[TowerTalk] crank down automation was Re: Crank Up towers

[Jim Lux]

At 07:05 PM 12/23/2005, Jason Creager wrote:
>One advantage to crank up towers is that they can be motorized and automated.
>
>Of course, I can't find it right now, but I remember reading about one ham 
>who was also a home automation buff. He built a new house and used 
>HomeSeer (HA software) to automatically lower his tower if the winds 
>reached a certain speed. It was very cool and easily implementable.

While this is easily implemented, it's non trivial to do it safely.  Just a 
few issues pop to mind with automated systems capable of serious damage:
1) What if the wind comes up and the crankup wedges, but the winch keeps 
paying out cable (assuming a non-positive pulldown system).  Does the 
automated system have feedback from the tower to confirm that it's actually 
moving as expected.  Or, when the wedge breaks free, does the tower drop to 
the end of the slack?
2) What if somebody has their hand in the tower, and the wind comes 
up?  Does the automated system have safeguards to prevent actuation when 
there's someone around the tower?  (Along the same lines, if you're in an 
area with icing, the tower is up, and you start to lower it, and huge 
chunks of ice fall down?

There's a lot of things that can be done safely with an operator watching 
or monitoring that can't be done (trivially) with an automated 
system.  Automated systems require a fair amount of preplanning and "What 
if X happens" kind of thinking.  I don't want to imply that the ham didn't 
do this for his system, but I've seen people leap into this kind of project 
thinking they're going to use X-10 powerline type remote control, or a 
Windows control application, without a hardwire interlock or safety system 
for life critical applications.  The scary thing is, you'll get away with 
it most of the time.


   I have first hand knowledge (as in, I saw the event occur or saw it's 
immediate aftermath)  of two fairly big F-Us (where severe property damage 
or personal injury was involved) because of "trusting that software 
application to control the RF power in the system".  I also have zeroth 
hand (as in I did it) knowledge of an automated hydraulic motion control 
system that came real close to accidentally seriously injuring someone when 
the feedback encoder failed, and there wasn't a mechanical rate limiter, 
nor had we contemplated that failure mode. I think one needs these "near 
death" experiences to really appreciate what's needed.  Stuff that works 
well most of the time, particularly software control, tends to make one a 
bit complacent.

Jim W6RMK