Partially 3D printed high powered rocket

[Ben Martin]

Hello, I am currently working on a design that involves 3D printed components. I am looking for some feedback on my design idea.

My current idea is that it is will be a 3" rocket with:
- 54mm engine tube (either fiberglass or blue tube)
- 3" Fiberglass body tube
- G10 Fiberglass fins
- 3D printed centering rings (3 total, 2 on bottom with slots for fin alignment)
- 3D printed tail cone motor retainer
- 3D printed nosecone
- 48" nylon parachute using Jolly Logic for deployment.

For the printing I am using PETG due to its durability and layer adhesion. I am attaching photos for reference to my design.


Any tips or ideas would be greatly appreciated. I don't know if I should go with full fiberglass or just go with blue tube/other.

Thanks,
Ben

 

[Andrew_ASC]

Maybe you could extend the tailcone shoulder to aid in alignment and epoxying. I do worry the motor overhang isn’t enough and you will melt your PETG tailcone. Perhaps if you offset the motor overhang flush with the end of the tailcone then you wouldn’t have a rocket exhaust flame melting the plastic printed component. That’s all I see that I would personally possibly change. I have more experience with minimum diameter printed rockets though; 3 X L-1, two were multistage. Another two non min diameter L2 rockets I made cad files of but ran out of money to build. On the nosecone 1.5- 2.0mm thickness should be sufficient. I’ve run nylons thinner for competition rockets using SLS print. But FDM printing wouldn’t hold those thin tolerances.

 

[KC3KNM]

Maybe you could extend the tailcone shoulder to aid in alignment and epoxying. I do worry the motor overhang isn’t enough and you will melt your PETG tailcone. Perhaps if you offset the motor overhang flush with the end of the tailcone then you wouldn’t have a rocket exhaust flame melting the plastic printed component. That’s all I see that I would personally possibly change. I have more experience with minimum diameter printed rockets though; 3 X L-1, two were multistage. Another two non min diameter L2 rockets I made cad files of but ran out of money to build. On the nosecone 1.5- 2.0mm thickness should be sufficient. I’ve run nylons thinner for competition rockets using SLS print. But FDM printing wouldn’t hold those thin tolerances.

What’s the point in a paper thin cone? I’ve seen people get good prints at 1mm wall thickness with a hobby FDM machine. It’s not impossible, but seems pointless. What’s the real benefit to having such a thin wall? The minor weight savings will probably be removed after you balance the rocket anyway. A decent wall thickness with low infill percentage would yeild a very strong nose cone that’s still sufficiently light.


I agree with the nozzle distance to tailcone issue. I can’t tell from the drawings, but the cone appears to be pretty long. I’m sure the cone’s taper is an issue and may limit how far back you can get the motor, but you could likely offset the motor tube further back. I’ve got a 3D printed retainer on a 3” rocket and the cone section hasn’t shown any signs of heat damage after a handful of flights. It was printed in CF PLA, so it’s not the most thermal resistant plastic either. I do have more clearance than you do, though. Scooting the motor back some will likely be sufficient.

What are your plans for retention? I can’t see any kind of fasteners or holes in the drawing. I like the slots for the fin tabs on the centering rings. Looks like it’ll be pretty sturdy.

 

[Ben Martin]

I like the tabbed centering rings.

What’s the point in a paper thin cone? I’ve seen people get good prints at 1mm wall thickness with a hobby FDM machine. It’s not impossible, but seems pointless. What’s the real benefit to having such a thin wall? The minor weight savings will probably be removed after you balance the rocket anyway. A decent wall thickness with low infill percentage would yeild a very strong nose cone that’s still sufficiently light.


I agree with the nozzle distance to tailcone issue. I can’t tell from the drawings, but the cone appears to be pretty long. I’m sure the cone’s taper is an issue and may limit how far back you can get the motor, but you could likely offset the motor tube further back. I’ve got a 3D printed retainer on a 3” rocket and the cone section hasn’t shown any signs of heat damage after a handful of flights. It was printed in CF PLA, so it’s not the most thermal resistant plastic either. I do have more clearance than you do, though. Scooting the motor back some will likely be sufficient.

What are your plans for retention? I can’t see any kind of fasteners or holes in the drawing. I like the slots for the fin tabs on the centering rings. Looks like it’ll be pretty sturdy.

Thank you for your reply.

I am certainly thinking about making a thicket nose one because as you said, the nose needs weight anyways. As for the centering rings, I certainly see the advantage of having the fin notches in them.

For retention I was thinking about experimenting with 3D printing the tailcone with threads so it could just screw on and then have a rubber seal to keep it tight. For the heat issue I was thinking about either reducing the length of the tailcone or moving the motor tube further back. It should not melt as long as it is not directly being affected by the motor. I've heard that the CF PLA is very heat resistant (160C) compared to normal PLA or PETG (60C).

Thanks for the feedback and let me know if anything else comes to mind.

Ben

 

[Andrew_ASC]

Not the entire nosecone but you can make certain walls thinner then shoehorn FCC long range electronics into it for competition contest reasons walls in some places were thinner than half mill to accommodate electronics packages. My experience with that. That’s getting off topic from what op wants.

 

[Ben Martin]

Maybe you could extend the tailcone shoulder to aid in alignment and epoxying. I do worry the motor overhang isn’t enough and you will melt your PETG tailcone. Perhaps if you offset the motor overhang flush with the end of the tailcone then you wouldn’t have a rocket exhaust flame melting the plastic printed component. That’s all I see that I would personally possibly change. I have more experience with minimum diameter printed rockets though; 3 X L-1, two were multistage. Another two non min diameter L2 rockets I made cad files of but ran out of money to build. On the nosecone 1.5- 2.0mm thickness should be sufficient. I’ve run nylons thinner for competition rockets using SLS print. But FDM printing wouldn’t hold those thin tolerances.

I am certainly going to either shorten the tailcone or extend the motor tube. I was thinking about making it threaded.

Do you have any recommendations when it comes the tubes? For these speeds (mach 1+) is fiberglass pretty much mandatory? Also, what type of motor retention devices did you use on your rocket and how did you connect your shockcord to your body?

Thanks,
Ben

 

[KC3KNM]

Thank you for your reply.

I am certainly thinking about making a thicket nose one because as you said, the nose needs weight anyways. As for the centering rings, I certainly see the advantage of having the fin notches in them.

For retention I was thinking about experimenting with 3D printing the tailcone with threads so it could just screw on and then have a rubber seal to keep it tight. For the heat issue I was thinking about either reducing the length of the tailcone or moving the motor tube further back. It should not melt as long as it is not directly being affected by the motor. I've heard that the CF PLA is very heat resistant (160C) compared to normal PLA or PETG (60C).

Thanks for the feedback and let me know if anything else comes to mind.

Ben

This is how I went about mine. Uses #6 screws with countersunk heads. The center ring was for motors that didn’t have retaining rings or didn’t match the retaining rings on the DMS motors, which is what it was designed around. This would be hard to implement around a longer cone, but might give some ideas. I considered having it twist on and off, but I haven’t had much luck with the longevity of 3D printed threads. However, printing an undersized hole with decent wall thickness around it makes for a very good mate to a wood screw or something with an aggressive thread.

 

[Ben Martin]

This is how I went about mine. Uses #6 screws with countersunk heads. The center ring was for motors that didn’t have retaining rings or didn’t match the retaining rings on the DMS motors, which is what it was designed around. This would be hard to implement around a longer cone, but might give some ideas. I considered having it twist on and off, but I haven’t had much luck with the longevity of 3D printed threads. However, printing an undersized hole with decent wall thickness around it makes for a very good mate to a wood screw or something with an aggressive thread.

That is a brilliant idea. I am certainly going to start prototyping a few different versions of it to see which one would work best for my rocket. Do many of the motors at this size not have a retaining ring? As for the tailcone adhesion to the bottom of the rocket/centering ring you would just use epoxy, correct?

 

[Andrew_ASC]

In my experience we were using fiberglass for well over mach 1 flights. Some flights used carbon fiber. We tested nylons up to M1.89. We chose epoxy shock cord to coupler and friction fit motors. They were smaller diameter faster rockets lightweight type. I notice a lot of people on the forum go to Aeropack retainers or whatnot once they hit 54mm. You can always friction fit unless the club doesn’t allow it. Many prefer other methods than friction fit.

 

[KC3KNM]

Not the entire nosecone but you can make certain walls thinner then shoehorn FCC long range electronics into it for competition contest reasons walls in some places were thinner than half mill to accommodate electronics packages. My experience with that. That’s getting off topic from what op wants.

FCC electronics? I think you’re mixing up terms here. None of my 70cm band gear is FCC certified, but as long as the operator is licensed it’s legal.

I understand that... your previous post read as though you’ve got a sub millimeter thin egg shell for a nose cone.

 

[Ben Martin]

In my experience we were using fiberglass for well over mach 1 flights. Some flights used carbon fiber. We tested nylons up to M1.89. We chose epoxy shock cord to coupler and friction fit motors. They were smaller diameter faster rockets lightweight type. I notice a lot of people on the forum go to Aeropack retainers or whatnot once they hit 54mm. You can always friction fit unless the club doesn’t allow it. Many prefer other methods than friction fit.

So pretty much fiberglass would be the only way for this build? Not blue tube or anything else? I was thinking about using an eye bolt with quick connect for shock cord on the upper centering ring then one on the nosecone as well

 

[Andrew_ASC]

You could push blue tube, I just have no experience where it’s failure point is. And it would suck to find out the hard way. Briefly looked at phenolics then decided a tube failure above Mach wasn’t worth that savings.

 

[KC3KNM]

That is a brilliant idea. I am certainly going to start prototyping a few different versions of it to see which one would work best for my rocket. Do many of the motors at this size not have a retaining ring? As for the tailcone adhesion to the bottom of the rocket/centering ring you would just use epoxy, correct?

That was more planning ahead for some home built motors. If I remember correctly some of the DMS motors had thrust ring issues, which was another reason I printed a few of those rings. I’ve only really flown AT stuff, so I can’t speak on other brands.

Yup, that’s what I did. I also sanded and filled around the joint. This was on a 3.1” LOC IRIS with cardboard body tube.

I’ve never used blue tube, but I’ve heard good things. Fiberglass is great to work with, just make sure to wear a mask if you’re sanding and wear gloves.

 

[KC3KNM]

That was more planning ahead for some home built motors. If I remember correctly some of the DMS motors had thrust ring issues, which was another reason I printed a few of those rings. I’ve only really flown AT stuff, so I can’t speak on other brands.

Yup, that’s what I did. I also sanded and filled around the joint. This was on a 3.1” LOC IRIS with cardboard body tube.

I’ve never used blue tube, but I’ve heard good things. Fiberglass is great to work with, just make sure to wear a mask if you’re sanding and wear gloves.

What I forgot to mention was that the ID of the mount matches the OD of the motor tube. It’s epoxied to both the body tube and the motor tube. So, it’s acting as a force spreader when the motor is burning. It transfers some of the force to the end of the body tube.

 

[Andrew_ASC]

Eyebolts should do it fine for this rocket.

 

[Ben Martin]

What I forgot to mention was that the ID of the mount matches the OD of the motor tube. It’s epoxied to both the body tube and the motor tube. So, it’s acting as a force spreader when the motor is burning. It transfers some of the force to the end of the body tube.

Seems like a perfect fit for this project. With the max motor it is supposed to reach 13K with max speed of mach 1.5.

 

[Ben Martin]

That was more planning ahead for some home built motors. If I remember correctly some of the DMS motors had thrust ring issues, which was another reason I printed a few of those rings. I’ve only really flown AT stuff, so I can’t speak on other brands.

Yup, that’s what I did. I also sanded and filled around the joint. This was on a 3.1” LOC IRIS with cardboard body tube.

I’ve never used blue tube, but I’ve heard good things. Fiberglass is great to work with, just make sure to wear a mask if you’re sanding and wear gloves.

Do you have any tips for recovery? I was thinking about doing single deployment with a jolly logic setting it for like 500-1000ft but after consideration I would think it would be a ton of force suddenly being applied to the rocket. The other issue would be the ejection charge for separation, as it would be the only means of separating the nosecone from the body.

Any tips would be helpful,
Thanks

 

[KC3KNM]

Seems like a perfect fit for this project. With the max motor it is supposed to reach 13K with max speed of mach 1.5.

I can’t speak to how well it would hold up there. I’m also using PLA compared to PETG, so you’d likely have a tougher mount. I do have the motor tube butted up to the end of the mount, so the mount itself doesn’t take the brunt of the load. I wasn’t worried about a failure as much as the plastic compressing and introducing some play.

Do you have any tips for recovery? I was thinking about doing single deployment with a jolly logic setting it for like 500-1000ft but after consideration I would think it would be a ton of force suddenly being applied to the rocket. The other issue would be the ejection charge for separation, as it would be the only means of separating the nosecone from the body.

Any tips would be helpful,
Thanks

There’s a lot of different takes on recovery. Have you flown a dual deploy rocket? If not, I’d do some testing with something smaller first. I’m assuming you’ve got at least your L1?

There’s a few threads here that go into different recovery methods and have some really good information. Searing “dual deploy” would probably turn up what you need. I’m on my phone right now so I don’t have any links, otherwise I’d try to find them.

 

[Ben Martin]

I can’t speak to how well it would hold up there. I’m also using PLA compared to PETG, so you’d likely have a tougher mount. I do have the motor tube butted up to the end of the mount, so the mount itself doesn’t take the brunt of the load. I wasn’t worried about a failure as much as the plastic compressing and introducing some play.


There’s a lot of different takes on recovery. Have you flown a dual deploy rocket? If not, I’d do some testing with something smaller first. I’m assuming you’ve got at least your L1?

There’s a few threads here that go into different recovery methods and have some really good information. Searing “dual deploy” would probably turn up what you need. I’m on my phone right now so I don’t have any links, otherwise I’d try to find them.

I am familiar with dual deployment but I wanted to save some weight. Maybe I should have a drogue that comes out at separation and jolly logic for lower?

 

[KC3KNM]

I am familiar with dual deployment but I wanted to save some weight. Maybe I should have a drogue that comes out at separation and jolly logic for lower?

I’ve thought about a JL type assembly that has a drogue attached to it. When it releases the main chute, the release assembly parachutes down under the drogue. I was thinking a spool shaped part that has the chute stappped into it, with a drogue packed above it in the tube. If the OD is just under the ID of the tube it should slide in and out easily and also protect the chute from the ejection charge. I’ve got a 38mm MD project that seems like a good candidate for a trial, but I’m not sure I’ll get to it before winter. The downside is that it would take up space (though, wouldn’t require an AV bay), but should be pretty light. Not sure how your background in electronics is, but an ATTiny based system with a small servo would be cheap and easy to put together. They sell BMP180 breakouts on amazon for around 5$.

 

[Ben Martin]

I’ve thought about a JL type assembly that has a drogue attached to it. When it releases the main chute, the release assembly parachutes down under the drogue. I was thinking a spool shaped part that has the chute stappped into it, with a drogue packed above it in the tube. If the OD is just under the ID of the tube it should slide in and out easily and also protect the chute from the ejection charge. I’ve got a 38mm MD project that seems like a good candidate for a trial, but I’m not sure I’ll get to it before winter. The downside is that it would take up space (though, wouldn’t require an AV bay), but should be pretty light. Not sure how your background in electronics is, but an ATTiny based system with a small servo would be cheap and easy to put together. They sell BMP180 breakouts on amazon for around 5$.

I am not too familiar with electronics but I can learn and experiment.

 

[Nytrunner]

So pretty much fiberglass would be the only way for this build? Not blue tube or anything else? I was thinking about using an eye bolt with quick connect for shock cord on the upper centering ring then one on the nosecone as well

Just want to chime in and mention that fiberglass is not the only way for the build. Blue tube us a very capable material, and even paper LOC tube airframe constructed sufficiently is very strong. There's also Canvas phenolic by Mac Performance.

Fiberglass is strong but heavy.

 

[Ben Martin]

Just want to chime in and mention that fiberglass is not the only way for the build. Blue tube us a very capable material, and even paper LOC tube airframe constructed sufficiently is very strong. There's also Canvas phenolic by Mac Performance.

Fiberglass is strong but heavy.

I was considering blue tube since it's lighter and still pretty darn strong. I wasn't sure how it would withstand to the mach speeds and forces though. Do you have any experience with it?

 

[Andrew_ASC]

Well I was curious too. This is what other users report about Blue Tube and higher Mach. I personally have no experience with that material.

https://www.rocketryforum.com/threads/bluetube-speed-limit.120592/

 

[Nytrunner]

I use paper tubes from LOC and Madcow w/ couplers for internal reinforcement.

One day I'll get around to using bluetube. That thread Andrew posted has more good anecdata as well.

 

[Andrew_ASC]

To what Mach have you pushed internal reinforced paper tubes? What was the internal reinforcement material?

 

[Nytrunner]

I don't fly supersonic, I like to see my flights.

That being said, I use the same build methods that Eric Cayemberg does, (see his LOC N-Load thread) when he builds for speed. Full length couplers forward of the motor mount, stiffy's at the ebay or tube joints. Lighter than filament wound, cheaper than carbon, less epoxy hassle.

 

[Andrew_ASC]

You know if the OP put a lesser motor in that rocket he could save a lot of money on airframe tubes. Motor hardware and a reload would cost less too. My guess is he could pick up a FWFG Von Karman nosecone with a metal tip from Wildman dirt cheap in 54mm ID, 57.5mm OD. Throw a 54 to 38mm motor adapter in it with the money leftover and L-2 on an Aerotech single use. Keep it subsonic to low transonic. Just ideas. And it would still be a partially 3D printed rocket.

 

[cwbullet]

This is how I went about mine. Uses #6 screws with countersunk heads. The center ring was for motors that didn’t have retaining rings or didn’t match the retaining rings on the DMS motors, which is what it was designed around. This would be hard to implement around a longer cone, but might give some ideas. I considered having it twist on and off, but I haven’t had much luck with the longevity of 3D printed threads. However, printing an undersized hole with decent wall thickness around it makes for a very good mate to a wood screw or something with an aggressive thread.

Hello, I am currently working on a design that involves 3D printed components. I am looking for some feedback on my design idea.

My current idea is that it is will be a 3" rocket with:
- 54mm engine tube (either fiberglass or blue tube)
- 3" Fiberglass body tube
- G10 Fiberglass fins
- 3D printed centering rings (3 total, 2 on bottom with slots for fin alignment)
- 3D printed tail cone motor retainer
- 3D printed nosecone
- 48" nylon parachute using Jolly Logic for deployment.

For the printing I am using PETG due to its durability and layer adhesion. I am attaching photos for reference to my design.
View attachment 362713 View attachment 362714 View attachment 362716 View attachment 362717

Any tips or ideas would be greatly appreciated. I don't know if I should go with full fiberglass or just go with blue tube/other.

Thanks,
Ben

You should both enter the 3D printing contest.

 

[grouch]

I have several flights on unreinforced paper tube in excess of M1.4. That's with the Loc 54mm tube. I have done a good amount of .75ish on the 3" Loc tube.