Need help on launch lug sizing

[Ken PlattnerParticipant]

Assuming I do try and cert with H motors, other than the casings and reloads what else do I need?

[denverdoc]

Chris,
But how many series clusters do you personally know of where the circuit was broken? None I bet. How many anecdotal cases. maybe one? The problem is much more complicated than an ee 101 class. You have the rise time of the current to consider, the capacitances of the circuit drop in series, and triple in parallel so a factor of 9:1, the actual ignition point of the pyrogen, the heat capacity of the pyrogen, in other words its delta T/dT of the bridge, and the dependency of the pyrogen to spark at whatever temperature. Life just aint simple as a physics textbook, at least as currently written 😀

I’d say go parallel, as well, just cuz I don’t know enough.
JS

[Chris LaPanse]

I have never seen one in a rocket that failed this way. I tried 3 estes igniters in series, however, and 2 lit, one did not. I then tested the one to make sure it was good – it worked instantly. Never tried it with HPR igniters, but it should work the same way as the estes.

[Doug GerrardParticipant]

Never tried it with HPR igniters, but it should work the same way as the estes.

I would never make that assumption and I rarely use the word never. If there is one thing I’ve learned it is that what works for model rocketry rarely works for HPR.

Doug

[Chris LaPanse]

All I am assuming is that their resistance characteristics are similar. I know that they break when fired(I have tested that), and I know the resistance is generally significantly lower, but if anything that would seem to make them less reliable than estes when in series(they need more current to fire).I am not assuming that they are the same in all ways, just that the resistance and temperature characteristics can be scaled (A reasonable assumption if the HPR igniters use nichrome – not sure about conductive pyrogen).

[Warren B. MusselmanModerator]

Typical HPR igniter resistances I’ve measured range in the 1.5 to 5 Ohm range. This includes nichrome based as well as carbon fiber/nitrocellulose pyrogen as in the Igniterman kit.

Warren

[denverdoc]

Warren.

I’m getting a tighter read on things, but haven’t sampled the universe. The magnelite igniters which i use for the most part use 4-5 coils of nichrome bridge, the resistance is 1.2 +/- 0.3 Ohms. When I bothered with such, I tried rolling my own, with 34 gauge or something NiCh, then dipping them in nitrocellulose laquer–the real stuff, not dissolved ping pong balls, followed by a varity of secondary pyrogens. Never had much variability. However, some motors, specifically Ellis worst and CTI best, show various propensities to ignition.

Every davey fire chip based e-match ive seen is between 1.1 and 2 ohms and that was an outlyer. I only had three blister packs of estes but in an effort to confirm CJ’s results, was unable to get an open circuit in three efforts. I used stacked Li photo batteries. But the difference between an Estes igniter and any decent HPR is literally night v day. the estes these days are low amperage devices with the most pathetic blob of pyrogen imagianable. they work in BP motors with proper installation, barely.

To the more cynical among you, i would even suggest an intended design flaw, as extra igniters cost a decent percentage of the motor themselves, no extras are included, AND ARE THE SOURCE OF HEARTBREAK EVERYWHERE. Don’t get me started on crapperheads………
J

[Chris LaPanse]

Yeah – no kidding. As for the designed to fail? I wouldn’t go that far, but they’re certainly overpriced. $9 for a 3-pack of firstfires? Give me a break 🙄

[denverdoc]

Chris,
where was that? I like firstfires but last paid 6/3.Not quite designed to fail. more like no room or error……….
J

[Chris LaPanse]

That was the last time I saw them – not sure where. I’ll never use them again though, unless they came with the motor. Quickbursts work as well or better for $1 each. (about $1.50 each for the K and up igniters).

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