[TowerTalk] Ham IV Rotor Issue- need help! - LONG

[Tony Brock-Fisher]

Potential Remedy for Stuck Hygain Tailtwister Rotators

Tony Brock-Fisher K1KP

Originally published in YCCC Scuttlebutt

Should also apply to HAM-IV


Everyone is probably aware that the T2X series rotators get stuck. 
Common knowledge has it that the brake wedge gets stuck, and to fix it, 
one can 'rock' the rotator in the opposite direction to get the brake 
unstuck, then move in the desired direction. This 'T2X rock' is a 
standard part of many automated rotator controllers like Green Heron and 
Rotor-EZ.


But often this does not work for my rotator. I have replaced the rotator 
and still had the problem. I replaced a thrust bearing above the rotator 
and still had the problem.


The problem recurred during the RTTY contest. I had a chance to play 
around with it and accidentally learned something that may lead to a 
cure. Thinking that sometimes the brake got stuck and sometimes it 
didn't, it seemed like there was something marginal about it. Maybe if I 
just drove it a tad harder it would work. So I hooked my rotator 
controller (standard Hy-Gain, with Rotor-EZ mod) up to a variac, with 
the idea of feeding it a slightly higher line voltage. And low and 
behold, I discovered that when in this 'stuck' state, the rotator 
control box (and rotator) brake drew **LOTS** more current from the AC 
supply than usual. When I finally got it unstuck, retracting the brake 
drew a normal amount of current. The critical observation was that the 
current draw was **drastically increased** when the brake was stuck.


So here's my working hypothesis:


The rotator gets stuck, when the gear backlash and motor are forcing the 
wedge against the sides of the wedge channel and the grooves in the 
bottom housing. (Bear in mind that the cheaper Hy-Gain rotators use this 
gear ratio as the primary brake). One would think that releasing the 
brake (which is actuating the solenoid) and rotating the motor in the 
right direction would release this load and allow the brake wedge to 
retract. However, the solenoid is an inductor. The inductance changes as 
a function of position. In normal operation, the brake solenoid quickly 
retracts, and the moving iron core completes the magnetic circuit, 
resulting in a high inductance, which limits the current in the brake 
circuit. With the brake wedge stuck, the solenoid is stuck in it's low 
inductance position. The circuit consists of a transformer, switches, 
the rotor cable, and the brake solenoid. The only thing that limits the 
current is the inductance of the solenoid and the resistance of the 
cable. So when the solenoid is stuck extended, it's inductance is very 
low and tons of current can flow. This high load current on the 
secondary of the power transformer saturates its core and reduces the 
voltage available for the motor to start moving. Therefore the motor 
cannot start to move to release the solenoid. Catch-22, everything is stuck.


My experiment:


I added a simple switch in series with pin 2 of the rotator cable so I 
can open the brake solenoid circuit. When the rotator gets stuck, I 
/open that switch/. This allows me to activate the motor to do the 'T2X 
rock' without allowing the stuck brake solenoid to load down the 
available voltage. I do a quick back and forth with the motor with the 
brake engaged. Then I close the switch, which allows the brake solenoid 
to retract. Voila! It moves again. So far, this has worked several 
times. Obviously, if attempting to move the motor with the brake stuck 
doesn't hurt anything, moving the motor with the brake engaged won't either.


So the common knowledge about stuck T2X rotators may be incomplete, and 
it might make sense for automated rotator controllers to do the 'T2X 
Rock' with the brake solenoid de-energized.


Try it and let me know if it works for you!



p.s. The transformer does have a thermal cutout, which will open if it 
gets too hot, then close again on cool down.