Constant continuity checking

Hi Wayne,

more and more I see launch controllers being build with NO continuity checking.

the club I belong to does not have any continuity checks and launches go just as fine if not better then launches I attend with continuity checked.

I built mine this way also and it serve me well, and I never need fear a continuity check ignition.

I mean why run current into an igniter if you don't plan to set it off ?

Really, if the igniter you chose had continuity when you checked it outside the motor, why check it inside the motor and run any risk ?

Also, I really would not want to have current running into my igniters or matches at a launch continuously.

Just some food for thought.

CD

We have quite a few High Power flights, using copperheads. Continuity serves us well there.

Hi Wayne,

Hi power flight is where having no continuity checks the best.

Most hi powered flight is done with either Hi-current igniters like quick-burst , or with ematches like Oxral. Both are better to check before they are put in the motor.

Copperheads and Hi-power are contradictory right ?

AT hi power motors come with first fires, Pro38/54 come with E-match, Loki and AMW have you use your own, we use quick-burst.

Aero-Tech mid power still comes with Copperheads, and those are best split with a match or many of the other tricks.

I still don't want to run current into something while I'm at the pad.

CD

Old skool Aerotech HPR loads came with copperheads. They sucked just as bad for HPR then as they do for mid-power now.

The system I've used for over a decade now does a continious continuity check using an audible piezo buzzer rather than an LED. That way I can hear what I'm doing when at the pad. The current flow through a piezo is on the order of 10ma, quite safe for any ignitor I've ever encountered.

The NARAM system (and its predecessor) also do low level continious continuity check. From the LCO control, you've got continious readout on all pads continuity status. It really helps keep track of what's going on.

One problem with going as low as you're suggestion is spurious continuity. The old NARAM system used too low a current, and got all sorts of false readings from high humidity conditions.

To make sure it's connected properly to the launch system. To make sure that the clips are clean and it's got a solid connection. So that the LCO can tell it's ready to go.

Are you going to limit the current input to the igniter, or limit the current on the detect circuit?

If you connect the +12v clip to the igniter, then connect the ground clip, then leg go of the ground clip, dropping it onto the blast deflector, and if the blast deflector is on a metal launch pad staked into the ground, will the igniter fire?

I liked the arrangement on the LMR / HPR pads at the McGregor NARAM a few years ago: A 3-way switch: ON, OFF, Continuity. When I was at the pad, I could turn the switch OFF and the LCO could not mistakenly fire the pad. Continuity was only on when it was on.

Chris Kraft wrote in his book that during the Gemini program, NASA learned a lesson to leave things (like thrusters) powered off when they were not needed.

Glen Overby

Hi Bob,

at our last club launch before winter, the club launched over 300 rockets in one day.

no continuity checks needed, as their GSE does not do it, on purpose.

I'm not a big fan of continuity either. Check your igniter before you head to the pad, may save you a trip back for a good one.

One thing I will share, We had a small grass fire (not uncommon in AZ) due to a mis-fire on another pad that burned and shorted the wires to my controller. My wires were running past this pad and no one noticed they were burned. Fortunately I am in the habit of checking the for continuity to the clips before hooking them to the igniter by touching them together and I saw a spark. I am planning on adding an buzzer at the pad that will sound if the line gets shorted again.

Before anyone freaks about the grass fire we do cancel launches if the danger is too great. We take all fires very seriously in AZ.

Bob Heninger Glendale, AZ

1 uamp is way too low. You should be able to use 10 ma safely for any continuity tester. If you can't, the igniter is far too sensitive.

Check out the specifications for your ignitor (if they exist). All professional ignitors have a specified no-fire and all-fire current rating. The common Estes ignitors have a 2 amp all-fire rating and their continuity checker uses 50 ma for the check.

The old daveyfire N28F has an all fire rating of 1 amp and a no-fire rating of 0.4 amps. You could pass 0.4 amps through the igniter indefinitely!

Using a very low currents in the uamp range is likely to give a lot of false readings simply due to leakage. You are definitely best using currents in the low ma range to prevent this. A simple piezo buzzer in series with the igniter usually limits the current to ~ 10 ma. A 1K resistor in series with a led will also limit the current through the igniter to ~10 ma, as will the piezo buzzer in series with a led. Copperheads, Quickbursts, all e-matches and dipped igniters that I am aware of will not actuate witha 10 ma constant current.

Bob Krech

I hate pads with this type of switch. Quite simply, people forget that they are there. So they connect up their clips without turning the switch off. Or they turn it off, then forget to turn it back on, which causes a long HOLD before that pad can be fired.

And how many times did someone press the button and nothing happened?

BTW, what club / event is this? When NIRA ran big MRFF launches on the NARAM-33 site, we'd break 600 on Saturday, but never got enough people on Sunday to get over 1000. IIRC we came close a couple times...

sent you a PM

The reason I'm pushing the low current is that long ago, I had a friend use flashbulb ignition (a flashbulb and several segments of jetx wick) on a clustered D Saturn V. The LCO ran a continuity test (this was an Estes launch controller) and the flash went off. Steve was standing a few feet away and couldn't hear for several hours afterward.

I just want to prevent incidents like that.