[TowerTalk] Preventing tic ring motor from freezing

[Bill N7VM]

Howard writes:
>  ... The rotor is the 1048D. Abut 3 years old. The pot resistance 
> measurements do not vary with temperature. More likely mechanical in the 
> area of the motor interface to the ring. I allowed it to stall for 
> several minutes a couple of times, probably not a good idea, and when it 
> heated up enough it turned.

Summary of mechanical failure modes for TIC Ring Rotor and solutions:

1. Motor shaft rotating within first external gear (rather than turning the 
gear).  This gear is connected to the motor using two small (#6 I believe) 
set screws.  On one of my rotors, the set screws simply bear on the round 
motor shaft.  No way can these be tightened up enough.  Both of my rotators 
experienced this failure mode.  Solution: Remove gear and machine two flat 
spots onto shaft for the set screws to bear against.

2. Mechanical interference between rotating parts of the ring and the fixed 
parts on the tower.  There are several different pieces and places that 
things can hang up - too numerous to try and describe here.   Solution: 
Remove motor and check for free rotation through all 360 degrees.  If 
anything is found hitting, correct the leveling of the unit, adjust the 
various rollers, or simply remove offending structural material (if 
possible).

3. Lack of proper gear engagement between motor unit and gears on ring. 
Solution: This is an installation problem: loosen the motor and slide it to 
provide tighter gear engagement with the ring and retighten.

4. Motor too tighly engaged with the ring.  Either due to tolerance problems 
with the design/manufacture or due to installation problems, the ring gears 
are not at a constant distance from the motor mount throughout the full 360 
degrees of rotation on one of my units.  Thus, I believe it is possible to 
mount the motor too close to the ring gears (e.g., at a point in the 360 
degree rotation with a large ring-motor spacing) that will then cause the 
system to bind up (e.g., at a point in the 360 degree rotation with a small 
ring-motor spacing).  This is a theoretical failure mode - I have not 
actually observed this...  Solution: Try moving the motor to provide looser 
gear engagement with the ring.

Temperature changes could certainly aggrevate any of the problems, as 
various pieces change size subtly with temperature.

It is extremely helpful to have someone in the shack operate the rotator 
while you are on the tower (safely attached by your fall arrest lanyard 
positioned where it does not interfere with the rotor) so you can watch.  Of 
course, you need a comm link to the shack... avoid using FRS radios, as once 
you are 100-feet in the air every bozo within 20 miles will be able to hear 
you...

On the electrical side, I would mention that I had a pot fail with open 
center tap.  When repairing, I noticed that only the ends had bypass caps, 
but not the center tap.  So I added another 0.01 uF bypass cap on the center 
tap.  The replacement pot is  Bourns 3590S-2-501L available from Digikey for 
about $10.

Good luck...

73 de Bill N7VM