Terry,
Sounds like a plan…great research and discussion. Just to reinforce what Mike
and others have said, make sure whatever ignitor combination you come up with
stays at the top end of your motor. I was using Pyrodex pellets for a while,
just cramming them (or pieces) into the core of the top grain. What I noticed
is that when they started to burn, they shrank in diameter and fell to the
bottom of the core, leading to an embarrassing series of chuff-chuff-starts
(and consequential early ejections!). I am also a fan of taping the igniter and
enhancement to a thin dowel to hold it in place near the top of the motor. The
red Aerotech caps are useful for holding these dowel/igniters in place.
Looking forward to seeing this rocket fly at RocStock. And no Mike, it’s NOT
too early to start having RocStock fever! 😊 (ask me how I know!)
Chris
From: roc-chat-bounce@xxxxxxxxxxxxx [mailto:roc-chat-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Terry McKiernan
Sent: Thursday, May 24, 2018 10:37 PM
To: roc-chat@xxxxxxxxxxxxx
Subject: [roc-chat] Re: choice of igniters / ematches for airstart of H or I
class motor
Thanks everyone for all the suggestions on igniters. I'm glad I asked.
Originally when I had planned to use the PET2+ for airstarts, I was just going
to have some 9V batteries since that's what the PET2+ instructions suggested.
It was my son actually who noticed the Aerotech voltage requirement in a forum
posting and brought it to my attention, leading to this email thread. I'm glad
he noticed and I didn't come out to ROCstock with a combination that would
never have worked!
I decided to go with the ClusterFire pyrogen dip kit and a bunch of chipboards
to make ematches. Seemed like a good investment compared to buying pre-made
igniters at a couple dollars each. I'll save the Aerotech igniters that come
with the motors as backups for future ground-based launches. Maybe I'll dab a
little Pyrogen on the sustainer motor grain. Also, Kurt G. offered to give me a
Pyrodex pellet to put up in the sustainer to help ensure ignition.
For the Raven battery power I'm going to use a 9V for the electronics -- that's
what they recommend in the manual to avoid damage from overcurrent, and I
already have a 9V mount in my e-bay. You can use a 1S LiPo for the electronics
instead, but even then you have to be careful to get one under 170 mAh. LiPos
are certainly nice and light but since I already have ten pounds of rocket,
saving a few grams on the battery didn't seem worthwhile.
For the pyro charges I will be using some CrazePony 400 mAh 2S 30C LiPos, both
for the motor ignition off the Raven and for the backup ejection charges on my
EggTimer. They were the right combination of size, capacity, current etc. --
small enough to fit in my crowded e-bay, plenty of juice to run the EggTimer
GPS / finder for hours if necessary, enough voltage & current to light the
ClusterFire igniters. There will be 3 of them -- 2 on the EggTimer and 1 on
the Raven. So, I've got redundant everything on the electronics.
https://smile.amazon.com/gp/product/B072BH1XP6/ref=oh_aui_detailpage_o02_s04?ie=UTF8&psc=1
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
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.
Thanks again everyone
Terry
On 5/24/2018 4:12 PM, Paul Pittenger wrote:
Two advice points.
1. MJG new blue wire ematches dipped in pyrogen. I use magnalite. If enough
room in motor core I fold over the top this reduces any tendency of ematch to
slide down the motor core during the liftoff Gs or to spit itself out the aft
end of motor upon ignition.
2. Test on the ground use your chosen ematch and pyrogen to launch motors from
the ground. During my testing I had a chance at one launch to run my own wires
out to the pad. For testing pyrogen dips I was launching 29mm and 38mm motors
using a AA battery. That made me really confident my airstarts would work with
LIPO or 9V battery
Just my opinions - have fun experimenting!!!
Paul
Sent from my iPhone
On May 24, 2018, at 2:44 PM, Mike Riss (Redacted sender "rockt_dude" for DMARC)
<dmarc-noreply@xxxxxxxxxxxxx<mailto:dmarc-noreply@xxxxxxxxxxxxx>> wrote:
My suggestions are to first start with your electronics. Since you're using a
Raven, contact Featherweight to see what they recommend. Adrian is pretty good
about providing advice, and has a lot of experience.
Also check out the online forums and look to see what other Raven users have
had success with.
The MJG and similar initiators aren't intended for starting composite motors by
themselves. They can be used when augmented, either with a pyrogen dip or some
other energetic material like a pyrodex pellet or a small piece of easy to
light propellant. Their main advantage is the low current required to ignite
them, but the disadvantage is that by themselves they don't generate enough
energy to get a motor started.
Slim Gem and similar initiators like those provided with Aerotech motors are
generally intended for use with ground-based 12 volt launch systems. It's not
so much the voltage but the current that they need to get going.
And as I mentioned in a previous thread, remember to take into account the mass
of whatever you do use for an initiator, and make sure it stays up at the top
of the motor.
Mike
P.S. Is it too early for ROCStock fever to be setting in?
On Wednesday, May 23, 2018 10:16 PM, Terry McKiernan
<terry@xxxxxxxxxxxxx<mailto:terry@xxxxxxxxxxxxx>> wrote:
Hello all,
Still trying to get my 2-stage high-power rocket project ready for the
June launch. I have a question about igniters I hope you can all help
me with. Basically I am looking for a recommendation: should I use the
igniter that comes with the motor, or buy an igniter more suitable for
airstarts, if there is such a thing?
My design uses two 3" rockets which are outfitted with Aerotech motor
retainers, and I have Aerotech casings, so I've only used Aerotech
motors with them. These are 38mm motor mounts and I'll be using class H
or I motors for the sustainer stage.
I am concerned that the Aerotech motors will be hard to start with a
small battery that can fit in a payload bay. I found a few posting
online indicating that Aerotech's igniters require 12V and can pull 15A+
momentarily when they short & burn. This is OK I guess for a ground
control system with a big fat car battery or marine battery attached.
But, it seems like an awful lot for an altimeter battery.
The airstart will be controlled an a Raven altimeter, and it does
support having a small 1S LiPo for the altimeter and a second battery up
to 20V for the pyro channel. And, yes, I can get a 2S 30C 12V LiPo on
Amazon. So, theoretically it should be able to start the motor using
the Aerotech igniter.
Alternatively I could buy some other igniter, or ematch, or make my
own. Any recommendations?
I am tempted by this ClusterFire kit, which promises 1 second burn at
5400F, using 6V and 2.3A:
https://www.rocketflite.com/store/index.php?route=product/category&path=61
Or maybe H-3 Compound?
https://www.apogeerockets.com/Rocket-Motors/Motor-Starters/H3-Igniter-Dip
Or MJG?
https://electricmatch.com/pyrotechnics/see/6/5/mjg-firewire-initiator
Note that at the March launch my Aerotech igniter on one launch failed,
and I tried an MJG ematch I had bought from
buyrocketmotors.com<http://buyrocketmotors.com> as a
replacement and it failed, and then I bought a FirstFire and it worked.
But, that was a ground launch not an airstart. In any case my only
experience with MJG was not good.
Or Slim Gem?
https://www.apogeerockets.com/Rocket_Motors/Motor_Starters/Slim_Gem_Starters
One thing i note about Slim Gem is they also require 12V just like
Aerotech. Also according to the Apogee site they burn at 1400F, vs. the
5400F claimed for ClusterFire. Quite a difference...
Or Quest Q2G2?
http://www.buyrocketmotors.com/quest-q2g2-3-initiators-6-pack/
Or ... probably lots of other choices out there?
Thanks for any suggestions!
Terry McKiernan
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