[roc-chat] Re: Switch Warning with StratoLogger CF
- From: Gregory Lyzenga <lyzenga@xxxxxxxxx>
- To: Richard Dierking <applerocketry@xxxxxxxxxxx>, "roc-chat@xxxxxxxxxxxxx" <roc-chat@xxxxxxxxxxxxx>
- Date: Thu, 12 Jan 2017 11:07:40 -0800
On Jan 12, 2017, at 10:18 AM, R Dierking <applerocketry@xxxxxxxxxxx> wrote:
*The topic of redundancy is interesting and maybe deserves a separate thread.
I’ve seen it has different meanings. For example, someone says their
deployment system is redundant but the two systems share the same battery or
activation switch, which can be done with the 110/220 because it has two
circuits. So, what if you are using the same type of switch, or say
deployment system (i.e. two e-matches from the two triggering systems in the
same BP canister), is your system truly redundant? I’ve even considered
using different makes of batteries, or not using ones from the same package.
This is a slight digression from the original thread, but yes Richard you make
an excellent point. I barely dodged a serious redundancy bullet at the last
launch I flew at… My standard operating procedure on my L2 electronic
deployment flights is to provide redundant systems for drogue deployment as a
guard against a ballistic crash. My primary is a Perfectflite altimeter firing
an ematch in a BP charge tube. My backup is a g-switch timer firing a separate
ematch in the same BP charge.
Sounds pretty redundant, right? Well, yes and no. I made a serious error in
judgement by trying to save weight and powered both electronics from the same
9v battery. Although I’ve done this dozens of times and it always worked
perfectly, I guess in my heart I knew it was a disaster waiting to happen…
Like all good disaster stories, this just needed to wait for the intersection
of a second triggering factor. My second error in judgement was that I found
what seemed to be a great deal on eBay for ematch replacements, and since my
ematch supply is dwindling I decided to buy a batch. I tried one out with a 12
volt battery in the garage and it seemed to fire nice and hot, so I decided
what the heck, I’ll put one in my next flight. Thinking I was being wisely
redundant, I used only one of these matches for the primary drogue and one of
my old tried and true matches for the backup, thinking I’d be safe that way.
Wrong.
It all seems so obvious now, but I guess I wasn’t thinking. The el cheapo
ematch has a much higher current draw than a good match (duh) and at apogee
firing it pulled the battery voltage down to almost zero and the charge did NOT
fire. The voltage brownout sent the Perfectflite into a coma and the rocket
was on its way to oblivion. Now I guess it’s true that God protects fools,
drunkards and rocketeers, because against all odds, the backup timer survived
the brownout without resetting, so the rocket landed under drogue after all and
I didn’t have to recover the rocket with a shovel. Only after doing the flight
post-mortem did I realize how close I’d come to a really bad day. A good
reminder not to get complacent!
- Greg
----------------------------------------------------------
Gregory A. Lyzenga <lyzenga@xxxxxxx <
mailto:lyzenga@xxxxxxx>>
Dept. of Physics, Harvey Mudd College (909) 621-8378
<tel:%28909%29%20621-8378>
Claremont, CA 91711-5990 mobile (626) 808-5314
<tel:%28626%29%20808-5314>
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