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Joshua F Thomas

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:facepalm:

Yeah, ok, I'm an idiot. This was the first time I ever used t-nuts. Your explanation makes perfect sense. The instructions that come with the Goblin are not helpful in this regard, having close to no actual diagrams or pictures, and very much not of these.

So... now what? Any suggestions on what I can do to solve this particular issue - preferably without having to remove the aft centering ring which is epoxied firmly into place with the body and fins?
 

gtg738w

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:facepalm:

Yeah, ok, I'm an idiot. This was the first time I ever used t-nuts. Your explanation makes perfect sense. The instructions that come with the Goblin are not helpful in this regard, having close to no actual diagrams or pictures, and very much not of these.

So... now what? Any suggestions on what I can do to solve this particular issue - preferably without having to remove the aft centering ring which is epoxied firmly into place with the body and fins?
Pop out the T nuts and you can probably use a threaded insert in the hole. Or just drill a new pair of holes and use wood screws. Luckily thrust is pushing in the good direction, you just need to retain the motor at ejection.
 

Joshua F Thomas

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The threaded inserts are an idea, but don't they have the same problem of pulling loose? Do I make them oversize so that they grip the wood, or would I use epoxy to hold them into the existing holes?

The wood screws are probally the easiest idea, but makes the adaptor semi-permanent. I guess that doesn't bother me much, I'm not planning on using 38mm or 54mm motors in this any time soon.
 

gtg738w

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The threaded inserts are an idea, but don't they have the same problem of pulling loose? Do I make them oversize so that they grip the wood, or would I use epoxy to hold them into the existing holes?

The wood screws are probally the easiest idea, but makes the adaptor semi-permanent. I guess that doesn't bother me much, I'm not planning on using 38mm or 54mm motors in this any time soon.
Inserts for wood should have coarse threads on the OD that screw in like a regular wood screw. You should be able to find them locally at Home Depot or similar. You may have to either drill out the holes to fit or go up to the next size depending on what size holes are there for the t nuts.
#8-32 tpi Solid Brass Wood Insert Nut (2-Pack)

 

dr wogz

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or just buy the Aeropack retainer & adapters..

Sorry, I know it's rude, and I sound like a broken record. I apologize, not my intent.

But the logical course a lot of us take is:
  • Start with MPR, and move into 29mm rockets; typically 2.6" or 3" dia rockets, with a 29mm mount.
  • We then plan to do our L1, and get either a larger 29mm case (for a small H) or get a rocket with a 38mm hole.
  • we then acquire a few 38mm cases, and move up to L2 planning,
  • We then start looking at larger rockets with a 54mm hole..
Eventually we "want" to have some cases (more motor selection, cheaper flights in the long run), and you'll get a 29mm case (40-120), then another one (180 or 240 with RAS), and soon you'll want a (need?!) a 38mm case.. Then you'll want a 38-29mm adapter.. and you may also eventually want a 54-38mm adapter..


It's hard to do HPR on the cheap..
 
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dr wogz

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Quoting myself from a few replies ago:

54mm with flange.. use wood screws.

you can also, pot the hole with epoxy and insert a screw with greased threads, then let set. this will allow you to 'cast' some threads into the epoxy for a custom threaded hole..


sorry Joshua, I'm not trying to be a know it all, or come across as crass, or assume you have $$.. just trying to help you fix your mistake. (And yeah, as you've discovered, HPR kits tend to be light on directions.. Its pretty much assumed you know what you're doing when you buy these kits. Like buying a vintage sports car.. you're kinda expected to know how to use a clutch..)


The other possible fix for you is to glue the smaller adapters in place. You said you didn't plan to fly anything larger than 29mm (or 38mm)


some words of wisdom for your journey:
  • It's not a question of "if" your rocket breaks, but a question of when..
  • All rockets have a finite number of flights in them. it's up to you to figure that number out!
 
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Joshua F Thomas

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Ok, so two things:

I still need some way to go down from 54mm to 29mm - I assume Aeropack has some kind of adaptor for that. The thing itself is $40, so this is already getting expensive. Secondly, I need a better way to visualize the actual dimensions of how that adaptor works, because it's not clear to me from the diagram. Is there a picture or something I can see, elsewhere?
 

dr wogz

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And (d'uh!) you can tap a hole in plywood. drill an undersized hole, run a tap, then flood the hole with thin CA. wait a day or two to ensure the CA is fully cured (don't ask me how I know!!) then chase the threads again with a tap. this method is used on a number of R/C airplanes to hold their wings on..
 

dr wogz

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OK, just took some pics & such for you:

20200907_162751.jpg the parts: the two adapters & a motor case. the adapter are tubes, with flanges. They also come with a 'cap' to hold the end of the smaller motor case. the end of eh motor case is sandwiched in between the adapter & this 'cap'. the outer retainer ring screws on as normal, and hold it all in place. (the external retainer ring is not shown, forgot to dig it out of my box as I took the pics..) And yes, they all stack up,, the end caps nest into each other..

20200907_162843.jpg the order in which they will be inserted into the aft end of the rocket: 54mm adapter, 38mm adapter, motor case, 38mm cap, 54mm cap, 54mm retaining ring (not shown)

20200907_162915.jpg as the adapters are inserted, with the 29mm case

20200907_162935.jpg all inserted

20200907_163024.jpg all inserted with the caps, and retaining ring in place. Technically this would be ready to fly

Yeah, they add up quickly, but remember you only need buy the adapters once. They can be used in any rocket (unlike the LOC ones, where they are unique to only that rocket / product line)

So, as mentioned get teh 54-38mm adapter, and a small 38mm case. that should get you flying as about a cheaply as you can with these.. if you intend to stick with HPR, you will soon want / spend the $$ for the cases & such..
 

gtg738w

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#1 - I Love Aeropack, most of my builds use their retainers and I use the adapters of various sizes regularly.

#2 - I also use the LOC Z clips and adapters and they work really well. I use them on any kit that comes with them. There is no need to upgrade, it’s just personal preference.

#3 Certs are required because there is some knowledge and experience required to be successful. Anyone asking questions along the way and figuring out the right way to do it before they get to the field is way ahead of most others. The best way to gain experience is to build & learn & have fun flying! The Goblin is a very robust and forgiving kit. It is a great choice for an L1 build.
 

Joshua F Thomas

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sorry Joshua, I'm not trying to be a know it all, or come across as crass, or assume you have $$.. just trying to help you fix your mistake. (And yeah, as you've discovered, HPR kits tend to be light on directions.. Its pretty much assumed you know what you're doing when you buy these kits. Like buying a vintage sports car.. you're kinda expected to know how to use a clutch..)
It's all good, I didn't take any offense and you are being helpful. It is appreciated.

The other possible fix for you is to glue the smaller adapters in place. You said you didn't plan to fly anything larger than 29mm (or 38mm)
... that's a fair point. I guess I want the ability to be able to fly with the larger motors later if I can, I just don't see myself doing so any time soon due to altitude limits near me. An I or J 54mm motor in the Goblin can go to 4000 feet, and I have neither the field or the wavier at my local club to be able to fly that. Rocketry is all trade offs, perhaps I should just go with that option.

some words of wisdom for your journey:
  • It's not a question of "if" your rocket breaks, but a question of when..
  • All rockets have a finite number of flights in them. it's up to you to figure that number out!
Don't jinx me, man! But seriously, I hear what you're saying, I would like to be able to get, you know, at least a half-dozen launches out of this thing.

Thanks a bunch for the pictures. I hate to be asking more, but I can't quite tell how the retainer attaches to the original paper motor mount. Does it just epoxy to exposed part that protrudes after the after centering ring? The smaller (18mm) retainers I've used do that, where you epoxy on the threaded retainer, insert the motor, and then use the screw-on retainer. Is this the same?

Thanks again.
 

Joshua F Thomas

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Ok, I've had a good look at the Aeropack site and some videos, and figured it out. They offer two types of retainers; one type bonds to the end of the motor mount tube, and the other screws into the aft centering ring.

I would need to use a 54mm retainer ($40) with a 29m-to-38mm adaptor ($26) and also a 38-to-54mm adaptor ($39)... that's adding up a lot. For my first, not-yet-flown HPR rocket, I don't think I want to outlay $105 (more than the Goblin kit!). I very well might get there! But not yet :)

I believe I'm going to go with using wood screws to secure the 29mm LOC Z adaptor for the moment. I'll be able to evaluate how well it worked after my first flight.

Great info all around, thanks all.
 

Joshua F Thomas

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I’m finally done! With everything!

BDFE5E2E-6335-436E-AE8C-61C44E4E423B.jpeg


Chose orange because the Goblin just feels like a Halloween themed rocket. I like how it looks.

This is the 11th rocket I’ve built and my first HPR. I learn something new with every build. For this rocket I learned:

* Epoxy is much more of a pain to work with than wood glue, mainly due to viscosity.
* 15 minute epoxy is Goldilocks: Not too fast, not too slow, just right.
* Drilling needed holes *before* painting works better than the reverse
* Plywood needs to be sealed for a smooth finish; just sanding it down fine isn’t going to cut it
* How to correctly use t-nuts :facepalm:
* How to build an AV bay / shock mount into a nosecone
* Yet again, I learn that you need to measure three times before actually cutting or drilling, and when possible, from different directions to ensure alignment in all axises
 

Tobor

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Congrats on completion. Looks good!
 

Joshua F Thomas

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Two successful flights! Only have video for the first due to "technical issues" (push the button, dummy).

First was on a G79-4W LMS, and appeared to have the ejection charge fire early. Chute didn't fully open, but no damage on landing. Video:

Second flight was on a single-use G79-4W purchased at field, and had a perfectly flight and recovery. Flight data here: https://flightsketch.com/flights/1323/
 

3stoogesrocketry

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Two successful flights! Only have video for the first due to "technical issues" (push the button, dummy).

First was on a G79-4W LMS, and appeared to have the ejection charge fire early. Chute didn't fully open, but no damage on landing. Video:

Second flight was on a single-use G79-4W purchased at field, and had a perfectly flight and recovery. Flight data here: https://flightsketch.com/flights/1323/

The chute did not fully open because it either shreaded from opening at max Q (notice how it opens overfull , then deflates in the next frame ) or your nose cone went threw the lines and tangled it. Did the parachute survive undamaged?
 

HHaase

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The chute went out almost exactly at motor burnout. I don't see any smoke or debris from the top of the sustainer that suggests the charge went off, I think it may have been a drag separation issue.

Did you have altimeter data from the first flight as well? The data for the good flight suggests high negative G's after burnout, it decelerates almost as quickly as it accelerates. The csv file does show your raw accelerometer data too, I'd suggest plotting it for this rocket.

-Hans
 
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Joshua F Thomas

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Not sure why people keep saying "drag separation" when multiple people at the field clearly heard the ejection charge sound. I can also confirm from examination of the motor case and the interior of the rocket that the ejection charge did go off.

The only question here is why the LMS motor went off early, but I have an answer for that in a different thread.
 

HHaase

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....... I'm the only one that used the term in this topic.

If I touched a nerve, I do apologize. I'll go check out some other areas of the forum.
 

Joshua F Thomas

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It keeps showing up in the thread I posted in the Propulsion section about the motor, despite many other people who were there that day commenting on the ejection noise. https://www.rocketryforum.com/threads/give-me-your-aerotech-lms-tips.161831/

Including by 3stoogesrocketry who seems to think internet analysis of a few seconds of bad video is superior to in-person observation.

Anyways, rant mode off. I don't have altimeter data for that flight (press the button, dummy), but I did get good data from the next flight, on the same motor: https://flightsketch.com/flights/1323/
 

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Hot off the production line, Loc's newest release, a 4" upscale of the Goblin is sure to be a hit! This thread is devoted to the 4" Loc Goblin; all are welcome to post their builds, flight photos, and anything else Loc Goblin related here!

The classic lines of the Estes Goblin recreated with excellence at the Loc shop....I'm in. I started my build yesterday; the plan is to fly it at the local Class 1 launch this Sunday. I'm not doing a fully detailed build thread, but here's the general idea of the build thus far.

Parts: Nothing but high quality here. A very complete kit!!! Careful not to throw out the little bag of hardware...mine was wrapped up in the paper packaging.

[/IMG]

First step: Prep the rings. Pound in the T-nuts, secure the eye-bolt, hold it all in place with a small batch of 5 minute epoxy.

[/IMG]

Test fit all the rings and fins to make sure they fit and understand where they go. Then mix up a batch of glue and secure the rings in place. Note: my fins aren't ready to be glued yet...so I just glued the rings at this time. Love the interlocking design: SOLID.

[/url][/IMG]

Glue the adapters together. I used Titebond. I like to peel the glassine off the tubes in the area to be bonded...right, wrong, or indifferent, it's what I do.

[/IMG]

And that's when I ran out of free time for the evening. More to come shortly...again others please feel free to join in; this ain't a solo gig here!:D
I don't get how the adapters work. Do I glue in the 54mm rings and then attach the adapters using the T nuts? This is my first high power kit going for L1 Cert.
 

Joshua F Thomas

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I don't get how the adapters work. Do I glue in the 54mm rings and then attach the adapters using the T nuts? This is my first high power kit going for L1 Cert.
I had the same question. You build the fin can around the 54mm tube. The 38mm and 29mm adaptors are built separately. They slide into the 54mm tube and then you screw them in place to the T-nuts (on the rocket body side) using the slots on the adaptor centering ring. The T-nuts on the adaptor are for the motor retainer brackets.
 
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