Ground testing ejection charge for MPR motor deploy

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shawn_rocket

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I launched my Aerotech Arreauxbee-HI a couple of weeks ago on a F52. Beautiful flight up, but the down part was ballistic. Altimeter said I hit 1500ft. I watched it hit apogee, come over a bit, saw a puff of spoke, but the rocket did not separate. So, I recovered the rocket (many pieces) and checked the motor assembly (only piece still together besides my Estes Altimeter which survived!) for residue of the ejection charge, and yes, it did fire. Parachute and shock cord in perfect condition. So, I pulled out the MM to inspect the baffle and "pot scrubber". The cooling mesh came out with residue on it, but it looks like it was only 5" long, not the recommended 6". Just scratching all this up to a lesson learned. I started thinking about how to ground test, and am coming up short. Is there a way to ground test an MPR motor deploy with a 29/40-120 case? Do I buy some delay kits (one's for the motors I want to use), black powder and a bunch of igniters? I looked up the specs for the F52, F40 and G53 and it looks like AeroTech puts in .7g of powder. So I went to calculate 10psi on a 2.6" tube and the max length of tube it can pressurize is 25", assuming all the black powder burns. I'll take any advice I can get on how to ground test without burning up a motor.
 

markg

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Do I buy some delay kits (one's for the motors I want to use), black powder and a bunch of igniters? I looked up the specs for the F52, F40 and G53 and it looks like AeroTech puts in .7g of powder. So I went to calculate 10psi on a 2.6" tube and the max length of tube it can pressurize is 25", assuming all the black powder burns. I'll take any advice I can get on how to ground test without burning up a motor.
I'd skip the delay kit. Just make up a separation charge with an ematch/blackpowder, seal the MMT with a casing and set the charge off with a long length of wire (15ft+) & a 9V battery. You can use ethernet cable as the long wire if you've got any lying around. Prop the rocket up on something so the nose cone is pointing up at about 30 degrees, away from you into a clear area where there is enough room to fully extend the harness.

For the separation charge, cut the finger off a disposable glove, put the end of the ematch in it and the seal it together with some electrical tape.

I don't have a link handy, but I'm sure there are pictures someone here on how to make separation charges with glove tips if you've never done it before.

FWIW, 0.7g sounds about right for a 2.6". Though I'd probably round up to 1g if I was making my own charges for dual deployment.

cheers - mark
 

shawn_rocket

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I'd skip the delay kit. Just make up a separation charge with an ematch/blackpowder, seal the MMT with a casing and set the charge off with a long length of wire (15ft+) & a 9V battery. You can use ethernet cable as the long wire if you've got any lying around. Prop the rocket up on something so the nose cone is pointing up at about 30 degrees, away from you into a clear area where there is enough room to fully extend the harness.

For the separation charge, cut the finger off a disposable glove, put the end of the ematch in it and the seal it together with some electrical tape.

I don't have a link handy, but I'm sure there are pictures someone here on how to make separation charges with glove tips if you've never done it before.

FWIW, 0.7g sounds about right for a 2.6". Though I'd probably round up to 1g if I was making my own charges for dual deployment.

cheers - mark
I am getting ready to do a test this weekend. As I see it, I make up an ejection charge with an ematch with a lengthy cord. I would feed the wire through the forward closure out the rear closure, tape the ejection charge into the the forward closures ejection charge cap, insert the motor, screw on the end cap, stand back and touch the wires to a battery with sufficient voltage. I just want to make sure I am doing this right as it's the first time I've tried this.
 

markg

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I am getting ready to do a test this weekend. As I see it, I make up an ejection charge with an ematch with a lengthy cord. I would feed the wire through the forward closure out the rear closure, tape the ejection charge into the the forward closures ejection charge cap, insert the motor, screw on the end cap, stand back and touch the wires to a battery with sufficient voltage. I just want to make sure I am doing this right as it's the first time I've tried this.
Yep, that's pretty much what I would do. I usually put the rocket onto the lawn, leaning it on a patio cushion or something so that the nose is pointed away from me about 30 degrees off the ground. Have something heavy on the aft end to secure rocket in place. Try and be about 15 feet away from the rocket and have it pointed away from you in a safe direction.

cheers
 

shawn_rocket

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Yep, that's pretty much what I would do. I usually put the rocket onto the lawn, leaning it on a patio cushion or something so that the nose is pointed away from me about 30 degrees off the ground. Have something heavy on the aft end to secure rocket in place. Try and be about 15 feet away from the rocket and have it pointed away from you in a safe direction.

cheers
Awww man! I can't point it at my cat? lol Thanks for the confirmation!
 

shawn_rocket

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So I did my first ground test with my Eradicator. Went perfect. Used .7g of BP as is spec for AT F RMS motors. I am going to measure before building the motor since I had one rocket crash already. Used CAT 5 wire (one pair) to wire to ignitor and be able to stand back with a battery.
 

Saint_Tiki

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So I did my first ground test with my Eradicator. Went perfect. Used .7g of BP as is spec for AT F RMS motors. I am going to measure before building the motor since I had one rocket crash already. Used CAT 5 wire (one pair) to wire to ignitor and be able to stand back with a battery.
Do you not do the blow test first?

On my MPR and my HPR, I can eject all the laundry or at least the nose cone+ with my breath. That’s my litmus test.
 

shawn_rocket

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I had an unsuccessful deploy with my Arreauxbee-Hi; couldn't figure out the cause, so I tested a few things, including the charge to insure that it was sufficient. I suspect that my nose cone was not on tight enough. I do the breath test as well. It was also good practice as I move to non-motor deployment and dual deployment in my MPR's. And, who doesn't like to ignite a little BP on occasion! 🤓
 
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