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[TowerTalk] design for failure tolerance.. wasRe: LP v SteppIR

To: "Tower and HF antenna construction topics." <towertalk@contesting.com>
Subject: [TowerTalk] design for failure tolerance.. wasRe: LP v SteppIR
From: jimlux <jimlux@earthlink.net>
Reply-to: "Tower and HF antenna construction topics." <towertalk@contesting.com>
Date: Sat, 23 Jan 2010 09:40:50 -0800
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
Mike wrote:
> I know what you meant, that's why I put a smiley after my rumor comment.  I
> was making clear that the Stepper motor is a reliable technology and
> certainly not new and something to worry about. 
> 
> I am sure most failures attributed to Motor failure are tape snarls or
> driver chips in the control unit.  The weak point causing many of the so
> called motor failures is usually the control cable which gets damaged
> through poor installation or animals eating through them causing a short and
> blowing the driver chips and of course resulting in a "Motor Failure". 


Now this is an interesting thing.. There are stepper driver chips 
available have overcurrent/overtemp protection (e.g. from Allegro), so a 
short shouldn't kill the chip. There might be other design reasons why 
one wouldn't pick them (the ones that use PWM to regulate the current 
for microstepping, for instance... RFI nightmare in a ham environment).

In some ways, this is where consumer and ham gear differs from 
professional stuff. Consumer stuff is designed for absolutely lowest 
manufacturing cost, so if the unprotected chip is cheaper, use it. Ham 
stuff (from smaller mfrs in particular) is often a "manufactured" 
version of an original breadboard design which "did the function 
required" but may not have done any more.  Professional gear (by which I 
mean things that people's jobs or lives depend on) tends to be designed 
to be more robust and failure tolerant, but more expensive, because the 
buyers do a cost benefit analysis and a day of downtime can be pretty 
expensive.
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