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>
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 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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