Need retention ideas

I'm playing around with a design for a 3" upscale Sprint XL. I would turn my own wood nose cone and tail cone. If I use a 38mm motor tube, I would have to drill a 1.75" hole through the tail cone, which doesn't leave enough room for a normal Aeropack retainer. There are tail cone style retainers, but they're $37. I'm looking for retention ideas. And no, I'm not interested in friction fit.





View attachment Sprint XL baffle 38mm.ork

Slimline style retainer?

https://giantleaprocketry.com/products/components_retainers_adapters.aspx

You could recess that in the tailcone. I think it'd look pretty slick.

Turn the nose and tail out of hardwood, then groove the inside of the tailcone for a snap ring?

qquake2k said:

Hmmm, I wonder if that would work...

Click to expand...

It would probably work okay, if you turned the groove so the snap ring didn't put too much pressure on the wood. Of course that also depended on the wood used as to how much expansion it could resist.

Use the whole tailcone as your retainer, & pin it to the tube?

Weird idea. You are turning the tailcone. Take it one step further and make it the retainer. Bore the ID such that the motor fits inside of it. Then make the tailcone removable. Insert motor, insert tailcone, and screw into place.


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I do this on several rockets:

Measure length of MM tube. Say 7inches, that far from rear of motor case [7in.] wrap several turns of masking tape around it.
Load your case with reload, but do NOT screw on rear closure YET.



Drop/insert case with reload from front end of rocket. You may have to hold stuff upside down so re-load parts don't fall out. But by now, I know you can figure out the details, you've been around awhile.....LOL

Now screw on rear closure. Motor is held in place by masking tape ring in front and closure in rear. Can't go anywhere. You may need a section of PVC pipe or dowel to put pressure on front of motor , while screwing rear closure on/off.

Works for me. Total cost, few wraps of tape!

Only gotcha is flying small motors in loooong motor mount tubes won't work. When building....size tube short as possible for small motors.

markkoelsch said:

Weird idea. You are turning the tailcone. Take it one step further and make it the retainer. Bore the ID such that the motor fits inside of it. Then make the tailcone removable. Insert motor, insert tailcone, and screw into place.


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Click to expand...

I like the idea, however, I'd use aft rail button to pin it in place like dhbarr suggested.

Making the tailcone the retainer is a good idea. Unfortunately, I don't know how I would turn a ridge in the aft end of it. When it's mounted on the lathe, the smaller end is free, and I would use a Forstner bit to drill it out. I would have to somehow drill it smaller, then use some sort of boring bar to increase the size of the hole from the ridge to the wide end.
Hmmm...

qquake2k said:

Making the tailcone the retainer is a good idea. Unfortunately, I don't know how I would turn a ridge in the aft end of it. When it's mounted on the lathe, the smaller end is free, and I would use a Forstner bit to drill it out. I would have to somehow drill it smaller, then use some sort of boring bar to increase the size of the hole from the ridge to the wide end.
Hmmm...

Click to expand...

I vote for Jim's method, unless you just want to figure out how to do special lathe work on the cone just for fun...which it might be. I realize my vote counts for 0.

blackjack2564 said:

I do this on several rockets:

Measure length of MM tube. Say 7inches, that far from rear of motor case [7in.] wrap several turns of masking tape around it.
Load your case with reload, but do NOT screw on rear closure YET.

Drop/insert case with reload from front end of rocket. You may have to hold stuff upside down so re-load parts don't fall out. But by now, I know you can figure out the details, you've been around awhile.....LOL

Now screw on rear closure. Motor is held in place by masking tape ring in front and closure in rear. Can't go anywhere. You may need a section of PVC pipe or dowel to put pressure on front of motor , while screwing rear closure on/off.

Works for me. Total cost, few wraps of tape!

Only gotcha is flying small motors in loooong motor mount tubes won't work. When building....size tube short as possible for small motors.

Click to expand...

Very interesting concept. But then I couldn't make it zipperless.

K'Tesh said:

I like the idea, however, I'd use aft rail button to pin it in place like dhbarr suggested.

Click to expand...

I was planning on doing that anyway, the rail button and two other screws..

It's a standard 3" airframe? Buy a LOC PNC-3.00, saw off the end cap, saw off the nose tip to the motor diameter. Gives a nice transition on the cheap.

https://www.madcowrocketry.com/search.php?search_query=slimline

no idea if anything there of use , just remember seeing in closeout or something

qquake2k said:

Making the tailcone the retainer is a good idea. Unfortunately, I don't know how I would turn a ridge in the aft end of it. When it's mounted on the lathe, the smaller end is free, and I would use a Forstner bit to drill it out. I would have to somehow drill it smaller, then use some sort of boring bar to increase the size of the hole from the ridge to the wide end.
Hmmm...

Click to expand...

Turn it from the other end? Use the small end as your mount end. Then you could use the large forstner for the bulk, then the small one for the retainer step. Part it off when done.

qquake2k said:

Very interesting concept. But then I couldn't make it zipperless.

Click to expand...

Sure you could. Make the anti zipper coupler attached with screws. I have been doing that since about 1999-2000 timeframe, and never have had an issue.


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qquake2k said:

I'm playing around with a design for a 3" upscale Sprint XL. I would turn my own wood nose cone and tail cone. If I use a 38mm motor tube, I would have to drill a 1.75" hole through the tail cone, which doesn't leave enough room for a normal Aeropack retainer. There are tail cone style retainers, but they're $37. I'm looking for retention ideas. And no, I'm not interested in friction fit.

Click to expand...

Here's an idea...

Epoxy a threaded rod to the MMT and hollow out a small channel in the tailcone for it. Make it stick out 1"-ish and throw a nut or two on it. The only downside is that it's kinda ugly- it looks a bit like an engine hook though... Total cost only a few $.

I used this on a 38mm rocket w/ 29mm mount (very much in the style of the Star Orbiter) and I haven't flown it yet, but it feels very solid. Yes, an Aeropack would've fit, but this was way cheaper.

I don't have a pic handy but I can take one if it would help.

Other solution I can offer:

Leave MM tube stick out about 3/8. If paper MM... CA exterior/interior last inch to harden & keep tape from pulling layer of paper off every time you tape motor in.



Simply friction fit and a wrap of Aluminum Duct tape over exterior of rear closure and MM tube. It will NOT come off, I have done this on 98mmm M-motors. [I don't use masking tape anymore, although it works fine on small motor]

This is a motor with a 1inch tape thrust ring on it. Normal reload case will not stick out near this far.


This is tape I use now. Shown on 54mm motor.


Proper way to friction fit. Wrap just 3-4 wraps near REAR of case, like a screw thread, so each wrap covers previous edge, so tape won't roll and gum up inside. Need more/too loose... just overlap more when wrapping.

Screw in-screw out. because it's done on rear of case, you don't fight it, when time to remove & have a gooey mess up inside MMtube.



Stupid simple and cheap...only mod is leaving MM stick out a bit.

Jim,

What type of tape do you use on the bigger motors??


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Lowpuller said:

Jim,

What type of tape do you use on the bigger motors??


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Click to expand...

blackjack2564 said:

Aluminum Duct tape

Click to expand...

Actual aluminum ducting tape.

qquake2k said:

I'm playing around with a design for a 3" upscale Sprint XL. I would turn my own wood nose cone and tail cone. If I use a 38mm motor tube, I would have to drill a 1.75" hole through the tail cone, which doesn't leave enough room for a normal Aeropack retainer. There are tail cone style retainers, but they're $37. I'm looking for retention ideas. And no, I'm not interested in friction fit.

Click to expand...

38mm Aeropack retainer is $25 from here:
https://www.rocketarium.com/Build/Motor-Retainers?sort=20a&page=2

If you are flying other 38mm MMT rockets, then just buy the retainer base for $14!
https://www.rocketarium.com/Build/Motor-Retainers/RB/38-mm-L

The motors you will be flying will cost you at least that much, likely more than that, per each flight. The casings 4x that.

Wouldn't it be nice not to loose/waste them by trying to save $14-25 now?
:confused2:

a

I'll be the first to admit, I'm cheap when it comes to retention. My normal method is homemade clips. But in my defense, I've never lost a motor.

Quake I've seen others use your method but I have been hesitant. What are you screwing in into, T nuts??


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Correct. I put t-nuts in the aft centering ring, and cover them with epoxy to keep them from coming out. They've served me well over the years.

I've been a cheap $ob for years too!!!

Used everything from screws/washers-friction fit/masking tape- T nuts - sheet rock screws/washers for M-motors etc.

Ya just got to think outside the box. Folks forget, that for many, many years we all were on our own for motor retention. There were no fancy [expensive] motor retainers]

One of my favorite's for retro-fitting [or building for that matter] when there is room.
Just a barrel nut [or 2 or 3 depending on motor size] Another cheap method, cost 1.50
Drill hole, screw in barrel, mirror clip & machine screw...done.

Use the machine screw to mount barrel nut. After screwing machine/screw onto barrel nut....use head of screw to twist barrel nut into BP. Then just remove screw, leaving barrel nut in place & undamaged.





Back to your issue at hand...good luck, at least now you have several good choices!

This is how I did the retention on a rocket I built with a urethane tail cone. The ring is just a scrap piece of aluminum I made with a drill press. There are nuts buried in the tail cone from the back side.

It works well and looks kind of cool, in my opinion.


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This one has he MMT recessed, so the ring sits as-is with the motor loaded, just the nozzle pokes through the hole.


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