[roc-chat] Re: choice of igniters / ematches for airstart of H or I class motor
- From: Gregory Lyzenga <lyzenga@xxxxxxxxx>
- To: roc-chat@xxxxxxxxxxxxx
- Date: Thu, 24 May 2018 23:14:41 -0700
On May 24, 2018, at 10:37 PM, Terry McKiernan <terry@xxxxxxxxxxxxx> wrote:
BTW last year I bought some fireworks starters on eBay, similar these:
https://www.ebay.com/itm/100pcs-50cm-Length-fireworks-firing-system-copper-wire-E-matches-Safety-igniter/273196526167
<https://www.ebay.com/itm/100pcs-50cm-Length-fireworks-firing-system-copper-wire-E-matches-Safety-igniter/273196526167>
I tried one out with a 9V an it made quite a pop. I expect these would light
an ejection charge without any problem, though I have my doubts about
lighting a motor. They were certainly cheap compared to buying e-matches
from rocketry vendors. Anyone ever tried these for use with rockets? I'm
not planning on using them at ROCstock since I have the ClusterFire kit
coming and that seems more likely to work, but I'm just curious if anyone has
gone the fireworks starter route.
Hi Terry:
I would be VERY wary of using these starters in a rocket! I was tempted
exactly as you were by the low price and they certainly look just like the
e-matches we know and love. But oh was I ever wrong about that! Yes, they
make a satisfying pop when you set them off with a 9v battery, but what that
doesn’t tell you is the current drain on the battery. These are HIGH CURRENT
devices, and they are basically a dead short on your 9v volt battery and
anything it depends on.
I made the mistake of using one to fire the apogee charge on a K550 dual deploy
flight using my ever dependable Perfectflite Stratologger. When the apogee
charge was commanded, the battery voltage recorded by the Stratologger
plummeted to 0.2 volts and the altimeter went into a coma. The match did NOT
fire either, I’m guessing because the Stratologger couldn’t provide enough
current. When it finally recovered its senses seconds later, it didn’t know it
was in flight and did nothing. The only thing that saved the rocket from a
ballistic crash from 7000 feet was that I luckily had a backup charge (using a
REAL match, not one of the fireworks starters!) connected to a timer set to
fire a few seconds after apogee. It was a high-speed deployment and it landed
under drogue only, since the main release was controlled by the now-comatose
Stratologger, but the rocket survived to fly another day. And I learned a
lesson about eBay fireworks starters. Now the only thing I use them for is
ground testing. I’ll never use them all up!
- 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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