The azimuth drive motor is a 24 DC motor with integral 30:1 spur gear train. An optical encoder is mounted
to other end of motor output shaft to provide real time positional information to TracStar Systems
controller.
The motor armature rotates at up to 3000 rpm causing a high frequency noise that will vary depending of
the loading condition of the motor.
The maximum output speed is 100 rpm. The output shaft is "D" shaped with a special adapter with a slot
for a square key.
Since the low backlash worm gear drive isolates the backlash from the motor, any backlash between the
shaft adapter, square key or motor gear train will not be seen by the reflector bore sight. The motor is
mounted to an adapter plate that is bolted to gearbox with (4) screws.
No maintenance of the azimuth motor is required.
Figure 3.1