What is considered as "too many fins"? (L2 high powered build)

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I have a few questions for you guys.

So I have been shopping for components for my 3D printed build and I had a few things I was not certain about. I also have some questions about the fins. This is all of course just to see what your recommendations/opinions are so I can grow my concepts.

- Should I go with a 54mm blue tube motor tube or with a LOC one? My body will be .1in wall mailing tube so I was not certain if the blue tube would really be worth it.
- For the 3D printed fins, do you guys think that epoxy would be the best thing to attach the carbon fiber rods with? The epoxy I have get pretty hot and I wouldn't want it to melt the fins.
- For the fins, what do you guys think about me coating the entire fin in a thin coat of epoxy to fill in all the imperfections and then sand it down to a nice finish? This could also harden the fin and add additional variety of resonance.

Attached is a list of all the components I will be buying for the rocket.

All feedback/ideas are welcome, I have open ears!Screenshot_20181017-014653_Chrome.jpeg
 
My opinion, for what it’s worth, and it is only my opinion.. And, I am somewhat old school..

Blue tube for a MMT is overkill. A regular tube is just fine. Some will argue that you really don’t need a MMT as long as your CRs are concentric, and you have a guideway of some sort to help insert the motor. And that you have structure to transfer the force of the motor to the airframe. While the tube gives you all that, most of the modern HPR set ups, the structure comes from the TTW fin tabs butted up against the CRs..

If you’ve 3D primed fins & CRs, why not print out aerodynamic rail guides? (And, do you really get an advantage over regular round ones?!)

Epoxy clay is to fix plumbing. Liquid epoxy will run into the pores, scratches & dents and really bond your pieces. (And, the longer the cure time, the more time it has to seep into the crevices & indents to bond..) The clay just sits on top of whatever you’ve pressed it to.

Glass the fins. Coat the fins in epoxy, then lay in a glass or nylon fabric and squeegee smooth. Let cure. A 1 or 2 oz cloth should do you well. You may have a hard time, as some (most?) epoxies don’t stick too well to plastics..
https://sigmfg.com/products/sig-glass-cloth
 
Ben Martin said:
I have a few questions for you guys.

- Should I go with a 54mm blue tube motor tube or with a LOC one? My body will be .1in wall mailing tube so I was not certain if the blue tube would really be worth it.
- For the 3D printed fins, do you guys think that epoxy would be the best thing to attach the carbon fiber rods with? The epoxy I have get pretty hot and I wouldn't want it to melt the fins.
- For the fins, what do you guys think about me coating the entire fin in a thin coat of epoxy to fill in all the imperfections and then sand it down to a nice finish? This could also harden the fin and add additional variety of resonance.

Attached is a list of all the components I will be buying for the rocket.

All feedback/ideas are welcome, I have open ears!View attachment 364263
Click to expand...

LOC tubes are quite strong. Scuff up the exterior or remove the glassine coating entirely to maximize the bond strength.

(That 1/4" eyebolt is nice, but may be overkill for this size project. What's your projected weight?)
 
I think I might have gone a *bit* overkill with my ubolt size.

Also, what is the best way of securing the ubolt? Right now it has two nuts and the plate on the back but none on the front. Should I add 2 more to the front and switch them out for nylon locking nuts or epoxy them?20181021_013145.jpeg
 
Ben Martin said:
I think I might have gone a *bit* overkill with my ubolt size.

Also, what is the best way of securing the ubolt? Right now it has two nuts and the plate on the back but none on the front. Should I add 2 more to the front and switch them out for nylon locking nuts or epoxy them?View attachment 364580
Click to expand...

I would put thin nuts on the outside of the bulkplate. Also, when you glue in the bulkpate, set it further into the nosecone shoulder so you can build a fillet around its perimeter on the outside.
I would just loctite the nuts in place or use epoxy since you’ll have some anyway.
 
Steve Shannon said:
I would put thin nuts on the outside of the bulkplate. Also, when you glue in the bulkpate, set it further into the nosecone shoulder so you can build a fillet around its perimeter on the outside.
Click to expand...
I plan on sanding down the outside a bit so I can fit it down further into the nosecone. Do you think the ubolt size is overkill or just right? Also, should I just epoxy the threads for the nuts or use nylon nuts?
 
Ben Martin said:
I plan on sanding down the outside a bit so I can fit it down further into the nosecone. Do you think the ubolt size is overkill or just right? Also, should I just epoxy the threads for the nuts or use nylon nuts?
Click to expand...

The u-bolt is plenty big. As long as things fit that’s only an æsthetic issue.
I would just epoxy the threads. Unless you plan to take them apart. Then locking nuts make sense.
 
Steve Shannon said:
The u-bolt is plenty big. As long as things fit that’s only an æsthetic issue.
I would just epoxy the threads. Unless you plan to take them apart. Then locking nuts make sense.
Click to expand...

Do you think that a 17in motor tube would be strong enough for this build? There's a $10 difference in shipping between the long 54mm tube and the pre-cut 17in version. The longest motor would be a bit longer than the 17in tube.
 
Plenty long, you only need enough motor tube to keep the motor concentric withe the airframe axis, even 12" most likely would be plenty, as long as the fin roots are fully attached to the mmt, generally if I use longer mmt's it on zipperless style fincans.
 
Plenty strong enough. You'd probably have 3 centering rings on the long one same as the shorter one. Most of the force will be transferred through the rear ring and the fin roots anyway.
 
Nytrunner said:
Plenty strong enough. You'd probably have 3 centering rings on the long one same as the shorter one. Most of the force will be transferred through the rear ring and the fin roots anyway.
Click to expand...
Just bought at 34in 54mm tube from LOC because it was only a few dollars more than the shorter one and has faster shipping. I'll probably cut it in two or just use a longer section for additional strength further up in the tube.
 
Progress:

Ordered the motor tube, coupler, carbon fiber rods, and kevlar rope.

Everything is printed besides a few fins and the motor retainer.
20181022_005324.jpeg
 
What are your guys opinions on using screws in addition to epoxy to secure the centering rings, baffle system, coupler, and motor retainer? I'm not confident that epoxy will grip to PETG even when roughened up. They would be small screws and I would use 4 on each.
 
Ben Martin said:
What are your guys opinions on using screws in addition to epoxy to secure the centering rings, baffle system, coupler, and motor retainer? I'm not confident that epoxy will grip to PETG even when roughened up. They would be small screws and I would use 4 on each.
Click to expand...

one of the main reasons why I (personally) would rather use wood or fiberglass, and not rely on 3D printed parts for these..
 
Last edited:
Ben Martin said:
3D printed is "free" and experimental. Someone has to test what it's capable of.
Click to expand...

Ben, I'm not going to argue that with you! We have a 3D printer, that is currently 1 hr into a 6 hr print to prove a design concept here at work. Yes, to prove a design works, and to show it in a design review meeting. 6 hrs printing for a 5 minute demo. We love the thing! It's paid for itself a few times over at this point. (Fusion3-360 if you're curious)

We've also used it to print out cutting templates for the machinists & tin bashers. They love it too for that..

But for structure, where you're building something up, expecting a certain level of assembly, especially with glue, I'd have used a material that is proven "glueable". Most plastics don't glue too well. In this particular example, I would have gone with ABS, as you can glue to it.. mostly. And, for this, I would have spent the few $$ and got the parts laser cut. Or, CNC milled if in FG.. Again, something that can be bonded, and also offers greater structure.

So far, from the may prints I've made, (PLA), the parts aren't robust enough for me to consider using in a situation as this. 3D fabricated parts just isn't as strong as a solid sheet / block material.

But then again, I like using my hands, fabricating parts, shaping things. I have a few tools that allow me to do it; drill press & fly-bar cutter, band saw, belt & disk sander.. I would have designed the parts, made 2d printouts, and made the parts myself..

While 3D printers are trendy now, I will get a 2D laser cutter before getting a 3D printer..
 
dr wogz said:
Ben, I'm not going to argue that with you! We have a 3D printer, that is currently 1 hr into a 6 hr print to prove a design concept here at work. Yes, to prove a design works, and to show it in a design review meeting. 6 hrs printing for a 5 minute demo. We love the thing! It's paid for itself a few times over at this point. (Fusion3-360 if you're curious)

We've also used it to print out cutting templates for the machinists & tin bashers. They love it too for that..

But for structure, where you're building something up, expecting a certain level of assembly, especially with glue, I'd have used a material that is proven "glueable". Most plastics don't glue too well. In this particular example, I would have gone with ABS, as you can glue to it.. mostly. And, for this, I would have spent the few $$ and got the parts laser cut. Or, CNC milled if in FG.. Again, something that can be bonded, and also offers greater structure.

So far, from the may prints I've made, (PLA), the parts aren't robust enough for me to consider using in a situation as this. 3D fabricated parts just isn't as strong as a solid sheet / block material.

But then again, I like using my hands, fabricating parts, shaping things. I have a few tools that allow me to do it; drill press & fly-bar cutter, band saw, belt & disk sander.. I would have designed the parts, made 2d printouts, and made the parts myself..

While 3D printers are trendy now, I will get a 2D laser cutter before getting a 3D printer..
Click to expand...
Guess theres only one way to find out how well my design is going to work. To build the thing and test it.
 
dr wogz said:
Ben, I'm not going to argue that with you! We have a 3D printer, that is currently 1 hr into a 6 hr print to prove a design concept here at work. Yes, to prove a design works, and to show it in a design review meeting. 6 hrs printing for a 5 minute demo. We love the thing! It's paid for itself a few times over at this point. (Fusion3-360 if you're curious)

We've also used it to print out cutting templates for the machinists & tin bashers. They love it too for that..

But for structure, where you're building something up, expecting a certain level of assembly, especially with glue, I'd have used a material that is proven "glueable". Most plastics don't glue too well. In this particular example, I would have gone with ABS, as you can glue to it.. mostly. And, for this, I would have spent the few $$ and got the parts laser cut. Or, CNC milled if in FG.. Again, something that can be bonded, and also offers greater structure.

So far, from the may prints I've made, (PLA), the parts aren't robust enough for me to consider using in a situation as this. 3D fabricated parts just isn't as strong as a solid sheet / block material.

But then again, I like using my hands, fabricating parts, shaping things. I have a few tools that allow me to do it; drill press & fly-bar cutter, band saw, belt & disk sander.. I would have designed the parts, made 2d printouts, and made the parts myself..

While 3D printers are trendy now, I will get a 2D laser cutter before getting a 3D printer..
Click to expand...
I would have used ABS but it is not safe to print it in a dorm room, hence PETG. PETG should be plenty strong once properly epoxied.
 
Progress:

Motor retainer is done, only thing that I have left to print are two of the fins. The motor tube and coupler came in today from LOC. I have to say that their customer service and shipping are excellent.20181024_233859.jpeg20181024_233837.jpeg
 
I have a 2.5" rocket with 5 fins. Flies on 38mm H motors. I have 15-20 flights currently.

Edward
 

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