AvL Proprietary and Confidential
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7.2.2 Elevation Positioning
The elevation cable drive produces a drive system with zero backlash, high stiffness, no wear, no
lubrication, and maximum reliability. The system consists of stainless steel aircraft control cables
reverse wrapped twice around the grooved capstan, and once around the drum, with solid
connections on one end and high force Belleville springs on the other end. The additional cables are
used to provide increased stiffness and drive redundancy.
If a cable becomes damaged during usage, remove the cable and continue to use the positioner. The
positioner is design to operate using a single cable if necessary. When time permits the damaged
cable should be repaired by an authorized service facility.
The cables are sized to last the life of the positioner. No replacement from wear is expected. The
spring packages at one end will automatically compensate for any elongation of the cables. Cable
position and stiffness should be checked as per a periodic maintenance schedule. The Elevation
drive components are described in this section.
7.2.2.1
Elevation Pivot Assembly
The elevation pivot assembly consists of two elevation drum assemblies pivoting between two clevis
blade assemblies. The drum shafts pivot in hi-tech plastic (Delrin) bushings.
7.2.2.2
Elevation Gear Box
The elevation gearbox is a low backlash worm gear box. The worm gear drive isolates any backlash
in the motor drive from the system. In addition, the gear box eliminates back-drive, eliminating any
need for a brake on the drive train.
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 hand crank is utilized to manually
manipulate the positioner in the event the controller fails. The elevation capstan is secured to the
output shaft with a clam shell coupling to eliminate any backlash between the capstan and gearbox.
The low backlash is achieved by the selective fit of the worm and worm gear. The gearbox contains
synthetic grease to help prevent wear in the gears. Because of the design capacity of the gearbox
and low rpm, no maintenance is required.