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MMX Ejection Question

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Mike

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Just a quick question...would a MMX ejection charge be able to pressurise about 8" of BT-5?

Thanks
 

Micromeister

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Mike:
MMX motors have a very hot ejection charge, I've deployed a 2" x 20" streamer from a 12" Bt-20 model with the old 5662 motor's. Carl and I both use bt-5 on a regular basis for micro-maxx models. I'm kinda partical to 10.5mm and T-3 (.375") tubes but BT-5 is just fine. Remember Weight is the enemy, Try to stay under 10grams for the best flights.
 

Mike

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Great, thanks for your help John!
 

Fore Check

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Originally posted by Micromister
Mike:
MMX motors have a very hot ejection charge, I've deployed a 2" x 20" streamer from a 12" Bt-20 model with the old 5662 motor's. Carl and I both use bt-5 on a regular basis for micro-maxx models. I'm kinda partical to 10.5mm and T-3 (.375") tubes but BT-5 is just fine. Remember Weight is the enemy, Try to stay under 10grams for the best flights.
I have a 10.5 mm model that I would like to start on, but I'm not sure what to do on a few things and make it fit. This will be my smallest model yet and I have no experience working with the small stuff.

The nose cone is balsa. How do I attach the shock cord to it? I cant find a screw eye small enough to fit in the 10.5 tube.

Also, what do you use for a shock cord and make it fit? My body tube is only 3" long, and the MMX motor mount still has to go in. So, minus that 1.5" and about .25" of shoulder on the NC, that leaves me only 1.25" of space inside the 10.5 tube to fit the recovery system!

How high do these little boogers go, anyway?

Thanks for your help!
 

Micromeister

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Fore Check:
10.5mm is the BIG stuff, wait til ya start using T-2+(.281") minimum dia tubing for your Micro models:D

Seriously, I stopped using eye screws and eye bolts years ago on ALL models micro to LMR's. Depending on the weight of the model a Kevlar loop of 50 to 130lb material replaces the hardware and does a great job.

For all micro models I use 50 - 70lb kevlar. make a 1" long loop tied with an overhand knot, trim the excess loose ends below the knot. Dremel out your nosecone. I hollow most balsa and basswood cones to allow addition of nose weight if needed. Remember weight is the enemy every .01 gram is important. CA the loop in the tip of the nosecone with just enough CA to cover the knot.

Motor mounts can be made in several ways. if you have a burn 10.5mm casing or two laying around they can be used to cut 1/16" thick centering rings with an X-acto saw and mitre box. OR a much better, lighter method... buy die cut fiberboard rings from Totally Tubular or ASP. These thing are great! Your motor mount should be a 1" long piece of T-2+(.281"OD) tubing I use a 1/4" piece of T-2 (.246"OD) 6mm tubing as the motor stop, to this apply two T-2+/T-4 fibre rings 1/4" from the aft end and almost flush with the forward end, CA the rings in place. cut a slight notch in the edge of the foreward ring and tie 26" to 30" of 50 -70lb kevlar shock line to the motor tube, leading it out over the notch. I bring the line back outside the mount through the motor tube when inserting the mount into the model. CA or Epoxy the mount into the model body. When the glue is set drop the shockline back through the motor mount out the forward end of the body then tie on your nose cone to the shock line end.
If you want a motor retainer hook, one can be fashioned from .020 music wire, I've seen them made from paper clips but they are simply WAY to big and heavy for these little models.
I use 1/2" or 3/4" teflon plumbers white pipe tape as streamers/wadding. You can tie it directly to the shock line, baby powder the heck out of both sides before fold/rolling the streamer the first time. McMaster Carr has several sizes of heavier expanded PTFE colored teflon that is even better.
Altitude is directly dependent on weight in these little guys, 10.5mm models under 10grams will get you over the 100-120' mark. My micro interceptor .281" body goes over 200 feet, I have some 281" x 3" micro S/D and P/D models that have been
tracked to over 300 feet so the sky is really the limit:D
I'm going to try to stick a couple of pics of a nose cone with loop, .020 motor hook, and a minimum dia shock line mount below.
Hope this helps!
You might also want to join us over on the MicroMaxRockets yahoo group, there is a ton of data and info, plans ect there for the taking.
 

Fore Check

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So you use Kevlar as the shock line, not anything elastic? Got it.

I need to send you a pic of the motor mount assembly that Sandman put together for the project in question. It looks a LOT like a regular ol' motor mount for a 13 - 24mm motor, just downsized. It's a 1.5" length of tubing that appears to be minimum diameter for the MMX motor (the motor tube) with a small wire motor hook in place. There is a 1" long "sleeve" tube that goes over the engine tube and over the motor hook, and then two 3/16" wide centering rings (that basically look like 3/16" lengths of a relatively thick-walled tube) that slide over the 1" sleeve and then center it in the 10.5 mm body tube. It seems that I could relatively easily attach a kevlar shock cord to this mount, in a very similar fashion to the way we attach kevlar shock ancors to standard motor mounts.

Thanks for the info!
 

Micromeister

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Fore Check:
Just remember loose all the unnesessary weight you can! .31n/sec's isn't a lot of power, but used wisely will go a pretty good way:)
that extra 1/2" of motor tube and sleeve may not seem like a lot of extra weight but I'd pear it down to the bare minimum. micro motors are 1" long, you will want about 3/16" extending out of the model to accept 1/4" masking tape over the motor hook. so a 1" long T-2+ motor tube is all that's required. I'd cut the sleeve tube down to 1/2" or less positioned about 3/8" to 1/2" from the aft end. speaking of this over tube, exactly what does it look like? I am not aware of a telescoping tube that fits over a .281" minimum dia motor tube. The next size paper tube available is a T-3 with a .349" ID... way to sloppy to be used as a motor hook retainer sleeve. Did Sandman roll a special tube or is it some other material? If you have a digital camera I'd really like to see these parts. You didn't mention the centering rings what are they made of?

Attached it a full size drawing of the 2 most common methods I use for Micro-Maxx motor mounts. Hope this helps a little.
 

Fore Check

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Not sure what the "sleeve" tube is, but it looks lake a white colored factory rolled paper tube to me. Perhaps Sandman would be better to answer the question of what it is and where it came from. It fits very nicely over the MMX motor tube, and the "centering rings" fit very nicely over that sleeve and then inside the 10.5 body tube. I will take your advice and trim some of it off.
 

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