[NLRS] FW: Stuck rotor brakes

[John Allen]

Here is some information on solving the stuck rotator brake issue.

 

Regards, John K1AE

John Allen - PC Support Solutions www.pcsupportsolutions.com
<http://www.pcsupportsolutions.com/>  
M: 508 361-6229





From: Chuck ONeal K1KW

Subject: Re: Stuck rotor brakes

 

I had that problem on my Wilson WR-1000's and fixed it by running the brake
solenoid on DC, using a big output cap to handle the initial inrush current.
AC solenoids work very well on DC the DC will not work on AC. 

 

The other issue with AC solenoids is that their initial pull in force is
dependent upon where in the AC cycle it gets switched in.  At the peak of
the voltage waveform, the initial force will be much greater than at a zero
crossing which results in a "soft" increase in force over the cycle and is
less likely to break free a stuck brake..  

 

From:   YCCC <yccc-bounces at contesting.com> on behalf of Tony Brock-

Fisher via YCCC <yccc at contesting.com>

Sent:    Friday, January 16, 2015 2:47 PM

To:       YCCC at YCCC.ORG

Subject:           [YCCC] New Learnings on Stuck HyGain Tailtwisters

 

I think I discovered something interesting about T2X rotators.

 

Everyone is probably aware that they 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 Rotro-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. 

Obviously, if attempting to move the motor with the brake stuck doesn't hurt
anything, moving 

the motor with the brake engaged wont 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!

 

-Tony, K1KP

 

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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