Its an issue about safety :)
we've had a relay controller fail in the closed position, luckily it was
durign storage and drained teh battery, without accidentally lighting off a
rocket while a roclketeer was underfoot.
best way to avoid this is to know your equipment. keep it simple and have
I notice that in this cautionary tale, no mention is made of just exactly what
was wrong with the launch controller which leaves me with far more questions
1) Just what was the circuit design and how was it intended to operate?
2) How much current was available?
3) At what voltage?
4) Did the circuit operate as designed or was there a failure?
This is of more than academic interest as I assist with the design and
construction of my clubs equipment.
The electric matches supplied with Pro38 motors have a maximum safe test current
of a few tens of milliamps.
And to add, always touch the clips together to verify no current. Saved
my ass last Aug. Wish I could say the same for guy on the pad next to me ;/
Simplest thing in the world to do yet so many overlook it.
I can't remember where I heard it (think it was here...) but there
was a suggestion that igniters should be connected to the controller,
*before* being inserted into the motor. That way, if the controller
is indeed faulty, all you've gotten is a scare... instead of first- or
(Wish I could remember where I saw it posted before, so I could
give the original poster credit...)
I prefer attach the igniters to the (shorted) launch leads and then at a
safer distance plug those into the controller then your hands are never in
the flame path at the critical moment. And always continuity test the
igniters outside the motor.
Also the measurement of '8 volts' across people isn't especially
meaningful - if indeed it is a valid test (I remember meters we had a school
that indicated that I was a 60v source!) - it gives no idea of how much
Others have pointed out that sticking ignitor leads in ones mouth is not a
good idea, since there is no telling what is connected at the other end. I
wouldn't want 12v across my tongue, but what if someone had erroneously
connected the launch controller to an inverter ? (unlikely one would hope
but possible, some people use mains connectors on LCs)
Would static charge not be a more likely explanation? The oxral igniters
supplied with Pro38's have been fired by continuity tests before, does
anyone know conclusively of e-matches being fired by static?
I remember seeing this suggestion proposed in an issue of Extreme Rocketry.
Anyone come up with a downside to this idea?
Len Lekx writes:
George L. Rachor Jr. email@example.com
Hillsboro, Oregon http:rachors.com
United States of America Amateur Radio : KD7DCX
Safety keys can experience fused contacts, too... ;-)
Isn't a little extra caution better than a whole lotta hurt?
One little modification I'd make to the procedure, though. After
connecting the igniter outside the motor, and making sure it didn't go
off in my face, I'd short the two igniter wires together temporarily
while inserting the igniter into the motor. In the event that the LCO
triggers your pad by accident, the short will prevent current from
setting off the igniter when it's halfway into the motor.
re-read the article, the faulty controller passed that test. better to have
a bevice in parralel with the clips that give indication of power.
C'mon just stick an LED with resistor in there. two extra parts that are
worth pennies to keep this from happeneing.
I once worked in an electronics shop that had an antenna on the roof. One
very windy, low humidity, day, about this time of year, I heard some popping
from near the wall. Tracing it down, I found that a arc, or spark, would
jump across the PL-259 connecter. That was a distance od about 1/4". The
wind, blowing on the antenna wire, was producing some very high voltages on
the coax cable. The article states that it was a very windy day. It may be
possible that the wind had built up a very high voltage on the ignition
wire, which discharged through the igniter when the person touched the other
lead. It would be a rare event, since conditions would have to be just
Maybe it's just me, but I find a buzzer pretty irritating -- so it could
lead one (well, me) to 'hurry up' doing something that I don't want to
'hurry up' on.
What I mean is, sometimes the buzzer is irritating enough that the
continuity is only tested very briefly - when in fact it ought to be
monitored most (or all) of the time.
I understand and agree that this is a personal preference issue, but
thought I'd add my two cents worth.
I assume Ted means a buzzer connected across the output of the launch
controller firing circuit, or from a multi-contact relay that switches the
output, so that if the buzzer is going you know the clips are energised.
Across the clips would be better in that case, but I'd be inclined to put a
large (say 10K) resistor in parallel with the buzzer and igniter, so that
any capacitance in the buzzer (which will likely have some kind of drive
circuit) or static charge on the clips can discharge.
Alternatively, how about a small box, with a buzzer inside and a couple of
terminals. Connect it to the clips, if it buzzes you're live. You'd just
have to make sure that the current required by the buzzer was less than the
safe level for an e-match.