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.
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